Module:Date: Difference between revisions

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tweak formatted output; extract_date to parse an input date string
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-- Date functions for implementing templates and for use by other modules.
-- Date functions for use by other modules.
-- I18N and time zones are not supported.
-- I18N and time zones are not supported.


local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
local floor = math.floor
local Date, DateDiff, diffmt  -- forward declarations
local uniq = { 'unique identifier' }
local function is_date(t)
-- The system used to make a date read-only means there is no unique
-- metatable that is conveniently accessible to check.
return type(t) == 'table' and t._id == uniq
end
local function is_diff(t)
return type(t) == 'table' and getmetatable(t) == diffmt
end
local function _list_join(list, sep)
return table.concat(list, sep)
end


local function collection()
local function collection()
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self[self.n] = item
self[self.n] = item
end,
end,
join = function (self, sep)
join = _list_join,
return table.concat(self, sep)
end,
}
}
end
end


local function strip_to_nil(text)
local function strip_to_nil(text)
-- Return nil if text is nil or is an empty string after trimming.
-- If text is a string, return its trimmed content, or nil if empty.
-- If text is a non-blank string, return its content after trimming.
-- Otherwise return text (convenient when Date fields are provided from
-- Otherwise return text (convenient when accessed via another module).
-- another module which may pass a string, a number, or another type).
if type(text) == 'string' then
if type(text) == 'string' then
local result = text:match("^%s*(.-)%s*$")
text = text:match('(%S.-)%s*$')
if result == '' then
return nil
end
return result
end
if text == nil then
return nil
end
end
return text
return text
end
local function number_name(number, singular, plural, sep)
-- Return the given number, converted to a string, with the
-- separator (default space) and singular or plural name appended.
plural = plural or (singular .. 's')
sep = sep or ' '
return tostring(number) .. sep .. ((number == 1) and singular or plural)
end
end


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local function days_in_month(year, month, calname)
local function days_in_month(year, month, calname)
-- Return number of days (1..31) in given month (1..12).
-- Return number of days (1..31) in given month (1..12).
local month_days = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 }
if month == 2 and is_leap_year(year, calname) then
if month == 2 and is_leap_year(year, calname) then
return 29
return 29
end
end
return month_days[month]
return ({ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 })[month]
end
 
local function h_m_s(time)
-- Return hour, minute, second extracted from fraction of a day.
time = floor(time * 24 * 3600 + 0.5)  -- number of seconds
local second = time % 60
time = floor(time / 60)
return floor(time / 60), time % 60, second
end
 
local function hms(date)
-- Return fraction of a day from date's time, where (0 <= fraction < 1)
-- if the values are valid, but could be anything if outside range.
return (date.hour + (date.minute + date.second / 60) / 60) / 24
end
end


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-- Return jd, jdz from a Julian or Gregorian calendar date where
-- Return jd, jdz from a Julian or Gregorian calendar date where
--  jd = Julian date and its fractional part is zero at noon
--  jd = Julian date and its fractional part is zero at noon
--  jdz = similar, but fractional part is zero at 00:00:00
--  jdz = same, but assume time is 00:00:00 if no time given
-- http://www.tondering.dk/claus/cal/julperiod.php#formula
-- http://www.tondering.dk/claus/cal/julperiod.php#formula
-- Testing shows this works for all dates from year -9999 to 9999!
-- Testing shows this works for all dates from year -9999 to 9999!
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--    1 January 4713 BC  = (-4712, 1, 1)  Julian calendar
--    1 January 4713 BC  = (-4712, 1, 1)  Julian calendar
--  24 November 4714 BC = (-4713, 11, 24) Gregorian calendar
--  24 November 4714 BC = (-4713, 11, 24) Gregorian calendar
if not date.isvalid then
return 0, 0  -- always return numbers to simplify usage
end
local floor = math.floor
local offset
local offset
local a = floor((14 - date.month)/12)
local a = floor((14 - date.month)/12)
local y = date.year + 4800 - a
local y = date.year + 4800 - a
if date.calname == 'Julian' then
if date.calendar == 'Julian' then
offset = floor(y/4) - 32083
offset = floor(y/4) - 32083
else
else
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end
end
local m = date.month + 12*a - 3
local m = date.month + 12*a - 3
local date_part = date.day + floor((153*m + 2)/5) + 365*y + offset
local jd = date.day + floor((153*m + 2)/5) + 365*y + offset
local time_part, zbias
if date.hastime then
if date.hastime then
time_part = (date.hour + (date.minute + date.second / 60) /60) / 24 - 0.5
jd = jd + hms(date) - 0.5
zbias = 0
return jd, jd
else
time_part = 0
zbias = -0.5
end
end
local jd = date_part + time_part
return jd, jd - 0.5
return jd, jd + zbias
end
end


local function set_date_from_jd(date)
local function set_date_from_jd(date)
-- Set the fields of table date from its Julian date field.
-- Set the fields of table date from its Julian date field.
-- Return true if date is valid.
-- http://www.tondering.dk/claus/cal/julperiod.php#formula
-- http://www.tondering.dk/claus/cal/julperiod.php#formula
-- This handles the proleptic Julian and Gregorian calendars.
-- This handles the proleptic Julian and Gregorian calendars.
-- Negative Julian dates are not defined but they work.
-- Negative Julian dates are not defined but they work.
local floor = math.floor
local calname = date.calendar
local calname = date.calname
local low, high -- min/max limits for date ranges −9999-01-01 to 9999-12-31
local jd = date.jd
if calname == 'Gregorian' then
local limits -- min/max limits for date ranges −9999-01-01 to 9999-12-31
low, high = -1930999.5, 5373484.49999
if calname == 'Julian' then
elseif calname == 'Julian' then
limits = { -1931076.5, 5373557.49999 }
low, high = -1931076.5, 5373557.49999
elseif calname == 'Gregorian' then
limits = { -1930999.5, 5373484.49999 }
else
else
limits = { 1, 0 }  -- impossible
return
end
end
if not (limits[1] <= jd and jd <= limits[2]) then
local jd = date.jd
date.isvalid = false
if not (type(jd) == 'number' and low <= jd and jd <= high) then
return
return
end
end
date.isvalid = true
local jdn = floor(jd)
local jdn = floor(jd)
if date.hastime then
if date.hastime then
local time = jd - jdn
local time = jd - jdn -- 0 <= time < 1
local hour
if time >= 0.5 then   -- if at or after midnight of next day
if time >= 0.5 then
jdn = jdn + 1
jdn = jdn + 1
time = time - 0.5
time = time - 0.5
hour = 0
else
else
hour = 12
time = time + 0.5
end
end
time = floor(time * 24 * 3600 + 0.5)  -- number of seconds after hour
date.hour, date.minute, date.second = h_m_s(time)
date.second = time % 60
time = floor(time / 60)
date.minute = time % 60
date.hour = hour + floor(time / 60)
else
else
date.second = 0
date.second = 0
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date.month = m + 3 - 12*floor(m/10)
date.month = m + 3 - 12*floor(m/10)
date.year = 100*b + d - 4800 + floor(m/10)
date.year = 100*b + d - 4800 + floor(m/10)
return true
end
local function fix_numbers(numbers, y, m, d, H, M, S, partial, hastime, calendar)
-- Put the result of normalizing the given values in table numbers.
-- The result will have valid m, d values if y is valid; caller checks y.
-- The logic of PHP mktime is followed where m or d can be zero to mean
-- the previous unit, and -1 is the one before that, etc.
-- Positive values carry forward.
local date
if not (1 <= m and m <= 12) then
date = Date(y, 1, 1)
if not date then return end
date = date + ((m - 1) .. 'm')
y, m = date.year, date.month
end
local days_hms
if not partial then
if hastime and H and M and S then
if not (0 <= H and H <= 23 and
0 <= M and M <= 59 and
0 <= S and S <= 59) then
days_hms = hms({ hour = H, minute = M, second = S })
end
end
if days_hms or not (1 <= d and d <= days_in_month(y, m, calendar)) then
date = date or Date(y, m, 1)
if not date then return end
date = date + (d - 1 + (days_hms or 0))
y, m, d = date.year, date.month, date.day
if days_hms then
H, M, S = date.hour, date.minute, date.second
end
end
end
numbers.year = y
numbers.month = m
numbers.day = d
if days_hms then
-- Don't set H unless it was valid because a valid H will set hastime.
numbers.hour = H
numbers.minute = M
numbers.second = S
end
end
end


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return
return
end
end
local y = numbers.y or numbers[1]
local y = numbers.year  or date.year
local m = numbers.m or numbers[2]
local m = numbers.month  or date.month
local d = numbers.d or numbers[3]
local d = numbers.day    or date.day
local H = numbers.H or numbers[4]
local H = numbers.hour
local M = numbers.M or numbers[5] or 0
local M = numbers.minute or date.minute or 0
local S = numbers.S or numbers[6] or 0
local S = numbers.second or date.second or 0
if not (y and m and d) then
local need_fix
return
if y and m and d then
end
date.partial = nil
if not (-9999 <= y and y <= 9999 and 1 <= m and m <= 12 and
if not (-9999 <= y and y <= 9999 and
1 <= d and d <= days_in_month(y, m, date.calname)) then
1 <= m and m <= 12 and
1 <= d and d <= days_in_month(y, m, date.calendar)) then
if not date.want_fix then
return
end
need_fix = true
end
elseif y and date.partial then
if d or not (-9999 <= y and y <= 9999) then
return
end
if m and not (1 <= m and m <= 12) then
if not date.want_fix then
return
end
need_fix = true
end
else
return
return
end
end
if H then
if date.partial then
date.hastime = true
H = nil  -- ignore any time
M = nil
S = nil
else
else
H = 0
if H then
-- It is not possible to set M or S without also setting H.
date.hastime = true
else
H = 0
end
if not (0 <= H and H <= 23 and
0 <= M and M <= 59 and
0 <= S and S <= 59) then
if date.want_fix then
need_fix = true
else
return
end
end
end
end
if not (0 <= H and H <= 23 and
date.want_fix = nil
0 <= M and M <= 59 and
if need_fix then
0 <= S and S <= 59) then
fix_numbers(numbers, y, m, d, H, M, S, date.partial, date.hastime, date.calendar)
return
return set_date_from_numbers(date, numbers, options)
end
end
date.year = y    -- -9999 to 9999 ('n BC' → year = 1 - n)
date.year = y    -- -9999 to 9999 ('n BC' → year = 1 - n)
date.month = m  -- 1 to 12
date.month = m  -- 1 to 12 (may be nil if partial)
date.day = d    -- 1 to 31
date.day = d    -- 1 to 31 (* = nil if partial)
date.hour = H    -- 0 to 59
date.hour = H    -- 0 to 59 (*)
date.minute = M  -- 0 to 59
date.minute = M  -- 0 to 59 (*)
date.second = S  -- 0 to 59
date.second = S  -- 0 to 59 (*)
date.isvalid = true
if type(options) == 'table' then
if type(options) == 'table' then
for _, k in ipairs({ 'am', 'era' }) do
for _, k in ipairs({ 'am', 'era', 'format' }) do
if options[k] then
if options[k] then
date.options[k] = options[k]
date.options[k] = options[k]
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end
end


local function make_option_table(options)
local function make_option_table(options1, options2)
-- If options is a string, return a table with its settings.
-- If options1 is a string, return a table with its settings, or
-- Otherwise return options (it should already be a table).
-- if it is a table, use its settings.
if type(options) == 'string' then
-- Missing options are set from table options2 or defaults.
-- Example: 'am:AM era:BC'
-- If a default is used, a flag is set so caller knows the value was not intentionally set.
local result = {}
-- Valid option settings are:
for item in options:gmatch('%S+') do
-- am: 'am', 'a.m.', 'AM', 'A.M.'
local lhs, rhs = item:match('^(%w+):(.*)$')
--    'pm', 'p.m.', 'PM', 'P.M.' (each has same meaning as corresponding item above)
-- era: 'BCMINUS', 'BCNEGATIVE', 'BC', 'B.C.', 'BCE', 'B.C.E.', 'AD', 'A.D.', 'CE', 'C.E.'
-- Option am = 'am' does not mean the hour is AM; it means 'am' or 'pm' is used, depending on the hour,
--    and am = 'pm' has the same meaning.
-- Similarly, era = 'BC' means 'BC' is used if year <= 0.
-- BCMINUS displays a MINUS if year < 0 and the display format does not include %{era}.
-- BCNEGATIVE is similar but displays a hyphen.
local result = { bydefault = {} }
if type(options1) == 'table' then
result.am = options1.am
result.era = options1.era
elseif type(options1) == 'string' then
-- Example: 'am:AM era:BC' or 'am=AM era=BC'.
for item in options1:gmatch('%S+') do
local lhs, rhs = item:match('^(%w+)[:=](.+)$')
if lhs then
if lhs then
result[lhs] = rhs
result[lhs] = rhs
end
end
end
end
return result
end
end
return options
options2 = type(options2) == 'table' and options2 or {}
local defaults = { am = 'am', era = 'BC' }
for k, v in pairs(defaults) do
if not result[k] then
if options2[k] then
result[k] = options2[k]
else
result[k] = v
result.bydefault[k] = true
end
end
end
return result
end
 
local ampm_options = {
-- lhs = input text accepted as an am/pm option
-- rhs = code used internally
['am']  = 'am',
['AM']  = 'AM',
['a.m.'] = 'a.m.',
['A.M.'] = 'A.M.',
['pm']  = 'am',  -- same as am
['PM']  = 'AM',
['p.m.'] = 'a.m.',
['P.M.'] = 'A.M.',
}
 
local era_text = {
-- Text for displaying an era with a positive year (after adjusting
-- by replacing year with 1 - year if date.year <= 0).
-- options.era = { year<=0 , year>0 }
['BCMINUS']    = { 'BC'    , ''    , isbc = true, sign = MINUS },
['BCNEGATIVE'] = { 'BC'    , ''    , isbc = true, sign = '-'  },
['BC']        = { 'BC'    , ''    , isbc = true },
['B.C.']      = { 'B.C.'  , ''    , isbc = true },
['BCE']        = { 'BCE'  , ''    , isbc = true },
['B.C.E.']    = { 'B.C.E.', ''    , isbc = true },
['AD']        = { 'BC'    , 'AD'  },
['A.D.']      = { 'B.C.'  , 'A.D.' },
['CE']        = { 'BCE'  , 'CE'  },
['C.E.']      = { 'B.C.E.', 'C.E.' },
}
 
local function get_era_for_year(era, year)
return (era_text[era] or era_text['BC'])[year > 0 and 2 or 1] or ''
end
end


