bigben

-module(bigben@fake_clock).
-compile([no_auto_import, nowarn_unused_vars, nowarn_unused_function, nowarn_nomatch]).

-export([now/1, set_now/2, advance/2, new_at/1, new/0]).
-export_type([fake_clock/0, message/0]).

-opaque fake_clock() :: {fake_clock, gleam@erlang@process:subject(message())}.

-type message() :: {get, gleam@erlang@process:subject(birl:time())} |
    {set, birl:time()} |
    {advance, birl@duration:duration()}.

-spec now(fake_clock()) -> birl:time().
now(Clock) ->
    gleam@erlang@process:call(
        erlang:element(2, Clock),
        fun(Field@0) -> {get, Field@0} end,
        10
    ).

-spec set_now(fake_clock(), birl:time()) -> nil.
set_now(Clock, Now) ->
    gleam@erlang@process:send(erlang:element(2, Clock), {set, Now}).

-spec advance(fake_clock(), birl@duration:duration()) -> nil.
advance(Clock, Duration) ->
    gleam@erlang@process:send(erlang:element(2, Clock), {advance, Duration}).

-spec handle_message(message(), birl:time()) -> gleam@otp@actor:next(any(), birl:time()).
handle_message(Message, State) ->
    case Message of
        {get, Client} ->
            gleam@erlang@process:send(Client, State),
            gleam@otp@actor:continue(State);

        {set, Now} ->
            gleam@otp@actor:continue(Now);

        {advance, Duration} ->
            gleam@otp@actor:continue(birl:add(State, Duration))
    end.

-spec new_at(birl:time()) -> fake_clock().
new_at(Now) ->
    _assert_subject = gleam@otp@actor:start(Now, fun handle_message/2),
    {ok, Subject} = case _assert_subject of
        {ok, _} -> _assert_subject;
        _assert_fail ->
            erlang:error(#{gleam_error => let_assert,
                        message => <<"Assertion pattern match failed"/utf8>>,
                        value => _assert_fail,
                        module => <<"bigben/fake_clock"/utf8>>,
                        function => <<"new_at"/utf8>>,
                        line => 22})
    end,
    {fake_clock, Subject}.

-spec new() -> fake_clock().
new() ->
    new_at(birl:utc_now()).