/**
 * @file
 * Provides Ajax page updating via jQuery $.ajax.
 *
 * Ajax is a method of making a request via JavaScript while viewing an HTML
 * page. The request returns an array of commands encoded in JSON, which is
 * then executed to make any changes that are necessary to the page.
 *
 * Drupal uses this file to enhance form elements with `#ajax['url']` and
 * `#ajax['wrapper']` properties. If set, this file will automatically be
 * included to provide Ajax capabilities.
 */

(function ($, window, Drupal, drupalSettings) {
  /**
   * Attaches the Ajax behavior to each Ajax form element.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Initialize all {@link Drupal.Ajax} objects declared in
   *   `drupalSettings.ajax` or initialize {@link Drupal.Ajax} objects from
   *   DOM elements having the `use-ajax-submit` or `use-ajax` css class.
   * @prop {Drupal~behaviorDetach} detach
   *   During `unload` remove all {@link Drupal.Ajax} objects related to
   *   the removed content.
   */
  Drupal.behaviors.AJAX = {
    attach(context, settings) {
      function loadAjaxBehavior(base) {
        const element_settings = settings.ajax[base];
        if (typeof element_settings.selector === 'undefined') {
          element_settings.selector = `#${base}`;
        }
        $(element_settings.selector).once('drupal-ajax').each(function () {
          element_settings.element = this;
          element_settings.base = base;
          Drupal.ajax(element_settings);
        });
      }

      // Load all Ajax behaviors specified in the settings.
      for (const base in settings.ajax) {
        if (settings.ajax.hasOwnProperty(base)) {
          loadAjaxBehavior(base);
        }
      }

      // Bind Ajax behaviors to all items showing the class.
      $('.use-ajax').once('ajax').each(function () {
        const element_settings = {};
        // Clicked links look better with the throbber than the progress bar.
        element_settings.progress = { type: 'throbber' };

        // For anchor tags, these will go to the target of the anchor rather
        // than the usual location.
        const href = $(this).attr('href');
        if (href) {
          element_settings.url = href;
          element_settings.event = 'click';
        }
        element_settings.dialogType = $(this).data('dialog-type');
        element_settings.dialogRenderer = $(this).data('dialog-renderer');
        element_settings.dialog = $(this).data('dialog-options');
        element_settings.base = $(this).attr('id');
        element_settings.element = this;
        Drupal.ajax(element_settings);
      });

      // This class means to submit the form to the action using Ajax.
      $('.use-ajax-submit').once('ajax').each(function () {
        const element_settings = {};

        // Ajax submits specified in this manner automatically submit to the
        // normal form action.
        element_settings.url = $(this.form).attr('action');
        // Form submit button clicks need to tell the form what was clicked so
        // it gets passed in the POST request.
        element_settings.setClick = true;
        // Form buttons use the 'click' event rather than mousedown.
        element_settings.event = 'click';
        // Clicked form buttons look better with the throbber than the progress
        // bar.
        element_settings.progress = { type: 'throbber' };
        element_settings.base = $(this).attr('id');
        element_settings.element = this;

        Drupal.ajax(element_settings);
      });
    },

    detach(context, settings, trigger) {
      if (trigger === 'unload') {
        Drupal.ajax.expired().forEach((instance) => {
          // Set this to null and allow garbage collection to reclaim
          // the memory.
          Drupal.ajax.instances[instance.instanceIndex] = null;
        });
      }
    },
  };

  /**
   * Extends Error to provide handling for Errors in Ajax.
   *
   * @constructor
   *
   * @augments Error
   *
   * @param {XMLHttpRequest} xmlhttp
   *   XMLHttpRequest object used for the failed request.
   * @param {string} uri
   *   The URI where the error occurred.
   * @param {string} customMessage
   *   The custom message.
   */
  Drupal.AjaxError = function (xmlhttp, uri, customMessage) {
    let statusCode;
    let statusText;
    let pathText;
    let responseText;
    let readyStateText;
    if (xmlhttp.status) {
      statusCode = `\n${Drupal.t('An AJAX HTTP error occurred.')}\n${Drupal.t('HTTP Result Code: !status', { '!status': xmlhttp.status })}`;
    }
    else {
      statusCode = `\n${Drupal.t('An AJAX HTTP request terminated abnormally.')}`;
    }
    statusCode += `\n${Drupal.t('Debugging information follows.')}`;
    pathText = `\n${Drupal.t('Path: !uri', { '!uri': uri })}`;
    statusText = '';
    // In some cases, when statusCode === 0, xmlhttp.statusText may not be
    // defined. Unfortunately, testing for it with typeof, etc, doesn't seem to
    // catch that and the test causes an exception. So we need to catch the
    // exception here.
    try {
      statusText = `\n${Drupal.t('StatusText: !statusText', { '!statusText': $.trim(xmlhttp.statusText) })}`;
    }
    catch (e) {
      // Empty.
    }

    responseText = '';
    // Again, we don't have a way to know for sure whether accessing
    // xmlhttp.responseText is going to throw an exception. So we'll catch it.
    try {
      responseText = `\n${Drupal.t('ResponseText: !responseText', { '!responseText': $.trim(xmlhttp.responseText) })}`;
    }
    catch (e) {
      // Empty.
    }

