-module(scrypt_port).

-behaviour(gen_server).

-export([start_link/0, scrypt/6]).
-export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2,
         handle_info/2]).

%% -----------------------------------------------------------------------------

start_link() ->
    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).

-spec scrypt(binary(), binary(), pos_integer(), pos_integer(), pos_integer(),
             pos_integer()) -> binary().
scrypt(Passwd, Salt, N, R, P, Buflen) ->
    gen_server:call(?MODULE, {scrypt, Passwd, Salt, N, R, P, Buflen}, infinity).

%% -----------------------------------------------------------------------------

-record(state, {port :: port()}).

init([]) ->
    {ok, #state{port = open_port({spawn_executable,
                                  erlscrypt:priv_dir() ++ "/scrypt"},
                                 [{packet, 4}, binary, use_stdio])}}.

terminate(_Reason, _State = #state{port = Port}) ->
    catch port_command(Port, <<>>),
    catch port_close(Port),
    ok.

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

handle_call({scrypt, Passwd, Salt, N, R, P, Buflen}, _From,
            State = #state{port = Port}) ->
    port_command(Port, <<(size(Passwd)):32, (size(Salt)):32, N:32, R:32, P:32,
                         Buflen:32, Passwd/binary, Salt/binary>>),
    receive
        {Port, {data, Buf}} ->
            if
                size(Buf) =:= Buflen ->
                    {reply, Buf, State};
                true ->
                    exit(bad_scrypt_port_buflen)
            end
    end;
handle_call(_Request, _From, State) ->
    {stop, {bad_call, _Request}, State}.

handle_cast(_Request, State) ->
    {stop, {bad_cast, _Request}, State}.

handle_info(_Message, State) ->
    {stop, {bad_info, _Message}, State}.