/*
 * Copyright (c) 2013 IBM Corp.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *    Seth Hoenig
 *    Allan Stockdill-Mander
 *    Mike Robertson
 */

package mqtt

import (
	"container/list"
	"strings"
	"sync"

	"github.com/eclipse/paho.mqtt.golang/packets"
)

// route is a type which associates MQTT Topic strings with a
// callback to be executed upon the arrival of a message associated
// with a subscription to that topic.
type route struct {
	topic    string
	callback MessageHandler
}

// match takes a slice of strings which represent the route being tested having been split on '/'
// separators, and a slice of strings representing the topic string in the published message, similarly
// split.
// The function determines if the topic string matches the route according to the MQTT topic rules
// and returns a boolean of the outcome
func match(route []string, topic []string) bool {
	if len(route) == 0 {
		if len(topic) == 0 {
			return true
		}
		return false
	}

	if len(topic) == 0 {
		if route[0] == "#" {
			return true
		}
		return false
	}

	if route[0] == "#" {
		return true
	}

	if (route[0] == "+") || (route[0] == topic[0]) {
		return match(route[1:], topic[1:])
	}
	return false
}

func routeIncludesTopic(route, topic string) bool {
	return match(routeSplit(route), strings.Split(topic, "/"))
}

// removes $share and sharename when splitting the route to allow
// shared subscription routes to correctly match the topic
func routeSplit(route string) []string {
	var result []string
	if strings.HasPrefix(route, "$share") {
		result = strings.Split(route, "/")[2:]
	} else {
		result = strings.Split(route, "/")
	}
	return result
}

// match takes the topic string of the published message and does a basic compare to the
// string of the current Route, if they match it returns true
func (r *route) match(topic string) bool {
	return r.topic == topic || routeIncludesTopic(r.topic, topic)
}

type router struct {
	sync.RWMutex
	routes         *list.List
	defaultHandler MessageHandler
	messages       chan *packets.PublishPacket
	stop           chan bool
}

// newRouter returns a new instance of a Router and channel which can be used to tell the Router
// to stop
func newRouter() (*router, chan bool) {
	router := &router{routes: list.New(), messages: make(chan *packets.PublishPacket), stop: make(chan bool)}
	stop := router.stop
	return router, stop
}

// addRoute takes a topic string and MessageHandler callback. It looks in the current list of
// routes to see if there is already a matching Route. If there is it replaces the current
// callback with the new one. If not it add a new entry to the list of Routes.
func (r *router) addRoute(topic string, callback MessageHandler) {
	r.Lock()
	defer r.Unlock()
	for e := r.routes.Front(); e != nil; e = e.Next() {
		if e.Value.(*route).match(topic) {
			r := e.Value.(*route)
			r.callback = callback
			return
		}
	}
	r.routes.PushBack(&route{topic: topic, callback: callback})
}

// deleteRoute takes a route string, looks for a matching Route in the list of Routes. If
// found it removes the Route from the list.
func (r *router) deleteRoute(topic string) {
	r.Lock()
	defer r.Unlock()
	for e := r.routes.Front(); e != nil; e = e.Next() {
		if e.Value.(*route).match(topic) {
			r.routes.Remove(e)
			return
		}
	}
}

// setDefaultHandler assigns a default callback that will be called if no matching Route
// is found for an incoming Publish.
func (r *router) setDefaultHandler(handler MessageHandler) {
	r.Lock()
	defer r.Unlock()
	r.defaultHandler = handler
}

// matchAndDispatch takes a channel of Message pointers as input and starts a go routine that
// takes messages off the channel, matches them against the internal route list and calls the
// associated callback (or the defaultHandler, if one exists and no other route matched). If
// anything is sent down the stop channel the function will end.
func (r *router) matchAndDispatch(messages <-chan *packets.PublishPacket, order bool, client *client) {
	go func() {
		for {
			select {
			case message := <-messages:
				sent := false
				r.RLock()
				handlers := []MessageHandler{}
				for e := r.routes.Front(); e != nil; e = e.Next() {
					if e.Value.(*route).match(message.TopicName) {
						if order {
							handlers = append(handlers, e.Value.(*route).callback)
						} else {
							go e.Value.(*route).callback(client, messageFromPublish(message))
						}
						sent = true
					}
				}
				if !sent && r.defaultHandler != nil {
					if order {
						handlers = append(handlers, r.defaultHandler)
					} else {
						go r.defaultHandler(client, messageFromPublish(message))
					}
				}
				r.RUnlock()
				for _, handler := range handlers {
					handler(client, messageFromPublish(message))
				}
			case <-r.stop:
				return
			}
		}
	}()
}