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-- Return date formatted as a string using codes similar to those
-- Return date formatted as a string using codes similar to those
-- in the C strftime library function.
-- in the C strftime library function.
if not date.isvalid then
local sformat = string.format
return '(invalid)'
end
local shortcuts = {
local shortcuts = {
['%c'] = '%-I:%M %p %-d %B %Y%{era}',  -- date and time: 2:30 pm 1 April 2016
['%c'] = '%-I:%M %p %-d %B %-Y %{era}',  -- date and time: 2:30 pm 1 April 2016
['%x'] = '%-d %B %Y%{era}',            -- date:          1 April 2016
['%x'] = '%-d %B %-Y %{era}',            -- date:          1 April 2016
['%X'] = '%-I:%M %p',                 -- time:          2:30 pm
['%X'] = '%-I:%M %p',                   -- time:          2:30 pm
}
}
if shortcuts[format] then
format = shortcuts[format]
end
local codes = {
local codes = {
a = { field = 'dayabbr' },
a = { field = 'dayabbr' },
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M = { fmt = '%02d', fmt2 = '%d', field = 'minute' },
M = { fmt = '%02d', fmt2 = '%d', field = 'minute' },
S = { fmt = '%02d', fmt2 = '%d', field = 'second' },
S = { fmt = '%02d', fmt2 = '%d', field = 'second' },
j = { fmt = '%03d', fmt2 = '%d', field = 'doy' },
j = { fmt = '%03d', fmt2 = '%d', field = 'dayofyear' },
I = { fmt = '%02d', fmt2 = '%d', field = 'hour', special = 'hour12' },
I = { fmt = '%02d', fmt2 = '%d', field = 'hour', special = 'hour12' },
p = { field = 'hour', special = 'am' },
p = { field = 'hour', special = 'am' },
}
}
options = make_option_table(options or date.options)
options = make_option_table(options, date.options)
local amopt = options.am
local amopt = options.am
local eraopt = options.era
local eraopt = options.era
local function replace_code(modifier, id)
local function replace_code(spaces, modifier, id)
local code = codes[id]
local code = codes[id]
if code then
if code then
Line 256: Line 388:
end
end
local value = date[code.field]
local value = date[code.field]
if not value then
return nil  -- an undefined field in a partial date
end
local special = code.special
local special = code.special
if special then
if special then
Line 266: Line 401:
['AM'] = { 'AM', 'PM' },
['AM'] = { 'AM', 'PM' },
['A.M.'] = { 'A.M.', 'P.M.' },
['A.M.'] = { 'A.M.', 'P.M.' },
})[amopt] or { 'am', 'pm' }
})[ampm_options[amopt]] or { 'am', 'pm' }
return value < 12 and ap[1] or ap[2]
return (spaces == '' and '' or '&nbsp;') .. (value < 12 and ap[1] or ap[2])
end
end
end
end
if code.field == 'year' then
if code.field == 'year' then
if eraopt == 'BCMINUS' or eraopt == 'BCNEGATIVE' then
local sign = (era_text[eraopt] or {}).sign
local sign
if not sign or format:find('%{era}', 1, true) then
sign = ''
if value <= 0 then
value = 1 - value
end
else
if value >= 0 then
if value >= 0 then
sign = ''
sign = ''
else
else
sign = eraopt == 'BCMINUS' and MINUS or '-'
value = -value
value = -value
end
end
return sign .. string.format(fmt, value)
end
if value <= 0 then
value = 1 - value
end
end
return spaces .. sign .. sformat(fmt, value)
end
end
return fmt and string.format(fmt, value) or value
return spaces .. (fmt and sformat(fmt, value) or value)
end
end
end
end
local function replace_property(id)
local function replace_property(spaces, id)
if id == 'era' then
-- Special case so can use local era option.
local result = get_era_for_year(eraopt, date.year)
if result == '' then
return ''
end
return (spaces == '' and '' or '&nbsp;') .. result
end
local result = date[id]
local result = date[id]
if type(result) == 'string' then
if type(result) == 'string' then
if id == 'era' and result ~= '' then
return spaces .. result
-- Assume era follows a date.
return '&nbsp;' .. result
end
return result
end
end
if type(result) == 'number' then
if type(result) == 'number' then
return tostring(result)
return spaces .. tostring(result)
end
end
if type(result) == 'boolean' then
if type(result) == 'boolean' then
return result and '1' or '0'
return spaces .. (result and '1' or '0')
end
end
-- This occurs, for example, if id is the name of a function.
-- This occurs if id is an undefined field in a partial date, or is the name of a function.
return nil
return nil
end
if shortcuts[format] then
format = shortcuts[format]
end
end
local PERCENT = '\127PERCENT\127'
local PERCENT = '\127PERCENT\127'
return (format
return (format
:gsub('%%%%', PERCENT)
:gsub('%%%%', PERCENT)
:gsub('%%{(%w+)}', replace_property)
:gsub('(%s*)%%{(%w+)}', replace_property)
:gsub('%%(-?)(%a)', replace_code)
:gsub('(%s*)%%(%-?)(%a)', replace_code)
:gsub(PERCENT, '%%')
:gsub(PERCENT, '%%')
)
)
end
end


local function date_text(date, fmt, options)
local function _date_text(date, fmt, options)
-- Return formatted string from given date.
-- Return a formatted string representing the given date.
if not (type(date) == 'table' and date.isvalid) then
if not is_date(date) then
return '(invalid)'
error('date:text: need a date (use "date:text()" with a colon)', 2)
end
end
if type(fmt) ~= 'string' then
if type(fmt) == 'string' and fmt:match('%S') then
fmt = '%Y-%m-%d'
if fmt:find('%', 1, true) then
return strftime(date, fmt, options)
end
elseif date.partial then
fmt = date.month and 'my' or 'y'
else
fmt = 'dmy'
if date.hastime then
if date.hastime then
if date.second > 0 then
fmt = (date.second > 0 and 'hms ' or 'hm ') .. fmt
fmt = fmt .. ' %H:%M:%S'
else
fmt = fmt .. ' %H:%M'
end
end
end
return strftime(date, fmt, options or { era = 'BCMINUS' })
end
end
if fmt:find('%', 1, true) then
local function bad_format()
-- For consistency with other format processing, return given format
-- (or cleaned format if original was not a string) if invalid.
return mw.text.nowiki(fmt)
end
if date.partial then
-- Ignore days in standard formats like 'ymd'.
if fmt == 'ym' or fmt == 'ymd' then
fmt = date.month and '%Y-%m %{era}' or '%Y %{era}'
elseif fmt == 'my' or fmt == 'dmy' or fmt == 'mdy' then
fmt = date.month and '%B %-Y %{era}' or '%-Y %{era}'
elseif fmt == 'y' then
fmt = date.month and '%-Y %{era}' or '%-Y %{era}'
else
return bad_format()
end
return strftime(date, fmt, options)
return strftime(date, fmt, options)
end
end
local function hm_fmt()
local plain = make_option_table(options, date.options).bydefault.am
return plain and '%H:%M' or '%-I:%M %p'
end
local need_time = date.hastime
local t = collection()
local t = collection()
for item in fmt:gmatch('%S+') do
for item in fmt:gmatch('%S+') do
local f
local f
if item == 'hm' then
if item == 'hm' then
f = '%H:%M'
f = hm_fmt()
need_time = false
elseif item == 'hms' then
elseif item == 'hms' then
f = '%H:%M:%S'
f = '%H:%M:%S'
need_time = false
elseif item == 'ymd' then
elseif item == 'ymd' then
f = '%Y:%m:%d%{era}'
f = '%Y-%m-%d %{era}'
elseif item == 'mdy' then
elseif item == 'mdy' then
f = '%B %-d, %Y%{era}'
f = '%B %-d, %-Y %{era}'
elseif item == 'dmy' then
elseif item == 'dmy' then
f = '%-d %B %Y%{era}'
f = '%-d %B %-Y %{era}'
else
else
return '(invalid format)'
return bad_format()
end
end
t:add(f)
t:add(f)
end
end
return strftime(date, t:join(' '), options)
fmt = t:join(' ')
if need_time then
fmt = hm_fmt() .. ' ' .. fmt
end
return strftime(date, fmt, options)
end
end


Line 385: Line 549:
}
}


local function month_number(text)
local function name_to_number(text, translate)
if type(text) == 'string' then
if type(text) == 'string' then
local month_names = {
return translate[text:lower()]
jan = 1, january = 1,
feb = 2, february = 2,
mar = 3, march = 3,
apr = 4, april = 4,
may = 5,
jun = 6, june = 6,
jul = 7, july = 7,
aug = 8, august = 8,
sep = 9, september = 9,
oct = 10, october = 10,
nov = 11, november = 11,
dec = 12, december = 12
}
return month_names[text:lower()]
end
end
end
end


-- A table to get the current year/month/day (UTC), but only if needed.
local function day_number(text)
local current = setmetatable({}, {
return name_to_number(text, {
__index = function (self, key)
sun = 0, sunday = 0,
local d = os.date('!*t')
mon = 1, monday = 1,
self.year = d.year
tue = 2, tuesday = 2,
self.month = d.month
wed = 3, wednesday = 3,
self.day = d.day
thu = 4, thursday = 4,
self.hour = d.hour
fri = 5, friday = 5,
self.minute = d.min
sat = 6, saturday = 6,
self.second = d.sec
})
return rawget(self, key)
end
 
local function month_number(text)
return name_to_number(text, {
jan = 1, january = 1,
feb = 2, february = 2,
mar = 3, march = 3,
apr = 4, april = 4,
may = 5,
jun = 6, june = 6,
jul = 7, july = 7,
aug = 8, august = 8,
sep = 9, september = 9, sept = 9,
oct = 10, october = 10,
nov = 11, november = 11,
dec = 12, december = 12,
})
end
 
local function _list_text(list, fmt)
-- Return a list of formatted strings from a list of dates.
if not type(list) == 'table' then
error('date:list:text: need "list:text()" with a colon', 2)
end
local result = { join = _list_join }
for i, date in ipairs(list) do
result[i] = date:text(fmt)
end
end
})
return result
end


local function date_component(named, positional, component)
local function _date_list(date, spec)
-- Return the first of the two arguments (named like {{example|year=2001}}
-- Return a possibly empty numbered table of dates meeting the specification.
-- or positional like {{example|2001}}) that is not nil and is not empty.
-- Dates in the list are in ascending order (oldest date first).
-- If both are nil, return the current date component, if specified.
-- The spec should be a string of form "<count> <day> <op>"
-- This translates empty arguments passed to the template to nil, and
-- where each item is optional and
-- optionally replaces a nil argument with a value from the current date.
--  count = number of items wanted in list
named = strip_to_nil(named)
--   day = abbreviation or name such as Mon or Monday
if named then
--  op = >, >=, <, <= (default is > meaning after date)
return named
-- If no count is given, the list is for the specified days in date's month.
-- The default day is date's day.
-- The spec can also be a positive or negative number:
--  -5 is equivalent to '5 <'
--   5  is equivalent to '5' which is '5 >'
if not is_date(date) then
error('date:list: need a date (use "date:list()" with a colon)', 2)
end
local list = { text = _list_text }
if date.partial then
return list
end
local count, offset, operation
local ops = {
['>='] = { before = false, include = true  },
['>']  = { before = false, include = false },
['<='] = { before = true , include = true  },
['<']  = { before = true , include = false },
}
if spec then
if type(spec) == 'number' then
count = floor(spec + 0.5)
if count < 0 then
count = -count
operation = ops['<']
end
elseif type(spec) == 'string' then
local num, day, op = spec:match('^%s*(%d*)%s*(%a*)%s*([<>=]*)%s*$')
if not num then
return list
end
if num ~= '' then
count = tonumber(num)
end
if day ~= '' then
local dow = day_number(day:gsub('[sS]$', ''))  -- accept plural days
if not dow then
return list
end
offset = dow - date.dow
end
operation = ops[op]
else
return list
end
end
end
positional = strip_to_nil(positional)
offset = offset or 0
if positional then
operation = operation or ops['>']
return positional
local datefrom, dayfirst, daylast
if operation.before then
if offset > 0 or (offset == 0 and not operation.include) then
offset = offset - 7
end
if count then
if count > 1 then
offset = offset - 7*(count - 1)
end
datefrom = date + offset
else
daylast = date.day + offset
dayfirst = daylast % 7
if dayfirst == 0 then
dayfirst = 7
end
end
else
if offset < 0 or (offset == 0 and not operation.include) then
offset = offset + 7
end
if count then
datefrom = date + offset
else
dayfirst = date.day + offset
daylast = date.monthdays
end
end
if not count then
if daylast < dayfirst then
return list
end
count = floor((daylast - dayfirst)/7) + 1
datefrom = Date(date, {day = dayfirst})
end
end
if component then
for i = 1, count do
return current[component]
if not datefrom then break end  -- exceeds date limits
list[i] = datefrom
datefrom = datefrom + 7
end
end
return nil
return list
end
end


local era_text = {
-- A table to get the current date/time (UTC), but only if needed.
-- options.era = { year<0  , year>0 }
local current = setmetatable({}, {
['BCMINUS']    = { MINUS  , ''    },
__index = function (self, key)
['BCNEGATIVE'] = { '-'    , ''    },
local d = os.date('!*t')
['BC']        = { 'BC'   , ''    },
self.year = d.year
['B.C.']      = { 'B.C.'  , ''    },
self.month = d.month
['BCE']        = { 'BCE'  , ''    },
self.day = d.day
['B.C.E.']    = { 'B.C.E.', ''    },
self.hour = d.hour
['AD']        = { 'BC'    , 'AD'  },
self.minute = d.min
['A.D.']      = { 'B.C.'  , 'A.D.' },
self.second = d.sec
['CE']        = { 'BCE'  , 'CE'  },
return rawget(self, key)
['C.E.']      = { 'B.C.E.', 'C.E.' },
end })
}


