%% @doc This module is responsible for running the game VM:s. You can issue
%% commands to a vm using this module.

-module(ggs_gamevm).
-behaviour(gen_server).

%% gen_server callbacks
-export([init/1, handle_call/3, handle_cast/2, handle_info/2,
         terminate/2, code_change/3]).

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

%% API
-export([start_link/1, define/2, user_command/4, stop/1, call_js/2]).

-include_lib("eunit/include/eunit.hrl").


%% ----------------------------------------------------------------------
% API implementation

%% @doc Create a new VM process. The process ID is returned and can be used
%% with for example the define method of this module.
start_link(Table) ->
    erlang_js:start(), %% @TODO: should only be done once
    {ok, Pid} = gen_server:start_link(?MODULE, [Table], []),
    Pid.

%% @doc Define some new code on the specified VM, returns the atom ok.
define(GameVM, SourceCode) ->
    gen_server:cast(GameVM, {define, SourceCode}).

%% @doc Execute a user command on the specified VM. This function is
%% asynchronous, and returns ok.
%% @spec user_command(GameVM, User, Command, Args) -> ok
%%      GameVM  = process IS of VM
%%      Player  = the player running the command
%%      Command = a game command to run
%%      Args    = arguments for the Command parameter
user_command(GameVM, Player, Command, Args) ->
    gen_server:cast(GameVM, {user_command, Player, Command, Args}).

%% @private
% only for tests
call_js(GameVM, SourceCode) ->
    gen_server:call(GameVM, {eval, SourceCode}).
    
% @doc stops the gamevm process
stop(GameVM) ->
    gen_server:cast(GameVM, stop).


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

%% @private
init([Table]) ->
    process_flag(trap_exit, true),
    {ok, Port} = js_driver:new(),
    %% @TODO: add here default JS API instead
    {ok, #state { port = Port, table = Table }}.

%% private
% only needed for the tests
handle_call({eval, SourceCode}, _From, #state { port = Port } = State) ->
    {ok, Ret} = js:eval(Port, list_to_binary(SourceCode)),
    {reply, Ret, State}.

%% @private    
handle_cast({define, SourceCode}, #state { port = Port } = State) ->
    ok = js:define(Port, list_to_binary(SourceCode)),
    {noreply, State};
handle_cast({user_command, Player, Command, Args}, #state { port = Port } = State) ->
    Arguments = string:concat("'", string:concat(
		string:join([js_escape(Player), js_escape(Command), js_escape(Args)], "','"), "'")),
    Js = list_to_binary(string:concat(string:concat("userCommand(", Arguments), ");")),
    js_driver:define_js(Port, Js),
    {noreply, State};
handle_cast(stop, State) ->
    {stop, normal, State};
handle_cast(Msg, S) ->
    error_logger:error_report([unknown_msg, Msg]),
    {noreply, S}.

%% @private
handle_info(Msg, S) ->
    error_logger:error_report([unknown_msg, Msg]),
    {noreply, S}.

%% @private
terminate(_Reason, _State) ->
    ok.

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

js_escape(S) ->
	lists:flatmap(fun($\') -> [$\\, $\']; (X) -> [X] end, S).

%% ----------------------------------------------------------------------
% Tests

start_link_test() ->
    erlang_js:start(), %% @TODO: should only be done once
	GameVM = start_link(test_table),
	?assertNot(GameVM =:= undefined).
	
define_test() ->
    GameVM = start_link(test_table),
    define(GameVM, "function hello(test) { return test; }"),
    ?assertMatch(<<"jeena">>, gen_server:call(GameVM, {eval, "hello('jeena')"})).
    
stop_test() ->
	GameVM = start_link(test_table),
	ok = stop(GameVM).

user_command_test() ->
    GameVM = start_link(test_table),
    define(GameVM, "var t = '';\nfunction userCommand(user, command, args) { t = user + command + args; }\n"),
    user_command(GameVM, "'jeena", "thecommand", "theargs'"),
    ?assertMatch(<<"'jeenathecommandtheargs'">>, gen_server:call(GameVM, {eval, "t;"})).

js_erlang_test() ->
    GameVM = start_link(test_table),
    define(GameVM, "var t = '';\nfunction userCommand(user, command, args) { t = callErlang('erlang time') + ''; }\n"),
    user_command(GameVM, "", "", ""),
	{A, B, C} = erlang:time(),
	T = "{" ++ integer_to_list(A) ++ ", " ++ integer_to_list(B) ++ ", " ++ integer_to_list(C) ++ "}",
	?assertMatch(T, binary_to_list(gen_server:call(GameVM, {eval, "t;"}))).