Re-implemented PR #8

src/localtime.erl

@@ -17,6 +17,9 @@
      ,tz_name/2
      ,tz_shift/2
      ,tz_shift/3
+     ,get_timezone/1
+     ,list_timezones/0
+     ,adjust_datetime/2
   ]).
 
 % utc_to_local(UtcDateTime, Timezone) -> LocalDateTime | [LocalDateTime, DstLocalDateTime] | {error, ErrDescr}
@@ -185,14 +188,20 @@ tz_shift(LocalDateTime, TimezoneFrom, TimezoneTo) ->
          Err
    end.
 
-% =======================================================================
-% privates
-% =======================================================================
-
 adjust_datetime(DateTime, Minutes) ->
    Seconds = calendar:datetime_to_gregorian_seconds(DateTime) + Minutes * 60,
    calendar:gregorian_seconds_to_datetime(Seconds).
 
+get_timezone(TimeZone) ->
+    get_timezone_inner(TimeZone).
+
+list_timezones() ->
+    dict:fetch_keys(?tz_index).
+
+% =======================================================================
+% privates
+% =======================================================================
+
 invert_shift(Minutes) ->
    -Minutes.
 
@@ -222,7 +231,7 @@ tr_char([H|T], From, To, Acc) ->
    end.
 
 -define(SPACE_CHAR, 32).
-get_timezone(TimeZone) ->
+get_timezone_inner(TimeZone) ->
    TimeZoneNoSpaces = tr_char(TimeZone, ?SPACE_CHAR, $_),
    case dict:find(TimeZoneNoSpaces, ?tz_index)  of
       error ->

src/localtime_dst.erl

@@ -5,6 +5,9 @@
 
 -author("Dmitry Melnikov <dmitryme@gmail.com>").
 
+-include("tz_database.hrl").
+-include("tz_index.hrl").
+
 -export(
    [
       check/2
@@ -16,6 +19,13 @@
 % check(DateTime, TimeZone) -> is_in_dst | is_not_in_dst | ambiguous_time | time_not_exists
 %  DateTime = DateTime()
 %  TimeZone = tuple()
+check(DateTime, Timezone) when is_list(Timezone) ->
+    case lists:keyfind(localtime:get_timezone(Timezone), 1, ?tz_database) of
+        false ->
+            {error, unknown_tz};
+        TZ -> 
+            check(DateTime, TZ)
+    end;
 check({Date = {Year, _, _},Time}, {_, _, _, _Shift, DstShift, DstStartRule, DstStartTime, DstEndRule, DstEndTime}) ->
    DstStartDay = get_dst_day_of_year(DstStartRule, Year),
    DstEndDay = get_dst_day_of_year(DstEndRule, Year),