-module(gleam@otp@task).
-compile(no_auto_import).

-export([async/1, try_await/2, await/2]).
-export_type([task/1, await_error/0, message/1]).

-opaque task(FR) :: {task,
                     gleam@otp@process:pid_(),
                     gleam@otp@process:pid_(),
                     gleam@otp@process:receiver(message(FR))}.

-type await_error() :: timeout | {exit, gleam@dynamic:dynamic()}.

-type message(FS) :: {mon, gleam@otp@process:process_down()} | {chan, FS}.

-spec async(fun(() -> FX)) -> task(FX).
async(Work) ->
    Owner = gleam@otp@process:self(),
    {Sender, Receiver} = gleam@otp@process:new_channel(),
    Pid = gleam@otp@process:start(
        fun() -> gleam@otp@process:send(Sender, Work()) end
    ),
    Receiver@1 = begin
        _pipe = Pid,
        _pipe@1 = gleam@otp@process:monitor_process(_pipe),
        _pipe@2 = gleam@otp@process:map_receiver(
            _pipe@1,
            fun(A) -> {mon, A} end
        ),
        gleam@otp@process:merge_receiver(
            _pipe@2,
            begin
                _pipe@3 = Receiver,
                gleam@otp@process:map_receiver(_pipe@3, fun(A) -> {chan, A} end)
            end
        )
    end,
    {task, Owner, Pid, Receiver@1}.

-spec assert_owner(task(any())) -> nil.
assert_owner(Task) ->
    Self = gleam@otp@process:self(),
    case erlang:element(2, Task) =:= Self of
        true ->
            nil;

        false ->
            gleam@otp@process:send_exit(
                Self,
                <<"awaited on a task that does not belong to this process"/utf8>>
            )
    end.

-spec try_await(task(GB), integer()) -> {ok, GB} | {error, await_error()}.
try_await(Task, Timeout) ->
    assert_owner(Task),
    case gleam@otp@process:'receive'(erlang:element(4, Task), Timeout) of
        {ok, {chan, X}} ->
            gleam@otp@process:close_channels(erlang:element(4, Task)),
            {ok, X};

        {ok, {mon, {process_down, _@1, Reason}}} ->
            gleam@otp@process:close_channels(erlang:element(4, Task)),
            {error, {exit, Reason}};

        {error, nil} ->
            {error, timeout}
    end.

-spec await(task(GF), integer()) -> GF.
await(Task, Timeout) ->
    {ok, Value@1} = case try_await(Task, Timeout) of
        {ok, Value} -> {ok, Value};
        _try ->
            erlang:error(#{gleam_error => assert,
                           message => <<"Assertion pattern match failed"/utf8>>,
                           value => _try,
                           module => <<"gleam/otp/task"/utf8>>,
                           function => <<"await"/utf8>>,
                           line => 116})
    end,
    Value@1.