Module:Date

-- 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 (0 <= fraction < 1) from date's time. 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 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 if not (y and m and d) or 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 return end if H then -- It is not possible to set M or S without also setting H.		date.hastime = true else H = date.hour or 0 end if not (0 <= H and H <= 23 and			0 <= M and M <= 59 and			0 <= S and S <= 59) then return end date.year = y   -- -9999 to 9999 ('n BC' → year = 1 - n)	date.month = m   -- 1 to 12 date.day = d    -- 1 to 31 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] 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 ' ') .. (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 ' ') .. 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, for example, if id 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 else fmt = 'dmy' if date.hastime then fmt = (date.second > 0 and 'hms ' or 'hm ') .. fmt 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 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 error('date:text: invalid format', 2) 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,		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 " " -- 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 >' local list = { text = _list_text } if not is_date(date) then error('date:list: need a date (use "date:list" with a colon)', 2) 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. -- A local test can set the global variable to produce fixed results. local current = setmetatable(	set_current_for_test or {}, {	__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(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 = {}, {} local function extract_ymd(item) local ystr, mstr, dstr = item:match('^(%d%d%d%d)%-(%w+)%-(%d%d?)$') if ystr then local m			if mstr:match('^%d%d?$') then m = tonumber(mstr) else m = month_number(mstr) end if m then options.format = 'ymd' date.year = tonumber(ystr) date.month = m				date.day = tonumber(dstr) 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] 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(' ', ' '):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?)$') then return end date.year = tonumber(item) elseif date.day then if not extract_month(item) then return end elseif date.month then if not item:match('^(%d%d?)$') then return end date.day = tonumber(item) elseif not extract_ymd(item) then if item:match('^(%d%d?)$') then date.day = tonumber(item) options.format = 'dmy' elseif extract_month(item) then options.format = 'mdy' 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 return date, options 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. 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' (unsigned integer only). local num, id = rhs:match('^%s*(%d+)%s*(%a+)$') if num then local y, m			num = tonumber(num) 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 return do_days(num * 7) elseif is_prefix(id, 'days') then return do_days(num) elseif is_prefix(id, 'hours') then return do_days(num / 24) elseif is_prefix(id, 'minutes', 3) then return do_days(num / (24 * 60)) elseif is_prefix(id, 'seconds') then return do_days(num / (24 * 3600)) else 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

-- Metatable for a date's calculated fields. local datemt = { __index = function (self, key) 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 only called if lhs and rhs have the same metatable. 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 only called if lhs and rhs have the same metatable. 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. 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, 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 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.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(datetext)) then return end elseif argtype == 'juliandate' then newdate.jd = jd_number if not set_date_from_jd(newdate) then return end elseif argtype == 'currentdate' or argtype == 'currentdatetime' then 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 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 values from diff as specified by code. -- If options == 'duration', an extra day is added. if not is_diff(diff) then local f = options == 'duration' and 'duration' or 'age' error(f .. ': need a date difference (use "diff:' .. f .. '" with a colon)', 2) end local extra_day = options == 'duration' and 1 or 0 if code == 'wd' or code == 'w' or code == 'd' then local d = diff.age_days + extra_day if code == 'd' then return d		end local w = floor(d / 7) if code == 'w' then return w		end return w, d % 7 end local y, m, d = diff.years, diff.months, diff.days if extra_day > 0 then d = d + extra_day local to_date = diff.date1 if d > days_in_month(to_date.year, to_date.month, to_date.calendar) then d = 1 m = m + 1 if m > 12 then m = 1 y = y + 1 end end end if code == 'ymd' then return y, m, d	end if code == 'ym' then return y, m	end if code == 'm' then return y * 12 + m	end if code == 'ymwd' then return y, m, floor(d / 7), d % 7 end return y -- default: assume code == 'y'; ignore invalid codes end

local function _diff_duration(diff, code) return _diff_age(diff, code, 'duration') 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 value = self.date1.jdz - self.date2.jdz end if value ~= nil then rawset(self, key, value) return value end end, }

function DateDiff(date1, date2) -- 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 isnegative = false if date1 < date2 then isnegative = true date1, date2 = date2, date1 end -- It is known that date1 >= date2 (period is from date2 to date1). 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		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,		years = years,		months = months,		days = days,		hours = H,		minutes = M,		seconds = S,		isnegative = isnegative,		age = _diff_age,		duration = _diff_duration,	}, diffmt) end

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