From: daurnimator <quae@daurnimator.com>
Date: Mon, 22 Jul 2013 21:48:55 +0000 (-0400)
Subject: src/tzinfo: Add utctime function to convert local -> utc
X-Git-Url: https://git.madduck.net/etc/awesome.git/commitdiff_plain/4cdcecedc224992d80f04f677e12bb79e9a91e55?ds=sidebyside;hp=fdc736b35e4525fffa01fc2f20403997f2626381

src/tzinfo: Add utctime function to convert local -> utc
---

diff --git a/src/tzinfo.lua b/src/tzinfo.lua
index d347e05..34b7048 100644
--- a/src/tzinfo.lua
+++ b/src/tzinfo.lua
@@ -17,6 +17,40 @@ local function _find_current ( tzinfo , target , i , j )
 		return _find_current ( tzinfo , target , i , half-1 )
 	end
 end
+
+local function find_current_local ( tzinfo , ts_local )
+	-- Find two best possibilities by searching back and forward a day (assumes transition is never by more than 24 hours)
+	local tz_first = _find_current ( tzinfo , ts_local-86400 , 0 , #tzinfo )
+	local tz_last  = _find_current ( tzinfo , ts_local+86400 , 0 , #tzinfo )
+
+	local n_candidates = tz_last - tz_first + 1
+
+	if n_candidates == 1 then
+		return tz_first
+	elseif n_candidates == 2 then
+		local tz_first_ob = tzinfo [ tz_first ]
+		local tz_last_ob  = tzinfo [ tz_last ]
+
+		local first_gmtoffset = tz_first_ob.info.gmtoff
+		local last_gmtoffset  = tz_last_ob .info.gmtoff
+
+		local t_start = tz_last_ob.transition_time + first_gmtoffset
+		local t_end   = tz_last_ob.transition_time + last_gmtoffset
+
+		-- If timestamp is before start or after end
+		if ts_local < t_start then
+			return tz_first
+		elseif ts_local > t_end then
+			return tz_last
+		end
+
+		-- If we get this far, the local time is ambiguous
+		return tz_first , tz_last
+	else
+		error ( "Too many transitions in a 2 day period" )
+	end
+end
+
 function tz_info_methods:find_current ( current )
 	return self [ _find_current ( self , current , 0 , #self ) ].info
 end
@@ -26,6 +60,18 @@ function tz_info_methods:localize ( utc_ts )
 	return utc_ts + self:find_current ( utc_ts ).gmtoff
 end
 
+function tz_info_methods:utctime ( ts_local , is_dst )
+	local tz1 , tz2 = find_current_local ( self , ts_local )
+	tz1 = self [ tz1 ].info
+	if tz2 == nil then
+		return ts_local - tz1.gmtoff
+	else -- Local time is ambiguous
+		tz2 = self [ tz2 ].info
+
+		return ts_local - tz2.gmtoff , ts_local - tz2.gmtoff
+	end
+end
+
 return {
 	tz_info_mt = tz_info_mt ;
 }