local function extract_date(text)
local function extract_date(newdate, text)
-- Parse the date/time in text and return n, o where
-- Parse the date/time in text and return n, o where
--  n = table of numbers with date/time fields
--  n = table of numbers with date/time fields
--  o = table of options for AM/PM or AD/BC, if any
--  o = table of options for AM/PM or AD/BC or format, if any
-- or return nothing if date is known to be invalid.
-- or return nothing if date is known to be invalid.
-- Caller determines if the values in n are valid.
-- Caller determines if the values in n are valid.
-- Dates of form d/m/y, m/d/y, y/m/d are rejected as ambiguous and undesirable.
-- A year must be positive ('1' to '9999'); use 'BC' for BC.
-- In a y-m-d string, the year must be four digits to avoid ambiguity
-- ('0001' to '9999'). The only way to enter year <= 0 is by specifying
-- the date as three numeric parameters like ymd Date(-1, 1, 1).
-- Dates of form d/m/y, m/d/y, y/m/d are rejected as potentially ambiguous.
local date, options = {}, {}
local date, options = {}, {}
if text:sub(-1) == 'Z' then
-- Extract date/time from a Wikidata timestamp.
-- The year can be 1 to 16 digits but this module handles 1 to 4 digits only.
-- Examples: '+2016-06-21T14:30:00Z', '-0000000180-00-00T00:00:00Z'.
local sign, y, m, d, H, M, S = text:match('^([+%-])(%d+)%-(%d%d)%-(%d%d)T(%d%d):(%d%d):(%d%d)Z$')
if sign then
y = tonumber(y)
if sign == '-' and y > 0 then
y = -y
end
if y <= 0 then
options.era = 'BCE'
end
date.year = y
m = tonumber(m)
d = tonumber(d)
H = tonumber(H)
M = tonumber(M)
S = tonumber(S)
if m == 0 then
newdate.partial = true
return date, options
end
date.month = m
if d == 0 then
newdate.partial = true
return date, options
end
date.day = d
if H > 0 or M > 0 or S > 0 then
date.hour = H
date.minute = M
date.second = S
end
return date, options
end
return
end
local function extract_ymd(item)
local function extract_ymd(item)
local ystr, mstr, dstr = item:match('^(%d%d%d%d)-(%w+)-(%d%d?)$')
-- Called when no day or month has been set.
if ystr then
local y, m, d = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')
local m
if y then
if mstr:match('^%d%d?$') then
if date.year then
m = tonumber(mstr)
return
end
if m:match('^%d%d?$') then
m = tonumber(m)
else
else
m = month_number(mstr)
m = month_number(m)
end
end
if m then
if m then
date.y = tonumber(ystr)
date.year = tonumber(y)
date.m = m
date.month = m
date.d = tonumber(dstr)
date.day = tonumber(d)
return true
end
end
end
local function extract_day_or_year(item)
-- Called when a day would be valid, or
-- when a year would be valid if no year has been set and partial is set.
local number, suffix = item:match('^(%d%d?%d?%d?)(.*)$')
if number then
local n = tonumber(number)
if #number <= 2 and n <= 31 then
suffix = suffix:lower()
if suffix == '' or suffix == 'st' or suffix == 'nd' or suffix == 'rd' or suffix == 'th' then
date.day = n
return true
end
elseif suffix == '' and newdate.partial and not date.year then
date.year = n
return true
return true
end
end
Line 479: Line 797:
end
end
local function extract_month(item)
local function extract_month(item)
-- A month must be given as a name or abbreviation; a number would be ambiguous.
-- A month must be given as a name or abbreviation; a number could be ambiguous.
local m = month_number(item)
local m = month_number(item)
if m then
if m then
date.m = m
date.month = m
return true
return true
end
end
Line 488: Line 806:
local function extract_time(item)
local function extract_time(item)
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
if date.H or not h then
if date.hour or not h then
return
return
end
end
Line 497: Line 815:
end
end
end
end
date.H = tonumber(h)
date.hour = tonumber(h)
date.M = tonumber(m)
date.minute = tonumber(m)
date.S = tonumber(s)  -- nil if empty string
date.second = tonumber(s)  -- nil if empty string
return true
return true
end
end
local ampm_options = {
['am']  = 'am',
['AM']  = 'AM',
['a.m.'] = 'a.m.',
['A.M.'] = 'A.M.',
['pm']  = 'am',  -- same as am
['PM']  = 'AM',
['p.m.'] = 'a.m.',
['P.M.'] = 'A.M.',
}
local item_count = 0
local item_count = 0
local index_time
local index_time
local function set_ampm(item)
local function set_ampm(item)
local H = date.H
local H = date.hour
if H and not options.am and index_time + 1 == item_count then
if H and not options.am and index_time + 1 == item_count then
options.am = ampm_options[item]
options.am = ampm_options[item] -- caller checked this is not nil
if item:match('^[Aa]') then
if item:match('^[Aa]') then
if not (1 <= H and H <= 12) then
if not (1 <= H and H <= 12) then
Line 523: Line 831:
end
end
if H == 12 then
if H == 12 then
date.H = 0
date.hour = 0
end
end
else
else
Line 530: Line 838:
end
end
if H <= 11 then
if H <= 11 then
date.H = H + 12
date.hour = H + 12
end
end
end
end
Line 536: Line 844:
end
end
end
end
for item in text:gsub(',', ' '):gmatch('%S+') do
for item in text:gsub(',', ' '):gsub('&nbsp;', ' '):gmatch('%S+') do
-- Accept options in peculiar places; if duplicated, last wins.
item_count = item_count + 1
item_count = item_count + 1
if era_text[item] then
if era_text[item] then
-- Era is accepted in peculiar places.
if options.era then
return
end
options.era = item
options.era = item
elseif ampm_options[item] then
elseif ampm_options[item] then
Line 550: Line 861:
end
end
index_time = item_count
index_time = item_count
elseif date.d and date.m then
elseif date.day and date.month then
if date.y then
if date.year then
return  -- should be nothing more so item is invalid
return  -- should be nothing more so item is invalid
end
end
Line 557: Line 868:
return
return
end
end
date.y = tonumber(item)
date.year = tonumber(item)
elseif date.d then
elseif date.day then
if not extract_month(item) then
if not extract_month(item) then
return
return
end
end
elseif date.m then
elseif date.month then
if not item:match('^(%d%d?)$') then
if not extract_day_or_year(item) then
return
return
end
end
date.d = tonumber(item)
elseif extract_month(item) then
elseif not extract_ymd(item) then
options.format = 'mdy'
if item:match('^(%d%d?)$') then
elseif extract_ymd(item) then
date.d = tonumber(item)
options.format = 'ymd'
elseif not extract_month(item) then
elseif extract_day_or_year(item) then
return
if date.day then
options.format = 'dmy'
end
end
else
return
end
end
end
if not date.year or date.year == 0 then
return
end
local era = era_text[options.era]
if era and era.isbc then
date.year = 1 - date.year
end
end
return date, options
return date, options
end
end


-- Metatable for some operations on dates.
local function autofill(date1, date2)
-- For Lua 5.1, __lt does not work if the metatable is an anonymous table.
-- Fill any missing month or day in each date using the
local Date -- forward declaration
-- corresponding component from the other date, if present,
local datemt = {
-- or with 1 if both dates are missing the month or day.
__eq = function (lhs, rhs)
-- This gives a good result for calculating the difference
-- Return true if dates identify same date/time where, for example,
-- between two partial dates when no range is wanted.
-- (-4712, 1, 1, 'Julian') == (-4713, 11, 24, 'Gregorian').
-- Return filled date1, date2 (two full dates).
return lhs.isvalid and rhs.isvalid and lhs.jdz == rhs.jdz
local function filled(a, b)
end,
-- Return date a filled, if necessary, with month and/or day from date b.
__lt = function (lhs, rhs)
-- The filled day is truncated to fit the number of days in the month.
-- Return true if lhs < rhs.
local fillmonth, fillday
if not lhs.isvalid then
if not a.month then
return true
fillmonth = b.month or 1
end
if not a.day then
fillday = b.day or 1
end
if fillmonth or fillday then -- need to create a new date
a = Date(a, {
month = fillmonth,
day = math.min(fillday or a.day, days_in_month(a.year, fillmonth or a.month, a.calendar))
})
end
return a
end
return filled(date1, date2), filled(date2, date1)
end
 
local function date_add_sub(lhs, rhs, is_sub)
-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
-- or return nothing if invalid.
-- The result is nil if the calculated date exceeds allowable limits.
-- Caller ensures that lhs is a date; its properties are copied for the new date.
if lhs.partial then
-- Adding to a partial is not supported.
-- Can subtract a date or partial from a partial, but this is not called for that.
return
end
local function is_prefix(text, word, minlen)
local n = #text
return (minlen or 1) <= n and n <= #word and text == word:sub(1, n)
end
local function do_days(n)
local forcetime, jd
if floor(n) == n then
jd = lhs.jd
else
forcetime = not lhs.hastime
jd = lhs.jdz
end
jd = jd + (is_sub and -n or n)
if forcetime then
jd = tostring(jd)
if not jd:find('.', 1, true) then
jd = jd .. '.0'
end
end
return Date(lhs, 'juliandate', jd)
end
if type(rhs) == 'number' then
-- Add/subtract days, including fractional days.
return do_days(rhs)
end
if type(rhs) == 'string' then
-- rhs is a single component like '26m' or '26 months' (with optional sign).
-- Fractions like '3.25d' are accepted for the units which are handled as days.
local sign, numstr, id = rhs:match('^%s*([+-]?)([%d%.]+)%s*(%a+)$')
if sign then
if sign == '-' then
is_sub = not (is_sub and true or false)
end
local y, m, days
local num = tonumber(numstr)
if not num then
return
end
id = id:lower()
if is_prefix(id, 'years') then
y = num
m = 0
elseif is_prefix(id, 'months') then
y = floor(num / 12)
m = num % 12
elseif is_prefix(id, 'weeks') then
days = num * 7
elseif is_prefix(id, 'days') then
days = num
elseif is_prefix(id, 'hours') then
days = num / 24
elseif is_prefix(id, 'minutes', 3) then
days = num / (24 * 60)
elseif is_prefix(id, 'seconds') then
days = num / (24 * 3600)
else
return
end
if days then
return do_days(days)
end
if numstr:find('.', 1, true) then
return
end
if is_sub then
y = -y
m = -m
end
assert(-11 <= m and m <= 11)
y = lhs.year + y
m = lhs.month + m
if m > 12 then
y = y + 1
m = m - 12
elseif m < 1 then
y = y - 1
m = m + 12
end
local d = math.min(lhs.day, days_in_month(y, m, lhs.calendar))
return Date(lhs, y, m, d)
end
end
if not rhs.isvalid then
end
return false
if is_diff(rhs) then
local days = rhs.age_days
if (is_sub or false) ~= (rhs.isnegative or false) then
days = -days
end
end
return lhs.jdz < rhs.jdz
return lhs + days
end,
end
end
 
local full_date_only = {
dayabbr = true,
dayname = true,
dow = true,
dayofweek = true,
dowiso = true,
dayofweekiso = true,
dayofyear = true,
gsd = true,
juliandate = true,
jd = true,
jdz = true,
jdnoon = true,
}
 
-- Metatable for a date's calculated fields.
local datemt = {
__index = function (self, key)
__index = function (self, key)
if rawget(self, 'partial') then
if full_date_only[key] then return end
if key == 'monthabbr' or key == 'monthdays' or key == 'monthname' then
if not self.month then return end
end
end
local value
local value
if key == 'dayabbr' then
if key == 'dayabbr' then
Line 604: Line 1,058:
value = day_info[self.dow][2]
value = day_info[self.dow][2]
elseif key == 'dow' then
elseif key == 'dow' then
value = (self.jd + 1) % 7  -- day-of-week 0=Sun to 6=Sat
value = (self.jdnoon + 1) % 7  -- day-of-week 0=Sun to 6=Sat
elseif key == 'dayofweek' then
value = self.dow
elseif key == 'dowiso' then
elseif key == 'dowiso' then
value = (self.jd % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
value = (self.jdnoon % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
elseif key == 'doy' then
elseif key == 'dayofweekiso' then
local first = Date(self.year, 1, 1, self.calname).jd
value = self.dowiso
value = self.jd - first + 1  -- day-of-year 1 to 366
elseif key == 'dayofyear' then
local first = Date(self.year, 1, 1, self.calendar).jdnoon
value = self.jdnoon - first + 1  -- day-of-year 1 to 366
elseif key == 'era' then
elseif key == 'era' then
-- Era text from year and options.
-- Era text (never a negative sign) from year and options.
local eraopt = self.options.era
value = get_era_for_year(self.options.era, self.year)
local sign
elseif key == 'format' then
if self.year == 0 then
value = self.options.format or 'dmy'
sign = (eraopt == 'BCMINUS' or eraopt == 'BCNEGATIVE') and 2 or 1
else
sign = self.year > 0 and 2 or 1
end
value = era_text[eraopt][sign]
elseif key == 'gsd' then
elseif key == 'gsd' then
-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
-- which is JDN = 1721426, and is from jd 1721425.5 to 1721426.49999.
-- which is from jd 1721425.5 to 1721426.49999.
value = math.floor(self.jd - 1721424.5)
value = floor(self.jd - 1721424.5)
elseif key == 'jd' or key == 'jdz' then
elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
local jd, jdz = julian_date(self)
local jd, jdz = julian_date(self)
rawset(self, 'juliandate', jd)
rawset(self, 'jd', jd)
rawset(self, 'jd', jd)
rawset(self, 'jdz', jdz)
rawset(self, 'jdz', jdz)
return key == 'jd' and jd or jdz
return key == 'jdz' and jdz or jd
elseif key == 'is_leap_year' then
elseif key == 'jdnoon' then
value = is_leap_year(self.year, self.calname)
-- Julian date at noon (an integer) on the calendar day when jd occurs.
value = floor(self.jd + 0.5)
elseif key == 'isleapyear' then
value = is_leap_year(self.year, self.calendar)
elseif key == 'monthabbr' then
elseif key == 'monthabbr' then
value = month_info[self.month][1]
value = month_info[self.month][1]
elseif key == 'monthdays' then
value = days_in_month(self.year, self.month, self.calendar)
elseif key == 'monthname' then
elseif key == 'monthname' then
value = month_info[self.month][2]
value = month_info[self.month][2]
Line 642: Line 1,101:
end,
end,
}
}
-- Date operators.
local function mt_date_add(lhs, rhs)
if not is_date(lhs) then
lhs, rhs = rhs, lhs  -- put date on left (it must be a date for this to have been called)
end
return date_add_sub(lhs, rhs)
end
local function mt_date_sub(lhs, rhs)
if is_date(lhs) then
if is_date(rhs) then
return DateDiff(lhs, rhs)
end
return date_add_sub(lhs, rhs, true)
end
end
local function mt_date_concat(lhs, rhs)
return tostring(lhs) .. tostring(rhs)
end
local function mt_date_tostring(self)
return self:text()
end
local function mt_date_eq(lhs, rhs)
-- Return true if dates identify same date/time where, for example,
-- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.
-- This is called only if lhs and rhs have the same type and the same metamethod.
if lhs.partial or rhs.partial then
-- One date is partial; the other is a partial or a full date.
-- The months may both be nil, but must be the same.
return lhs.year == rhs.year and lhs.month == rhs.month and lhs.calendar == rhs.calendar
end
return lhs.jdz == rhs.jdz
end
local function mt_date_lt(lhs, rhs)
-- Return true if lhs < rhs, for example,
-- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
-- This is called only if lhs and rhs have the same type and the same metamethod.
if lhs.partial or rhs.partial then
-- One date is partial; the other is a partial or a full date.
if lhs.calendar ~= rhs.calendar then
return lhs.calendar == 'Julian'
end
if lhs.partial then
lhs = lhs.partial.first
end
if rhs.partial then
rhs = rhs.partial.first
end
end
return lhs.jdz < rhs.jdz
end


