From 86e57ee7249734545974d4b8ba2de3bcea6575a3 Mon Sep 17 00:00:00 2001
From: daurnimator <quae@daurnimator.com>
Date: Wed, 24 Jul 2013 11:53:24 -0400
Subject: [PATCH] src/timetable: Fix timestamp function; add test

---
 spec/timetable_spec.lua | 14 ++++++++++++++
 src/timetable.lua       | 14 +++++++++-----
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/spec/timetable_spec.lua b/spec/timetable_spec.lua
index a72a0f9..a80b9ad 100644
--- a/spec/timetable_spec.lua
+++ b/spec/timetable_spec.lua
@@ -34,4 +34,18 @@ describe ( "Time table library" , function ( )
 		assert_same_wday ( 2013 , 7 , 28 )
 		assert_same_wday ( 2013 , 7 , 29 )
 	end )
+
+	local function native_timestamp ( year , month , day )
+		return assert ( tonumber ( assert ( io.popen (
+						string.format('date -u -d "%d-%d-%d" +%%s', year , month , day )
+					) ):read "*l" ) )
+	end
+
+	it ( "Timestamp creation is valid" , function ( )
+		for y=1950,2013 do
+			for m=1,12 do
+				assert.same ( native_timestamp ( y,m,1 ) , timetable.timestamp(y,m,1,0,0,0) )
+			end
+		end
+	end)
 end )
diff --git a/src/timetable.lua b/src/timetable.lua
index b58ad0f..e7f2816 100644
--- a/src/timetable.lua
+++ b/src/timetable.lua
@@ -102,12 +102,16 @@ local function normalise ( year , month , day , hour , min , sec )
 	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 )
-	return 60*60*24*(
-			year * year_length ( year )
-			+ month * month_length ( month , year )
-			+ day
-		)
+	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
-- 
2.39.2