-module(qdate).

-export([
	to_string/1,
	to_string/2,
	to_string/3,
	to_date/1,
	to_date/2,
	to_now/1,
	to_unixtime/1,
	unixtime/0
]).

%% -export([
%% 	register_parser/2,
%% 	register_parser/1
%% ]).
%%
%% -export([
%% 	register_format/2,
%% 	register_format/1
%% ]).
%% 
%% -export([
%% 	set_timezone/1,
%% 	set_timezone/2,
%% 	get_timezone/0,
%% 	get_timezone/1
%% ]).


%% Exported for API compatibility with ec_date
-export([
	format/1,format/2,
	nparse/1,
	parse/1
]).

%% This the value in gregorian seconds for jan 1st 1970, 12am
%% It's used to convert to and from unixtime, since unixtime starts 
%% 1970-01-01 12:00am
-define(UNIXTIME_BASE,62167219200).
-define(DEFAULT_TZ, "GMT").

to_string(Format) ->
	to_string(Format, now()).

to_string(Format, Date) ->
	to_string(Format, ?DEFAULT_TZ, Date).

to_string(Format, ToTZ, Date) ->
	ec_date:format(Format,to_date(Date,ToTZ)).

format(Format) ->
	to_string(Format).

format(Format, Date) ->
	to_string(Format, Date).

parse(String) ->
	to_date(String).

nparse(String) ->
	to_now(String).

%% This converts dates without regard to timezone.
%% Unixtime just goes to UTC
raw_to_date(Unixtime) when is_integer(Unixtime) ->
	unixtime_to_date(Unixtime);
raw_to_date(DateString) when is_list(DateString) ->
	ec_date:parse(DateString);
raw_to_date(Now = {_,_,_}) ->
	calendar:now_to_datetime(Now);
raw_to_date(Date = {{_,_,_},{_,_,_}}) ->
	Date.

to_date(RawDate) ->
	to_date(RawDate, ?DEFAULT_TZ).

to_date(RawDate, ToTZ)  ->
	{RawDate2,FromTZ} = extract_timezone(RawDate),
	Date = raw_to_date(RawDate2),
	localtime:local_to_local(Date,FromTZ,ToTZ).

extract_timezone(Unixtime) when is_integer(Unixtime) ->
	{Unixtime, ?DEFAULT_TZ};
extract_timezone(DateString) when is_list(DateString) ->
	AllTimezones = localtime:list_timezones(),
	RevDate = lists:reverse(DateString),
	extract_timezone_helper(RevDate, AllTimezones);
extract_timezone(Date={{_,_,_},{_,_,_}}) ->
	{Date, ?DEFAULT_TZ};
extract_timezone(Now={_,_,_}) ->
	{Now, ?DEFAULT_TZ};
extract_timezone({MiscDate,TZ}) ->
	{MiscDate,TZ}.
	
extract_timezone_helper(RevDate, []) ->
	{lists:reverse(RevDate), ?DEFAULT_TZ};
extract_timezone_helper(RevDate, [TZ | TZs]) ->
	RevTZ = lists:reverse(TZ),
	case lists:split(length(TZ),RevDate) of
		{RevTZ," " ++ Remainder} ->
			{lists:reverse(Remainder), TZ};
		_ ->
			extract_timezone_helper(RevDate, TZs)
	end.

to_unixtime(Unixtime) when is_integer(Unixtime) ->
	Unixtime;
to_unixtime({MegaSecs,Secs,_}) ->
	MegaSecs*1000000 + Secs;
to_unixtime(ToParse) ->
	Date = to_date(ToParse),
	calendar:datetime_to_gregorian_seconds(Date) - ?UNIXTIME_BASE.

unixtime() ->
	to_unixtime(now()).

to_now(Now = {_,_,_}) ->
	Now;
to_now(ToParse) ->
	Unixtime = to_unixtime(ToParse),
	unixtime_to_now(Unixtime).


unixtime_to_now(T) when is_integer(T) ->
	MegaSec = floor(T/1000000),
	Secs = T - MegaSec*1000000,
	{MegaSec,Secs,0}.

unixtime_to_date(T) ->
	Now = unixtime_to_now(T),
	calendar:now_to_datetime(Now).

floor(N) when N >= 0 ->
	trunc(N);
floor(N) when N < 0 ->
	Int = trunc(N),
	if
		Int==N -> Int;
		true -> Int-1
	end.
	

%% TESTS
-include_lib("eunit/include/eunit.hrl").

all_test_() ->
	[
		?_assertEqual(0,to_unixtime({0,0,0})),
		?_assertEqual({0,0,0},to_now(0)),
		?_assertEqual(0,to_unixtime("1970-01-01 12:00am GMT")),
		?_assertEqual(21600,to_unixtime("1970-01-01 12:00am CST")),
		?_assertEqual(0,to_unixtime({{1970,1,1},{0,0,0}})),
		?_assertEqual({{1970,1,1},{0,0,0}},to_date(0)),
		?_assertEqual({{2013,03,07},{0,0,0}},to_date(to_unixtime("2013-03-07 12am"))),
		?_assertEqual("2012-12-01 1:00pm", to_string("Y-m-d g:ia","EST","2012-12-01 12:00pm CST")),
		?_assertEqual(to_unixtime("2012-01-01 12:00pm CST"), to_unixtime("2012-01-01 10:00am PST")),
		?_assertEqual({{2012,12,31},{18,15,15}},to_date("Dec 31, 2012 6:15:15pm")),
		?_assertEqual({{2013,1,1},{0,15,15}},to_date("December 31, 2012 6:15:15pm CST","GMT"))
	].