%%% Copyright (c) 2019, Sunet.
%%% See LICENSE for licensing information.

%% Spawn an Erlang port running a proxy app. We use the 'remote'
%% program from p11-kit as the proxy app.

%% Receive PKCS#11 requests from a p11p_server, forward them to the
%% proxy app, wait for a reply. If a reply is received within a
%% timeout period, proxy the reply to the requesting p11p_server. If
%% the request times out, inform the manager (our parent) and exit.

%% Track a subset of the PKCS#11 state in order to handle token
%% restarts. We start in state 'started'. While in 'started', we allow
%% only a few "opening" calls (Initialize, OpenSession and Login)
%% through to the token. Corresponding "closing" calls (Finalize,
%% CloseSession and Logout) are sent an immediate OK response without
%% forwarding them to the token. Any other call is rejected by
%% responding with an error. This should make well behaving P11
%% applications be able to deal with us switching the token under
%% their feet.

-module(p11p_client).
-behaviour(gen_server).

%% API.
-export([start_link/6]).
-export([request/2,			   % Request from p11p-server.
	 stop/2]).			   % Manager stopping us.

-include("p11p_rpc.hrl").

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

%% Records and types.
-type token_state() :: started |
		       initialized |
		       session |
		       loggedin |
		       opact |
		       finalized.

-record(state, {
	  token :: string(),			% Token name.
	  timeout :: non_neg_integer(),

	  port :: port(),
	  replyto :: pid() | undefined,

	  p11state = started :: token_state(),
	  timer :: reference() | undefined,
	  response :: p11rpc:msg() | undefined,
	  recv_count = 0 :: non_neg_integer(),
	  send_count = 0 :: non_neg_integer()
	 }).

%% API.
-spec start_link(atom(), string(), pid(), string(), list(),
		 non_neg_integer()) -> {ok, pid()} | {error, term()}.
start_link(ServName, TokName, Server, ModPath, ModEnv, Timeout) ->
    lager:info("~p: starting p11p_client for ~s", [self(), TokName]),
    gen_server:start_link({local, ServName}, ?MODULE,
			  [TokName, Server, ModPath, ModEnv, Timeout], []).

-spec request(pid(), p11rpc_msg()) -> ack | nack | {ok, non_neg_integer()}.
request(Client, Request) ->
    gen_server:call(Client, {request, Request}).

%% You should invoke stop/1 instead of gen_server:stop/1 if you're
%% uncertain whether we (Pid) are alive or not. An example of when
%% that can happen is when the manager receives a server_event about a
%% lost P11 app -- if the server process terminated on request from us
%% because we timed out on an RPC call, chances are that we have
%% already terminated by the time the manager acts on the information
%% about the lost app.
stop(Pid, Reason) ->
    gen_server:cast(Pid, {stop, Reason}).

%% Genserver callbacks.
init([TokName, Server, ModPath, ModEnv, Timeout]) ->
    ProxyAppBinPath = p11p_config:proxyapp_bin_path(),
    Port = open_port({spawn_executable, ProxyAppBinPath},
		     [stream,
		      exit_status,
		      {env, ModEnv},
		      {args, [ModPath, "-v"]}	% FIXME: Remove -v
		     ]),
    true = is_port(Port),
    lager:debug("~p: ~s: new proxy app port: ~p", [self(), ProxyAppBinPath, Port]),
    lager:debug("~p: ~s: module: ~s, env: ~p", [self(), ProxyAppBinPath, ModPath, ModEnv]),
    {ok, #state{port = Port,
		token = TokName,
		replyto = Server,
		timeout = Timeout}}.

handle_call({request, Request},
	    {FromPid, _Tag},
	    State = #state{port = Port, send_count = Sent}) ->
    case
	case State#state.p11state of
	    started ->
		case p11p_rpc:req_id(Request) of
		    ?P11_RPC_CALL_C_Logout -> ack;
		    ?P11_RPC_CALL_C_CloseSession -> ack;
		    ?P11_RPC_CALL_C_Finalize -> ack;

		    ?P11_RPC_CALL_C_Initialize -> pass;
		    ?P11_RPC_CALL_C_OpenSession -> pass;
		    ?P11_RPC_CALL_C_Login -> pass;

		    _ -> nack
		end;
	    _ ->
		pass
	end
    of
	ack ->
	    {reply, ack, State};
	nack ->
	    {reply, nack, State};
	pass ->
	    lager:debug("~p: sending request from ~p to prxoy app ~p", [self(), FromPid, Port]),
	    D = p11p_rpc:serialise(Request),
	    Buf = case Sent of
		      0 -> <<?RPC_VERSION:8, D/binary>>;
		      _ -> D
		  end,
	    {ok, _} = do_send(Port, Buf),

	    {reply,
	     {ok, size(Buf)},
	     State#state{replyto = FromPid,
			 timer = start_timer(State#state.timeout, Port),
			 send_count = Sent + 1}}
    end;

handle_call(Call, _From, State) ->
    lager:debug("~p: Unhandled call: ~p~n", [self(), Call]),
    {reply, unhandled, State}.

handle_cast({stop, Reason}, State) ->
    {stop, Reason, State};

handle_cast(Cast, State) ->
    lager:debug("~p: unhandled cast: ~p~n", [self(), Cast]),
    {noreply, State}.

