(function (_, $, Backbone, Drupal, drupalSettings) {

  "use strict";

  /**
   * State of an in-place editable entity in the DOM.
   */
  Drupal.quickedit.EntityModel = Drupal.quickedit.BaseModel.extend({

    defaults: {
      // The DOM element that represents this entity. It may seem bizarre to
      // have a DOM element in a Backbone Model, but we need to be able to map
      // entities in the DOM to EntityModels in memory.
      el: null,
      // An entity ID, of the form "<entity type>/<entity ID>", e.g. "node/1".
      entityID: null,
      // An entity instance ID. The first intance of a specific entity (i.e. with
      // a given entity ID) is assigned 0, the second 1, and so on.
      entityInstanceID: null,
      // The unique ID of this entity instance on the page, of the form "<entity
      // type>/<entity ID>[entity instance ID]", e.g. "node/1[0]".
      id: null,
      // The label of the entity.
      label: null,
      // A Drupal.quickedit.FieldCollection for all fields of this entity.
      fields: null,

      // The attributes below are stateful. The ones above will never change
      // during the life of a EntityModel instance.

      // Indicates whether this instance of this entity is currently being
      // edited in-place.
      isActive: false,
      // Whether one or more fields have already been stored in TempStore.
      inTempStore: false,
      // Whether one or more fields have already been stored in TempStore *or*
      // the field that's currently being edited is in the 'changed' or a later
      // state. In other words, this boolean indicates whether a "Save" button is
      // necessary or not.
      isDirty: false,
      // Whether the request to the server has been made to commit this entity.
      // Used to prevent multiple such requests.
      isCommitting: false,
      // The current processing state of an entity.
      state: 'closed',
      // The IDs of the fields whose new values have been stored in TempStore. We
      // must store this on the EntityModel as well (even though it already is on
      // the FieldModel) because when a field is rerendered, its FieldModel is
      // destroyed and this allows us to transition it back to the proper state.
      fieldsInTempStore: [],
      // A flag the tells the application that this EntityModel must be reloaded
      // in order to restore the original values to its fields in the client.
      reload: false
    },

    /**
     * {@inheritdoc}
     */
    initialize: function () {
      this.set('fields', new Drupal.quickedit.FieldCollection());

      // Respond to entity state changes.
      this.listenTo(this, 'change:state', this.stateChange);

      // The state of the entity is largely dependent on the state of its
      // fields.
      this.listenTo(this.get('fields'), 'change:state', this.fieldStateChange);

      // Call Drupal.quickedit.BaseModel's initialize() method.
      Drupal.quickedit.BaseModel.prototype.initialize.call(this);
    },

    /**
     * Updates FieldModels' states when an EntityModel change occurs.
     *
     * @param Drupal.quickedit.EntityModel entityModel
     * @param String state
     *   The state of the associated entity. One of Drupal.quickedit.EntityModel.states.
     * @param Object options
     */
    stateChange: function (entityModel, state, options) {
      var to = state;
      switch (to) {
        case 'closed':
          this.set({
            'isActive': false,
            'inTempStore': false,
            'isDirty': false
          });
          break;

        case 'launching':
          break;

        case 'opening':
          // Set the fields to candidate state.
          entityModel.get('fields').each(function (fieldModel) {
            fieldModel.set('state', 'candidate', options);
          });
          break;

        case 'opened':
          // The entity is now ready for editing!
          this.set('isActive', true);
          break;

        case 'committing':
          // The user indicated they want to save the entity.
          var fields = this.get('fields');
          // For fields that are in an active state, transition them to candidate.
          fields.chain()
            .filter(function (fieldModel) {
              return _.intersection([fieldModel.get('state')], ['active']).length;
            })
            .each(function (fieldModel) {
              fieldModel.set('state', 'candidate');
            });
          // For fields that are in a changed state, field values must first be
          // stored in TempStore.
          fields.chain()
            .filter(function (fieldModel) {
              return _.intersection([fieldModel.get('state')], Drupal.quickedit.app.changedFieldStates).length;
            })
            .each(function (fieldModel) {
              fieldModel.set('state', 'saving');
            });
          break;

