%%% Copyright (C) 2009 - Will Glozer.  All rights reserved.

-module(pgsql_sock).

-behavior(gen_server).

-export([start_link/4, cancel/3]).
-export([decode_string/1, lower_atom/1]).

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

-include("pgsql.hrl").
-include("pgsql_binary.hrl").

-record(state, {mod, sock, decoder, backend}).

%% -- client interface --

start_link(Host, Username, Opts) ->
    gen_server:start_link(?MODULE, [Host, Username, Opts], []).

cancel(S) ->
    gen_server:cast(S, cancel}).

%% -- gen_server implementation --

init([C, Host, Username, Opts]) ->
    Opts2 = ["user", 0, Username, 0],
    case proplists:get_value(database, Opts, undefined) of
        undefined -> Opts3 = Opts2;
        Database  -> Opts3 = [Opts2 | ["database", 0, Database, 0]]
    end,

    Port = proplists:get_value(port, Opts, 5432),
    SockOpts = [{active, false}, {packet, raw}, binary, {nodelay, true}],
    {ok, S} = gen_tcp:connect(Host, Port, SockOpts),

    State = #state{
      mod  = gen_tcp,
      sock = S,
      tail = <<>>},

    case proplists:get_value(ssl, Opts) of
        T when T == true; T == required ->
            ok = gen_tcp:send(S, <<8:?int32, 80877103:?int32>>),
            {ok, <<Code>>} = gen_tcp:recv(S, 1),
            State2 = start_ssl(Code, T, Opts, State);
        _ ->
            State2 = State
    end,

    setopts(State2, [{active, true}]),
    send(self(), [<<196608:32>>, Opts3, 0]),
    {ok, State2}.

handle_call(Call, _From, State) ->
    {stop, {unsupported_call, Call}, State}.

handle_cast({send, Data}, State) ->
    #state{mod = Mod, sock = Sock} = State,
    ok = Mod:send(Sock, Data),
    {noreply, State};

handle_cast(cancel, State = #state{backend = {Pid, Key}}) ->
    {ok, {Addr, Port}} = inet:peername(State#state.sock),
    SockOpts = [{active, false}, {packet, raw}, binary],
    {ok, Sock} = gen_tcp:connect(Addr, Port, SockOpts),
    Msg = <<16:?int32, 80877102:?int32, Pid:?int32, Key:?int32>>,
    ok = gen_tcp:send(Sock, Msg),
    gen_tcp:close(Sock),
    {noreply, State};

handle_cast(Cast, State) ->
    {stop, {unsupported_cast, Cast}, State}.

handle_info({_, _Sock, Data}, #state{tail = Tail} = State) ->
    State2 = decode(<<Tail/binary, Data/binary>>, State),
    {noreply, State2};

handle_info({Closed, _Sock}, State)
  when Closed == tcp_closed; Closed == ssl_closed ->
    {stop, sock_closed, State};

handle_info({Error, _Sock, Reason}, State)
  when Error == tcp_error; Error == ssl_error ->
    {stop, {sock_error, Reason}, State}.

terminate(_Reason, _State) ->
    ok.

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

%% -- internal functions --

start_ssl($S, _Flag, Opts, State) ->
    #state{sock = S1} = State,
    case ssl:connect(S1, Opts) of
        {ok, S2}        -> State#state{mod = ssl, sock = S2};
        {error, Reason} -> exit({ssl_negotiation_failed, Reason})
    end;

start_ssl($N, Flag, _Opts, State) ->
    case Flag of
        true     -> State;
        required -> exit(ssl_not_available)
    end.

setopts(#state{mod = Mod, sock = Sock}, Opts) ->
    case Mod of
        gen_tcp -> inet:setopts(Sock, Opts);
        ssl     -> ssl:setopts(Sock, Opts)
    end.

decode(<<Type:8, Len:?int32, Rest/binary>> = Bin, #state{c = C} = State) ->
    Len2 = Len - 4,
    case Rest of
        <<Data:Len2/binary, Tail/binary>> when Type == $N ->
            gen_fsm:send_all_state_event(C, {notice, decode_error(Data)}),
            decode(Tail, State);
        <<Data:Len2/binary, Tail/binary>> when Type == $S ->
            [Name, Value] = decode_strings(Data),
            gen_fsm:send_all_state_event(C, {parameter_status, Name, Value}),
            decode(Tail, State);
        <<Data:Len2/binary, Tail/binary>> when Type == $E ->
            gen_fsm:send_event(C, {error, decode_error(Data)}),
            decode(Tail, State);
        <<Data:Len2/binary, Tail/binary>> when Type == $A ->
            <<Pid:?int32, Strings/binary>> = Data,
            case decode_strings(Strings) of
                [Channel, Payload] -> ok;
                [Channel]          -> Payload = <<>>
            end,
            gen_fsm:send_all_state_event(C, {notification, Channel, Pid, Payload}),
            decode(Tail, State);
        <<Data:Len2/binary, Tail/binary>> ->
            gen_fsm:send_event(C, {Type, Data}),
            decode(Tail, State);
        _Other ->
            State#state{tail = Bin}
    end;
decode(Bin, State) ->
    State#state{tail = Bin}.

%% decode a single null-terminated string
decode_string(Bin) ->
    decode_string(Bin, <<>>).

decode_string(<<0, Rest/binary>>, Str) ->
    {Str, Rest};
decode_string(<<C, Rest/binary>>, Str) ->
    decode_string(Rest, <<Str/binary, C>>).

%% decode multiple null-terminated string
decode_strings(Bin) ->
    decode_strings(Bin, []).

decode_strings(<<>>, Acc) ->
    lists:reverse(Acc);
decode_strings(Bin, Acc) ->
    {Str, Rest} = decode_string(Bin),
    decode_strings(Rest, [Str | Acc]).

%% decode field
decode_fields(Bin) ->
    decode_fields(Bin, []).

decode_fields(<<0>>, Acc) ->
    Acc;
decode_fields(<<Type:8, Rest/binary>>, Acc) ->
    {Str, Rest2} = decode_string(Rest),
    decode_fields(Rest2, [{Type, Str} | Acc]).

%% decode ErrorResponse
decode_error(Bin) ->
    Fields = decode_fields(Bin),
    Error = #error{
      severity = lower_atom(proplists:get_value($S, Fields)),
      code     = proplists:get_value($C, Fields),
      message  = proplists:get_value($M, Fields),
      extra    = decode_error_extra(Fields)},
    Error.

decode_error_extra(Fields) ->
    Types = [{$D, detail}, {$H, hint}, {$P, position}],
    decode_error_extra(Types, Fields, []).

decode_error_extra([], _Fields, Extra) ->
    Extra;
decode_error_extra([{Type, Name} | T], Fields, Extra) ->
    case proplists:get_value(Type, Fields) of
        undefined -> decode_error_extra(T, Fields, Extra);
        Value     -> decode_error_extra(T, Fields, [{Name, Value} | Extra])
    end.

lower_atom(Str) when is_binary(Str) ->
    lower_atom(binary_to_list(Str));
lower_atom(Str) when is_list(Str) ->
    list_to_atom(string:to_lower(Str)).