-module(echo).
-export([start/0, loop/0, send/2]).

start() ->
	Pid = spawn(echo, loop, []),
	io:format("Started server.~nPid: ~w~n",[Pid]) .

loop() ->
	receive
		{From, Msg} ->
			if
				is_integer(Msg), Msg >= 0 ->
					From ! {self(), "~w",factorial(Msg)},
					loop();
				Msg == stop ->
					From ! {self(), "exiting"},
					true;
				true ->
					From ! {self(), Msg},
					loop()
			end
	end.

send(SPid, Msg) ->
	Pid = list_to_pid(SPid),
	Alive = is_process_alive(Pid),
	if
		Alive ->
			Pid ! {self(), Msg},
			receive
				{Pid, Msg} ->
					io:format("Server is online.~nIt's respond: ~w~n", [Msg])
			end;
		true ->
			io:format("Server is offline.~n")
   end.

factorial(N) ->
	if
		N == 0 -> 1;
		N > 0 -> N * factorial(N-1)
	end.