    // Make the responseText more readable by stripping HTML tags and newlines.
    responseText = responseText.replace(/<("[^"]*"|'[^']*'|[^'">])*>/gi, '');
    responseText = responseText.replace(/[\n]+\s+/g, '\n');

    // We don't need readyState except for status == 0.
    readyStateText = xmlhttp.status === 0 ? (`\n${Drupal.t('ReadyState: !readyState', { '!readyState': xmlhttp.readyState })}`) : '';

    customMessage = customMessage ? (`\n${Drupal.t('CustomMessage: !customMessage', { '!customMessage': customMessage })}`) : '';

    /**
     * Formatted and translated error message.
     *
     * @type {string}
     */
    this.message = statusCode + pathText + statusText + customMessage + responseText + readyStateText;

    /**
     * Used by some browsers to display a more accurate stack trace.
     *
     * @type {string}
     */
    this.name = 'AjaxError';
  };

  Drupal.AjaxError.prototype = new Error();
  Drupal.AjaxError.prototype.constructor = Drupal.AjaxError;

  /**
   * Provides Ajax page updating via jQuery $.ajax.
   *
   * This function is designed to improve developer experience by wrapping the
   * initialization of {@link Drupal.Ajax} objects and storing all created
   * objects in the {@link Drupal.ajax.instances} array.
   *
   * @example
   * Drupal.behaviors.myCustomAJAXStuff = {
   *   attach: function (context, settings) {
   *
   *     var ajaxSettings = {
   *       url: 'my/url/path',
   *       // If the old version of Drupal.ajax() needs to be used those
   *       // properties can be added
   *       base: 'myBase',
   *       element: $(context).find('.someElement')
   *     };
   *
   *     var myAjaxObject = Drupal.ajax(ajaxSettings);
   *
   *     // Declare a new Ajax command specifically for this Ajax object.
   *     myAjaxObject.commands.insert = function (ajax, response, status) {
   *       $('#my-wrapper').append(response.data);
   *       alert('New content was appended to #my-wrapper');
   *     };
   *
   *     // This command will remove this Ajax object from the page.
   *     myAjaxObject.commands.destroyObject = function (ajax, response, status) {
   *       Drupal.ajax.instances[this.instanceIndex] = null;
   *     };
   *
   *     // Programmatically trigger the Ajax request.
   *     myAjaxObject.execute();
   *   }
   * };
   *
   * @param {object} settings
   *   The settings object passed to {@link Drupal.Ajax} constructor.
   * @param {string} [settings.base]
   *   Base is passed to {@link Drupal.Ajax} constructor as the 'base'
   *   parameter.
   * @param {HTMLElement} [settings.element]
   *   Element parameter of {@link Drupal.Ajax} constructor, element on which
   *   event listeners will be bound.
   *
   * @return {Drupal.Ajax}
   *   The created Ajax object.
   *
   * @see Drupal.AjaxCommands
   */
  Drupal.ajax = function (settings) {
    if (arguments.length !== 1) {
      throw new Error('Drupal.ajax() function must be called with one configuration object only');
    }
    // Map those config keys to variables for the old Drupal.ajax function.
    const base = settings.base || false;
    const element = settings.element || false;
    delete settings.base;
    delete settings.element;

    // By default do not display progress for ajax calls without an element.
    if (!settings.progress && !element) {
      settings.progress = false;
    }

    const ajax = new Drupal.Ajax(base, element, settings);
    ajax.instanceIndex = Drupal.ajax.instances.length;
    Drupal.ajax.instances.push(ajax);

    return ajax;
  };

  /**
   * Contains all created Ajax objects.
   *
   * @type {Array.<Drupal.Ajax|null>}
   */
  Drupal.ajax.instances = [];

  /**
   * List all objects where the associated element is not in the DOM
   *
   * This method ignores {@link Drupal.Ajax} objects not bound to DOM elements
   * when created with {@link Drupal.ajax}.
   *
   * @return {Array.<Drupal.Ajax>}
   *   The list of expired {@link Drupal.Ajax} objects.
   */
  Drupal.ajax.expired = function () {
    return Drupal.ajax.instances.filter(instance => instance && instance.element !== false && !document.body.contains(instance.element));
  };

