(function (ionic) {

  ionic.DelegateService = function(methodNames) {

    if (methodNames.indexOf('$getByHandle') > -1) {
      throw new Error("Method '$getByHandle' is implicitly added to each delegate service. Do not list it as a method.");
    }

    function trueFn() { return true; }

    return ['$log', function($log) {

      /*
       * Creates a new object that will have all the methodNames given,
       * and call them on the given the controller instance matching given
       * handle.
       * The reason we don't just let $getByHandle return the controller instance
       * itself is that the controller instance might not exist yet.
       *
       * We want people to be able to do
       * `var instance = $ionicScrollDelegate.$getByHandle('foo')` on controller
       * instantiation, but on controller instantiation a child directive
       * may not have been compiled yet!
       *
       * So this is our way of solving this problem: we create an object
       * that will only try to fetch the controller with given handle
       * once the methods are actually called.
       */
      function DelegateInstance(instances, handle) {
        this._instances = instances;
        this.handle = handle;
      }
      methodNames.forEach(function(methodName) {
        DelegateInstance.prototype[methodName] = instanceMethodCaller(methodName);
      });


      /**
       * The delegate service (eg $ionicNavBarDelegate) is just an instance
       * with a non-defined handle, a couple extra methods for registering
       * and narrowing down to a specific handle.
       */
      function DelegateService() {
        this._instances = [];
      }
      DelegateService.prototype = DelegateInstance.prototype;
      DelegateService.prototype._registerInstance = function(instance, handle, filterFn) {
        var instances = this._instances;
        instance.$$delegateHandle = handle;
        instance.$$filterFn = filterFn || trueFn;
        instances.push(instance);

        return function deregister() {
          var index = instances.indexOf(instance);
          if (index !== -1) {
            instances.splice(index, 1);
          }
        };
      };
      DelegateService.prototype.$getByHandle = function(handle) {
        return new DelegateInstance(this._instances, handle);
      };

      return new DelegateService();

      function instanceMethodCaller(methodName) {
        return function caller() {
          var handle = this.handle;
          var args = arguments;
          var foundInstancesCount = 0;
          var returnValue;

          this._instances.forEach(function(instance) {
            if ((!handle || handle == instance.$$delegateHandle) && instance.$$filterFn(instance)) {
              foundInstancesCount++;
              var ret = instance[methodName].apply(instance, args);
              //Only return the value from the first call
              if (foundInstancesCount === 1) {
                returnValue = ret;
              }
            }
          });

          if (!foundInstancesCount && handle) {
            return $log.warn(
              'Delegate for handle "' + handle + '" could not find a ' +
              'corresponding element with delegate-handle="' + handle + '"! ' +
              methodName + '() was not called!\n' +
              'Possible cause: If you are calling ' + methodName + '() immediately, and ' +
              'your element with delegate-handle="' + handle + '" is a child of your ' +
              'controller, then your element may not be compiled yet. Put a $timeout ' +
              'around your call to ' + methodName + '() and try again.'
            );
          }
          return returnValue;
        };
      }

    }];
  };

})(window.ionic);