// Backbone.History
// ----------------

// Handles cross-browser history management, based on URL fragments. If the
// browser does not support `onhashchange`, falls back to polling.
Backbone.History = function() {
  this.handlers = [];
  _.bindAll(this, 'checkUrl');
};

// Cached regex for cleaning hashes.
var hashStrip = /^#*/;

// Cached regex for detecting MSIE.
var isExplorer = /msie [\w.]+/;

// Has the history handling already been started?
var historyStarted = false;

// Set up all inheritable **Backbone.History** properties and methods.
_.extend(Backbone.History.prototype, {

  // The default interval to poll for hash changes, if necessary, is
  // twenty times a second.
  interval: 50,

  // Get the cross-browser normalized URL fragment, either from the URL,
  // the hash, or the override.
  getFragment : function(fragment, forcePushState) {
    if (fragment == null) {
      if (this._hasPushState || forcePushState) {
        fragment = window.location.pathname;
        var search = window.location.search;
        if (search) fragment += search;
      } else {
        fragment = window.location.hash;
      }
    }
    fragment = decodeURIComponent(fragment.replace(hashStrip, ''));
    if (!fragment.indexOf(this.options.root)) fragment = fragment.substr(this.options.root.length);
    return fragment;
  },

  // Start the hash change handling, returning `true` if the current URL matches
  // an existing route, and `false` otherwise.
  start : function(options) {

    // Figure out the initial configuration. Do we need an iframe?
    // Is pushState desired ... is it available?
    if (historyStarted) throw new Error("Backbone.history has already been started");
    this.options          = _.extend({}, {root: '/'}, this.options, options);
    this._wantsPushState  = !!this.options.pushState;
    this._hasPushState    = !!(this.options.pushState && window.history && window.history.pushState);
    var fragment          = this.getFragment();
    var docMode           = document.documentMode;
    var oldIE             = (isExplorer.exec(navigator.userAgent.toLowerCase()) && (!docMode || docMode <= 7));
    if (oldIE) {
      this.iframe = $('<iframe src="javascript:0" tabindex="-1" />').hide().appendTo('body')[0].contentWindow;
      this.navigate(fragment);
    }

    // Depending on whether we're using pushState or hashes, and whether
    // 'onhashchange' is supported, determine how we check the URL state.
    if (this._hasPushState) {
      $(window).bind('popstate', this.checkUrl);
    } else if ('onhashchange' in window && !oldIE) {
      $(window).bind('hashchange', this.checkUrl);
    } else {
      setInterval(this.checkUrl, this.interval);
    }

    // Determine if we need to change the base url, for a pushState link
    // opened by a non-pushState browser.
    this.fragment = fragment;
    historyStarted = true;
    var loc = window.location;
    var atRoot  = loc.pathname == this.options.root;
    if (this._wantsPushState && !this._hasPushState && !atRoot) {
      this.fragment = this.getFragment(null, true);
      window.location.replace(this.options.root + '#' + this.fragment);
      // Return immediately as browser will do redirect to new url
      return true;
    } else if (this._wantsPushState && this._hasPushState && atRoot && loc.hash) {
      this.fragment = loc.hash.replace(hashStrip, '');
      window.history.replaceState({}, document.title, loc.protocol + '//' + loc.host + this.options.root + this.fragment);
    }

    if (!this.options.silent) {
      return this.loadUrl();
    }
  },

  // Add a route to be tested when the fragment changes. Routes added later may
  // override previous routes.
  route : function(route, callback) {
    this.handlers.unshift({route : route, callback : callback});
  },

  // Checks the current URL to see if it has changed, and if it has,
  // calls `loadUrl`, normalizing across the hidden iframe.
  checkUrl : function(e) {
    var current = this.getFragment();
    if (current == this.fragment && this.iframe) current = this.getFragment(this.iframe.location.hash);
    if (current == this.fragment || current == decodeURIComponent(this.fragment)) return false;
    if (this.iframe) this.navigate(current);
    this.loadUrl() || this.loadUrl(window.location.hash);
  },

  // Attempt to load the current URL fragment. If a route succeeds with a
  // match, returns `true`. If no defined routes matches the fragment,
  // returns `false`.
  loadUrl : function(fragmentOverride) {
    var fragment = this.fragment = this.getFragment(fragmentOverride);
    var matched = _.any(this.handlers, function(handler) {
      if (handler.route.test(fragment)) {
        handler.callback(fragment);
        return true;
      }
    });
    return matched;
  },

  // Save a fragment into the hash history. You are responsible for properly
  // URL-encoding the fragment in advance. This does not trigger
  // a `hashchange` event.
  navigate : function(fragment, triggerRoute) {
    var frag = (fragment || '').replace(hashStrip, '');
    if (this.fragment == frag || this.fragment == decodeURIComponent(frag)) return;
    if (this._hasPushState) {
      var loc = window.location;
      if (frag.indexOf(this.options.root) != 0) frag = this.options.root + frag;
      this.fragment = frag;
      window.history.pushState({}, document.title, loc.protocol + '//' + loc.host + frag);
    } else {
      window.location.hash = this.fragment = frag;
      if (this.iframe && (frag != this.getFragment(this.iframe.location.hash))) {
        this.iframe.document.open().close();
        this.iframe.location.hash = frag;
      }
    }
    if (triggerRoute) this.loadUrl(fragment);
  }

});