  /**
   * Settings for an Ajax object.
   *
   * @typedef {object} Drupal.Ajax~element_settings
   *
   * @prop {string} url
   *   Target of the Ajax request.
   * @prop {?string} [event]
   *   Event bound to settings.element which will trigger the Ajax request.
   * @prop {bool} [keypress=true]
   *   Triggers a request on keypress events.
   * @prop {?string} selector
   *   jQuery selector targeting the element to bind events to or used with
   *   {@link Drupal.AjaxCommands}.
   * @prop {string} [effect='none']
   *   Name of the jQuery method to use for displaying new Ajax content.
   * @prop {string|number} [speed='none']
   *   Speed with which to apply the effect.
   * @prop {string} [method]
   *   Name of the jQuery method used to insert new content in the targeted
   *   element.
   * @prop {object} [progress]
   *   Settings for the display of a user-friendly loader.
   * @prop {string} [progress.type='throbber']
   *   Type of progress element, core provides `'bar'`, `'throbber'` and
   *   `'fullscreen'`.
   * @prop {string} [progress.message=Drupal.t('Please wait...')]
   *   Custom message to be used with the bar indicator.
   * @prop {object} [submit]
   *   Extra data to be sent with the Ajax request.
   * @prop {bool} [submit.js=true]
   *   Allows the PHP side to know this comes from an Ajax request.
   * @prop {object} [dialog]
   *   Options for {@link Drupal.dialog}.
   * @prop {string} [dialogType]
   *   One of `'modal'` or `'dialog'`.
   * @prop {string} [prevent]
   *   List of events on which to stop default action and stop propagation.
   */

  /**
   * Ajax constructor.
   *
   * The Ajax request returns an array of commands encoded in JSON, which is
   * then executed to make any changes that are necessary to the page.
   *
   * Drupal uses this file to enhance form elements with `#ajax['url']` and
   * `#ajax['wrapper']` properties. If set, this file will automatically be
   * included to provide Ajax capabilities.
   *
   * @constructor
   *
   * @param {string} [base]
   *   Base parameter of {@link Drupal.Ajax} constructor
   * @param {HTMLElement} [element]
   *   Element parameter of {@link Drupal.Ajax} constructor, element on which
   *   event listeners will be bound.
   * @param {Drupal.Ajax~element_settings} element_settings
   *   Settings for this Ajax object.
   */
  Drupal.Ajax = function (base, element, element_settings) {
    const defaults = {
      event: element ? 'mousedown' : null,
      keypress: true,
      selector: base ? `#${base}` : null,
      effect: 'none',
      speed: 'none',
      method: 'replaceWith',
      progress: {
        type: 'throbber',
        message: Drupal.t('Please wait...'),
      },
      submit: {
        js: true,
      },
    };

    $.extend(this, defaults, element_settings);

    /**
     * @type {Drupal.AjaxCommands}
     */
    this.commands = new Drupal.AjaxCommands();

    /**
     * @type {bool|number}
     */
    this.instanceIndex = false;

    // @todo Remove this after refactoring the PHP code to:
    //   - Call this 'selector'.
    //   - Include the '#' for ID-based selectors.
    //   - Support non-ID-based selectors.
    if (this.wrapper) {
      /**
       * @type {string}
       */
      this.wrapper = `#${this.wrapper}`;
    }

    /**
     * @type {HTMLElement}
     */
    this.element = element;

    /**
     * @type {Drupal.Ajax~element_settings}
     */
    this.element_settings = element_settings;

    // If there isn't a form, jQuery.ajax() will be used instead, allowing us to
    // bind Ajax to links as well.
    if (this.element && this.element.form) {
      /**
       * @type {jQuery}
       */
      this.$form = $(this.element.form);
    }

    // If no Ajax callback URL was given, use the link href or form action.
    if (!this.url) {
      const $element = $(this.element);
      if ($element.is('a')) {
        this.url = $element.attr('href');
      }
      else if (this.element && element.form) {
        this.url = this.$form.attr('action');
      }
    }

    // Replacing 'nojs' with 'ajax' in the URL allows for an easy method to let
    // the server detect when it needs to degrade gracefully.
    // There are four scenarios to check for:
    // 1. /nojs/
    // 2. /nojs$ - The end of a URL string.
    // 3. /nojs? - Followed by a query (e.g. path/nojs?destination=foobar).
    // 4. /nojs# - Followed by a fragment (e.g.: path/nojs#myfragment).
    const originalUrl = this.url;

    /**
     * Processed Ajax URL.
     *
     * @type {string}
     */
    this.url = this.url.replace(/\/nojs(\/|$|\?|#)/g, '/ajax$1');
    // If the 'nojs' version of the URL is trusted, also trust the 'ajax'
    // version.
    if (drupalSettings.ajaxTrustedUrl[originalUrl]) {
      drupalSettings.ajaxTrustedUrl[this.url] = true;
    }

    // Set the options for the ajaxSubmit function.
    // The 'this' variable will not persist inside of the options object.
    const ajax = this;