--[[ Examples of syntax to construct a date:
--[[ Examples of syntax to construct a date:
Line 649: Line 1,164:
Date('currentdate')
Date('currentdate')
Date('currentdatetime')
Date('currentdatetime')
LATER: Following are not yet implemented:
Date('currentdate', H, M, S)        current date with given time
Date('1 April 1995', 'julian')      parse date from text
Date('1 April 1995', 'julian')      parse date from text
Date('1 April 1995 AD', 'julian')  AD, CE, BC, BCE (using one of these sets a flag to do same for output)
Date('1 April 1995 AD', 'julian')  using an era sets a flag to do the same for output
Date('04:30:59 1 April 1995', 'julian')
Date('04:30:59 1 April 1995', 'julian')
Date(date)                          copy of an existing date
Date(date, t)                      same, updated with y,m,d,H,M,S fields from table t
Date(t)                      date with y,m,d,H,M,S fields from table t
]]
]]
function Date(...)  -- for forward declaration above
function Date(...)  -- for forward declaration above
-- Return a table to hold a date assuming a uniform calendar always applies (proleptic).
-- Return a table holding a date assuming a uniform calendar always applies
-- If invalid, return an empty table which is regarded as invalid.
-- (proleptic Gregorian calendar or proleptic Julian calendar), or
-- return nothing if date is invalid.
-- A partial date has a valid year, however its month may be nil, and
-- its day and time fields are nil.
-- Field partial is set to false (if a full date) or a table (if a partial date).
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
local result = {
local newdate = {
isvalid = false, -- false avoids __index lookup
_id = uniq,
calname = 'Gregorian',  -- default is Gregorian calendar
calendar = 'Gregorian',  -- default is Gregorian calendar
hastime = false,  -- true if input sets a time
hastime = false,  -- true if input sets a time
hour = 0,  -- always set hour/minute/second so don't have to handle nil
hour = 0,  -- always set hour/minute/second so don't have to handle nil
minute = 0,
minute = 0,
second = 0,
second = 0,
month_days = function (self, month)
options = {},
return days_in_month(self.year, month, self.calname)
list = _date_list,
subtract = function (self, rhs, options)
return DateDiff(self, rhs, options)
end,
end,
-- Valid option settings are:
text = _date_text,
-- am: 'am', 'a.m.', 'AM', 'A.M.'
-- era: 'BCMINUS', 'BCNEGATIVE', 'BC', 'B.C.', 'BCE', 'B.C.E.', 'AD', 'A.D.', 'CE', 'C.E.'
options = { am = 'am', era = 'BC' },
text = date_text,
}
}
local argtype, datetext
local argtype, datetext, is_copy, jd_number, tnums
local numbers = collection()
local numindex = 0
local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }
local numbers = {}
for _, v in ipairs({...}) do
for _, v in ipairs({...}) do
v = strip_to_nil(v)
v = strip_to_nil(v)
Line 683: Line 1,203:
-- Ignore empty arguments after stripping so modules can directly pass template parameters.
-- Ignore empty arguments after stripping so modules can directly pass template parameters.
elseif calendars[vlower] then
elseif calendars[vlower] then
result.calname = calendars[vlower]
newdate.calendar = calendars[vlower]
elseif vlower == 'partial' then
newdate.partial = true
elseif vlower == 'fix' then
newdate.want_fix = true
elseif is_date(v) then
-- Copy existing date (items can be overridden by other arguments).
if is_copy or tnums then
return
end
is_copy = true
newdate.calendar = v.calendar
newdate.partial = v.partial
newdate.hastime = v.hastime
newdate.options = v.options
newdate.year = v.year
newdate.month = v.month
newdate.day = v.day
newdate.hour = v.hour
newdate.minute = v.minute
newdate.second = v.second
elseif type(v) == 'table' then
if tnums then
return
end
tnums = {}
local tfields = { year=1, month=1, day=1, hour=2, minute=2, second=2 }
for tk, tv in pairs(v) do
if tfields[tk] then
tnums[tk] = tonumber(tv)
end
if tfields[tk] == 2 then
newdate.hastime = true
end
end
else
else
local num = tonumber(v)
local num = tonumber(v)
if not num and argtype == 'setdate' and numbers.n == 1 then
if not num and argtype == 'setdate' and numindex == 1 then
num = month_number(v)
num = month_number(v)
end
end
Line 693: Line 1,247:
argtype = 'setdate'
argtype = 'setdate'
end
end
numbers:add(num)
if argtype == 'setdate' and numindex < 6 then
if argtype == 'juliandate' then
numindex = numindex + 1
numbers[numfields[numindex]] = num
elseif argtype == 'juliandate' and not jd_number then
jd_number = num
if type(v) == 'string' then
if type(v) == 'string' then
if v:find('.', 1, true) then
if v:find('.', 1, true) then
result.hastime = true
newdate.hastime = true
end
end
elseif num ~= math.floor(num) then
elseif num ~= floor(num) then
-- The given value was a number. The time will be used
-- The given value was a number. The time will be used
-- if the fractional part is nonzero.
-- if the fractional part is nonzero.
result.hastime = true
newdate.hastime = true
end
end
else
return
end
end
elseif argtype then
elseif argtype then
return {}
return
elseif type(v) == 'string' then
elseif type(v) == 'string' then
if v == 'currentdate' or v == 'currentdatetime' or v == 'juliandate' then
if v == 'currentdate' or v == 'currentdatetime' or v == 'juliandate' then
Line 715: Line 1,274:
end
end
else
else
return {}
return
end
end
end
end
end
end
if argtype == 'datetext' then
if argtype == 'datetext' then
if not (numbers.n == 0 and
if tnums or not set_date_from_numbers(newdate, extract_date(newdate, datetext)) then
set_date_from_numbers(result,
return
extract_date(datetext))) then
return {}
end
end
elseif argtype == 'juliandate' then
elseif argtype == 'juliandate' then
if numbers.n == 1 then
newdate.partial = nil
result.jd = numbers[1]
newdate.jd = jd_number
set_date_from_jd(result)
if not set_date_from_jd(newdate) then
else
return
return {}
end
end
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
result.year = current.year
newdate.partial = nil
result.month = current.month
newdate.year = current.year
result.day = current.day
newdate.month = current.month
newdate.day = current.day
if argtype == 'currentdatetime' then
if argtype == 'currentdatetime' then
result.hour = current.hour
newdate.hour = current.hour
result.minute = current.minute
newdate.minute = current.minute
result.second = current.second
newdate.second = current.second
result.hastime = true
newdate.hastime = true
end
end
result.calname = 'Gregorian'  -- ignore any given calendar name
newdate.calendar = 'Gregorian'  -- ignore any given calendar name
result.isvalid = true
elseif argtype == 'setdate' then
elseif argtype == 'setdate' then
if not set_date_from_numbers(result, numbers) then
if tnums or not set_date_from_numbers(newdate, numbers) then
return {}
return
end
elseif not (is_copy or tnums) then
return
end
if tnums then
newdate.jd = nil  -- force recalculation in case jd was set before changes from tnums
if not set_date_from_numbers(newdate, tnums) then
return
end
end
end
if newdate.partial then
local year = newdate.year
local month = newdate.month
local first = Date(year, month or 1, 1, newdate.calendar)
month = month or 12
local last = Date(year, month, days_in_month(year, month), newdate.calendar)
newdate.partial = { first = first, last = last }
else
else
return {}
newdate.partial = false  -- avoid index lookup
end
end
return setmetatable(result, datemt)
setmetatable(newdate, datemt)
local readonly = {}
local mt = {
__index = newdate,
__newindex = function(t, k, v) error('date.' .. tostring(k) .. ' is read-only', 2) end,
__add = mt_date_add,
__sub = mt_date_sub,
__concat = mt_date_concat,
__tostring = mt_date_tostring,
__eq = mt_date_eq,
__lt = mt_date_lt,
}
return setmetatable(readonly, mt)
end
end


local function DateDiff(date1, date2)
local function _diff_age(diff, code, options)
-- Return a table to with the difference between the two given dates.
-- Return a tuple of integer values from diff as specified by code, except that
-- Difference is negative if the second date is older than the first.
-- each integer may be a list of two integers for a diff with a partial date, or
-- TODO Replace with something using Julian dates?
-- return nil if the code is not supported.
--     Who checks for isvalid()?
-- If want round, the least significant unit is rounded to nearest whole unit.
--      Handle calname == 'Julian'
-- For a duration, an extra day is added.
local calname = 'Gregorian'  -- TODO fix
local wantround, wantduration, wantrange
local isnegative
if type(options) == 'table' then
if date2 < date1 then
wantround = options.round
isnegative = true
wantduration = options.duration
date1, date2 = date2, date1
wantrange = options.range
else
wantround = options
end
if not is_diff(diff) then
local f = wantduration and 'duration' or 'age'
error(f .. ': need a date difference (use "diff:' .. f .. '()" with a colon)', 2)
end
end
-- It is known that date1 <= date2.
if diff.partial then
local y1, m1 = date1.year, date1.month
-- Ignore wantround, wantduration.
local y2, m2 = date2.year, date2.month
local function choose(v)
local years, months, days = y2 - y1, m2 - m1, date2.day - date1.day
if type(v) == 'table' then
if days < 0 then
if not wantrange or v[1] == v[2] then
days = days + days_in_month(y1, m1, calname)
-- Example: Date('partial', 2005) - Date('partial', 2001) gives
months = months - 1
-- diff.years = { 3, 4 } to show the range of possible results.
-- If do not want a range, choose the second value as more expected.
return v[2]
end
end
return v
end
if code == 'ym' or code == 'ymd' then
if not wantrange and diff.iszero then
-- This avoids an unexpected result such as
-- Date('partial', 2001) - Date('partial', 2001)
-- giving diff = { years = 0, months = { 0, 11 } }
-- which would be reported as 0 years and 11 months.
return 0, 0
end
return choose(diff.partial.years), choose(diff.partial.months)
end
if code == 'y' then
return choose(diff.partial.years)
end
if code == 'm' or code == 'w' or code == 'd' then
return choose({ diff.partial.mindiff:age(code), diff.partial.maxdiff:age(code) })
end
return nil
end
end
if months < 0 then
local extra_days = wantduration and 1 or 0
months = months + 12
if code == 'wd' or code == 'w' or code == 'd' then
years = years - 1
local offset = wantround and 0.5 or 0
local days = diff.age_days + extra_days
if code == 'wd' or code == 'd' then
days = floor(days + offset)
if code == 'd' then
return days
end
return floor(days/7), days % 7
end
return floor(days/7 + offset)
end
end
return {
local H, M, S = diff.hours, diff.minutes, diff.seconds
years = years,
if code == 'dh' or code == 'dhm' or code == 'dhms' or code == 'h' or code == 'hm' or code == 'hms' or code == 'M' or code == 's' then
months = months,
local days = floor(diff.age_days + extra_days)
days = days,
local inc_hour
isnegative = isnegative,
if wantround then
age_ym = function (self)
if code == 'dh' or code == 'h' then
-- Return text specifying difference in years, months.
if M >= 30 then
local sign = self.isnegative and MINUS or ''
inc_hour = true
local mtext = number_name(self.months, 'month')
end
local result
elseif code == 'dhm' or code == 'hm' then
if self.years > 0 then
if S >= 30 then
local ytext = number_name(self.years, 'year')
M = M + 1
if self.months == 0 then
if M >= 60 then
result = ytext
M = 0
else
inc_hour = true
result = ytext .. ',&nbsp;' .. mtext
end
end
elseif code == 'M' then
if S >= 30 then
M = M + 1
end
else
-- Nothing needed because S is an integer.
end
if inc_hour then
H = H + 1
if H >= 24 then
H = 0
days = days + 1
end
end
end
end
if code == 'dh' or code == 'dhm' or code == 'dhms' then
if code == 'dh' then
return days, H
elseif code == 'dhm' then
return days, H, M
else
else
if self.months == 0 then
return days, H, M, S
sign = ''
end
end
local hours = days * 24 + H
if code == 'h' then
return hours
elseif code == 'hm' then
return hours, M
elseif code == 'M' or code == 's' then
M = hours * 60 + M
if code == 'M' then
return M
end
return M * 60 + S
end
return hours, M, S
end
if wantround then
local inc_hour
if code == 'ymdh' or code == 'ymwdh' then
if M >= 30 then
inc_hour = true
end
elseif code == 'ymdhm' or code == 'ymwdhm' then
if S >= 30 then
M = M + 1
if M >= 60 then
M = 0
inc_hour = true
end
end
elseif code == 'ymd' or code == 'ymwd' or code == 'yd' or code == 'md' then
if H >= 12 then
extra_days = extra_days + 1
end
end
if inc_hour then
H = H + 1
if H >= 24 then
H = 0
extra_days = extra_days + 1
end
end
end
local y, m, d = diff.years, diff.months, diff.days
if extra_days > 0 then
d = d + extra_days
if d > 28 or code == 'yd' then
-- Recalculate in case have passed a month.
diff = diff.date1 + extra_days - diff.date2
y, m, d = diff.years, diff.months, diff.days
end
end
if code == 'ymd' then
return y, m, d
elseif code == 'yd' then
if y > 0 then
-- It is known that diff.date1 > diff.date2.
diff = diff.date1 - (diff.date2 + (y .. 'y'))
end
return y, floor(diff.age_days)
elseif code == 'md' then
return y * 12 + m, d
elseif code == 'ym' or code == 'm' then
if wantround then
if d >= 16 then
m = m + 1
if m >= 12 then
m = 0
y = y + 1
end
end
result = mtext
end
end
return sign .. result
end
end,
if code == 'ym' then
}
return y, m
end
return y * 12 + m
elseif code == 'ymw' then
local weeks = floor(d/7)
if wantround then
local days = d % 7
if days > 3 or (days == 3 and H >= 12) then
weeks = weeks + 1
end
end
return y, m, weeks
elseif code == 'ymwd' then
return y, m, floor(d/7), d % 7
elseif code == 'ymdh' then
return y, m, d, H
elseif code == 'ymwdh' then
return y, m, floor(d/7), d % 7, H
elseif code == 'ymdhm' then
return y, m, d, H, M
elseif code == 'ymwdhm' then
return y, m, floor(d/7), d % 7, H, M
end
if code == 'y' then
if wantround and m >= 6 then
y = y + 1
end
return y
end
return nil
end
end


local function message(msg, nocat)
local function _diff_duration(diff, code, options)
-- Return formatted message text for an error.
if type(options) ~= 'table' then
-- Can append "#FormattingError" to URL of a page with a problem to find it.
options = { round = options }
local anchor = '<span id="FormattingError" />'
local category
if not nocat and mw.title.getCurrentTitle():inNamespaces(0, 10) then
-- Category only in namespaces: 0=article, 10=template.
category = '[[Category:Age error]]'
else
category = ''
end
end
return anchor ..
options.duration = true
'<strong class="error">Error: ' ..
return _diff_age(diff, code, options)
msg ..
'</strong>' ..
category .. '\n'
end
end


