Module:Date

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

-- 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 {{example|year=2001}}
	-- or positional like {{example|2001}}) 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 .. ',&nbsp;' .. 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 = '<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
	return anchor ..
		'<strong class="error">Error: ' ..
		msg ..
		'</strong>' ..
		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 {{Age in 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 {{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
	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,
}