    /**
     * Options for the jQuery.ajax function.
     *
     * @name Drupal.Ajax#options
     *
     * @type {object}
     *
     * @prop {string} url
     *   Ajax URL to be called.
     * @prop {object} data
     *   Ajax payload.
     * @prop {function} beforeSerialize
     *   Implement jQuery beforeSerialize function to call
     *   {@link Drupal.Ajax#beforeSerialize}.
     * @prop {function} beforeSubmit
     *   Implement jQuery beforeSubmit function to call
     *   {@link Drupal.Ajax#beforeSubmit}.
     * @prop {function} beforeSend
     *   Implement jQuery beforeSend function to call
     *   {@link Drupal.Ajax#beforeSend}.
     * @prop {function} success
     *   Implement jQuery success function to call
     *   {@link Drupal.Ajax#success}.
     * @prop {function} complete
     *   Implement jQuery success function to clean up ajax state and trigger an
     *   error if needed.
     * @prop {string} dataType='json'
     *   Type of the response expected.
     * @prop {string} type='POST'
     *   HTTP method to use for the Ajax request.
     */
    ajax.options = {
      url: ajax.url,
      data: ajax.submit,
      beforeSerialize(element_settings, options) {
        return ajax.beforeSerialize(element_settings, options);
      },
      beforeSubmit(form_values, element_settings, options) {
        ajax.ajaxing = true;
        return ajax.beforeSubmit(form_values, element_settings, options);
      },
      beforeSend(xmlhttprequest, options) {
        ajax.ajaxing = true;
        return ajax.beforeSend(xmlhttprequest, options);
      },
      success(response, status, xmlhttprequest) {
        // Sanity check for browser support (object expected).
        // When using iFrame uploads, responses must be returned as a string.
        if (typeof response === 'string') {
          response = $.parseJSON(response);
        }

        // Prior to invoking the response's commands, verify that they can be
        // trusted by checking for a response header. See
        // \Drupal\Core\EventSubscriber\AjaxResponseSubscriber for details.
        // - Empty responses are harmless so can bypass verification. This
        //   avoids an alert message for server-generated no-op responses that
        //   skip Ajax rendering.
        // - Ajax objects with trusted URLs (e.g., ones defined server-side via
        //   #ajax) can bypass header verification. This is especially useful
        //   for Ajax with multipart forms. Because IFRAME transport is used,
        //   the response headers cannot be accessed for verification.
        if (response !== null && !drupalSettings.ajaxTrustedUrl[ajax.url]) {
          if (xmlhttprequest.getResponseHeader('X-Drupal-Ajax-Token') !== '1') {
            const customMessage = Drupal.t('The response failed verification so will not be processed.');
            return ajax.error(xmlhttprequest, ajax.url, customMessage);
          }
        }

        return ajax.success(response, status);
      },
      complete(xmlhttprequest, status) {
        ajax.ajaxing = false;
        if (status === 'error' || status === 'parsererror') {
          return ajax.error(xmlhttprequest, ajax.url);
        }
      },
      dataType: 'json',
      type: 'POST',
    };

    if (element_settings.dialog) {
      ajax.options.data.dialogOptions = element_settings.dialog;
    }

    // Ensure that we have a valid URL by adding ? when no query parameter is
    // yet available, otherwise append using &.
    if (ajax.options.url.indexOf('?') === -1) {
      ajax.options.url += '?';
    }
    else {
      ajax.options.url += '&';
    }
    // If this element has a dialog type use if for the wrapper if not use 'ajax'.
    let wrapper = `drupal_${(element_settings.dialogType || 'ajax')}`;
    if (element_settings.dialogRenderer) {
      wrapper += `.${element_settings.dialogRenderer}`;
    }
    ajax.options.url += `${Drupal.ajax.WRAPPER_FORMAT}=${wrapper}`;


    // Bind the ajaxSubmit function to the element event.
    $(ajax.element).on(element_settings.event, function (event) {
      if (!drupalSettings.ajaxTrustedUrl[ajax.url] && !Drupal.url.isLocal(ajax.url)) {
        throw new Error(Drupal.t('The callback URL is not local and not trusted: !url', { '!url': ajax.url }));
      }
      return ajax.eventResponse(this, event);
    });

    // If necessary, enable keyboard submission so that Ajax behaviors
    // can be triggered through keyboard input as well as e.g. a mousedown
    // action.
    if (element_settings.keypress) {
      $(ajax.element).on('keypress', function (event) {
        return ajax.keypressResponse(this, event);
      });
    }

    // If necessary, prevent the browser default action of an additional event.
    // For example, prevent the browser default action of a click, even if the
    // Ajax behavior binds to mousedown.
    if (element_settings.prevent) {
      $(ajax.element).on(element_settings.prevent, false);
    }
  };

  /**
   * URL query attribute to indicate the wrapper used to render a request.
   *
   * The wrapper format determines how the HTML is wrapped, for example in a
   * modal dialog.
   *
   * @const {string}
   *
   * @default
   */
  Drupal.ajax.WRAPPER_FORMAT = '_wrapper_format';

  /**
   * Request parameter to indicate that a request is a Drupal Ajax request.
   *
   * @const {string}
   *
   * @default
   */
  Drupal.Ajax.AJAX_REQUEST_PARAMETER = '_drupal_ajax';

