Module:Date

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

local MINUS = '−' -- Unicode U+2212 MINUS SIGN

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 = function (self, sep) return table.concat(self, sep) end, } end

local function strip_to_nil(text) -- Return nil if text is nil or is an empty string after trimming. -- If text is a non-blank string, return its content after trimming. -- Otherwise return text (convenient when accessed via another module). if type(text) == 'string' then local result = text:match("^%s*(.-)%s*$") if result == '' then return nil end return result end if text == nil then return nil end 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

local function is_leap_year(year, calname) -- Return true if year is a leap year. if calname == 'JCAL' 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). 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 return 29 end return month_days[month] 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 = similar, but fractional part is zero at 00:00:00 -- 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	--   1 January 4713 BC  = (-4712, 1, 1)   Julian 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 a = floor((14 - date.month)/12) local y = date.year + 4800 - a	if date.calname == 'JCAL' 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 date_part = date.day + floor((153*m + 2)/5) + 365*y + offset local time_part, zbias if date.hastime then time_part = (date.hour + (date.minute + date.second / 60) /60) / 24 - 0.5 zbias = 0 else time_part = 0 zbias = -0.5 end local jd = date_part + time_part return jd, jd + zbias end

local function set_date_from_jd(date) -- Set the fields of table date from its Julian date field. -- 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 floor = math.floor local calname = date.calname local jd = date.jd	local limits -- min/max limits for date ranges −9999-01-01 to 9999-12-31 if calname == 'JCAL' then limits = { -1931076.5, 5373557.5 } elseif calname == 'GCAL' then limits = { -1930999.5, 5373484.5 } else limits = { 1, 0 } -- impossible end if not (limits[1] <= jd and jd < limits[2]) then date.isvalid = false return end date.isvalid = true local jdn = floor(jd) if date.hastime then local time = jd - jdn local hour if time >= 0.5 then jdn = jdn + 1 time = time - 0.5 hour = 0 else hour = 12 end time = floor(time * 24 * 3600 + 0.5) -- number of seconds after hour date.second = time % 60 time = floor(time / 60) date.minute = time % 60 date.hour = hour + floor(time / 60) else date.second = 0 date.minute = 0 date.hour = 0 end local b, c	if calname == 'JCAL' 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) end

local function date_text(date) -- Return formatted string from given date. if not date.isvalid then return '(invalid)' end local time = '' if date.hastime then if date.second > 0 then time = string.format(' %02d:%02d:%02d',				date.hour,				date.minute,				date.second			) else time = string.format(' %02d:%02d',				date.hour,				date.minute			) end end local y = date.year local sign = '' if y < 0 then sign = MINUS y = -y end return string.format('%s%04d-%02d-%02d%s',		sign,		y,		date.month,		date.day,		time	) end

local function month_number(text) if type(text) == 'string' then local month_names = { 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

-- A table to get the current year/month/day (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 date_component(named, positional, component) -- Return the first of the two arguments (named like 	-- or positional like ) that is not nil and is not empty. -- If both are nil, return the current date component, if specified. -- This translates empty arguments passed to the template to nil, and -- optionally replaces a nil argument with a value from the current date. named = strip_to_nil(named) if named then return named end positional = strip_to_nil(positional) if positional then return positional end if component then return current[component] end return nil end

-- Metatable for some operations on dates. -- For Lua 5.1, __lt does not work if the metatable is an anonymous table. local datemt = { __eq = function (lhs, rhs) -- Return true if dates identify same date/time where, for example, -- (-4712, 1, 1, 'Julian') == (-4713, 11, 24, 'Gregorian'). return lhs.isvalid and rhs.isvalid and lhs.jdz == rhs.jdz end, __lt = function (lhs, rhs) -- Return true if lhs < rhs. if not lhs.isvalid then return true end if not rhs.isvalid then return false end return lhs.jdz < rhs.jdz end, __index = function (self, key) local value if key == 'jd' or key == 'jdz' then local jd, jdz = julian_date(self) rawset(self, 'jd', jd) rawset(self, 'jdz', jdz) return key == 'jd' and jd or jdz elseif key == 'gsd' then -- 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. value = math.floor(self.jd - 1721424.5) elseif key == 'is_leap_year' then value = is_leap_year(self.year, self.calname) end if value ~= nil then rawset(self, key, value) return value end 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') 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 AD', 'julian')   AD, CE, BC, BCE (using one of these sets a flag to do same for output) Date('04:30:59 1 April 1995', 'julian') local function Date(...) -- Return a table to hold a date assuming a uniform calendar always applies (proleptic). -- If invalid, return an empty table which is regarded as invalid. local calendars = { julian = 'JCAL', Julian = 'JCAL', gregorian = 'GCAL', Gregorian = 'GCAL' } local result = { isvalid = false,  -- false avoids __index lookup calname = 'GCAL', -- 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, month_days = function (self, month) return days_in_month(self.year, month, self.calname) end, text = date_text, }	local numbers = collection local datetext local argtype for _, v in ipairs({...}) do		v = strip_to_nil(v) if v == nil then -- Ignore empty arguments after stripping so modules can directly pass template parameters. elseif calendars[v] then result.calname = calendars[v] else local num = tonumber(v) if not num and argtype == 'setdate' and numbers.n == 1 then num = month_number(v) end if num then if not argtype then argtype = 'setdate' end numbers:add(num) if argtype == 'juliandate' then if type(v) == 'string' then if v:find('.', 1, true) then result.hastime = true end elseif num ~= math.floor(num) then -- The given value was a number. The time will be used -- if the fractional part is nonzero. result.hastime = true end 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 numbers.n > 0 then return {} end -- TODO Parse datetext to extract y,m,d,H,M,S. elseif argtype == 'juliandate' then if numbers.n == 1 then result.jd = numbers[1] set_date_from_jd(result) else return {} end elseif argtype == 'currentdate' or argtype == 'currentdatetime' then result.year = current.year result.month = current.month result.day = current.day if argtype == 'currentdatetime' then result.hour = current.hour result.minute = current.minute result.second = current.second result.hastime = true end result.calname = 'GCAL' -- ignore any given calendar name result.isvalid = true elseif argtype == 'setdate' then if not (3 <= numbers.n and numbers.n <= 6) then return {} end local y, m, d = numbers[1], numbers[2], numbers[3] if not (-9999 <= y and y <= 9999 and 1 <= m and m <= 12 and					1 <= d and d <= days_in_month(y, m, result.calname)) then return {} end local H = numbers[4] if H then result.hastime = true else H = 0 end local M = numbers[5] or 0 local S = numbers[6] or 0 if not (0 <= H and H <= 23 and				0 <= M and M <= 59 and				0 <= S and S <= 59) then return {} end result.year = y   -- -9999 to 9999; '1 BC' → year = 0; 'n BC' → year = 1 - n		result.month = m   -- 1 to 12 result.day = d    -- 1 to 31 result.hour = H   -- 0 to 59 result.minute = M -- 0 to 59 result.second = S -- 0 to 59 result.isvalid = true else return {} end return setmetatable(result, datemt) end

