# Modulo:Calendar

La documentazione per questo modulo può essere creata in Modulo:Calendar/man

```--[[
__  __           _       _         ____      _                _
|  \/  | ___   __| |_   _| | ___ _ / ___|__ _| | ___ _ __   __| | __ _ _ __
| |\/| |/ _ \ / _` | | | | |/ _ (_) |   / _` | |/ _ \ '_ \ / _` |/ _` | '__|
| |  | | (_) | (_| | |_| | |  __/_| |__| (_| | |  __/ | | | (_| | (_| | |
|_|  |_|\___/ \__,_|\__,_|_|\___(_)\____\__,_|_|\___|_| |_|\__,_|\__,_|_|

Maintainers:
* Jarekt
]]

local p = {}

-- 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>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

-- Convert calendar date to  "Julian day number" (jdn)
-- "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
-- explanation based on http://www.cs.utsa.edu/~cs1063/projects/Spring2011/Project1/project1.html
function p._date2jdn(ISOdate, gregorian)

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>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 a date from Gregorian to Julian calendar
function p.Gregorian2Julian(frame)
local JDN = p._date2jdn(frame.args, 1)
if JDN then
return p._jdn2date(JDN, 0)
else
return "Error parsing input date: " .. frame.args
end
end

-- Convert a date from Julian to Gregorian calendar
function p.Julian2Gregorian(frame)
local JDN = p._date2jdn(frame.args, 0)
if JDN then
return p._jdn2date(JDN, 1)
else
return "Error parsing input date: " .. frame.args
end
end

-- Return day of week based on gregorian date. Mon->1, Tue->2, ..., Sun->7
function p.DayOfWeek(frame)
local JDN = p._date2jdn(frame.args, 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
end
end

-- Convert calendar date to  "Julian day number" (jdn)
function p.date2jdn(frame)
return p._date2jdn(frame.args or os.date('%F'), frame.args or 1)
end

return p
```