local function age_days(frame)
-- Metatable for some operations on date differences.
-- Return age in days between two given dates, or
diffmt = { -- for forward declaration above
-- between given date and current date.
__concat = function (lhs, rhs)
-- This code implements the logic in [[Template:Age in days]].
return tostring(lhs) .. tostring(rhs)
-- Like {{Age in days}}, a missing argument is replaced from the current
end,
-- date, so can get a bizarre mixture of specified/current y/m/d.
__tostring = function (self)
local args = frame:getParent().args
return tostring(self.age_days)
local date1 = Date(
end,
date_component(args.year1 , args[1], 'year' ),
__index = function (self, key)
date_component(args.month1, args[2], 'month'),
local value
date_component(args.day1  , args[3], 'day'  )
if key == 'age_days' then
)
if rawget(self, 'partial') then
local date2 = Date(
local function jdz(date)
date_component(args.year2 , args[4], 'year' ),
return (date.partial and date.partial.first or date).jdz
date_component(args.month2, args[5], 'month'),
end
date_component(args.day2  , args[6], 'day' )
value = jdz(self.date1) - jdz(self.date2)
)
else
if not (date1.isvalid and date2.isvalid) then
value = self.date1.jdz - self.date2.jdz
return message('Need valid year, month, day')
end
end
end
local sign = ''
if value ~= nil then
local result = date2.jd - date1.jd
rawset(self, key, value)
if result < 0 then
return value
sign = MINUS
end
result = -result
end,
end
}
return sign .. tostring(result)
end


local function age_ym(frame)
function DateDiff(date1, date2, options) -- for forward declaration above
-- Return age in years and months between two given dates, or
-- Return a table with the difference between two dates (date1 - date2).
-- between given date and current date.
-- The difference is negative if date1 is older than date2.
local args = frame:getParent().args
-- Return nothing if invalid.
local fields = {}
-- If d = date1 - date2 then
for i = 1, 6 do
--    date1 = date2 + d
fields[i] = strip_to_nil(args[i])
-- If date1 >= date2 and the dates have no H:M:S time specified then
--    date1 = date2 + (d.years..'y') + (d.months..'m') + d.days
-- where the larger time units are added first.
-- The result of Date(2015,1,x) + '1m' is Date(2015,2,28) for
-- x = 28, 29, 30, 31. That means, for example,
--    d = Date(2015,3,3) - Date(2015,1,31)
-- gives d.years, d.months, d.days = 0, 1, 3 (excluding date1).
if not (is_date(date1) and is_date(date2) and date1.calendar == date2.calendar) then
return
end
end
local date1, date2
local wantfill
if fields[1] and fields[2] and fields[3] then
if type(options) == 'table' then
date1 = Date(fields[1], fields[2], fields[3])
wantfill = options.fill
end
end
if not (date1 and date1.isvalid) then
local isnegative = false
return message('Need valid year, month, day')
local iszero = false
if date1 < date2 then
isnegative = true
date1, date2 = date2, date1
elseif date1 == date2 then
iszero = true
end
end
if fields[4] and fields[5] and fields[6] then
-- It is known that date1 >= date2 (period is from date2 to date1).
date2 = Date(fields[4], fields[5], fields[6])
if date1.partial or date2.partial then
if not date2.isvalid then
-- Two partial dates might have timelines:
return message('Second date should be year, month, day')
---------------------A=================B--- date1 is from A to B inclusive
--------C=======D-------------------------- date2 is from C to D inclusive
-- date1 > date2 iff A > C (date1.partial.first > date2.partial.first)
-- The periods can overlap ('April 2001' - '2001'):
-------------A===B------------------------- A=2001-04-01  B=2001-04-30
--------C=====================D------------ C=2001-01-01  D=2001-12-31
if wantfill then
date1, date2 = autofill(date1, date2)
else
local function zdiff(date1, date2)
local diff = date1 - date2
if diff.isnegative then
return date1 - date1  -- a valid diff in case we call its methods
end
return diff
end
local function getdate(date, which)
return date.partial and date.partial[which] or date
end
local maxdiff = zdiff(getdate(date1, 'last'), getdate(date2, 'first'))
local mindiff = zdiff(getdate(date1, 'first'), getdate(date2, 'last'))
local years, months
if maxdiff.years == mindiff.years then
years = maxdiff.years
if maxdiff.months == mindiff.months then
months = maxdiff.months
else
months = { mindiff.months, maxdiff.months }
end
else
years = { mindiff.years, maxdiff.years }
end
return setmetatable({
date1 = date1,
date2 = date2,
partial = {
years = years,
months = months,
maxdiff = maxdiff,
mindiff = mindiff,
},
isnegative = isnegative,
iszero = iszero,
age = _diff_age,
duration = _diff_duration,
}, diffmt)
end
end
end
local y1, m1 = date1.year, date1.month
local y2, m2 = date2.year, date2.month
local years = y1 - y2
local months = m1 - m2
local d1 = date1.day + hms(date1)
local d2 = date2.day + hms(date2)
local days, time
if d1 >= d2 then
days = d1 - d2
else
else
date2 = Date('currentdate')
months = months - 1
-- Get days in previous month (before the "to" date) given December has 31 days.
local dpm = m1 > 1 and days_in_month(y1, m1 - 1, date1.calendar) or 31
if d2 >= dpm then
days = d1 - hms(date2)
else
days = dpm - d2 + d1
end
end
end
return DateDiff(date1, date2):age_ym()
if months < 0 then
end
years = years - 1
 
months = months + 12
local function gsd_ymd(frame)
-- Return Gregorian serial date of the given date, or the current date.
-- Like {{Gregorian serial date}}, a missing argument is replaced from the
-- current date, so can get a bizarre mixture of specified/current y/m/d.
-- This also accepts positional arguments, although the original template does not.
-- The returned value is negative for dates before 1 January 1 AD despite
-- the fact that GSD is not defined for earlier dates.
local args = frame:getParent().args
local date = Date(
date_component(args.year , args[1], 'year' ),
date_component(args.month, args[2], 'month'),
date_component(args.day  , args[3], 'day'  )
)
if date.isvalid then
return tostring(date.gsd)
end
end
return message('Need valid year, month, day')
days, time = math.modf(days)
end
local H, M, S = h_m_s(time)
 
return setmetatable({
local function ymd_from_jd(frame)
date1 = date1,
-- Return formatted date from a Julian date.
date2 = date2,
-- The result is y-m-d or y-m-d H:M:S if input includes a fraction.
partial = false, -- avoid index lookup
-- The word 'Julian' is accepted for the Julian calendar.
years = years,
local args = frame:getParent().args
months = months,
local date = Date('juliandate', args[1], args[2])
days = days,
if date.isvalid then
hours = H,
return date:text()
minutes = M,
end
seconds = S,
return message('Need valid Julian date number')
isnegative = isnegative,
end
iszero = iszero,
 
age = _diff_age,
local function ymd_to_jd(frame)
duration = _diff_duration,
-- Return Julian date (a number) from a date (y-m-d), or datetime (y-m-d H:M:S),
}, diffmt)
-- or the current date ('currentdate') or current datetime ('currentdatetime').
-- The word 'Julian' is accepted for the Julian calendar.
local args = frame:getParent().args
local date = Date(args[1], args[2], args[3], args[4], args[5], args[6], args[7])
if date.isvalid then
return tostring(date.jd)
end
return message('Need valid year/month/day or "currentdate"')
end
end


return {
return {
age_days = age_days,
_current = current,
age_ym = age_ym,
_Date = Date,
_Date = Date,
days_in_month = days_in_month,
_days_in_month = days_in_month,
gsd = gsd_ymd,
JULIANDAY = ymd_to_jd,
ymd_from_jd = ymd_from_jd,
ymd_to_jd = ymd_to_jd,
}
}

Latest revision as of 23:06, 3 September 2020

Documentation for this module may be created at Module:Date/doc 

-- Date functions for use by other modules.
-- I18N and time zones are not supported.

local MINUS = '−'  -- Unicode U+2212 MINUS SIGN
local floor = math.floor

local Date, DateDiff, diffmt  -- forward declarations
local uniq = { 'unique identifier' }

local function is_date(t)
	-- The system used to make a date read-only means there is no unique
	-- metatable that is conveniently accessible to check.
	return type(t) == 'table' and t._id == uniq
end

local function is_diff(t)
	return type(t) == 'table' and getmetatable(t) == diffmt
end

local function _list_join(list, sep)
	return table.concat(list, sep)
end

local function collection()
	-- Return a table to hold items.
	return {
		n = 0,
		add = function (self, item)
			self.n = self.n + 1
			self[self.n] = item
		end,
		join = _list_join,
	}
end

local function strip_to_nil(text)
	-- If text is a string, return its trimmed content, or nil if empty.
	-- Otherwise return text (convenient when Date fields are provided from
	-- another module which may pass a string, a number, or another type).
	if type(text) == 'string' then
		text = text:match('(%S.-)%s*$')
	end
	return text
end

local function is_leap_year(year, calname)
	-- Return true if year is a leap year.
	if calname == 'Julian' then
		return year % 4 == 0
	end
	return (year % 4 == 0 and year % 100 ~= 0) or year % 400 == 0
end

local function days_in_month(year, month, calname)
	-- Return number of days (1..31) in given month (1..12).
	if month == 2 and is_leap_year(year, calname) then
		return 29
	end
	return ({ 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 })[month]
end

local function h_m_s(time)
	-- Return hour, minute, second extracted from fraction of a day.
	time = floor(time * 24 * 3600 + 0.5)  -- number of seconds
	local second = time % 60
	time = floor(time / 60)
	return floor(time / 60), time % 60, second
end

local function hms(date)
	-- Return fraction of a day from date's time, where (0 <= fraction < 1)
	-- if the values are valid, but could be anything if outside range.
	return (date.hour + (date.minute + date.second / 60) / 60) / 24
end

local function julian_date(date)
	-- Return jd, jdz from a Julian or Gregorian calendar date where
	--   jd = Julian date and its fractional part is zero at noon
	--   jdz = same, but assume time is 00:00:00 if no time given
	-- http://www.tondering.dk/claus/cal/julperiod.php#formula
	-- Testing shows this works for all dates from year -9999 to 9999!
	-- JDN 0 is the 24-hour period starting at noon UTC on Monday
	--    1 January 4713 BC  = (-4712, 1, 1)   Julian calendar
	--   24 November 4714 BC = (-4713, 11, 24) Gregorian calendar
	local offset
	local a = floor((14 - date.month)/12)
	local y = date.year + 4800 - a
	if date.calendar == 'Julian' then
		offset = floor(y/4) - 32083
	else
		offset = floor(y/4) - floor(y/100) + floor(y/400) - 32045
	end
	local m = date.month + 12*a - 3
	local jd = date.day + floor((153*m + 2)/5) + 365*y + offset
	if date.hastime then
		jd = jd + hms(date) - 0.5
		return jd, jd
	end
	return jd, jd - 0.5
end

local function set_date_from_jd(date)
	-- Set the fields of table date from its Julian date field.
	-- Return true if date is valid.
	-- http://www.tondering.dk/claus/cal/julperiod.php#formula
	-- This handles the proleptic Julian and Gregorian calendars.
	-- Negative Julian dates are not defined but they work.
	local calname = date.calendar
	local low, high  -- min/max limits for date ranges −9999-01-01 to 9999-12-31
	if calname == 'Gregorian' then
		low, high = -1930999.5, 5373484.49999
	elseif calname == 'Julian' then
		low, high = -1931076.5, 5373557.49999
	else
		return
	end
	local jd = date.jd
	if not (type(jd) == 'number' and low <= jd and jd <= high) then
		return
	end
	local jdn = floor(jd)
	if date.hastime then
		local time = jd - jdn  -- 0 <= time < 1
		if time >= 0.5 then    -- if at or after midnight of next day
			jdn = jdn + 1
			time = time - 0.5
		else
			time = time + 0.5
		end
		date.hour, date.minute, date.second = h_m_s(time)
	else
		date.second = 0
		date.minute = 0
		date.hour = 0
	end
	local b, c
	if calname == 'Julian' then
		b = 0
		c = jdn + 32082
	else  -- Gregorian
		local a = jdn + 32044
		b = floor((4*a + 3)/146097)
		c = a - floor(146097*b/4)
	end
	local d = floor((4*c + 3)/1461)
	local e = c - floor(1461*d/4)
	local m = floor((5*e + 2)/153)
	date.day = e - floor((153*m + 2)/5) + 1
	date.month = m + 3 - 12*floor(m/10)
	date.year = 100*b + d - 4800 + floor(m/10)
	return true
end

local function fix_numbers(numbers, y, m, d, H, M, S, partial, hastime, calendar)
	-- Put the result of normalizing the given values in table numbers.
	-- The result will have valid m, d values if y is valid; caller checks y.
	-- The logic of PHP mktime is followed where m or d can be zero to mean
	-- the previous unit, and -1 is the one before that, etc.
	-- Positive values carry forward.
	local date
	if not (1 <= m and m <= 12) then
		date = Date(y, 1, 1)
		if not date then return end
		date = date + ((m - 1) .. 'm')
		y, m = date.year, date.month
	end
	local days_hms
	if not partial then
		if hastime and H and M and S then
			if not (0 <= H and H <= 23 and
					0 <= M and M <= 59 and
					0 <= S and S <= 59) then
				days_hms = hms({ hour = H, minute = M, second = S })
			end
		end
		if days_hms or not (1 <= d and d <= days_in_month(y, m, calendar)) then
			date = date or Date(y, m, 1)
			if not date then return end
			date = date + (d - 1 + (days_hms or 0))
			y, m, d = date.year, date.month, date.day
			if days_hms then
				H, M, S = date.hour, date.minute, date.second
			end
		end
	end
	numbers.year = y
	numbers.month = m
	numbers.day = d
	if days_hms then
		-- Don't set H unless it was valid because a valid H will set hastime.
		numbers.hour = H
		numbers.minute = M
		numbers.second = S
	end
end

local function set_date_from_numbers(date, numbers, options)
	-- Set the fields of table date from numeric values.
	-- Return true if date is valid.
	if type(numbers) ~= 'table' then
		return
	end
	local y = numbers.year   or date.year
	local m = numbers.month  or date.month
	local d = numbers.day    or date.day
	local H = numbers.hour
	local M = numbers.minute or date.minute or 0
	local S = numbers.second or date.second or 0
	local need_fix
	if y and m and d then
		date.partial = nil
		if not (-9999 <= y and y <= 9999 and
			1 <= m and m <= 12 and
			1 <= d and d <= days_in_month(y, m, date.calendar)) then
				if not date.want_fix then
					return
				end
				need_fix = true
		end
	elseif y and date.partial then
		if d or not (-9999 <= y and y <= 9999) then
			return
		end
		if m and not (1 <= m and m <= 12) then
			if not date.want_fix then
				return
			end
			need_fix = true
		end
	else
		return
	end
	if date.partial then
		H = nil  -- ignore any time
		M = nil
		S = nil
	else
		if H then
			-- It is not possible to set M or S without also setting H.
			date.hastime = true
		else
			H = 0
		end
		if not (0 <= H and H <= 23 and
				0 <= M and M <= 59 and
				0 <= S and S <= 59) then
			if date.want_fix then
				need_fix = true
			else
				return
			end
		end
	end
	date.want_fix = nil
	if need_fix then
		fix_numbers(numbers, y, m, d, H, M, S, date.partial, date.hastime, date.calendar)
		return set_date_from_numbers(date, numbers, options)
	end
	date.year = y    -- -9999 to 9999 ('n BC' → year = 1 - n)
	date.month = m   -- 1 to 12 (may be nil if partial)
	date.day = d     -- 1 to 31 (* = nil if partial)
	date.hour = H    -- 0 to 59 (*)
	date.minute = M  -- 0 to 59 (*)
	date.second = S  -- 0 to 59 (*)
	if type(options) == 'table' then
		for _, k in ipairs({ 'am', 'era', 'format' }) do
			if options[k] then
				date.options[k] = options[k]
			end
		end
	end
	return true
end

