urlRouter.js

$UrlRouterProvider.$inject = ['$urlMatcherFactoryProvider'];
function $UrlRouterProvider(  $urlMatcherFactory) {
  var rules = [], 
      otherwise = null;

  // Returns a string that is a prefix of all strings matching the RegExp
  function regExpPrefix(re) {
    var prefix = /^\^((?:\\[^a-zA-Z0-9]|[^\\\[\]\^$*+?.()|{}]+)*)/.exec(re.source);
    return (prefix != null) ? prefix[1].replace(/\\(.)/g, "$1") : '';
  }

  // Interpolates matched values into a String.replace()-style pattern
  function interpolate(pattern, match) {
    return pattern.replace(/\$(\$|\d{1,2})/, function (m, what) {
      return match[what === '$' ? 0 : Number(what)];
    });
  }

  this.rule =
    function (rule) {
      if (!isFunction(rule)) throw new Error("'rule' must be a function");
      rules.push(rule);
      return this;
    };

  this.otherwise =
    function (rule) {
      if (isString(rule)) {
        var redirect = rule;
        rule = function () { return redirect; };
      }
      else if (!isFunction(rule)) throw new Error("'rule' must be a function");
      otherwise = rule;
      return this;
    };


  function handleIfMatch($injector, handler, match) {
    if (!match) return false;
    var result = $injector.invoke(handler, handler, { $match: match });
    return isDefined(result) ? result : true;
  }

  this.when =
    function (what, handler) {
      var redirect, handlerIsString = isString(handler);
      if (isString(what)) what = $urlMatcherFactory.compile(what);

      if (!handlerIsString && !isFunction(handler) && !isArray(handler))
        throw new Error("invalid 'handler' in when()");

      var strategies = {
        matcher: function (what, handler) {
          if (handlerIsString) {
            redirect = $urlMatcherFactory.compile(handler);
            handler = ['$match', function ($match) { return redirect.format($match); }];
          }
          return extend(function ($injector, $location) {
            return handleIfMatch($injector, handler, what.exec($location.path(), $location.search()));
          }, {
            prefix: isString(what.prefix) ? what.prefix : ''
          });
        },
        regex: function (what, handler) {
          if (what.global || what.sticky) throw new Error("when() RegExp must not be global or sticky");

          if (handlerIsString) {
            redirect = handler;
            handler = ['$match', function ($match) { return interpolate(redirect, $match); }];
          }
          return extend(function ($injector, $location) {
            return handleIfMatch($injector, handler, what.exec($location.path()));
          }, {
            prefix: regExpPrefix(what)
          });
        }
      };

      var check = { matcher: $urlMatcherFactory.isMatcher(what), regex: what instanceof RegExp };

      for (var n in check) {
        if (check[n]) {
          return this.rule(strategies[n](what, handler));
        }
      }

      throw new Error("invalid 'what' in when()");
    };

  this.$get =
    [        '$location', '$rootScope', '$injector',
    function ($location,   $rootScope,   $injector) {
      // TODO: Optimize groups of rules with non-empty prefix into some sort of decision tree
      function update() {
        function check(rule) {
          var handled = rule($injector, $location);
          if (handled) {
            if (isString(handled)) $location.replace().url(handled);
            return true;
          }
          return false;
        }
        var n=rules.length, i;
        for (i=0; i<n; i++) {
          if (check(rules[i])) return;
        }
        // always check otherwise last to allow dynamic updates to the set of rules
        if (otherwise) check(otherwise);
      }

      $rootScope.$on('$locationChangeSuccess', update);
      return {};
    }];
}

angular.module('ui.router.router').provider('$urlRouter', $UrlRouterProvider);