define([
    "./Content",
    "./Path",
    "dojo/_base/declare",
    "dojo/_base/event",
    "dojo/_base/lang",
    "dojo/hash",
    "dojo/on",
    "dojo/topic",
    "require"
], function(Content, Path, declare, event, lang, hash, on, topic, require) {

    var Router = declare(null,{
        _started: false,
        _routes: null,
        _previousHash: null,
        _beforePreviousHash: null,

        constructor: function() {
            this._routes = [];
        },
        startup: function() {
            if ( this._started ) { return; }
            Content.startup();
            this._started = true;
            if ( hash() === "" ) {
                hash(Path.getDefault());
            }
            this._handleHashChange(hash());
            window.onbeforeunload = function(evt) {
                var msg;
                if ( Content.isDirty() ) { 
                    msg = "Unsaved changes, leave anyway?";
                    evt.returnValue = msg;
                }
                return msg;
            };
			topic.subscribe("/dojo/hashchange",
                            lang.hitch(this,'_handleHashChange'));
        },
        register: function(route) {
            if ( this._started ) {
                console.warn('Registering routes after startup() is called is discouraged.');
            }
            var callback = this._normalizeCallback(route);
            if ( callback ) {
                if ( route.path ) {
                    route.callback = callback;
                    route.path = new Path(route.path);
                    this._routes.push(route);
                } else {
                    this._defaultCallback = callback;
                }
            } else {
                console.warn("Route "+(route.path||"default")+" has no action.");
            }
        },
        _normalizeCallback: function(route) {
            var self = this;
            var callback = null;
            if ( route.callback ) {
                callback = function(params){
                    Content.set(route.callback(params));
                };
            } else if ( route.redirect ) {
                callback = function(params){
                    self.go(route.redirect);
                };
            } else if ( route.constructor ) {
                callback = function(params){
                    Content.set( new route.constructor(params) );
                };
            }
            return callback;
        },
        _handleHashChange: function(newHash) {
            if ( this._previousHash === newHash ) {
                return false;
            }
            if ( Content.isDirty() ) {
                if ( !confirm("Unsaved changes, leave anyway?") ) {
                    var probablyBack = this._beforePreviousHash === newHash;
                    // if we think we go backwards, we re-add the history
                    // entry, otherwise we reset the current one,
                    // resulting in minor annoyance of double back
                    // behaviour.
                    hash(this._previousHash,!probablyBack);
                    return false;
                } else {
                    Content.markClean();
                }
            }
            this._beforePreviousHash = this._previousHash;
            this._previousHash = newHash;
            for (var i = this._routes.length-1; i >= 0; i--) {
                var route = this._routes[i];
                var params = null;
                if ((params = route.path.match(newHash)) !== null) {
                    try {
                        route.callback(params);
                    } catch(err) {
                        console.error("Page change failed with",err,err.stack,err.toString());
                    }
                    return true;
                }
            }
            try {
                this._defaultCallback();
            } catch(err) {
                console.error("Default page failed.",err);
            }
            return true;
        },
        go: function(path,args,replace) {
            if ( !this._started ) { return; }
            var newHash = Path.format(path,args);
            if ( replace === true ) {
                this._beforePreviousHash = this._previousHash;
                this._previousHash = newHash;
            }
            hash(newHash,replace);
        },
        _defaultCallback: function() {
            var Page = require("./Page");
            Content.set(new Page({
                templateString: "<div>Requested page not found. Go <a href=\"#"+Path.getDefault()+"\">home</a>.</div>"
            }));
        }
    });

    return new Router();
});