import Queue, threading

should_exit = False


class DummyReply:
    """
        A reply object that does nothing. Useful when we need an object to seem
        like it has a channel, and during testing.
    """
    def __init__(self):
        self.acked = False

    def __call__(self, msg=False):
        self.acked = True


class Reply:
    """
        Messages sent through a channel are decorated with a "reply" attribute.
        This object is used to respond to the message through the return
        channel.
    """
    def __init__(self, obj):
        self.obj = obj
        self.q = Queue.Queue()
        self.acked = False

    def __call__(self, msg=None):
        if not self.acked:
            self.acked = True
            if msg is None:
                self.q.put(self.obj)
            else:
                self.q.put(msg)


class Channel:
    def __init__(self, q):
        self.q = q

    def ask(self, m):
        """
            Decorate a message with a reply attribute, and send it to the
            master.  then wait for a response.
        """
        m.reply = Reply(m)
        self.q.put(m)
        while not should_exit:
            try:
                # The timeout is here so we can handle a should_exit event.
                g = m.reply.q.get(timeout=0.5)
            except Queue.Empty: # pragma: nocover
                continue
            return g

    def tell(self, m):
        """
            Decorate a message with a dummy reply attribute, send it to the
            master, then return immediately.
        """
        m.reply = DummyReply()
        self.q.put(m)


class Slave(threading.Thread):
    """
        Slaves get a channel end-point through which they can send messages to
        the master.
    """
    def __init__(self, channel, server):
        self.channel, self.server = channel, server
        self.server.set_channel(channel)
        threading.Thread.__init__(self)

    def run(self):
        self.server.serve_forever()


class Master:
    """
        Masters get and respond to messages from slaves.
    """
    def __init__(self, server):
        """
            server may be None if no server is needed.
        """
        self.server = server
        self.masterq = Queue.Queue()

    def tick(self, q):
        changed = False
        try:
            # This endless loop runs until the 'Queue.Empty'
            # exception is thrown. If more than one request is in
            # the queue, this speeds up every request by 0.1 seconds,
            # because get_input(..) function is not blocking.
            while True:
                # Small timeout to prevent pegging the CPU
                msg = q.get(timeout=0.01)
                self.handle(msg)
                changed = True
        except Queue.Empty:
            pass
        return changed

    def run(self):
        global should_exit
        should_exit = False
        self.server.start_slave(Slave, Channel(self.masterq))
        while not should_exit:
            self.tick(self.masterq)
        self.shutdown()

    def handle(self, msg):
        c = "handle_" + msg.__class__.__name__.lower()
        m = getattr(self, c, None)
        if m:
            m(msg)
        else:
            msg.reply()

    def shutdown(self):
        global should_exit
        if not should_exit:
            should_exit = True
            if self.server:
                self.server.shutdown()
