-module(echoserver).

-export([start/0]).

start() ->
    Port = 5999,
    CounterPid = spawn(fun () ->
                               timer:send_interval(2000, report_stats),
                               counter(0)
                       end),
    {ok, LSock} = gen_tcp:listen(Port, [{active, true}, {packet, line}, {reuseaddr, true}]),
    io:format("Erlang echo server running on port ~p.~n", [Port]),
    accept_loop(LSock, CounterPid).

counter(Count) ->
    receive
        inc ->
            counter(Count + 1);
        dec ->
            case Count - 1 of
                0 ->
                    io:format("Exiting on zero connection count.~n"),
                    init:stop();
                NewCount ->
                    counter(NewCount)
            end;
        report_stats ->
            io:format("~p connections~n", [Count]),
            counter(Count)
    end.

accept_loop(LSock, CounterPid) ->
    case gen_tcp:accept(LSock) of
        {ok, Sock} ->
            CounterPid ! inc,
            gen_tcp:controlling_process(Sock, spawn(fun () -> connection(Sock, CounterPid) end)),
            accept_loop(LSock, CounterPid)
    end.

connection(Sock, CounterPid) ->
    receive
        {tcp, _, Line} ->
            gen_tcp:send(Sock, Line),
            connection(Sock, CounterPid);
        {tcp_closed, _} ->
            CounterPid ! dec,
            ok;
        Other ->
            error_logger:error_report({connection, unhandled, Other})
    end.