local function make_option_table(options1, options2)
	-- If options1 is a string, return a table with its settings, or
	-- if it is a table, use its settings.
	-- Missing options are set from table options2 or defaults.
	-- If a default is used, a flag is set so caller knows the value was not intentionally set.
	-- Valid option settings are:
	-- am: 'am', 'a.m.', 'AM', 'A.M.'
	--     'pm', 'p.m.', 'PM', 'P.M.' (each has same meaning as corresponding item above)
	-- era: 'BCMINUS', 'BCNEGATIVE', 'BC', 'B.C.', 'BCE', 'B.C.E.', 'AD', 'A.D.', 'CE', 'C.E.'
	-- Option am = 'am' does not mean the hour is AM; it means 'am' or 'pm' is used, depending on the hour,
	--    and am = 'pm' has the same meaning.
	-- Similarly, era = 'BC' means 'BC' is used if year <= 0.
	-- BCMINUS displays a MINUS if year < 0 and the display format does not include %{era}.
	-- BCNEGATIVE is similar but displays a hyphen.
	local result = { bydefault = {} }
	if type(options1) == 'table' then
		result.am = options1.am
		result.era = options1.era
	elseif type(options1) == 'string' then
		-- Example: 'am:AM era:BC' or 'am=AM era=BC'.
		for item in options1:gmatch('%S+') do
			local lhs, rhs = item:match('^(%w+)[:=](.+)$')
			if lhs then
				result[lhs] = rhs
			end
		end
	end
	options2 = type(options2) == 'table' and options2 or {}
	local defaults = { am = 'am', era = 'BC' }
	for k, v in pairs(defaults) do
		if not result[k] then
			if options2[k] then
				result[k] = options2[k]
			else
				result[k] = v
				result.bydefault[k] = true
			end
		end
	end
	return result
end

local ampm_options = {
	-- lhs = input text accepted as an am/pm option
	-- rhs = code used internally
	['am']   = 'am',
	['AM']   = 'AM',
	['a.m.'] = 'a.m.',
	['A.M.'] = 'A.M.',
	['pm']   = 'am',  -- same as am
	['PM']   = 'AM',
	['p.m.'] = 'a.m.',
	['P.M.'] = 'A.M.',
}

local era_text = {
	-- Text for displaying an era with a positive year (after adjusting
	-- by replacing year with 1 - year if date.year <= 0).
	-- options.era = { year<=0 , year>0 }
	['BCMINUS']    = { 'BC'    , ''    , isbc = true, sign = MINUS },
	['BCNEGATIVE'] = { 'BC'    , ''    , isbc = true, sign = '-'   },
	['BC']         = { 'BC'    , ''    , isbc = true },
	['B.C.']       = { 'B.C.'  , ''    , isbc = true },
	['BCE']        = { 'BCE'   , ''    , isbc = true },
	['B.C.E.']     = { 'B.C.E.', ''    , isbc = true },
	['AD']         = { 'BC'    , 'AD'   },
	['A.D.']       = { 'B.C.'  , 'A.D.' },
	['CE']         = { 'BCE'   , 'CE'   },
	['C.E.']       = { 'B.C.E.', 'C.E.' },
}

local function get_era_for_year(era, year)
	return (era_text[era] or era_text['BC'])[year > 0 and 2 or 1] or ''
end

local function strftime(date, format, options)
	-- Return date formatted as a string using codes similar to those
	-- in the C strftime library function.
	local sformat = string.format
	local shortcuts = {
		['%c'] = '%-I:%M %p %-d %B %-Y %{era}',  -- date and time: 2:30 pm 1 April 2016
		['%x'] = '%-d %B %-Y %{era}',            -- date:          1 April 2016
		['%X'] = '%-I:%M %p',                    -- time:          2:30 pm
	}
	if shortcuts[format] then
		format = shortcuts[format]
	end
	local codes = {
		a = { field = 'dayabbr' },
		A = { field = 'dayname' },
		b = { field = 'monthabbr' },
		B = { field = 'monthname' },
		u = { fmt = '%d'  , field = 'dowiso' },
		w = { fmt = '%d'  , field = 'dow' },
		d = { fmt = '%02d', fmt2 = '%d', field = 'day' },
		m = { fmt = '%02d', fmt2 = '%d', field = 'month' },
		Y = { fmt = '%04d', fmt2 = '%d', field = 'year' },
		H = { fmt = '%02d', fmt2 = '%d', field = 'hour' },
		M = { fmt = '%02d', fmt2 = '%d', field = 'minute' },
		S = { fmt = '%02d', fmt2 = '%d', field = 'second' },
		j = { fmt = '%03d', fmt2 = '%d', field = 'dayofyear' },
		I = { fmt = '%02d', fmt2 = '%d', field = 'hour', special = 'hour12' },
		p = { field = 'hour', special = 'am' },
	}
	options = make_option_table(options, date.options)
	local amopt = options.am
	local eraopt = options.era
	local function replace_code(spaces, modifier, id)
		local code = codes[id]
		if code then
			local fmt = code.fmt
			if modifier == '-' and code.fmt2 then
				fmt = code.fmt2
			end
			local value = date[code.field]
			if not value then
				return nil  -- an undefined field in a partial date
			end
			local special = code.special
			if special then
				if special == 'hour12' then
					value = value % 12
					value = value == 0 and 12 or value
				elseif special == 'am' then
					local ap = ({
						['a.m.'] = { 'a.m.', 'p.m.' },
						['AM'] = { 'AM', 'PM' },
						['A.M.'] = { 'A.M.', 'P.M.' },
					})[ampm_options[amopt]] or { 'am', 'pm' }
					return (spaces == '' and '' or '&nbsp;') .. (value < 12 and ap[1] or ap[2])
				end
			end
			if code.field == 'year' then
				local sign = (era_text[eraopt] or {}).sign
				if not sign or format:find('%{era}', 1, true) then
					sign = ''
					if value <= 0 then
						value = 1 - value
					end
				else
					if value >= 0 then
						sign = ''
					else
						value = -value
					end
				end
				return spaces .. sign .. sformat(fmt, value)
			end
			return spaces .. (fmt and sformat(fmt, value) or value)
		end
	end
	local function replace_property(spaces, id)
		if id == 'era' then
			-- Special case so can use local era option.
			local result = get_era_for_year(eraopt, date.year)
			if result == '' then
				return ''
			end
			return (spaces == '' and '' or '&nbsp;') .. result
		end
		local result = date[id]
		if type(result) == 'string' then
			return spaces .. result
		end
		if type(result) == 'number' then
			return  spaces .. tostring(result)
		end
		if type(result) == 'boolean' then
			return  spaces .. (result and '1' or '0')
		end
		-- This occurs if id is an undefined field in a partial date, or is the name of a function.
		return nil
	end
	local PERCENT = '\127PERCENT\127'
	return (format
		:gsub('%%%%', PERCENT)
		:gsub('(%s*)%%{(%w+)}', replace_property)
		:gsub('(%s*)%%(%-?)(%a)', replace_code)
		:gsub(PERCENT, '%%')
	)
end

local function _date_text(date, fmt, options)
	-- Return a formatted string representing the given date.
	if not is_date(date) then
		error('date:text: need a date (use "date:text()" with a colon)', 2)
	end
	if type(fmt) == 'string' and fmt:match('%S') then
		if fmt:find('%', 1, true) then
			return strftime(date, fmt, options)
		end
	elseif date.partial then
		fmt = date.month and 'my' or 'y'
	else
		fmt = 'dmy'
		if date.hastime then
			fmt = (date.second > 0 and 'hms ' or 'hm ') .. fmt
		end
	end
	local function bad_format()
		-- For consistency with other format processing, return given format
		-- (or cleaned format if original was not a string) if invalid.
		return mw.text.nowiki(fmt)
	end
	if date.partial then
		-- Ignore days in standard formats like 'ymd'.
		if fmt == 'ym' or fmt == 'ymd' then
			fmt = date.month and '%Y-%m %{era}' or '%Y %{era}'
		elseif fmt == 'my' or fmt == 'dmy' or fmt == 'mdy' then
			fmt = date.month and '%B %-Y %{era}' or '%-Y %{era}'
		elseif fmt == 'y' then
			fmt = date.month and '%-Y %{era}' or '%-Y %{era}'
		else
			return bad_format()
		end
		return strftime(date, fmt, options)
	end
	local function hm_fmt()
		local plain = make_option_table(options, date.options).bydefault.am
		return plain and '%H:%M' or '%-I:%M %p'
	end
	local need_time = date.hastime
	local t = collection()
	for item in fmt:gmatch('%S+') do
		local f
		if item == 'hm' then
			f = hm_fmt()
			need_time = false
		elseif item == 'hms' then
			f = '%H:%M:%S'
			need_time = false
		elseif item == 'ymd' then
			f = '%Y-%m-%d %{era}'
		elseif item == 'mdy' then
			f = '%B %-d, %-Y %{era}'
		elseif item == 'dmy' then
			f = '%-d %B %-Y %{era}'
		else
			return bad_format()
		end
		t:add(f)
	end
	fmt = t:join(' ')
	if need_time then
		fmt = hm_fmt() .. ' ' .. fmt
	end
	return strftime(date, fmt, options)
end

local day_info = {
	-- 0=Sun to 6=Sat
	[0] = { 'Sun', 'Sunday' },
	{ 'Mon', 'Monday' },
	{ 'Tue', 'Tuesday' },
	{ 'Wed', 'Wednesday' },
	{ 'Thu', 'Thursday' },
	{ 'Fri', 'Friday' },
	{ 'Sat', 'Saturday' },
}

local month_info = {
	-- 1=Jan to 12=Dec
	{ 'Jan', 'January' },
	{ 'Feb', 'February' },
	{ 'Mar', 'March' },
	{ 'Apr', 'April' },
	{ 'May', 'May' },
	{ 'Jun', 'June' },
	{ 'Jul', 'July' },
	{ 'Aug', 'August' },
	{ 'Sep', 'September' },
	{ 'Oct', 'October' },
	{ 'Nov', 'November' },
	{ 'Dec', 'December' },
}

local function name_to_number(text, translate)
	if type(text) == 'string' then
		return translate[text:lower()]
	end
end

local function day_number(text)
	return name_to_number(text, {
		sun = 0, sunday = 0,
		mon = 1, monday = 1,
		tue = 2, tuesday = 2,
		wed = 3, wednesday = 3,
		thu = 4, thursday = 4,
		fri = 5, friday = 5,
		sat = 6, saturday = 6,
	})
end

local function month_number(text)
	return name_to_number(text, {
		jan = 1, january = 1,
		feb = 2, february = 2,
		mar = 3, march = 3,
		apr = 4, april = 4,
		may = 5,
		jun = 6, june = 6,
		jul = 7, july = 7,
		aug = 8, august = 8,
		sep = 9, september = 9, sept = 9,
		oct = 10, october = 10,
		nov = 11, november = 11,
		dec = 12, december = 12,
	})
end

local function _list_text(list, fmt)
	-- Return a list of formatted strings from a list of dates.
	if not type(list) == 'table' then
		error('date:list:text: need "list:text()" with a colon', 2)
	end
	local result = { join = _list_join }
	for i, date in ipairs(list) do
		result[i] = date:text(fmt)
	end
	return result
end

local function _date_list(date, spec)
	-- Return a possibly empty numbered table of dates meeting the specification.
	-- Dates in the list are in ascending order (oldest date first).
	-- The spec should be a string of form "<count> <day> <op>"
	-- where each item is optional and
	--   count = number of items wanted in list
	--   day = abbreviation or name such as Mon or Monday
	--   op = >, >=, <, <= (default is > meaning after date)
	-- If no count is given, the list is for the specified days in date's month.
	-- The default day is date's day.
	-- The spec can also be a positive or negative number:
	--   -5 is equivalent to '5 <'
	--   5  is equivalent to '5' which is '5 >'
	if not is_date(date) then
		error('date:list: need a date (use "date:list()" with a colon)', 2)
	end
	local list = { text = _list_text }
	if date.partial then
		return list
	end
	local count, offset, operation
	local ops = {
		['>='] = { before = false, include = true  },
		['>']  = { before = false, include = false },
		['<='] = { before = true , include = true  },
		['<']  = { before = true , include = false },
	}
	if spec then
		if type(spec) == 'number' then
			count = floor(spec + 0.5)
			if count < 0 then
				count = -count
				operation = ops['<']
			end
		elseif type(spec) == 'string' then
			local num, day, op = spec:match('^%s*(%d*)%s*(%a*)%s*([<>=]*)%s*$')
			if not num then
				return list
			end
			if num ~= '' then
				count = tonumber(num)
			end
			if day ~= '' then
				local dow = day_number(day:gsub('[sS]$', ''))  -- accept plural days
				if not dow then
					return list
				end
				offset = dow - date.dow
			end
			operation = ops[op]
		else
			return list
		end
	end
	offset = offset or 0
	operation = operation or ops['>']
	local datefrom, dayfirst, daylast
	if operation.before then
		if offset > 0 or (offset == 0 and not operation.include) then
			offset = offset - 7
		end
		if count then
			if count > 1 then
				offset = offset - 7*(count - 1)
			end
			datefrom = date + offset
		else
			daylast = date.day + offset
			dayfirst = daylast % 7
			if dayfirst == 0 then
				dayfirst = 7
			end
		end
	else
		if offset < 0 or (offset == 0 and not operation.include) then
			offset = offset + 7
		end
		if count then
			datefrom = date + offset
		else
			dayfirst = date.day + offset
			daylast = date.monthdays
		end
	end
	if not count then
		if daylast < dayfirst then
			return list
		end
		count = floor((daylast - dayfirst)/7) + 1
		datefrom = Date(date, {day = dayfirst})
	end
	for i = 1, count do
		if not datefrom then break end  -- exceeds date limits
		list[i] = datefrom
		datefrom = datefrom + 7
	end
	return list
end

