New config opt for default_timezone with fun

README.markdown

@@ -98,7 +98,9 @@ will infer the timezone in the following order.
     `set_timezone/1` only applies to that *specific* process. If none is
     specified.
   + If no timezone is specified for the process, `qdate` looks at the `qdate`
-    application variable `default_timezone`.
+	application variable `default_timezone`. `default_timezone` can be either a
+    hard-specified timezone, or a `{Module, Function}` tuple.  The tuple format
+    should return either a timezone or the atom `undefined`.
   + If no timezone is specified by either of the above, `qdate` assumes "GMT"
     for all dates.
   + A timezone value of `auto` will act as if no timezone is specified.

qdate.config

@@ -1,5 +1,12 @@
 %% vim: ts=4 sw=4 et ft=erlang
 [{qdate, [
+    %% default_timezone can be one of two things:
+    %%   1) An actual timezone.  Either short-form like "GMT", "UTC", or a
+    %%      longer-form (but more likely to pick the correct daylight saving
+    %%      config timezone like "America/Chicago"
+    %%   2) A 2-tuple of {Module, Function}, which will be called as
+    %%      Module:Function() to determine the timezone (say you wanted to
+    %%      determine timezone based on some kind of environmental conditions)
     {default_timezone, "GMT"},
 
     %% See readme section here:

src/qdate.erl

@@ -125,16 +125,6 @@
 %% 1970-01-01 12:00am
 -define(UNIXTIME_BASE,62167219200).
 
-%% This is the timezone only if the qdate application variable 
-%% "default_timezone" isn't set or is set to undefined.
-%% It's recommended that your app sets the var in a config, or at least using
-%%
-%%      application:set_env(qdate, default_timezone, "GMT").
-%%
--define(DEFAULT_TZ, case application:get_env(qdate, default_timezone) of 
-                        undefined -> "GMT";
-                        {ok, TZ} -> TZ 
-                    end).
 
 -define(DETERMINE_TZ, determine_timezone()).
 -define(DEFAULT_DISAMBIG, prefer_standard).
@@ -825,9 +815,23 @@ extract_timezone_helper(RevDate, [TZ | TZs]) when length(RevDate) >= length(TZ)
 extract_timezone_helper(RevDate, [_TZ | TZs]) ->
     extract_timezone_helper(RevDate, TZs).
 
+
+%% This is the timezone only if the qdate application variable 
+%% "default_timezone" isn't set or is set to undefined.
+%% It's recommended that your app sets the var in a config, or at least using
+%%
+%%      application:set_env(qdate, default_timezone, "GMT").
+%%
+default_timezone() ->
+    case application:get_env(qdate, default_timezone) of 
+        undefined -> "GMT";
+        {ok, {Mod, Fun}} -> Mod:Fun();
+        {ok, TZ} -> TZ 
+    end.
+
 determine_timezone() ->
     case qdate_srv:get_timezone() of
-        undefined -> ?DEFAULT_TZ;
+        undefined -> default_timezone();
         TZ -> TZ
     end.