        case 'deactivating':
          var changedFields = this.get('fields')
            .filter(function (fieldModel) {
              return _.intersection([fieldModel.get('state')], ['changed', 'invalid']).length;
            });
          // If the entity contains unconfirmed or unsaved changes, return the
          // entity to an opened state and ask the user if they would like to save
          // the changes or discard the changes.
          //   1. One of the fields is in a changed state. The changed field might
          //   just be a change in the client or it might have been saved to
          //   tempstore.
          //   2. The saved flag is empty and the confirmed flag is empty. If the
          //   entity has been saved to the server, the fields changed in the
          //   client are irrelevant. If the changes are confirmed, then proceed
          //   to set the fields to candidate state.
          if ((changedFields.length || this.get('fieldsInTempStore').length) && (!options.saved && !options.confirmed)) {
            // Cancel deactivation until the user confirms save or discard.
            this.set('state', 'opened', {confirming: true});
            // An action in reaction to state change must be deferred.
            _.defer(function () {
              Drupal.quickedit.app.confirmEntityDeactivation(entityModel);
            });
          }
          else {
            var invalidFields = this.get('fields')
            .filter(function (fieldModel) {
              return _.intersection([fieldModel.get('state')], ['invalid']).length;
            });
            // Indicate if this EntityModel needs to be reloaded in order to
            // restore the original values of its fields.
            entityModel.set('reload', (this.get('fieldsInTempStore').length || invalidFields.length));
            // Set all fields to the 'candidate' state. A changed field may have to
            // go through confirmation first.
            entityModel.get('fields').each(function (fieldModel) {
              // If the field is already in the candidate state, trigger a change
              // event so that the entityModel can move to the next state in
              // deactivation.
              if (_.intersection([fieldModel.get('state')], ['candidate', 'highlighted']).length) {
                fieldModel.trigger('change:state', fieldModel, fieldModel.get('state'), options);
              }
              else {
                fieldModel.set('state', 'candidate', options);
              }
            });
          }
          break;

        case 'closing':
          // Set all fields to the 'inactive' state.
          options.reason = 'stop';
          this.get('fields').each(function (fieldModel) {
            fieldModel.set({
              'inTempStore': false,
              'state': 'inactive'
            }, options);
          });
          break;
      }
    },

    /**
     * Updates a Field and Entity model's "inTempStore" when appropriate.
     *
     * Helper function.
     *
     * @param Drupal.quickedit.EntityModel entityModel
     *   The model of the entity for which a field's state attribute has changed.
     * @param Drupal.quickedit.FieldModel fieldModel
     *   The model of the field whose state attribute has changed.
     *
     * @see fieldStateChange()
     */
    _updateInTempStoreAttributes: function (entityModel, fieldModel) {
      var current = fieldModel.get('state');
      var previous = fieldModel.previous('state');
      var fieldsInTempStore = entityModel.get('fieldsInTempStore');
      // If the fieldModel changed to the 'saved' state: remember that this
      // field was saved to TempStore.
      if (current === 'saved') {
        // Mark the entity as saved in TempStore, so that we can pass the
        // proper "reset TempStore" boolean value when communicating with the
        // server.
        entityModel.set('inTempStore', true);
        // Mark the field as saved in TempStore, so that visual indicators
        // signifying just that may be rendered.
        fieldModel.set('inTempStore', true);
        // Remember that this field is in TempStore, restore when rerendered.
        fieldsInTempStore.push(fieldModel.get('fieldID'));
        fieldsInTempStore = _.uniq(fieldsInTempStore);
        entityModel.set('fieldsInTempStore', fieldsInTempStore);
      }
      // If the fieldModel changed to the 'candidate' state from the
      // 'inactive' state, then this is a field for this entity that got
      // rerendered. Restore its previous 'inTempStore' attribute value.
      else if (current === 'candidate' && previous === 'inactive') {
        fieldModel.set('inTempStore', _.intersection([fieldModel.get('fieldID')], fieldsInTempStore).length > 0);
      }
    },

