function FormController(element, attrs) {
  var form = this,
      parentForm = element.parent().controller('form') || nullFormCtrl,
      invalidCount = 0, // used to easily determine if we are valid
      errors = form.$error = {},
      controls = [];

  // init state
  form.$name = attrs.name || attrs.ngForm;
  form.$dirty = false;
  form.$pristine = true;
  form.$valid = true;
  form.$invalid = false;

  parentForm.$addControl(form);

  // Setup initial state of the control
  element.addClass(PRISTINE_CLASS);
  toggleValidCss(true);

  // convenience method for easy toggling of classes
  function toggleValidCss(isValid, validationErrorKey) {
    validationErrorKey = validationErrorKey ? '-' + snake_case(validationErrorKey, '-') : '';
    element.
      removeClass((isValid ? INVALID_CLASS : VALID_CLASS) + validationErrorKey).
      addClass((isValid ? VALID_CLASS : INVALID_CLASS) + validationErrorKey);
  }

  /**
   * @ngdoc function
   * @name ng.directive:form.FormController#$addControl
   * @methodOf ng.directive:form.FormController
   *
   * @description
   * Register a control with the form.
   *
   * Input elements using ngModelController do this automatically when they are linked.
   */
  form.$addControl = function(control) {
    // Breaking change - before, inputs whose name was "hasOwnProperty" were quietly ignored
    // and not added to the scope.  Now we throw an error.
    assertNotHasOwnProperty(control.$name, 'input');
    controls.push(control);

    if (control.$name) {
      form[control.$name] = control;
    }
  };

  /**
   * @ngdoc function
   * @name ng.directive:form.FormController#$removeControl
   * @methodOf ng.directive:form.FormController
   *
   * @description
   * Deregister a control from the form.
   *
   * Input elements using ngModelController do this automatically when they are destroyed.
   */
  form.$removeControl = function(control) {
    if (control.$name && form[control.$name] === control) {
      delete form[control.$name];
    }
    forEach(errors, function(queue, validationToken) {
      form.$setValidity(validationToken, true, control);
    });

    arrayRemove(controls, control);
  };

  /**
   * @ngdoc function
   * @name ng.directive:form.FormController#$setValidity
   * @methodOf ng.directive:form.FormController
   *
   * @description
   * Sets the validity of a form control.
   *
   * This method will also propagate to parent forms.
   */
  form.$setValidity = function(validationToken, isValid, control) {
    var queue = errors[validationToken];

    if (isValid) {
      if (queue) {
        arrayRemove(queue, control);
        if (!queue.length) {
          invalidCount--;
          if (!invalidCount) {
            toggleValidCss(isValid);
            form.$valid = true;
            form.$invalid = false;
          }
          errors[validationToken] = false;
          toggleValidCss(true, validationToken);
          parentForm.$setValidity(validationToken, true, form);
        }
      }

    } else {
      if (!invalidCount) {
        toggleValidCss(isValid);
      }
      if (queue) {
        if (includes(queue, control)) return;
      } else {
        errors[validationToken] = queue = [];
        invalidCount++;
        toggleValidCss(false, validationToken);
        parentForm.$setValidity(validationToken, false, form);
      }
      queue.push(control);

      form.$valid = false;
      form.$invalid = true;
    }
  };

  /**
   * @ngdoc function
   * @name ng.directive:form.FormController#$setDirty
   * @methodOf ng.directive:form.FormController
   *
   * @description
   * Sets the form to a dirty state.
   *
   * This method can be called to add the 'ng-dirty' class and set the form to a dirty
   * state (ng-dirty class). This method will also propagate to parent forms.
   */
  form.$setDirty = function() {
    element.removeClass(PRISTINE_CLASS).addClass(DIRTY_CLASS);
    form.$dirty = true;
    form.$pristine = false;
    parentForm.$setDirty();
  };

  /**
   * @ngdoc function
   * @name ng.directive:form.FormController#$setPristine
   * @methodOf ng.directive:form.FormController
   *
   * @description
   * Sets the form to its pristine state.
   *
   * This method can be called to remove the 'ng-dirty' class and set the form to its pristine
   * state (ng-pristine class). This method will also propagate to all the controls contained
   * in this form.
   *
   * Setting a form back to a pristine state is often useful when we want to 'reuse' a form after
   * saving or resetting it.
   */
  form.$setPristine = function () {
    element.removeClass(DIRTY_CLASS).addClass(PRISTINE_CLASS);
    form.$dirty = false;
    form.$pristine = true;
    forEach(controls, function(control) {
      control.$setPristine();
    });
  };
}
@ngdoc object
@name ng.directive:form.FormController

@property {boolean} $pristine True if user has not interacted with the form yet.
@property {boolean} $dirty True if user has already interacted with the form.
@property {boolean} $valid True if all of the containing forms and controls are valid.
@property {boolean} $invalid True if at least one containing control or form is invalid.

@property {Object} $error Is an object hash, containing references to all invalid controls or
 forms, where:

 - keys are validation tokens (error names),
 - values are arrays of controls or forms that are invalid for given error name.


 Built-in validation tokens:

 - `email`
 - `max`
 - `maxlength`
 - `min`
 - `minlength`
 - `number`
 - `pattern`
 - `required`
 - `url`

@description
`FormController` keeps track of all its controls and nested forms as well as state of them,
such as being valid/invalid or dirty/pristine.

Each {@link ng.directive:form form} directive creates an instance
of `FormController`.