local function DateDiff(date1, date2) -- Return a table to with the difference between the two given dates. -- Difference is negative if the second date is older than the first. -- TODO Replace with something using Julian dates? --     Who checks for isvalid? --     Handle calname == 'JCAL' local calname = 'GCAL' -- TODO fix local isnegative if date2 < date1 then isnegative = true date1, date2 = date2, date1 end -- It is known that date1 <= date2. local y1, m1 = date1.year, date1.month local y2, m2 = date2.year, date2.month local years, months, days = y2 - y1, m2 - m1, date2.day - date1.day if days < 0 then days = days + days_in_month(y1, m1, calname) months = months - 1 end if months < 0 then months = months + 12 years = years - 1 end return { years = years, months = months, days = days, isnegative = isnegative, age_ym = function (self) -- Return text specifying difference in years, months. local sign = self.isnegative and MINUS or '' local mtext = number_name(self.months, 'month') local result if self.years > 0 then local ytext = number_name(self.years, 'year') if self.months == 0 then result = ytext else result = ytext .. ', ' .. mtext end else if self.months == 0 then sign = '' end result = mtext end return sign .. result end, } end

local function message(msg, nocat) -- Return formatted message text for an error. -- Can append "#FormattingError" to URL of a page with a problem to find it. local anchor = ' ' local category if not nocat and mw.title.getCurrentTitle:inNamespaces(0, 10) then -- Category only in namespaces: 0=article, 10=template. category = '' else category = '' end return anchor .. ' Error: ' .. msg .. ' ' ..		category .. '\n' end

local function age_days(frame) -- Return age in days between two given dates, or -- between given date and current date. -- This code implements the logic in Template:Age in days. -- Like 8974 days, a missing argument is replaced from the current -- date, so can get a bizarre mixture of specified/current y/m/d. local args = frame:getParent.args local date1 = Date(		date_component(args.year1, args[1], 'year' ),		date_component(args.month1, args[2], 'month'),		date_component(args.day1 , args[3], 'day'  )	) local date2 = Date(		date_component(args.year2, args[4], 'year' ),		date_component(args.month2, args[5], 'month'),		date_component(args.day2 , args[6], 'day'  )	) if not (date1.isvalid and date2.isvalid) then return message('Need valid year, month, day') end local sign = '' local result = date2.jd - date1.jd	if result < 0 then sign = MINUS result = -result end return sign .. tostring(result) end

local function age_ym(frame) -- Return age in years and months between two given dates, or -- between given date and current date. local args = frame:getParent.args local fields = {} for i = 1, 6 do		fields[i] = strip_to_nil(args[i]) end local date1, date2 if fields[1] and fields[2] and fields[3] then date1 = Date(fields[1], fields[2], fields[3]) end if not (date1 and date1.isvalid) then return message('Need valid year, month, day') end if fields[4] and fields[5] and fields[6] then date2 = Date(fields[4], fields[5], fields[6]) if not date2.isvalid then return message('Second date should be year, month, day') end else date2 = Date('currentdate') end return DateDiff(date1, date2):age_ym end

local function gsd_ymd(frame) -- Return Gregorian serial date of the given date, or the current date. -- Like, 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 return message('Need valid year, month, day') end

local function ymd_from_jd(frame) -- Return formatted date from a Julian date. -- The result is y-m-d or y-m-d H:M:S if input includes a fraction. -- The word 'Julian' is accepted for the Julian calendar. local args = frame:getParent.args local date = Date('juliandate', args[1], args[2]) if date.isvalid then return date:text end return message('Need valid Julian date number') end

local function ymd_to_jd(frame) -- Return Julian date (a number) from a date (y-m-d), or datetime (y-m-d H:M:S), -- 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

return { age_days = age_days, age_ym = age_ym, _Date = Date, 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, }