-- A table to get the current date/time (UTC), but only if needed.
local current = setmetatable({}, {
	__index = function (self, key)
		local d = os.date('!*t')
		self.year = d.year
		self.month = d.month
		self.day = d.day
		self.hour = d.hour
		self.minute = d.min
		self.second = d.sec
		return rawget(self, key)
	end })

local function extract_date(newdate, text)
	-- Parse the date/time in text and return n, o where
	--   n = table of numbers with date/time fields
	--   o = table of options for AM/PM or AD/BC or format, if any
	-- or return nothing if date is known to be invalid.
	-- Caller determines if the values in n are valid.
	-- A year must be positive ('1' to '9999'); use 'BC' for BC.
	-- In a y-m-d string, the year must be four digits to avoid ambiguity
	-- ('0001' to '9999'). The only way to enter year <= 0 is by specifying
	-- the date as three numeric parameters like ymd Date(-1, 1, 1).
	-- Dates of form d/m/y, m/d/y, y/m/d are rejected as potentially ambiguous.
	local date, options = {}, {}
	if text:sub(-1) == 'Z' then
		-- Extract date/time from a Wikidata timestamp.
		-- The year can be 1 to 16 digits but this module handles 1 to 4 digits only.
		-- Examples: '+2016-06-21T14:30:00Z', '-0000000180-00-00T00:00:00Z'.
		local sign, y, m, d, H, M, S = text:match('^([+%-])(%d+)%-(%d%d)%-(%d%d)T(%d%d):(%d%d):(%d%d)Z$')
		if sign then
			y = tonumber(y)
			if sign == '-' and y > 0 then
				y = -y
			end
			if y <= 0 then
				options.era = 'BCE'
			end
			date.year = y
			m = tonumber(m)
			d = tonumber(d)
			H = tonumber(H)
			M = tonumber(M)
			S = tonumber(S)
			if m == 0 then
				newdate.partial = true
				return date, options
			end
			date.month = m
			if d == 0 then
				newdate.partial = true
				return date, options
			end
			date.day = d
			if H > 0 or M > 0 or S > 0 then
				date.hour = H
				date.minute = M
				date.second = S
			end
			return date, options
		end
		return
	end
	local function extract_ymd(item)
		-- Called when no day or month has been set.
		local y, m, d = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$')
		if y then
			if date.year then
				return
			end
			if m:match('^%d%d?$') then
				m = tonumber(m)
			else
				m = month_number(m)
			end
			if m then
				date.year = tonumber(y)
				date.month = m
				date.day = tonumber(d)
				return true
			end
		end
	end
	local function extract_day_or_year(item)
		-- Called when a day would be valid, or
		-- when a year would be valid if no year has been set and partial is set.
		local number, suffix = item:match('^(%d%d?%d?%d?)(.*)$')
		if number then
			local n = tonumber(number)
			if #number <= 2 and n <= 31 then
				suffix = suffix:lower()
				if suffix == '' or suffix == 'st' or suffix == 'nd' or suffix == 'rd' or suffix == 'th' then
					date.day = n
					return true
				end
			elseif suffix == '' and newdate.partial and not date.year then
				date.year = n
				return true
			end
		end
	end
	local function extract_month(item)
		-- A month must be given as a name or abbreviation; a number could be ambiguous.
		local m = month_number(item)
		if m then
			date.month = m
			return true
		end
	end
	local function extract_time(item)
		local h, m, s = item:match('^(%d%d?):(%d%d)(:?%d*)$')
		if date.hour or not h then
			return
		end
		if s ~= '' then
			s = s:match('^:(%d%d)$')
			if not s then
				return
			end
		end
		date.hour = tonumber(h)
		date.minute = tonumber(m)
		date.second = tonumber(s)  -- nil if empty string
		return true
	end
	local item_count = 0
	local index_time
	local function set_ampm(item)
		local H = date.hour
		if H and not options.am and index_time + 1 == item_count then
			options.am = ampm_options[item]  -- caller checked this is not nil
			if item:match('^[Aa]') then
				if not (1 <= H and H <= 12) then
					return
				end
				if H == 12 then
					date.hour = 0
				end
			else
				if not (1 <= H and H <= 23) then
					return
				end
				if H <= 11 then
					date.hour = H + 12
				end
			end
			return true
		end
	end
	for item in text:gsub(',', ' '):gsub('&nbsp;', ' '):gmatch('%S+') do
		item_count = item_count + 1
		if era_text[item] then
			-- Era is accepted in peculiar places.
			if options.era then
				return
			end
			options.era = item
		elseif ampm_options[item] then
			if not set_ampm(item) then
				return
			end
		elseif item:find(':', 1, true) then
			if not extract_time(item) then
				return
			end
			index_time = item_count
		elseif date.day and date.month then
			if date.year then
				return  -- should be nothing more so item is invalid
			end
			if not item:match('^(%d%d?%d?%d?)$') then
				return
			end
			date.year = tonumber(item)
		elseif date.day then
			if not extract_month(item) then
				return
			end
		elseif date.month then
			if not extract_day_or_year(item) then
				return
			end
		elseif extract_month(item) then
			options.format = 'mdy'
		elseif extract_ymd(item) then
			options.format = 'ymd'
		elseif extract_day_or_year(item) then
			if date.day then
				options.format = 'dmy'
			end
		else
			return
		end
	end
	if not date.year or date.year == 0 then
		return
	end
	local era = era_text[options.era]
	if era and era.isbc then
		date.year = 1 - date.year
	end
	return date, options
end

local function autofill(date1, date2)
	-- Fill any missing month or day in each date using the
	-- corresponding component from the other date, if present,
	-- or with 1 if both dates are missing the month or day.
	-- This gives a good result for calculating the difference
	-- between two partial dates when no range is wanted.
	-- Return filled date1, date2 (two full dates).
	local function filled(a, b)
		-- Return date a filled, if necessary, with month and/or day from date b.
		-- The filled day is truncated to fit the number of days in the month.
		local fillmonth, fillday
		if not a.month then
			fillmonth = b.month or 1
		end
		if not a.day then
			fillday = b.day or 1
		end
		if fillmonth or fillday then  -- need to create a new date
			a = Date(a, {
				month = fillmonth,
				day = math.min(fillday or a.day, days_in_month(a.year, fillmonth or a.month, a.calendar))
			})
		end
		return a
	end
	return filled(date1, date2), filled(date2, date1)
end

local function date_add_sub(lhs, rhs, is_sub)
	-- Return a new date from calculating (lhs + rhs) or (lhs - rhs),
	-- or return nothing if invalid.
	-- The result is nil if the calculated date exceeds allowable limits.
	-- Caller ensures that lhs is a date; its properties are copied for the new date.
	if lhs.partial then
		-- Adding to a partial is not supported.
		-- Can subtract a date or partial from a partial, but this is not called for that.
		return
	end
	local function is_prefix(text, word, minlen)
		local n = #text
		return (minlen or 1) <= n and n <= #word and text == word:sub(1, n)
	end
	local function do_days(n)
		local forcetime, jd
		if floor(n) == n then
			jd = lhs.jd
		else
			forcetime = not lhs.hastime
			jd = lhs.jdz
		end
		jd = jd + (is_sub and -n or n)
		if forcetime then
			jd = tostring(jd)
			if not jd:find('.', 1, true) then
				jd = jd .. '.0'
			end
		end
		return Date(lhs, 'juliandate', jd)
	end
	if type(rhs) == 'number' then
		-- Add/subtract days, including fractional days.
		return do_days(rhs)
	end
	if type(rhs) == 'string' then
		-- rhs is a single component like '26m' or '26 months' (with optional sign).
		-- Fractions like '3.25d' are accepted for the units which are handled as days.
		local sign, numstr, id = rhs:match('^%s*([+-]?)([%d%.]+)%s*(%a+)$')
		if sign then
			if sign == '-' then
				is_sub = not (is_sub and true or false)
			end
			local y, m, days
			local num = tonumber(numstr)
			if not num then
				return
			end
			id = id:lower()
			if is_prefix(id, 'years') then
				y = num
				m = 0
			elseif is_prefix(id, 'months') then
				y = floor(num / 12)
				m = num % 12
			elseif is_prefix(id, 'weeks') then
				days = num * 7
			elseif is_prefix(id, 'days') then
				days = num
			elseif is_prefix(id, 'hours') then
				days = num / 24
			elseif is_prefix(id, 'minutes', 3) then
				days = num / (24 * 60)
			elseif is_prefix(id, 'seconds') then
				days = num / (24 * 3600)
			else
				return
			end
			if days then
				return do_days(days)
			end
			if numstr:find('.', 1, true) then
				return
			end
			if is_sub then
				y = -y
				m = -m
			end
			assert(-11 <= m and m <= 11)
			y = lhs.year + y
			m = lhs.month + m
			if m > 12 then
				y = y + 1
				m = m - 12
			elseif m < 1 then
				y = y - 1
				m = m + 12
			end
			local d = math.min(lhs.day, days_in_month(y, m, lhs.calendar))
			return Date(lhs, y, m, d)
		end
	end
	if is_diff(rhs) then
		local days = rhs.age_days
		if (is_sub or false) ~= (rhs.isnegative or false) then
			days = -days
		end
		return lhs + days
	end
end

local full_date_only = {
	dayabbr = true,
	dayname = true,
	dow = true,
	dayofweek = true,
	dowiso = true,
	dayofweekiso = true,
	dayofyear = true,
	gsd = true,
	juliandate = true,
	jd = true,
	jdz = true,
	jdnoon = true,
}

-- Metatable for a date's calculated fields.
local datemt = {
	__index = function (self, key)
		if rawget(self, 'partial') then
			if full_date_only[key] then return end
			if key == 'monthabbr' or key == 'monthdays' or key == 'monthname' then
				if not self.month then return end
			end
		end
		local value
		if key == 'dayabbr' then
			value = day_info[self.dow][1]
		elseif key == 'dayname' then
			value = day_info[self.dow][2]
		elseif key == 'dow' then
			value = (self.jdnoon + 1) % 7  -- day-of-week 0=Sun to 6=Sat
		elseif key == 'dayofweek' then
			value = self.dow
		elseif key == 'dowiso' then
			value = (self.jdnoon % 7) + 1  -- ISO day-of-week 1=Mon to 7=Sun
		elseif key == 'dayofweekiso' then
			value = self.dowiso
		elseif key == 'dayofyear' then
			local first = Date(self.year, 1, 1, self.calendar).jdnoon
			value = self.jdnoon - first + 1  -- day-of-year 1 to 366
		elseif key == 'era' then
			-- Era text (never a negative sign) from year and options.
			value = get_era_for_year(self.options.era, self.year)
		elseif key == 'format' then
			value = self.options.format or 'dmy'
		elseif key == 'gsd' then
			-- GSD = 1 from 00:00:00 to 23:59:59 on 1 January 1 AD Gregorian calendar,
			-- which is from jd 1721425.5 to 1721426.49999.
			value = floor(self.jd - 1721424.5)
		elseif key == 'juliandate' or key == 'jd' or key == 'jdz' then
			local jd, jdz = julian_date(self)
			rawset(self, 'juliandate', jd)
			rawset(self, 'jd', jd)
			rawset(self, 'jdz', jdz)
			return key == 'jdz' and jdz or jd
		elseif key == 'jdnoon' then
			-- Julian date at noon (an integer) on the calendar day when jd occurs.
			value = floor(self.jd + 0.5)
		elseif key == 'isleapyear' then
			value = is_leap_year(self.year, self.calendar)
		elseif key == 'monthabbr' then
			value = month_info[self.month][1]
		elseif key == 'monthdays' then
			value = days_in_month(self.year, self.month, self.calendar)
		elseif key == 'monthname' then
			value = month_info[self.month][2]
		end
		if value ~= nil then
			rawset(self, key, value)
			return value
		end
	end,
}

-- Date operators.
local function mt_date_add(lhs, rhs)
	if not is_date(lhs) then
		lhs, rhs = rhs, lhs  -- put date on left (it must be a date for this to have been called)
	end
	return date_add_sub(lhs, rhs)
end

local function mt_date_sub(lhs, rhs)
	if is_date(lhs) then
		if is_date(rhs) then
			return DateDiff(lhs, rhs)
		end
		return date_add_sub(lhs, rhs, true)
	end
end

local function mt_date_concat(lhs, rhs)
	return tostring(lhs) .. tostring(rhs)
end

local function mt_date_tostring(self)
	return self:text()
end

local function mt_date_eq(lhs, rhs)
	-- Return true if dates identify same date/time where, for example,
	-- Date(-4712, 1, 1, 'Julian') == Date(-4713, 11, 24, 'Gregorian') is true.
	-- This is called only if lhs and rhs have the same type and the same metamethod.
	if lhs.partial or rhs.partial then
		-- One date is partial; the other is a partial or a full date.
		-- The months may both be nil, but must be the same.
		return lhs.year == rhs.year and lhs.month == rhs.month and lhs.calendar == rhs.calendar
	end
	return lhs.jdz == rhs.jdz
end

local function mt_date_lt(lhs, rhs)
	-- Return true if lhs < rhs, for example,
	-- Date('1 Jan 2016') < Date('06:00 1 Jan 2016') is true.
	-- This is called only if lhs and rhs have the same type and the same metamethod.
	if lhs.partial or rhs.partial then
		-- One date is partial; the other is a partial or a full date.
		if lhs.calendar ~= rhs.calendar then
			return lhs.calendar == 'Julian'
		end
		if lhs.partial then
			lhs = lhs.partial.first
		end
		if rhs.partial then
			rhs = rhs.partial.first
		end
	end
	return lhs.jdz < rhs.jdz
end