    /**
     * Reacts to state changes in this entity's fields.
     *
     * @param Drupal.quickedit.FieldModel fieldModel
     *   The model of the field whose state attribute changed.
     * @param String state
     *   The state of the associated field. One of Drupal.quickedit.FieldModel.states.
     */
    fieldStateChange: function (fieldModel, state) {
      var entityModel = this;
      var fieldState = state;
      // Switch on the entityModel state.
      // The EntityModel responds to FieldModel state changes as a function of its
      // state. For example, a field switching back to 'candidate' state when its
      // entity is in the 'opened' state has no effect on the entity. But that
      // same switch back to 'candidate' state of a field when the entity is in
      // the 'committing' state might allow the entity to proceed with the commit
      // flow.
      switch (this.get('state')) {
        case 'closed':
        case 'launching':
          // It should be impossible to reach these: fields can't change state
          // while the entity is closed or still launching.
          break;

        case 'opening':
          // We must change the entity to the 'opened' state, but it must first be
          // confirmed that all of its fieldModels have transitioned to the
          // 'candidate' state.
          // We do this here, because this is called every time a fieldModel
          // changes state, hence each time this is called, we get closer to the
          // goal of having all fieldModels in the 'candidate' state.
          // A state change in reaction to another state change must be deferred.
          _.defer(function () {
            entityModel.set('state', 'opened', {
              'accept-field-states': Drupal.quickedit.app.readyFieldStates
            });
          });
          break;

        case 'opened':
          // Set the isDirty attribute when appropriate so that it is known when
          // to display the "Save" button in the entity toolbar.
          // Note that once a field has been changed, there's no way to discard
          // that change, hence it will have to be saved into TempStore, or the
          // in-place editing of this field will have to be stopped completely.
          // In other words: once any field enters the 'changed' field, then for
          // the remainder of the in-place editing session, the entity is by
          // definition dirty.
          if (fieldState === 'changed') {
            entityModel.set('isDirty', true);
          }
          else {
            this._updateInTempStoreAttributes(entityModel, fieldModel);
          }
          break;

        case 'committing':
          // If the field save returned a validation error, set the state of the
          // entity back to 'opened'.
          if (fieldState === 'invalid') {
            // A state change in reaction to another state change must be deferred.
            _.defer(function() {
              entityModel.set('state', 'opened', { reason: 'invalid' });
            });
          }
          else {
            this._updateInTempStoreAttributes(entityModel, fieldModel);
          }

          // Attempt to save the entity. If the entity's fields are not yet all in
          // a ready state, the save will not be processed.
          var options = {
            'accept-field-states': Drupal.quickedit.app.readyFieldStates
          };
          if (entityModel.set('isCommitting', true, options)) {
            entityModel.save({
              success: function () {
                entityModel.set({
                  'state': 'deactivating',
                  'isCommitting' : false
                }, {'saved': true});
              },
              error: function () {
                // Reset the "isCommitting" mutex.
                entityModel.set('isCommitting', false);
                // Change the state back to "opened", to allow the user to hit the
                // "Save" button again.
                entityModel.set('state', 'opened', { reason: 'networkerror' });
                // Show a modal to inform the user of the network error.
                var message = Drupal.t('Your changes to <q>@entity-title</q> could not be saved, either due to a website problem or a network connection problem.<br>Please try again.', { '@entity-title' : entityModel.get('label') });
                Drupal.quickedit.util.networkErrorModal(Drupal.t('Sorry!'), message);
              }
            });
          }
          break;

        case 'deactivating':
          // When setting the entity to 'closing', require that all fieldModels
          // are in either the 'candidate' or 'highlighted' state.
          // A state change in reaction to another state change must be deferred.
          _.defer(function() {
            entityModel.set('state', 'closing', {
              'accept-field-states': Drupal.quickedit.app.readyFieldStates
            });
          });
          break;

        case 'closing':
          // When setting the entity to 'closed', require that all fieldModels are
          // in the 'inactive' state.
          // A state change in reaction to another state change must be deferred.
          _.defer(function() {
            entityModel.set('state', 'closed', {
              'accept-field-states': ['inactive']
            });
          });
          break;
      }
    },

    /**
     * Fires an AJAX request to the REST save URL for an entity.
     *
     * @param options
     *   An object of options that contains:
     *     - success: (optional) A function to invoke if the entity is success-
     *     fully saved.
     */
    save: function (options) {
      var entityModel = this;