  /**
   * Execute the ajax request.
   *
   * Allows developers to execute an Ajax request manually without specifying
   * an event to respond to.
   *
   * @return {object}
   *   Returns the jQuery.Deferred object underlying the Ajax request. If
   *   pre-serialization fails, the Deferred will be returned in the rejected
   *   state.
   */
  Drupal.Ajax.prototype.execute = function () {
    // Do not perform another ajax command if one is already in progress.
    if (this.ajaxing) {
      return;
    }

    try {
      this.beforeSerialize(this.element, this.options);
      // Return the jqXHR so that external code can hook into the Deferred API.
      return $.ajax(this.options);
    }
    catch (e) {
      // Unset the ajax.ajaxing flag here because it won't be unset during
      // the complete response.
      this.ajaxing = false;
      window.alert(`An error occurred while attempting to process ${this.options.url}: ${e.message}`);
      // For consistency, return a rejected Deferred (i.e., jqXHR's superclass)
      // so that calling code can take appropriate action.
      return $.Deferred().reject();
    }
  };

  /**
   * Handle a key press.
   *
   * The Ajax object will, if instructed, bind to a key press response. This
   * will test to see if the key press is valid to trigger this event and
   * if it is, trigger it for us and prevent other keypresses from triggering.
   * In this case we're handling RETURN and SPACEBAR keypresses (event codes 13
   * and 32. RETURN is often used to submit a form when in a textfield, and
   * SPACE is often used to activate an element without submitting.
   *
   * @param {HTMLElement} element
   *   Element the event was triggered on.
   * @param {jQuery.Event} event
   *   Triggered event.
   */
  Drupal.Ajax.prototype.keypressResponse = function (element, event) {
    // Create a synonym for this to reduce code confusion.
    const ajax = this;

    // Detect enter key and space bar and allow the standard response for them,
    // except for form elements of type 'text', 'tel', 'number' and 'textarea',
    // where the spacebar activation causes inappropriate activation if
    // #ajax['keypress'] is TRUE. On a text-type widget a space should always
    // be a space.
    if (event.which === 13 || (event.which === 32 && element.type !== 'text' &&
      element.type !== 'textarea' && element.type !== 'tel' && element.type !== 'number')) {
      event.preventDefault();
      event.stopPropagation();
      $(element).trigger(ajax.element_settings.event);
    }
  };

  /**
   * Handle an event that triggers an Ajax response.
   *
   * When an event that triggers an Ajax response happens, this method will
   * perform the actual Ajax call. It is bound to the event using
   * bind() in the constructor, and it uses the options specified on the
   * Ajax object.
   *
   * @param {HTMLElement} element
   *   Element the event was triggered on.
   * @param {jQuery.Event} event
   *   Triggered event.
   */
  Drupal.Ajax.prototype.eventResponse = function (element, event) {
    event.preventDefault();
    event.stopPropagation();

    // Create a synonym for this to reduce code confusion.
    const ajax = this;

    // Do not perform another Ajax command if one is already in progress.
    if (ajax.ajaxing) {
      return;
    }

    try {
      if (ajax.$form) {
        // If setClick is set, we must set this to ensure that the button's
        // value is passed.
        if (ajax.setClick) {
          // Mark the clicked button. 'form.clk' is a special variable for
          // ajaxSubmit that tells the system which element got clicked to
          // trigger the submit. Without it there would be no 'op' or
          // equivalent.
          element.form.clk = element;
        }

        ajax.$form.ajaxSubmit(ajax.options);
      }
      else {
        ajax.beforeSerialize(ajax.element, ajax.options);
        $.ajax(ajax.options);
      }
    }
    catch (e) {
      // Unset the ajax.ajaxing flag here because it won't be unset during
      // the complete response.
      ajax.ajaxing = false;
      window.alert(`An error occurred while attempting to process ${ajax.options.url}: ${e.message}`);
    }
  };

  /**
   * Handler for the form serialization.
   *
   * Runs before the beforeSend() handler (see below), and unlike that one, runs
   * before field data is collected.
   *
   * @param {object} [element]
   *   Ajax object's `element_settings`.
   * @param {object} options
   *   jQuery.ajax options.
   */
  Drupal.Ajax.prototype.beforeSerialize = function (element, options) {
    // Allow detaching behaviors to update field values before collecting them.
    // This is only needed when field values are added to the POST data, so only
    // when there is a form such that this.$form.ajaxSubmit() is used instead of
    // $.ajax(). When there is no form and $.ajax() is used, beforeSerialize()
    // isn't called, but don't rely on that: explicitly check this.$form.
    if (this.$form) {
      const settings = this.settings || drupalSettings;
      Drupal.detachBehaviors(this.$form.get(0), settings, 'serialize');
    }

    // Inform Drupal that this is an AJAX request.
    options.data[Drupal.Ajax.AJAX_REQUEST_PARAMETER] = 1;