%% Receiving the very first octets from proxy app since it was started.
handle_info({Port, {data, Data}}, State)
  when Port == State#state.port, State#state.response == undefined ->
    case hd(Data) of		% First octet is RPC protocol version.
	?RPC_VERSION ->
	    NewState = response_in(State, p11p_rpc:new(), tl(Data)),
	    {noreply, NewState};
	BadVersion ->
	    lager:info("~p: ~p: invalid RPC version: ~p", [self(), Port,
							   BadVersion]),
	    {noreply, State}
    end;

%% Receiving more data from proxy app.
handle_info({Port, {data, Data}}, State)
  when Port == State#state.port ->
    NewState = response_in(State, State#state.response, Data),
    {noreply, NewState};

%% Proxy app timed out.
handle_info({timeout, Timer, Port}, State)
  when Port == State#state.port, Timer == State#state.timer ->
    lager:info("~p: rpc request for ~s timed out, exiting", [self(), State#state.token]),
    p11p_manager:client_event(timeout, State#state.token),
    NewState = State#state{timer = undefined},
    {stop, normal, NewState};

handle_info(Info, State) ->
    lager:debug("~p: Unhandled info: ~p~n", [self(), Info]),
    {noreply, State}.

terminate(Reason, #state{port = Port}) ->
    lager:debug("~p: client terminating with reason ~p", [self(), Reason]),
    port_close(Port),
    ok.

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

%% Private
send_request(Port, Buf) ->
    Rand = rand:uniform(100),
    Prob = p11p_config:testing_drop_prob(),
    if
	Rand =< Prob ->
    	    lager:debug("~p: faking unresponsive token (~p) by not sending",
			[self(), Port]);
    	true ->
	    lager:debug("~p: sending ~B octets to token", [self(), size(Buf)]),
    	    true = port_command(Port, Buf)
    end,
    {ok, size(Buf)}.

response_in(S = #state{replyto = Pid, timer = Timer, recv_count = Recv},
	    MsgIn, DataIn) ->
    case p11p_rpc:parse(MsgIn, list_to_binary(DataIn)) of
	{needmore, Msg} ->
	    S#state{response = Msg};
	{done, Msg} ->
	    cancel_timer(Timer),
	    lager:debug("~p: <- ~s", [self(), p11p_rpc:dump(Msg)]),
	    {ok, _BytesSent} = p11p_server:reply(Pid, Msg),
	    %% Saving potential data not consumed by parse/2 in new message.
	    S#state{response = p11p_rpc:new(Msg#p11rpc_msg.buffer),
		    p11state = runstate(S#state.p11state, p11p_rpc:req_id(Msg)),
		    recv_count = Recv + 1}
    end.

start_timer(Timeout, Port) ->
    %%lager:debug("~p: starting timer", [self()]),
    erlang:start_timer(Timeout, self(), Port).

cancel_timer(Timer) ->
    %%lager:debug("~p: canceling timer", [self()]),
    erlang:cancel_timer(Timer, [{async, true}, {info, false}]).

-spec runstate(token_state(), non_neg_integer()) -> token_state().
runstate(started, ReqId) ->
    case ReqId of
	?P11_RPC_CALL_C_Initialize ->
	    initialized;
	_ ->
	    started
    end;
runstate(initialized, ReqId) ->
    case ReqId of
	?P11_RPC_CALL_C_OpenSession ->
	    session;
	?P11_RPC_CALL_C_Finalize ->
	    finalized;
	_ ->
	    initialized
    end;
runstate(session, ReqId) ->
    case ReqId of
	?P11_RPC_CALL_C_Login ->
	    loggedin;
	?P11_RPC_CALL_C_CloseSession ->
	    initialized;
	?P11_RPC_CALL_C_Finalize ->
	    finalized;
	_ ->
	    session
    end;
runstate(loggedin, ReqId) ->
    case ReqId of
	?P11_RPC_CALL_C_Logout ->
	    session;
	?P11_RPC_CALL_C_CloseSession ->
	    initialized;
	?P11_RPC_CALL_C_Finalize ->
	    finalized;
	_ ->
	    loggedin
    end.