      // @todo Simplify this once https://drupal.org/node/1533366 lands.
      // @see https://drupal.org/node/2029999.
      var id = 'quickedit-save-entity';
      // Create a temporary element to be able to use Drupal.ajax.
      var $el = $('#quickedit-entity-toolbar').find('.action-save'); // This is the span element inside the button.
      // Create a Drupal.ajax instance to save the entity.
      var entitySaverAjax = new Drupal.ajax(id, $el, {
        url: Drupal.quickedit.util.buildUrl(entityModel.get('entityID'), drupalSettings.quickedit.entitySaveURL),
        event: 'quickedit-save.quickedit',
        progress: { type: 'none' },
        error: function () {
          $el.off('quickedit-save.quickedit');
          // Let the Drupal.quickedit.EntityModel Backbone model's error() method
          // handle errors.
          options.error.call(entityModel);
        }
      });
      // Work-around for https://drupal.org/node/2019481 in Drupal 7.
      entitySaverAjax.commands = {};
      // Entity saved successfully.
      entitySaverAjax.commands.quickeditEntitySaved = function(ajax, response, status) {
        // Clean up.
        $(ajax.element).off('quickedit-save.quickedit');
        // All fields have been moved from TempStore to permanent storage, update
        // the "inTempStore" attribute on FieldModels, on the EntityModel and
        // clear EntityModel's "fieldInTempStore" attribute.
        entityModel.get('fields').each(function (fieldModel) {
          fieldModel.set('inTempStore', false);
        });
        entityModel.set('inTempStore', false);
        entityModel.set('fieldsInTempStore', []);

        // Invoke the optional success callback.
        if (options.success) {
          options.success.call(entityModel);
        }
      };
      // Trigger the AJAX request, which will will return the quickeditEntitySaved AJAX
      // command to which we then react.
      $el.trigger('quickedit-save.quickedit');
    },

    /**
     * {@inheritdoc}
     *
     * @param Object attrs
     *   The attributes changes in the save or set call.
     * @param Object options
     *   An object with the following option:
     *     - String reason (optional): a string that conveys a particular reason
     *       to allow for an exceptional state change.
     *     - Array accept-field-states (optional) An array of strings that
     *     represent field states that the entities must be in to validate. For
     *     example, if accept-field-states is ['candidate', 'highlighted'], then
     *     all the fields of the entity must be in either of these two states
     *     for the save or set call to validate and proceed.
     */
    validate: function (attrs, options) {
      var acceptedFieldStates = options['accept-field-states'] || [];

      // Validate state change.
      var currentState = this.get('state');
      var nextState = attrs.state;
      if (currentState !== nextState) {
        // Ensure it's a valid state.
        if (_.indexOf(this.constructor.states, nextState) === -1) {
          return '"' + nextState + '" is an invalid state';
        }

        // Ensure it's a state change that is allowed.
        // Check if the acceptStateChange function accepts it.
        if (!this._acceptStateChange(currentState, nextState, options)) {
          return 'state change not accepted';
        }
        // If that function accepts it, then ensure all fields are also in an
        // acceptable state.
        else if (!this._fieldsHaveAcceptableStates(acceptedFieldStates)) {
          return 'state change not accepted because fields are not in acceptable state';
        }
      }

      // Validate setting isCommitting = true.
      var currentIsCommitting = this.get('isCommitting');
      var nextIsCommitting = attrs.isCommitting;
      if (currentIsCommitting === false && nextIsCommitting === true) {
        if (!this._fieldsHaveAcceptableStates(acceptedFieldStates)) {
          return 'isCommitting change not accepted because fields are not in acceptable state';
        }
      }
      else if (currentIsCommitting === true && nextIsCommitting === true) {
        return "isCommiting is a mutex, hence only changes are allowed";
      }
    },

    // Like @see AppView.acceptEditorStateChange()
    _acceptStateChange: function (from, to, context) {
      var accept = true;

      // In general, enforce the states sequence. Disallow going back from a
      // "later" state to an "earlier" state, except in explicitly allowed
      // cases.
      if (!this.constructor.followsStateSequence(from, to)) {
        accept = false;

        // Allow: closing -> closed.
        // Necessary to stop editing an entity.
        if (from === 'closing' && to === 'closed') {
          accept = true;
        }
        // Allow: committing -> opened.
        // Necessary to be able to correct an invalid field, or to hit the "Save"
        // button again after a server/network error.
        else if (from === 'committing' && to === 'opened' && context.reason && (context.reason === 'invalid' || context.reason === 'networkerror')) {
          accept = true;
        }
        // Allow: deactivating -> opened.
        // Necessary to be able to confirm changes with the user.
        else if (from === 'deactivating' && to === 'opened' && context.confirming) {
          accept = true;
        }
        // Allow: opened -> deactivating.
        // Necessary to be able to stop editing.
        else if (from === 'opened' && to === 'deactivating' && context.confirmed) {
          accept = true;
        }
      }

      return accept;
    },

    /**
     * @param Array acceptedFieldStates
     *   @see validate()
     * @return Boolean
     */
    _fieldsHaveAcceptableStates: function (acceptedFieldStates) {
      var accept = true;

