%% ---
%%  Excerpted from "Programming Erlang",
%%  published by The Pragmatic Bookshelf.
%%  Copyrights apply to this code. It may not be used to create training material, 
%%  courses, books, articles, and the like. Contact us if you are in doubt.
%%  We make no guarantees that this code is fit for any purpose. 
%%  Visit http://www.pragmaticprogrammer.com/titles/jaerlang for more book information.
%%---
-module(receivemod).

%% commonly used routines

-export([sleep/1,
	 flush_buffer/0,
	 priority_receive/0,
	 go/0]).

% This function waits T milliseconds before returning
sleep(T) ->
    receive
    after T ->
       true
    end.


% flushes all messages from the calling process's mailbox
flush_buffer() ->
    receive
	_Any ->
	    flush_buffer()
    after 0 ->
	true
    end.


% looks through the entirety of the mailbox for a message {alarm,X}
% (for any X).  If no such message exists, returns the first message.
priority_receive() ->
    receive
	{alarm, X} ->
	    {alarm, X}
    after 0 ->
	receive % why necessary? XXX
	    Any ->
		Any
	end
    end.

%% TESTS

server_loop() ->
    case (priority_receive()) of
	{alarm, Val} -> 
	    io:format ("PRIORITY: got ~p~n", [Val]),
	    case Val of
		flush -> 
		    io:format("  (flushed buffer)~n"),
		    flush_buffer(),
		    server_loop();
		_Val -> server_loop()
	    end;
	Val ->
	    io:format ("got ~p~n", [Val]),
	    sleep(200),
	    server_loop()
    end.

go() ->
    S = spawn(fun () -> server_loop() end),
    S ! hello,
    sleep(10),
    S ! "message",
    S ! "message2",
    S ! {alarm, "alert!"},
    S ! {alarm, flush},
    sleep(200),
    S ! "bye",
    ok.