flattening algorithm needs to be reworked.

also, datetime methods aren't consistent in their naming and return values.

src/ezic_zone.erl

@@ -7,11 +7,11 @@
 	 , current/1
 	 , current_as_of_utc/2
 	 , split_by_name/2
-	 , sort_ascending/2
-	 , sort_descending/2
 	 , offset_sec/1
 
 	 , project_end/2
+	 , project_end_utc/2
+	 , next/3
 	]).
 
 
@@ -50,16 +50,6 @@ current_as_of_utc(UTCDatetime, TzName) ->
 get_zone_utc(_, []) ->
     erlang:error(no_current);
 get_zone_utc(_UTCDatetime, Zones) ->
-    _SortedZones= lists:sort(fun sort_descending/2, Zones),
-%%    [CZone|_]= lists:dropwhile(fun(SZ)-> older_zone_utc(SZ, UTCDatetime) end, SortedZones),
-%%    CZone.
-
-
-    %% begin with GMT offset.
-    %% foreach rule (oldest first)
-    %%   see whether until=(standard|wall|utc) time
-    %%   
-
     not_done.
 			       
 
@@ -76,14 +66,6 @@ split_by_name(#zone{name=N}, Zones) ->
       , Zones).
 
 
-sort_descending(#zone{until=U1}, #zone{until=U2}) ->
-    ezic_date:compare(U2, U1).
-
-sort_ascending(Z1=#zone{}, Z2=#zone{}) ->
-    not sort_descending(Z1, Z2).
-
-
-
 % @bug doesn't normalize times. Times are self-relative (to standard time), and Now may come from any timezone unless we're careful about that.
 %% older_zone(#zone{until=Until}, UTCDatetime) ->
 %%     ezic_date:compare(Until, UTCDatetime).
@@ -98,9 +80,28 @@ offset_sec(Zone) ->
 
 % returns the UTC datetime projected for zone end (given current DST Offset)
 project_end(#zone{until=Until, gmtoff=Offset}, DSTOffset) ->
-    {_,_,UTCDatetime}= ezic_date:all_times(Until, Offset, DSTOffset),
+    ezic_date:all_times(Until, Offset, DSTOffset).
+
+% returns just the UTC datetime projected for zone end
+project_end_utc(Zone=#zone{}, DSTOffset) ->
+    {_,_,UTCDatetime}= project_end(Zone, DSTOffset),
     UTCDatetime.
+    
 
 
 
-
+% returns {Zone, Rest} where Zone is the next zone after UTCFrom,
+%  subject to the DST offset. 
+% Note that dst differences *can* change which zone comes next, 
+%  though it's very unlikely (and does not exist in the current tz database files). 
+%  this method covers that event, anyhow.
+next(ZoneList, UTCFrom, DSTOff) ->
+    DatedList= lists:map(
+		 fun(Z=#zone{until=Until, gmtoff=Offset})->
+			 NU= ezic_date:normalize(Until),
+			 {_,_,UTCDt}= ezic_date:all_times(NU, Offset, DSTOff),
+			 {UTCDt, Z}
+		 end
+		 , ZoneList),
+    [{_,Zone} | DRest]= lists:sort(DatedList),
+    {Zone, [R || {_,R}<- DRest]}.