local strftime = require "luatz.strftime".strftime local strformat = string.format local floor = math.floor local idiv do -- Try and use actual integer division when available (Lua 5.3+) local idiv_loader = (loadstring or load)([[return function(n,d) return n//d end]], "idiv") -- luacheck: ignore 113 if idiv_loader then idiv = idiv_loader() else idiv = function(n, d) return floor(n/d) end end end local mon_lengths = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 } -- Number of days in year until start of month; not corrected for leap years local months_to_days_cumulative = { 0 } for i = 2, 12 do months_to_days_cumulative [ i ] = months_to_days_cumulative [ i-1 ] + mon_lengths [ i-1 ] end -- For Sakamoto's Algorithm (day of week) local sakamoto = {0, 3, 2, 5, 0, 3, 5, 1, 4, 6, 2, 4}; local function is_leap ( y ) if (y % 4) ~= 0 then return false elseif (y % 100) ~= 0 then return true else return (y % 400) == 0 end end local function year_length ( y ) return is_leap ( y ) and 366 or 365 end local function month_length ( m , y ) if m == 2 then return is_leap ( y ) and 29 or 28 else return mon_lengths [ m ] end end local function leap_years_since ( year ) return idiv ( year , 4 ) - idiv ( year , 100 ) + idiv ( year , 400 ) end local function day_of_year ( day , month , year ) local yday = months_to_days_cumulative [ month ] if month > 2 and is_leap ( year ) then yday = yday + 1 end return yday + day end local function day_of_week ( day , month , year ) if month < 3 then year = year - 1 end return ( year + leap_years_since ( year ) + sakamoto[month] + day ) % 7 + 1 end local function borrow ( tens , units , base ) local frac = tens % 1 units = units + frac * base tens = tens - frac return tens , units end local function carry ( tens , units , base ) if units >= base then tens = tens + idiv ( units , base ) units = units % base elseif units < 0 then tens = tens - 1 + idiv ( -units , base ) units = base - ( -units % base ) end return tens , units end -- Modify parameters so they all fit within the "normal" range local function normalise ( year , month , day , hour , min , sec ) -- `month` and `day` start from 1, need -1 and +1 so it works modulo month , day = month - 1 , day - 1 -- Convert everything (except seconds) to an integer -- by propagating fractional components down. year , month = borrow ( year , month , 12 ) -- Carry from month to year first, so we get month length correct in next line around leap years year , month = carry ( year , month , 12 ) month , day = borrow ( month , day , month_length ( floor ( month + 1 ) , year ) ) day , hour = borrow ( day , hour , 24 ) hour , min = borrow ( hour , min , 60 ) min , sec = borrow ( min , sec , 60 ) -- Propagate out of range values up -- e.g. if `min` is 70, `hour` increments by 1 and `min` becomes 10 -- This has to happen for all columns after borrowing, as lower radixes may be pushed out of range min , sec = carry ( min , sec , 60 ) -- TODO: consider leap seconds? hour , min = carry ( hour , min , 60 ) day , hour = carry ( day , hour , 24 ) -- Ensure `day` is not underflowed -- Add a whole year of days at a time, this is later resolved by adding months -- TODO[OPTIMIZE]: This could be slow if `day` is far out of range while day < 0 do year = year - 1 day = day + year_length ( year ) end year , month = carry ( year , month , 12 ) -- TODO[OPTIMIZE]: This could potentially be slow if `day` is very large while true do local i = month_length ( month + 1 , year ) if day < i then break end day = day - i month = month + 1 if month >= 12 then month = 0 year = year + 1 end end -- Now we can place `day` and `month` back in their normal ranges -- e.g. month as 1-12 instead of 0-11 month , day = month + 1 , day + 1 return year , month , day , hour , min , sec end local leap_years_since_1970 = leap_years_since ( 1970 ) local function timestamp ( year , month , day , hour , min , sec ) year , month , day , hour , min , sec = normalise ( year , month , day , hour , min , sec ) local days_since_epoch = day_of_year ( day , month , year ) + 365 * ( year - 1970 ) -- Each leap year adds one day + ( leap_years_since ( year - 1 ) - leap_years_since_1970 ) - 1 return days_since_epoch * (60*60*24) + hour * (60*60) + min * 60 + sec end local timetable_methods = { } function timetable_methods:unpack ( ) return assert ( self.year , "year required" ) , assert ( self.month , "month required" ) , assert ( self.day , "day required" ) , self.hour or 12 , self.min or 0 , self.sec or 0 , self.yday , self.wday end function timetable_methods:normalise ( ) local year , month , day year , month , day , self.hour , self.min , self.sec = normalise ( self:unpack ( ) ) self.day = day self.month = month self.year = year self.yday = day_of_year ( day , month , year ) self.wday = day_of_week ( day , month , year ) return self end timetable_methods.normalize = timetable_methods.normalise -- American English function timetable_methods:timestamp ( ) return timestamp ( self:unpack ( ) ) end function timetable_methods:rfc_3339 ( ) local year, month, day, hour, min, fsec = self:unpack() local sec, msec = borrow(fsec, 0, 1000) msec = math.floor(msec) return strformat ( "%04u-%02u-%02uT%02u:%02u:%02d.%03d" , year , month , day , hour , min , sec , msec ) end function timetable_methods:strftime ( format_string ) return strftime ( format_string , self ) end local timetable_mt local function coerce_arg ( t ) if getmetatable ( t ) == timetable_mt then return t:timestamp ( ) end return t end timetable_mt = { __index = timetable_methods ; __tostring = timetable_methods.rfc_3339 ; __eq = function ( a , b ) return a:timestamp ( ) == b:timestamp ( ) end ; __lt = function ( a , b ) return a:timestamp ( ) < b:timestamp ( ) end ; __sub = function ( a , b ) return coerce_arg ( a ) - coerce_arg ( b ) end ; } local function cast_timetable ( tm ) return setmetatable ( tm , timetable_mt ) end local function new_timetable ( year , month , day , hour , min , sec , yday , wday ) return cast_timetable { year = year ; month = month ; day = day ; hour = hour ; min = min ; sec = sec ; yday = yday ; wday = wday ; } end function timetable_methods:clone ( ) return new_timetable ( self:unpack ( ) ) end local function new_from_timestamp ( ts ) if type ( ts ) ~= "number" then error ( "bad argument #1 to 'new_from_timestamp' (number expected, got " .. type ( ts ) .. ")" , 2 ) end return new_timetable ( 1970 , 1 , 1 , 0 , 0 , ts ):normalise ( ) end return { is_leap = is_leap ; day_of_year = day_of_year ; day_of_week = day_of_week ; normalise = normalise ; timestamp = timestamp ; new = new_timetable ; new_from_timestamp = new_from_timestamp ; cast = cast_timetable ; timetable_mt = timetable_mt ; }