-module(gtz).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([timezone/1, local_name/0]).

-if(?OTP_RELEASE >= 27).
-define(MODULEDOC(Str), -moduledoc(Str)).
-define(DOC(Str), -doc(Str)).
-else.
-define(MODULEDOC(Str), -compile([])).
-define(DOC(Str), -compile([])).
-endif.

?MODULEDOC(" Functions to provide simple timezone support for other Gleam datetime libraries.\n").

-file("src/gtz.gleam", 22).
?DOC(
    " Constructs a TimeZoneProvider type to be used with the Tempo package. \n"
    " Returns an error if the timezone is not valid.\n"
    " \n"
    " ## Examples\n"
    " \n"
    " ```gleam\n"
    " import tempo/datetime\n"
    "\n"
    " let assert Ok(tz) = gtz.timezone(\"America/New_York\")\n"
    " datetime.literal(\"2024-06-21T06:30:02.334Z\")\n"
    " |> datetime.to_timezone(tz)\n"
    " |> datetime.to_string\n"
    " // -> \"2024-01-03T02:30:02.334-04:00\"\n"
    " ```\n"
).
-spec timezone(binary()) -> {ok, tempo:time_zone_provider()} | {error, nil}.
timezone(Name) ->
    case 'Elixir.GTZ_FFI':is_valid_timezone(Name) of
        true ->
            {ok,
                {time_zone_provider,
                    fun() -> Name end,
                    fun(Utc_naive_datetime) ->
                        {{Year, Month, Day}, {Hour, Minute, Second}} = tempo@naive_datetime:to_tuple(
                            Utc_naive_datetime
                        ),
                        _assert_subject = begin
                            _pipe = 'Elixir.GTZ_FFI':calculate_offset(
                                Year,
                                Month,
                                Day,
                                Hour,
                                Minute,
                                Second,
                                Name
                            ),
                            _pipe@1 = tempo@duration:minutes(_pipe),
                            tempo@offset:from_duration(_pipe@1)
                        end,
                        {ok, Offset} = case _assert_subject of
                            {ok, _} -> _assert_subject;
                            _assert_fail ->
                                erlang:error(#{gleam_error => let_assert,
                                            message => <<"Pattern match failed, no pattern matched the value."/utf8>>,
                                            value => _assert_fail,
                                            module => <<"gtz"/utf8>>,
                                            function => <<"timezone"/utf8>>,
                                            line => 32})
                        end,
                        Offset
                    end}};

        false ->
            {error, nil}
    end.

-file("src/gtz.gleam", 71).
?DOC(
    " Returns the name of the host system's timezone.\n"
    " \n"
    " ## Examples\n"
    " \n"
    " ```gleam\n"
    " gtz.local_name()\n"
    " // -> \"Europe/London\"\n"
    " ```\n"
).
-spec local_name() -> binary().
local_name() ->
    'Elixir.Timex.Timezone.Local':lookup().