    // Allow Drupal to return new JavaScript and CSS files to load without
    // returning the ones already loaded.
    // @see \Drupal\Core\Theme\AjaxBasePageNegotiator
    // @see \Drupal\Core\Asset\LibraryDependencyResolverInterface::getMinimalRepresentativeSubset()
    // @see system_js_settings_alter()
    const pageState = drupalSettings.ajaxPageState;
    options.data['ajax_page_state[theme]'] = pageState.theme;
    options.data['ajax_page_state[theme_token]'] = pageState.theme_token;
    options.data['ajax_page_state[libraries]'] = pageState.libraries;
  };

  /**
   * Modify form values prior to form submission.
   *
   * @param {Array.<object>} form_values
   *   Processed form values.
   * @param {jQuery} element
   *   The form node as a jQuery object.
   * @param {object} options
   *   jQuery.ajax options.
   */
  Drupal.Ajax.prototype.beforeSubmit = function (form_values, element, options) {
    // This function is left empty to make it simple to override for modules
    // that wish to add functionality here.
  };

  /**
   * Prepare the Ajax request before it is sent.
   *
   * @param {XMLHttpRequest} xmlhttprequest
   *   Native Ajax object.
   * @param {object} options
   *   jQuery.ajax options.
   */
  Drupal.Ajax.prototype.beforeSend = function (xmlhttprequest, options) {
    // For forms without file inputs, the jQuery Form plugin serializes the
    // form values, and then calls jQuery's $.ajax() function, which invokes
    // this handler. In this circumstance, options.extraData is never used. For
    // forms with file inputs, the jQuery Form plugin uses the browser's normal
    // form submission mechanism, but captures the response in a hidden IFRAME.
    // In this circumstance, it calls this handler first, and then appends
    // hidden fields to the form to submit the values in options.extraData.
    // There is no simple way to know which submission mechanism will be used,
    // so we add to extraData regardless, and allow it to be ignored in the
    // former case.
    if (this.$form) {
      options.extraData = options.extraData || {};

      // Let the server know when the IFRAME submission mechanism is used. The
      // server can use this information to wrap the JSON response in a
      // TEXTAREA, as per http://jquery.malsup.com/form/#file-upload.
      options.extraData.ajax_iframe_upload = '1';

      // The triggering element is about to be disabled (see below), but if it
      // contains a value (e.g., a checkbox, textfield, select, etc.), ensure
      // that value is included in the submission. As per above, submissions
      // that use $.ajax() are already serialized prior to the element being
      // disabled, so this is only needed for IFRAME submissions.
      const v = $.fieldValue(this.element);
      if (v !== null) {
        options.extraData[this.element.name] = v;
      }
    }

    // Disable the element that received the change to prevent user interface
    // interaction while the Ajax request is in progress. ajax.ajaxing prevents
    // the element from triggering a new request, but does not prevent the user
    // from changing its value.
    $(this.element).prop('disabled', true);

    if (!this.progress || !this.progress.type) {
      return;
    }

    // Insert progress indicator.
    const progressIndicatorMethod = `setProgressIndicator${this.progress.type.slice(0, 1).toUpperCase()}${this.progress.type.slice(1).toLowerCase()}`;
    if (progressIndicatorMethod in this && typeof this[progressIndicatorMethod] === 'function') {
      this[progressIndicatorMethod].call(this);
    }
  };

  /**
   * Sets the progress bar progress indicator.
   */
  Drupal.Ajax.prototype.setProgressIndicatorBar = function () {
    const progressBar = new Drupal.ProgressBar(`ajax-progress-${this.element.id}`, $.noop, this.progress.method, $.noop);
    if (this.progress.message) {
      progressBar.setProgress(-1, this.progress.message);
    }
    if (this.progress.url) {
      progressBar.startMonitoring(this.progress.url, this.progress.interval || 1500);
    }
    this.progress.element = $(progressBar.element).addClass('ajax-progress ajax-progress-bar');
    this.progress.object = progressBar;
    $(this.element).after(this.progress.element);
  };

  /**
   * Sets the throbber progress indicator.
   */
  Drupal.Ajax.prototype.setProgressIndicatorThrobber = function () {
    this.progress.element = $('<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div></div>');
    if (this.progress.message) {
      this.progress.element.find('.throbber').after(`<div class="message">${this.progress.message}</div>`);
    }
    $(this.element).after(this.progress.element);
  };

  /**
   * Sets the fullscreen progress indicator.
   */
  Drupal.Ajax.prototype.setProgressIndicatorFullscreen = function () {
    this.progress.element = $('<div class="ajax-progress ajax-progress-fullscreen">&nbsp;</div>');
    $('body').after(this.progress.element);
  };

  /**
   * Handler for the form redirection completion.
   *
   * @param {Array.<Drupal.AjaxCommands~commandDefinition>} response
   *   Drupal Ajax response.
   * @param {number} status
   *   XMLHttpRequest status.
   */
  Drupal.Ajax.prototype.success = function (response, status) {
    // Remove the progress element.
    if (this.progress.element) {
      $(this.progress.element).remove();
    }
    if (this.progress.object) {
      this.progress.object.stopMonitoring();
    }
    $(this.element).prop('disabled', false);

