Module:Calendar

Lua
Code Discussion Edit History Links Link count Subpages:Documentation Tests Results Sandbox Live code All modules
This module is rated as ready for general use. It has reached a mature form and is thought to be bug-free and ready for use wherever appropriate. To reduce server load and bad output, it should be improved by sandbox testing rather than repeated trial-and-error editing.
This module is subject to page protection. It is a highly visible module in use by a very large number of pages, or is substituted very frequently. Because vandalism or mistakes would affect many pages, and even trivial editing might cause substantial load on the servers, it is protected from editing.
Convert dates between Gregorian and Julian Calendars. Used by Module:Complex date.
Code

--[[
  __  __           _       _         ____      _                _            
 |  \/  | ___   __| |_   _| | ___ _ / ___|__ _| | ___ _ __   __| | __ _ _ __ 
 | |\/| |/ _ \ / _` | | | | |/ _ (_) |   / _` | |/ _ \ '_ \ / _` |/ _` | '__|
 | |  | | (_) | (_| | |_| | |  __/_| |__| (_| | |  __/ | | | (_| | (_| | |   
 |_|  |_|\___/ \__,_|\__,_|_|\___(_)\____\__,_|_|\___|_| |_|\__,_|\__,_|_|   
                                                                             
This module is intended for date conversion between Gregorian and Julian calendars

Please do not modify this code without applying the changes first at Module:Calendar/sandbox 
and testing at Module:Calendar/sandbox/testcases 

Maintainers:
* Jarekt
]]
require('strict')

-- ==================================================
-- === External functions ===========================
-- ==================================================
local p = {}

-- ===========================================================================
-- === Version of the function to be called from other LUA codes
-- ===========================================================================

-----------------------------------------------------------------------------
--[[
Convert calendar date to  "Julian day number" (jdn) 
code based on  https://en.wikipedia.org/wiki/Julian_day#Converting_Julian_or_Gregorian_calendar_date_to_Julian_day_number
explanation based on http://www.cs.utsa.edu/~cs1063/projects/Spring2011/Project1/project1.html

Example usage:
  jdn = _date2jdn("2017-09-01", 1)

Inputs:
  ISOdate:    date in YYYY-MM-DD format
  gregorian:  int - "1" for gregorian calendar and "0" for Julian (optional with "1" as default)
  
Outputs:
  1: "Julian day number" as integer or number of days since Monday, January 1, 4713 BC

]]
function p._date2jdn(ISOdate, gregorian)
    ISOdate = mw.text.trim(ISOdate, "%s+") -- trim ASCII whitespace and leading "+"
    if (#ISOdate<10) then -- string is too short to have YYYY-MM-DD date
    	return nil
    end
    -- date string has to start with YYYY-MM-DD date, possibly with a "-" in front
	local year, month, day = ISOdate:match( "^(-?%d%d%d%d)-(%d%d)-(%d%d)" )
	if not year then
		return nil
	elseif tonumber(year) < 0 then
		-- If year is less than 0, add one to convert from  the common era system in which
	    -- the year -1 (1 B.C.E) is followed by year 1 (1 C.E.) to a zero based date system
		year = year + 1
	end
	local a, b, c, d, y, m
	a = math.floor((14-month) / 12) -- will be 1 for January and February, and 0 for other months.
	y = year + 4800 - a             -- years since year –4800
	m = month + 12*a - 3            -- month number where 10 for January, 11 for February, 0 for March, 1 for April
	c = math.floor((153*m + 2)/5)   -- number of days since March 1
	if (gregorian or 1) >0 then	
		b = math.floor(y/4) - math.floor(y/100) + math.floor(y/400) -- number of leap years since y==0 (year –4800)
		d = 32045                   -- offset so the result will be 0 for January 1, 4713 BCE
	else
		b = math.floor(y/4)         -- number of leap years since y==0 (year –4800)
		d = 32083                   -- offset so the result will be 0 for January 1, 4713 BCE
	end
	return day + c + 365*y + b - d
end

-----------------------------------------------------------------------------
--[[
Convert "Julian day number" (jdn) to a calendar date 
code based on  https://en.wikipedia.org/wiki/Julian_day#Converting_Julian_or_Gregorian_calendar_date_to_Julian_day_number
explanation based on http://www.cs.utsa.edu/~cs1063/projects/Spring2011/Project1/project1.html

Example usage:
  jdn = _date2jdn("2017-09-01", 1)

Inputs:
  jdn:       integer - Julian day number or number of days since Monday, January 1, 4713 BC
  gregorian: int - "1" for gregorian calendar and "0" for Julian (optional with "1" as default)
  
