-module(l4u@bif_datetime_ffi).
-compile(export_all).

% Timestampi == EpochTime

to_bin_string(X) when is_list(X) -> list_to_binary(X); 
to_bin_string(X) when is_binary(X) -> X. 

start()->
    qdate:start().

epoch() ->
    now_to_seconds(erlang:now())
.   

epoch_hires() ->
    now_to_seconds_hires(erlang:now())
.   

now_to_seconds({Mega, Sec, _}) ->
    (Mega * 1000000) + Sec
.   

now_to_milliseconds({Mega, Sec, Micro}) ->
    now_to_seconds({Mega, Sec, Micro}) * 1000
.   

now_to_seconds_hires({Mega, Sec, Micro}) ->
    now_to_seconds({Mega, Sec, Micro}) + (Micro / 1000000)
.   

now_to_milliseconds_hires({Mega, Sec, Micro}) ->
    now_to_seconds_hires({Mega, Sec, Micro}) * 1000
.   

epoch_gregorian_seconds() ->
    calendar:datetime_to_gregorian_seconds({{1970,1,1}, {0,0,0}})
.       

now_to_gregorian_seconds() ->
    epoch_to_gregorian_seconds(now())
.       

epoch_to_gregorian_seconds({Mega, Sec, Micro}) ->
    epoch_to_gregorian_seconds(now_to_seconds({Mega, Sec, Micro}));
epoch_to_gregorian_seconds(Now) ->
    EpochSecs = epoch_gregorian_seconds()
    , Now + EpochSecs
.       

gregorian_seconds_to_epoch(Secs) ->
    EpochSecs = epoch_gregorian_seconds()
    , Secs - EpochSecs
.

date_to_epoch(Date) ->
    datetime_to_epoch({Date, {0,0,0} })
.

datetime_to_epoch({Date, Time}) ->
    gregorian_seconds_to_epoch(
        calendar:datetime_to_gregorian_seconds({Date, Time}))
.

is_older_by(T1, T2, {days, N}) ->
    N1 = day_difference(T1, T2)
    , case N1 of
        N2 when (-N < N2) ->
            true;
        _ ->
            false
    end
.

is_sooner_by(T1, T2, {days, N}) ->
    case day_difference(T1, T2) of
        N1 when N > N1 ->
            true;
        _ ->
            false
    end
.

is_time_older_than({Date, Time}, Mark) ->
    is_time_older_than(calendar:datetime_to_gregorian_seconds({Date, Time})
        , Mark);
is_time_older_than(Time, {DateMark, TimeMark}) ->
    is_time_older_than(Time
        , calendar:datetime_to_gregorian_seconds({DateMark, TimeMark}));
is_time_older_than(Time, Mark)  when is_integer(Time), is_integer(Mark) ->
    Time < Mark
.

day_difference({D1, _}, D2) ->
    day_difference(D1, D2);
day_difference(D1, {D2, _}) ->
    day_difference(D1, D2);
day_difference(D1, D2) ->
    Days1 = calendar:date_to_gregorian_days(D1)
    , Days2 = calendar:date_to_gregorian_days(D2)
    , Days1 - Days2
.

is_time_sooner_than({Date, Time}, Mark) ->
    is_time_sooner_than(calendar:datetime_to_gregorian_seconds({Date, Time})
        , Mark);
is_time_sooner_than(Time, {DateMark, TimeMark}) ->
    is_time_sooner_than(Time
        , calendar:datetime_to_gregorian_seconds({DateMark, TimeMark}));
is_time_sooner_than(Time, Mark)  when is_integer(Time), is_integer(Mark) ->
    Time > Mark
.

subtract(Date, {days, N}) ->
    New = calendar:date_to_gregorian_days(Date) - N
    , calendar:gregorian_days_to_date(New)
.

add(Date, {days, N}) ->
    New = calendar:date_to_gregorian_days(Date) + N
    , calendar:gregorian_days_to_date(New)
.







timestamp({Mega, Secs, Micro}) ->
    Mega*1000*1000*1000*1000 + Secs * 1000 * 1000 + Micro.

time_tuple(Timestamp) ->
    TimeList = erlang:integer_to_list(Timestamp),
    Mega = erlang:list_to_integer(string:substr(TimeList, 1, 4)),
    Sec = erlang:list_to_integer(string:substr(TimeList, 5, 6)),
    Micro = erlang:list_to_integer(string:substr(TimeList, 11, 6)),
    {Mega, Sec, Micro}.

hires_epoch() ->
    TimeStampMicro = timestamp( erlang:now() ),
    TimeStampMicro / 1000000.0.

timestamp_to_datetime(Timestamp) ->
    {{Year,Month,Day},{Hour,Minute,Second}} = calendar:gregorian_seconds_to_datetime(Timestamp).

datetime_format(Timestamp,Format) ->
    GregorianSeconds = epoch_to_gregorian_seconds(Timestamp),
    DateTime = timestamp_to_datetime(GregorianSeconds),
    %io:format("datetime: ~p\n",[DateTime]),
    to_bin_string( qdate:to_string(Format, DateTime) ).