      // If no acceptable field states are provided, assume all field states are
      // acceptable. We want to let validation pass as a default and only
      // check validity on calls to set that explicitly request it.
      if (acceptedFieldStates.length > 0) {
        var fieldStates = this.get('fields').pluck('state') || [];
        // If not all fields are in one of the accepted field states, then we
        // still can't allow this state change.
        if (_.difference(fieldStates, acceptedFieldStates).length) {
          accept = false;
        }
      }

      return accept;
    },

    /**
     * {@inheritdoc}
     */
    destroy: function (options) {
      Drupal.quickedit.BaseModel.prototype.destroy.call(this, options);

      this.stopListening();

      // Destroy all fields of this entity.
      this.get('fields').each(function (fieldModel) {
        fieldModel.destroy();
      });
    },

    /**
     * {@inheritdoc}
     */
    sync: function () {
      // We don't use REST updates to sync.
      return;
    }

  }, {

    /**
     * A list (sequence) of all possible states an entity can be in during
     * in-place editing.
     */
    states: [
      // Initial state, like field's 'inactive' OR the user has just finished
      // in-place editing this entity.
      // - Trigger: none (initial) or EntityModel (finished).
      // - Expected behavior: (when not initial state): tear down
      //   EntityToolbarView, in-place editors and related views.
      'closed',
      // User has activated in-place editing of this entity.
      // - Trigger: user.
      // - Expected behavior: the EntityToolbarView is gets set up, in-place
      //   editors (EditorViews) and related views for this entity's fields are
      //   set up. Upon completion of those, the state is changed to 'opening'.
      'launching',
      // Launching has finished.
      // - Trigger: application.
      // - Guarantees: in-place editors ready for use, all entity and field views
      //   have been set up, all fields are in the 'inactive' state.
      // - Expected behavior: all fields are changed to the 'candidate' state and
      //   once this is completed, the entity state will be changed to 'opened'.
      'opening',
      // Opening has finished.
      // - Trigger: EntityModel.
      // - Guarantees: see 'opening', all fields are in the 'candidate' state.
      // - Expected behavior: the user is able to actually use in-place editing.
      'opened',
      // User has clicked the 'Save' button (and has thus changed at least one
      // field).
      // - Trigger: user.
      // - Guarantees: see 'opened', plus: either a changed field is in TempStore,
      //   or the user has just modified a field without activating (switching to)
      //   another field.
      // - Expected behavior: 1) if any of the fields are not yet in TempStore,
      //   save them to TempStore, 2) if then any of the fields has the 'invalid'
      //   state, then change the entity state back to 'opened', otherwise: save
      //   the entity by committing it from TempStore into permanent storage.
      'committing',
      // User has clicked the 'Close' button, or has clicked the 'Save' button and
      // that was successfully completed.
      // - Trigger: user or EntityModel.
      // - Guarantees: when having clicked 'Close' hardly any: fields may be in a
      //   variety of states; when having clicked 'Save': all fields are in the
      //   'candidate' state.
      // - Expected behavior: transition all fields to the 'candidate' state,
      //   possibly requiring confirmation in the case of having clicked 'Close'.
      'deactivating',
      // Deactivation has been completed.
      // - Trigger: EntityModel.
      // - Guarantees: all fields are in the 'candidate' state.
      // - Expected behavior: change all fields to the 'inactive' state.
      'closing'
    ],

    /**
     * Indicates whether the 'from' state comes before the 'to' state.
     *
     * @param String from
     *   One of Drupal.quickedit.EntityModel.states.
     * @param String to
     *   One of Drupal.quickedit.EntityModel.states.
     * @return Boolean
     */
    followsStateSequence: function (from, to) {
      return _.indexOf(this.states, from) < _.indexOf(this.states, to);
    }

  });

  Drupal.quickedit.EntityCollection = Backbone.Collection.extend({
    model: Drupal.quickedit.EntityModel
  });

}(_, jQuery, Backbone, Drupal, Drupal.settings));
