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

diff --git a/src/tzinfo.lua b/src/tzinfo.lua
index d347e059b9646f8882108caf2427ff2e0361acf8..34b704881ff9739e543ffdb100a3e3ae48aed52b 100644 (file)
--- 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 ;
 }