From: daurnimator <quae@daurnimator.com>
Date: Tue, 23 Jul 2013 19:39:52 +0000 (-0400)
Subject: Add src/timetable module (with tests)
X-Git-Url: https://git.madduck.net/etc/awesome.git/commitdiff_plain/81eaf243f3f28403292343af73e178f79ab5c0b3

Add src/timetable module (with tests)
---

diff --git a/luatz-scm-0.rockspec b/luatz-scm-0.rockspec
index 73b4dff..25b0f62 100644
--- a/luatz-scm-0.rockspec
+++ b/luatz-scm-0.rockspec
@@ -22,10 +22,11 @@ source = {
 build = {
 	type = "builtin" ;
 	modules = {
-		["luatz.init"]    = "src/init.lua" ;
-		["luatz.gettime"] = "src/gettime.lua" ;
-		["luatz.tzcache"] = "src/tzcache.lua" ;
-		["luatz.tzfile"]  = "src/tzfile.lua" ;
-		["luatz.tzinfo"]  = "src/tzinfo.lua" ;
+		["luatz.init"]      = "src/init.lua" ;
+		["luatz.gettime"]   = "src/gettime.lua" ;
+		["luatz.timetable"] = "src/timetable.lua" ;
+		["luatz.tzcache"]   = "src/tzcache.lua" ;
+		["luatz.tzfile"]    = "src/tzfile.lua" ;
+		["luatz.tzinfo"]    = "src/tzinfo.lua" ;
 	} ;
 }
diff --git a/spec/timetable_spec.lua b/spec/timetable_spec.lua
new file mode 100644
index 0000000..6536459
--- /dev/null
+++ b/spec/timetable_spec.lua
@@ -0,0 +1,37 @@
+describe ( "Time table library" , function ( )
+	local timetable = require "timetable"
+
+	it ( "Doomsday calculation" , function ( )
+		local doomsday = timetable.doomsday
+
+		-- Doomsday in Gregorian calendar for 2013 is Thursday.
+		assert.are.same ( 5 , doomsday(2013) )
+
+		assert.are.same ( 3 , doomsday(1967) )
+		assert.are.same ( 5 , doomsday(1968) )
+	end )
+
+	it ( "Get day of week correct" , function ( )
+		local function native_normalise ( tbl )
+			return os.date("*t",os.time(tbl))
+		end
+		local tbl = {
+			year = 2013 ;
+			month = 7 ;
+			day = 23 ;
+		}
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=24
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=25
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=26
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=27
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=28
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+		tbl.day=29
+		assert.are.same ( native_normalise ( tbl ).wday  , timetable.normalise ( tbl ).wday )
+	end )
+end )
diff --git a/src/timetable.lua b/src/timetable.lua
new file mode 100644
index 0000000..9af7994
--- /dev/null
+++ b/src/timetable.lua
@@ -0,0 +1,114 @@
+local floor = math.floor
+local function idiv ( n , d )
+	return floor ( n / d )
+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
+
+local function is_leap ( y )
+	return (y % 4) == 0 and (y % 100) ~= 0 or (y % 400) == 0
+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 doomsday ( year )
+	return ( 3 -- Tuesday
+		- 1 + year + idiv ( year , 4 ) - idiv ( year , 100 ) + idiv ( year , 400 ) )
+		% 7 + 1
+end
+local doomsday_cache = setmetatable ( { } , {
+	__index = function ( cache , year )
+		local d = doomsday ( year )
+		cache [ year ] = d
+		return d
+	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 ( yday , year )
+	return ( yday - doomsday_cache [ year ] - 1 ) % 7 + 1
+end
+
+local function increment ( 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
+
+local function normalise ( tm )
+	local sec   = tm.sec  or 0
+	local min   = tm.min  or 0
+	local hour  = tm.hour or 12
+	local day   = assert ( tm.day   , "day required" )
+	local month = assert ( tm.month , "month required" )
+	local year  = assert ( tm.year  , "year required" )
+
+	min  , sec  = increment ( min  , sec  , 60 ) -- TODO: consider leap seconds?
+	hour , min  = increment ( hour , min  , 60 )
+	day  , hour = increment ( day  , hour , 24 )
+
+	while day <= 0 do
+		year = year - 1
+		day  = day + year_length ( year )
+	end
+
+	-- This could potentially be slow if `day` is very large
+	while true do
+		local i = month_length ( month , year )
+		if day <= i then break end
+		day = day - i
+		month = month + 1
+	end
+
+	-- Lua months start from 1, need -1 and +1 around this increment
+	year , month = increment ( year , month - 1 , 12 )
+	month = month + 1
+
+	tm.sec   = sec
+	tm.min   = min
+	tm.hour  = hour
+	tm.day   = day
+	tm.month = month
+	tm.year  = year
+
+	local yday = day_of_year ( day , month , year )
+	local wday = day_of_week ( yday , year )
+
+	tm.yday = yday
+	tm.wday = wday
+
+	return tm
+end
+
+return {
+	doomsday  = doomsday ;
+	normalise = normalise ;
+}