Module:Date: Difference between revisions

Module:Date (edit)

Revision as of 16:29, 10 October 2017

46,225 bytes added , 8 years ago

m

Reverted edits by 181.112.152.222 (talk) to last version by Johnuniq

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+-- 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