    // Save element's ancestors tree so if the element is removed from the dom
    // we can try to refocus one of its parents. Using addBack reverse the
    // result array, meaning that index 0 is the highest parent in the hierarchy
    // in this situation it is usually a <form> element.
    const elementParents = $(this.element).parents('[data-drupal-selector]').addBack().toArray();

    // Track if any command is altering the focus so we can avoid changing the
    // focus set by the Ajax command.
    let focusChanged = false;
    for (const i in response) {
      if (response.hasOwnProperty(i) && response[i].command && this.commands[response[i].command]) {
        this.commands[response[i].command](this, response[i], status);
        if (response[i].command === 'invoke' && response[i].method === 'focus') {
          focusChanged = true;
        }
      }
    }

    // If the focus hasn't be changed by the ajax commands, try to refocus the
    // triggering element or one of its parents if that element does not exist
    // anymore.
    if (!focusChanged && this.element && !$(this.element).data('disable-refocus')) {
      let target = false;

      for (let n = elementParents.length - 1; !target && n > 0; n--) {
        target = document.querySelector(`[data-drupal-selector="${elementParents[n].getAttribute('data-drupal-selector')}"]`);
      }

      if (target) {
        $(target).trigger('focus');
      }
    }

    // Reattach behaviors, if they were detached in beforeSerialize(). The
    // attachBehaviors() called on the new content from processing the response
    // commands is not sufficient, because behaviors from the entire form need
    // to be reattached.
    if (this.$form) {
      const settings = this.settings || drupalSettings;
      Drupal.attachBehaviors(this.$form.get(0), settings);
    }

    // Remove any response-specific settings so they don't get used on the next
    // call by mistake.
    this.settings = null;
  };

  /**
   * Build an effect object to apply an effect when adding new HTML.
   *
   * @param {object} response
   *   Drupal Ajax response.
   * @param {string} [response.effect]
   *   Override the default value of {@link Drupal.Ajax#element_settings}.
   * @param {string|number} [response.speed]
   *   Override the default value of {@link Drupal.Ajax#element_settings}.
   *
   * @return {object}
   *   Returns an object with `showEffect`, `hideEffect` and `showSpeed`
   *   properties.
   */
  Drupal.Ajax.prototype.getEffect = function (response) {
    const type = response.effect || this.effect;
    const speed = response.speed || this.speed;

    const effect = {};
    if (type === 'none') {
      effect.showEffect = 'show';
      effect.hideEffect = 'hide';
      effect.showSpeed = '';
    }
    else if (type === 'fade') {
      effect.showEffect = 'fadeIn';
      effect.hideEffect = 'fadeOut';
      effect.showSpeed = speed;
    }
    else {
      effect.showEffect = `${type}Toggle`;
      effect.hideEffect = `${type}Toggle`;
      effect.showSpeed = speed;
    }

    return effect;
  };

  /**
   * Handler for the form redirection error.
   *
   * @param {object} xmlhttprequest
   *   Native XMLHttpRequest object.
   * @param {string} uri
   *   Ajax Request URI.
   * @param {string} [customMessage]
   *   Extra message to print with the Ajax error.
   */
  Drupal.Ajax.prototype.error = function (xmlhttprequest, uri, customMessage) {
    // Remove the progress element.
    if (this.progress.element) {
      $(this.progress.element).remove();
    }
    if (this.progress.object) {
      this.progress.object.stopMonitoring();
    }
    // Undo hide.
    $(this.wrapper).show();
    // Re-enable the element.
    $(this.element).prop('disabled', false);
    // Reattach behaviors, if they were detached in beforeSerialize().
    if (this.$form) {
      const settings = this.settings || drupalSettings;
      Drupal.attachBehaviors(this.$form.get(0), settings);
    }
    throw new Drupal.AjaxError(xmlhttprequest, uri, customMessage);
  };

  /**
   * @typedef {object} Drupal.AjaxCommands~commandDefinition
   *
   * @prop {string} command
   * @prop {string} [method]
   * @prop {string} [selector]
   * @prop {string} [data]
   * @prop {object} [settings]
   * @prop {bool} [asterisk]
   * @prop {string} [text]
   * @prop {string} [title]
   * @prop {string} [url]
   * @prop {object} [argument]
   * @prop {string} [name]
   * @prop {string} [value]
   * @prop {string} [old]
   * @prop {string} [new]
   * @prop {bool} [merge]
   * @prop {Array} [args]
   *
   * @see Drupal.AjaxCommands
   */

  /**
   * Provide a series of commands that the client will perform.
   *
   * @constructor
   */
  Drupal.AjaxCommands = function () {};
  Drupal.AjaxCommands.prototype = {