--[[ Examples of syntax to construct a date:
Date(y, m, d, 'julian')             default calendar is 'gregorian'
Date(y, m, d, H, M, S, 'julian')
Date('juliandate', jd, 'julian')    if jd contains "." text output includes H:M:S
Date('currentdate')
Date('currentdatetime')
Date('1 April 1995', 'julian')      parse date from text
Date('1 April 1995 AD', 'julian')   using an era sets a flag to do the same for output
Date('04:30:59 1 April 1995', 'julian')
Date(date)                          copy of an existing date
Date(date, t)                       same, updated with y,m,d,H,M,S fields from table t
Date(t)                       		date with y,m,d,H,M,S fields from table t
]]
function Date(...)  -- for forward declaration above
	-- Return a table holding a date assuming a uniform calendar always applies
	-- (proleptic Gregorian calendar or proleptic Julian calendar), or
	-- return nothing if date is invalid.
	-- A partial date has a valid year, however its month may be nil, and
	-- its day and time fields are nil.
	-- Field partial is set to false (if a full date) or a table (if a partial date).
	local calendars = { julian = 'Julian', gregorian = 'Gregorian' }
	local newdate = {
		_id = uniq,
		calendar = 'Gregorian',  -- default is Gregorian calendar
		hastime = false,  -- true if input sets a time
		hour = 0,  -- always set hour/minute/second so don't have to handle nil
		minute = 0,
		second = 0,
		options = {},
		list = _date_list,
		subtract = function (self, rhs, options)
			return DateDiff(self, rhs, options)
		end,
		text = _date_text,
	}
	local argtype, datetext, is_copy, jd_number, tnums
	local numindex = 0
	local numfields = { 'year', 'month', 'day', 'hour', 'minute', 'second' }
	local numbers = {}
	for _, v in ipairs({...}) do
		v = strip_to_nil(v)
		local vlower = type(v) == 'string' and v:lower() or nil
		if v == nil then
			-- Ignore empty arguments after stripping so modules can directly pass template parameters.
		elseif calendars[vlower] then
			newdate.calendar = calendars[vlower]
		elseif vlower == 'partial' then
			newdate.partial = true
		elseif vlower == 'fix' then
			newdate.want_fix = true
		elseif is_date(v) then
			-- Copy existing date (items can be overridden by other arguments).
			if is_copy or tnums then
				return
			end
			is_copy = true
			newdate.calendar = v.calendar
			newdate.partial = v.partial
			newdate.hastime = v.hastime
			newdate.options = v.options
			newdate.year = v.year
			newdate.month = v.month
			newdate.day = v.day
			newdate.hour = v.hour
			newdate.minute = v.minute
			newdate.second = v.second
		elseif type(v) == 'table' then
			if tnums then
				return
			end
			tnums = {}
			local tfields = { year=1, month=1, day=1, hour=2, minute=2, second=2 }
			for tk, tv in pairs(v) do
				if tfields[tk] then
					tnums[tk] = tonumber(tv)
				end
				if tfields[tk] == 2 then
					newdate.hastime = true
				end
			end
		else
			local num = tonumber(v)
			if not num and argtype == 'setdate' and numindex == 1 then
				num = month_number(v)
			end
			if num then
				if not argtype then
					argtype = 'setdate'
				end
				if argtype == 'setdate' and numindex < 6 then
					numindex = numindex + 1
					numbers[numfields[numindex]] = num
				elseif argtype == 'juliandate' and not jd_number then
					jd_number = num
					if type(v) == 'string' then
						if v:find('.', 1, true) then
							newdate.hastime = true
						end
					elseif num ~= floor(num) then
						-- The given value was a number. The time will be used
						-- if the fractional part is nonzero.
						newdate.hastime = true
					end
				else
					return
				end
			elseif argtype then
				return
			elseif type(v) == 'string' then
				if v == 'currentdate' or v == 'currentdatetime' or v == 'juliandate' then
					argtype = v
				else
					argtype = 'datetext'
					datetext = v
				end
			else
				return
			end
		end
	end
	if argtype == 'datetext' then
		if tnums or not set_date_from_numbers(newdate, extract_date(newdate, datetext)) then
			return
		end
	elseif argtype == 'juliandate' then
		newdate.partial = nil
		newdate.jd = jd_number
		if not set_date_from_jd(newdate) then
			return
		end
	elseif argtype == 'currentdate' or argtype == 'currentdatetime' then
		newdate.partial = nil
		newdate.year = current.year
		newdate.month = current.month
		newdate.day = current.day
		if argtype == 'currentdatetime' then
			newdate.hour = current.hour
			newdate.minute = current.minute
			newdate.second = current.second
			newdate.hastime = true
		end
		newdate.calendar = 'Gregorian'  -- ignore any given calendar name
	elseif argtype == 'setdate' then
		if tnums or not set_date_from_numbers(newdate, numbers) then
			return
		end
	elseif not (is_copy or tnums) then
		return
	end
	if tnums then
		newdate.jd = nil  -- force recalculation in case jd was set before changes from tnums
		if not set_date_from_numbers(newdate, tnums) then
			return
		end
	end
	if newdate.partial then
		local year = newdate.year
		local month = newdate.month
		local first = Date(year, month or 1, 1, newdate.calendar)
		month = month or 12
		local last = Date(year, month, days_in_month(year, month), newdate.calendar)
		newdate.partial = { first = first, last = last }
	else
		newdate.partial = false  -- avoid index lookup
	end
	setmetatable(newdate, datemt)
	local readonly = {}
	local mt = {
		__index = newdate,
		__newindex = function(t, k, v) error('date.' .. tostring(k) .. ' is read-only', 2) end,
		__add = mt_date_add,
		__sub = mt_date_sub,
		__concat = mt_date_concat,
		__tostring = mt_date_tostring,
		__eq = mt_date_eq,
		__lt = mt_date_lt,
	}
	return setmetatable(readonly, mt)
end

local function _diff_age(diff, code, options)
	-- Return a tuple of integer values from diff as specified by code, except that
	-- each integer may be a list of two integers for a diff with a partial date, or
	-- return nil if the code is not supported.
	-- If want round, the least significant unit is rounded to nearest whole unit.
	-- For a duration, an extra day is added.
	local wantround, wantduration, wantrange
	if type(options) == 'table' then
		wantround = options.round
		wantduration = options.duration
		wantrange = options.range
	else
		wantround = options
	end
	if not is_diff(diff) then
		local f = wantduration and 'duration' or 'age'
		error(f .. ': need a date difference (use "diff:' .. f .. '()" with a colon)', 2)
	end
	if diff.partial then
		-- Ignore wantround, wantduration.
		local function choose(v)
			if type(v) == 'table' then
				if not wantrange or v[1] == v[2] then
					-- Example: Date('partial', 2005) - Date('partial', 2001) gives
					-- diff.years = { 3, 4 } to show the range of possible results.
					-- If do not want a range, choose the second value as more expected.
					return v[2]
				end
			end
			return v
		end
		if code == 'ym' or code == 'ymd' then
			if not wantrange and diff.iszero then
				-- This avoids an unexpected result such as
				-- Date('partial', 2001) - Date('partial', 2001)
				-- giving diff = { years = 0, months = { 0, 11 } }
				-- which would be reported as 0 years and 11 months.
				return 0, 0
			end
			return choose(diff.partial.years), choose(diff.partial.months)
		end
		if code == 'y' then
			return choose(diff.partial.years)
		end
		if code == 'm' or code == 'w' or code == 'd' then
			return choose({ diff.partial.mindiff:age(code), diff.partial.maxdiff:age(code) })
		end
		return nil
	end
	local extra_days = wantduration and 1 or 0
	if code == 'wd' or code == 'w' or code == 'd' then
		local offset = wantround and 0.5 or 0
		local days = diff.age_days + extra_days
		if code == 'wd' or code == 'd' then
			days = floor(days + offset)
			if code == 'd' then
				return days
			end
			return floor(days/7), days % 7
		end
		return floor(days/7 + offset)
	end
	local H, M, S = diff.hours, diff.minutes, diff.seconds
	if code == 'dh' or code == 'dhm' or code == 'dhms' or code == 'h' or code == 'hm' or code == 'hms' or code == 'M' or code == 's' then
		local days = floor(diff.age_days + extra_days)
		local inc_hour
		if wantround then
			if code == 'dh' or code == 'h' then
				if M >= 30 then
					inc_hour = true
				end
			elseif code == 'dhm' or code == 'hm' then
				if S >= 30 then
					M = M + 1
					if M >= 60 then
						M = 0
						inc_hour = true
					end
				end
			elseif code == 'M' then
				if S >= 30 then
					M = M + 1
				end
			else
				-- Nothing needed because S is an integer.
			end
			if inc_hour then
				H = H + 1
				if H >= 24 then
					H = 0
					days = days + 1
				end
			end
		end
		if code == 'dh' or code == 'dhm' or code == 'dhms' then
			if code == 'dh' then
				return days, H
			elseif code == 'dhm' then
				return days, H, M
			else
				return days, H, M, S
			end
		end
		local hours = days * 24 + H
		if code == 'h' then
			return hours
		elseif code == 'hm' then
			return hours, M
		elseif code == 'M' or code == 's' then
			M = hours * 60 + M
			if code == 'M' then
				return M
			end
			return M * 60 + S
		end
		return hours, M, S
	end
	if wantround then
		local inc_hour
		if code == 'ymdh' or code == 'ymwdh' then
			if M >= 30 then
				inc_hour = true
			end
		elseif code == 'ymdhm' or code == 'ymwdhm' then
			if S >= 30 then
				M = M + 1
				if M >= 60 then
					M = 0
					inc_hour = true
				end
			end
		elseif code == 'ymd' or code == 'ymwd' or code == 'yd' or code == 'md' then
			if H >= 12 then
				extra_days = extra_days + 1
			end
		end
		if inc_hour then
			H = H + 1
			if H >= 24 then
				H = 0
				extra_days = extra_days + 1
			end
		end
	end
	local y, m, d = diff.years, diff.months, diff.days
	if extra_days > 0 then
		d = d + extra_days
		if d > 28 or code == 'yd' then
			-- Recalculate in case have passed a month.
			diff = diff.date1 + extra_days - diff.date2
			y, m, d = diff.years, diff.months, diff.days
		end
	end
	if code == 'ymd' then
		return y, m, d
	elseif code == 'yd' then
		if y > 0 then
			-- It is known that diff.date1 > diff.date2.
			diff = diff.date1 - (diff.date2 + (y .. 'y'))
		end
		return y, floor(diff.age_days)
	elseif code == 'md' then
		return y * 12 + m, d
	elseif code == 'ym' or code == 'm' then
		if wantround then
			if d >= 16 then
				m = m + 1
				if m >= 12 then
					m = 0
					y = y + 1
				end
			end
		end
		if code == 'ym' then
			return y, m
		end
		return y * 12 + m
	elseif code == 'ymw' then
		local weeks = floor(d/7)
		if wantround then
			local days = d % 7
			if days > 3 or (days == 3 and H >= 12) then
				weeks = weeks + 1
			end
		end
		return y, m, weeks
	elseif code == 'ymwd' then
		return y, m, floor(d/7), d % 7
	elseif code == 'ymdh' then
		return y, m, d, H
	elseif code == 'ymwdh' then
		return y, m, floor(d/7), d % 7, H
	elseif code == 'ymdhm' then
		return y, m, d, H, M
	elseif code == 'ymwdhm' then
		return y, m, floor(d/7), d % 7, H, M
	end
	if code == 'y' then
		if wantround and m >= 6 then
			y = y + 1
		end
		return y
	end
	return nil
end

local function _diff_duration(diff, code, options)
	if type(options) ~= 'table' then
		options = { round = options }
	end
	options.duration = true
	return _diff_age(diff, code, options)
end

-- Metatable for some operations on date differences.
diffmt = {  -- for forward declaration above
	__concat = function (lhs, rhs)
		return tostring(lhs) .. tostring(rhs)
	end,
	__tostring = function (self)
		return tostring(self.age_days)
	end,
	__index = function (self, key)
		local value
		if key == 'age_days' then
			if rawget(self, 'partial') then
				local function jdz(date)
					return (date.partial and date.partial.first or date).jdz
				end
				value = jdz(self.date1) - jdz(self.date2)
			else
				value = self.date1.jdz - self.date2.jdz
			end
		end
		if value ~= nil then
			rawset(self, key, value)
			return value
		end
	end,
}

function DateDiff(date1, date2, options)  -- for forward declaration above
	-- Return a table with the difference between two dates (date1 - date2).
	-- The difference is negative if date1 is older than date2.
	-- Return nothing if invalid.
	-- If d = date1 - date2 then
	--     date1 = date2 + d
	-- If date1 >= date2 and the dates have no H:M:S time specified then
	--     date1 = date2 + (d.years..'y') + (d.months..'m') + d.days
	-- where the larger time units are added first.
	-- The result of Date(2015,1,x) + '1m' is Date(2015,2,28) for
	-- x = 28, 29, 30, 31. That means, for example,
	--     d = Date(2015,3,3) - Date(2015,1,31)
	-- gives d.years, d.months, d.days = 0, 1, 3 (excluding date1).
	if not (is_date(date1) and is_date(date2) and date1.calendar == date2.calendar) then
		return
	end
	local wantfill
	if type(options) == 'table' then
		wantfill = options.fill
	end
	local isnegative = false
	local iszero = false
	if date1 < date2 then
		isnegative = true
		date1, date2 = date2, date1
	elseif date1 == date2 then
		iszero = true
	end
	-- It is known that date1 >= date2 (period is from date2 to date1).
	if date1.partial or date2.partial then
		-- Two partial dates might have timelines:
		---------------------A=================B--- date1 is from A to B inclusive
		--------C=======D-------------------------- date2 is from C to D inclusive
		-- date1 > date2 iff A > C (date1.partial.first > date2.partial.first)
		-- The periods can overlap ('April 2001' - '2001'):
		-------------A===B------------------------- A=2001-04-01  B=2001-04-30
		--------C=====================D------------ C=2001-01-01  D=2001-12-31
		if wantfill then
			date1, date2 = autofill(date1, date2)
		else
			local function zdiff(date1, date2)
				local diff = date1 - date2
				if diff.isnegative then
					return date1 - date1  -- a valid diff in case we call its methods
				end
				return diff
			end
			local function getdate(date, which)
				return date.partial and date.partial[which] or date
			end
			local maxdiff = zdiff(getdate(date1, 'last'), getdate(date2, 'first'))
			local mindiff = zdiff(getdate(date1, 'first'), getdate(date2, 'last'))
			local years, months
			if maxdiff.years == mindiff.years then
				years = maxdiff.years
				if maxdiff.months == mindiff.months then
					months = maxdiff.months
				else
					months = { mindiff.months, maxdiff.months }
				end
			else
				years = { mindiff.years, maxdiff.years }
			end
			return setmetatable({
				date1 = date1,
				date2 = date2,
				partial = {
					years = years,
					months = months,
					maxdiff = maxdiff,
					mindiff = mindiff,
				},
				isnegative = isnegative,
				iszero = iszero,
				age = _diff_age,
				duration = _diff_duration,
			}, diffmt)
		end
	end
	local y1, m1 = date1.year, date1.month
	local y2, m2 = date2.year, date2.month
	local years = y1 - y2
	local months = m1 - m2
	local d1 = date1.day + hms(date1)
	local d2 = date2.day + hms(date2)
	local days, time
	if d1 >= d2 then
		days = d1 - d2
	else
		months = months - 1
		-- Get days in previous month (before the "to" date) given December has 31 days.
		local dpm = m1 > 1 and days_in_month(y1, m1 - 1, date1.calendar) or 31
		if d2 >= dpm then
			days = d1 - hms(date2)
		else
			days = dpm - d2 + d1
		end
	end
	if months < 0 then
		years = years - 1
		months = months + 12
	end
	days, time = math.modf(days)
	local H, M, S = h_m_s(time)
	return setmetatable({
		date1 = date1,
		date2 = date2,
		partial = false,  -- avoid index lookup
		years = years,
		months = months,
		days = days,
		hours = H,
		minutes = M,
		seconds = S,
		isnegative = isnegative,
		iszero = iszero,
		age = _diff_age,
		duration = _diff_duration,
	}, diffmt)
end

return {
	_current = current,
	_Date = Date,
	_days_in_month = days_in_month,
}
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