/*
 * Copyright (c) 2013, 2014 Conformal Systems LLC <info@conformal.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

package main

import (
	"os"
	"os/signal"
)

// interruptChannel is used to receive SIGINT (Ctrl+C) signals.
var interruptChannel chan os.Signal

// addHandlerChannel is used to add an interrupt handler to the list of handlers
// to be invoked on SIGINT (Ctrl+C) signals.
var addHandlerChannel = make(chan func())

// mainInterruptHandler listens for SIGINT (Ctrl+C) signals on the
// interruptChannel and invokes the registered interruptCallbacks accordingly.
// It also listens for callback registration.  It must be run as a goroutine.
func mainInterruptHandler() {
	// interruptCallbacks is a list of callbacks to invoke when a
	// SIGINT (Ctrl+C) is received.
	var interruptCallbacks []func()

	for {
		select {
		case <-interruptChannel:
			log.Info("Received SIGINT (Ctrl+C).  Shutting down...")
			// run handlers in LIFO order.
			for i := range interruptCallbacks {
				idx := len(interruptCallbacks) - 1 - i
				interruptCallbacks[idx]()
			}

		case handler := <-addHandlerChannel:
			interruptCallbacks = append(interruptCallbacks, handler)
		}
	}
}

// addInterruptHandler adds a handler to call when a SIGINT (Ctrl+C) is
// received.
func addInterruptHandler(handler func()) {
	// Create the channel and start the main interrupt handler which invokes
	// all other callbacks and exits if not already done.
	if interruptChannel == nil {
		interruptChannel = make(chan os.Signal, 1)
		signal.Notify(interruptChannel, os.Interrupt)
		go mainInterruptHandler()
	}

	addHandlerChannel <- handler
}