Outputs:
  1: date in YYYY-MM-DD forma

]]
-- Convert "Julian day number" (jdn) to a calendar date
-- "gregorian" is a 1 for gregorian calendar and 0 for Julian
-- based on https://en.wikipedia.org/wiki/Julian_day#Converting_Julian_or_Gregorian_calendar_date_to_Julian_day_number
function p._jdn2date(jdn, gregorian)
  local f, e, g, h, year, month, day

	f = jdn + 1401
	if (gregorian or 1) >0 then
		 f = f + math.floor((math.floor((4*jdn + 274277) / 146097) * 3) / 4) - 38
	end
	e = 4*f + 3
	g = math.floor(math.fmod(e, 1461) / 4)
	h = 5*g + 2
	day   = math.floor(math.fmod (h,153) / 5) + 1
	month = math.fmod (math.floor(h/153) + 2, 12) + 1
	year  = math.floor(e/1461) - 4716 + math.floor((14 - month) / 12)
	
	-- If year is less than 1, subtract one to convert from a zero based date system to the
	-- common era system in which the year -1 (1 B.C.E) is followed by year 1 (1 C.E.).
	if year < 1 then
			year = year - 1
	end
	
	return string.format('%04i-%02i-%02i', year, month, day)
end

--[[
Tests if a string is a valid Gregorian date
Example usage:
  jdn = _valid_date("2017-02-30")

Inputs:
  ISOdate: date in YYYY-MM-DD string format  
  
Outputs:
  true or false

]]
function p._valid_date(ISOdate)
	local jdn = p._date2jdn(ISOdate, 1)
	if jdn then
		return (p._jdn2date(jdn, 1)==ISOdate)
	else
		return true -- date is not in YYYY-MM-DD format do not flag as invalid
	end
end


-- ===========================================================================
-- === Versions of the function to be called from template namespace
-- ===========================================================================
--[[
Gregorian2Julian
 
Convert a date from Gregorian to Julian calendar
 
Usage:
{{#invoke:Calendar|Gregorian2Julian|YYYY-MM-DD}}
 
Parameters:
    1: Gregorian date in YYYY-MM-DD format
Output:
	1: Julian date in YYYY-MM-DD format or error message "Error parsing input date: ....."
]]
function p.Gregorian2Julian(frame)
	local jdn = p._date2jdn(frame.args[1], 1)
	if jdn then
		return p._jdn2date(jdn, 0)
	else
		return "Error parsing input date: " .. frame.args[1]
	end
end

-----------------------------------------------------------------------------
--[[
Julian2Gregorian
 
Convert a date from Julian to Gregorian calendar
 
Usage:
{{#invoke:Calendar|Julian2Gregorian|YYYY-MM-DD}}
 
Parameters:
    1: Julian date in YYYY-MM-DD format
Output:
	1: Gregorian date in YYYY-MM-DD format or error message "Error parsing input date: ....."
]]
function p.Julian2Gregorian(frame)
	local jdn = p._date2jdn(frame.args[1], 0)
	if jdn then
		return p._jdn2date(jdn, 1)
	else
		return "Error parsing input date: " .. frame.args[1]
	end
end

-----------------------------------------------------------------------------
--[[
DayOfWeek
 
Return day of week based on gregorian date. Returned value is in English. However 
one can easily combine it with #Switch parser function [w:Help:Switch parser function]
to translate to other languages
 
Usage:
{{#invoke:Calendar|DayOfWeek|date|lang=}}
 
Parameters:
    1: date in YYYY-MM-DD format using Gregorian calendar
Output:
	1: day of the week in English or error message "Error parsing input date: ....."
]]

function p.DayOfWeek(frame)
	local jdn = p._date2jdn(frame.args[1], 1)
	local day = math.fmod(jdn, 7) + 1
	if day then
		local LUT = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" }
		return LUT[day]
	else
		return "Error parsing input date: " .. frame.args[1]
	end
end

-----------------------------------------------------------------------------
--[[
date2jdn
 
Convert calendar date to  "Julian day number" (jdn) 
 
Usage:
{{#invoke:Calendar|date2jdn|date}}
 
Parameters:
    1: date in YYYY-MM-DD format (optional, if missing than today's date will be used)
	2: calendar: "1" for Gregorian calendar and "0" for Julian (optional with "1" as default)
Output:
    1: "Julian day number" as integer or number of days since Monday, January 1, 4713 BC
]]

function p.date2jdn(frame)
	return p._date2jdn(frame.args[1] or os.date('%F'), frame.args[2] or 1)
end

-----------------------------------------------------------------------------
--[[
jdn2date
 
Convert "Julian day number" (jdn) to calendar date
 
Usage:
{{#invoke:Calendar|jdn2date|jdn}}
 
Parameters:
    1: "Julian day number" as integer or number of days since Monday, January 1, 4713 BC
	2: calendar: "1" for gregorian calendar and "0" for Julian (optional with "1" as default)
Output:
    1: date in YYYY-MM-DD format 
]]
function p.jdn2date(frame)
	return p._jdn2date(frame.args[1], frame.args[2] or 1)
end

--[[
Tests if a string is a valid Gregorian date
Example usage:
	{{#invoke:Calendar|valid_date|"2017-02-30"}}

Inputs:
  ISOdate: date in YYYY-MM-DD string format  
  
Outputs:
  true or false

]]
function p.valid_date(frame)
	if p._valid_date(frame.args[1]) then
		return 'date is valid'
	else
		return 'date is not valid'
	end
end

return p