    /**
     * Command to insert new content into the DOM.
     *
     * @param {Drupal.Ajax} ajax
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.data
     *   The data to use with the jQuery method.
     * @param {string} [response.method]
     *   The jQuery DOM manipulation method to be used.
     * @param {string} [response.selector]
     *   A optional jQuery selector string.
     * @param {object} [response.settings]
     *   An optional array of settings that will be used.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    insert(ajax, response, status) {
      // Get information from the response. If it is not there, default to
      // our presets.
      const $wrapper = response.selector ? $(response.selector) : $(ajax.wrapper);
      const method = response.method || ajax.method;
      const effect = ajax.getEffect(response);
      let settings;

      // We don't know what response.data contains: it might be a string of text
      // without HTML, so don't rely on jQuery correctly interpreting
      // $(response.data) as new HTML rather than a CSS selector. Also, if
      // response.data contains top-level text nodes, they get lost with either
      // $(response.data) or $('<div></div>').replaceWith(response.data).
      const $new_content_wrapped = $('<div></div>').html(response.data);
      let $new_content = $new_content_wrapped.contents();

      // For legacy reasons, the effects processing code assumes that
      // $new_content consists of a single top-level element. Also, it has not
      // been sufficiently tested whether attachBehaviors() can be successfully
      // called with a context object that includes top-level text nodes.
      // However, to give developers full control of the HTML appearing in the
      // page, and to enable Ajax content to be inserted in places where <div>
      // elements are not allowed (e.g., within <table>, <tr>, and <span>
      // parents), we check if the new content satisfies the requirement
      // of a single top-level element, and only use the container <div> created
      // above when it doesn't. For more information, please see
      // https://www.drupal.org/node/736066.
      if ($new_content.length !== 1 || $new_content.get(0).nodeType !== 1) {
        $new_content = $new_content_wrapped;
      }

      // If removing content from the wrapper, detach behaviors first.
      switch (method) {
        case 'html':
        case 'replaceWith':
        case 'replaceAll':
        case 'empty':
        case 'remove':
          settings = response.settings || ajax.settings || drupalSettings;
          Drupal.detachBehaviors($wrapper.get(0), settings);
      }

      // Add the new content to the page.
      $wrapper[method]($new_content);

      // Immediately hide the new content if we're using any effects.
      if (effect.showEffect !== 'show') {
        $new_content.hide();
      }

      // Determine which effect to use and what content will receive the
      // effect, then show the new content.
      if ($new_content.find('.ajax-new-content').length > 0) {
        $new_content.find('.ajax-new-content').hide();
        $new_content.show();
        $new_content.find('.ajax-new-content')[effect.showEffect](effect.showSpeed);
      }
      else if (effect.showEffect !== 'show') {
        $new_content[effect.showEffect](effect.showSpeed);
      }

      // Attach all JavaScript behaviors to the new content, if it was
      // successfully added to the page, this if statement allows
      // `#ajax['wrapper']` to be optional.
      if ($new_content.parents('html').length > 0) {
        // Apply any settings from the returned JSON if available.
        settings = response.settings || ajax.settings || drupalSettings;
        Drupal.attachBehaviors($new_content.get(0), settings);
      }
    },

    /**
     * Command to remove a chunk from the page.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {object} [response.settings]
     *   An optional array of settings that will be used.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    remove(ajax, response, status) {
      const settings = response.settings || ajax.settings || drupalSettings;
      $(response.selector).each(function () {
        Drupal.detachBehaviors(this, settings);
      })
        .remove();
    },

    /**
     * Command to mark a chunk changed.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The JSON response object from the Ajax request.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {bool} [response.asterisk]
     *   An optional CSS selector. If specified, an asterisk will be
     *   appended to the HTML inside the provided selector.
     * @param {number} [status]
     *   The request status.
     */
    changed(ajax, response, status) {
      const $element = $(response.selector);
      if (!$element.hasClass('ajax-changed')) {
        $element.addClass('ajax-changed');
        if (response.asterisk) {
          $element.find(response.asterisk).append(` <abbr class="ajax-changed" title="${Drupal.t('Changed')}">*</abbr> `);
        }
      }
    },

    /**
     * Command to provide an alert.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The JSON response from the Ajax request.
     * @param {string} response.text
     *   The text that will be displayed in an alert dialog.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    alert(ajax, response, status) {
      window.alert(response.text, response.title);
    },

    /**
     * Command to set the window.location, redirecting the browser.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.url
     *   The URL to redirect to.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    redirect(ajax, response, status) {
      window.location = response.url;
    },

    /**
     * Command to provide the jQuery css() function.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {object} response.argument
     *   An array of key/value pairs to set in the CSS for the selector.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    css(ajax, response, status) {
      $(response.selector).css(response.argument);
    },

    /**
     * Command to set the settings used for other commands in this response.
     *
     * This method will also remove expired `drupalSettings.ajax` settings.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {bool} response.merge
     *   Determines whether the additional settings should be merged to the
     *   global settings.
     * @param {object} response.settings
     *   Contains additional settings to add to the global settings.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    settings(ajax, response, status) {
      const ajaxSettings = drupalSettings.ajax;

      // Clean up drupalSettings.ajax.
      if (ajaxSettings) {
        Drupal.ajax.expired().forEach((instance) => {
          // If the Ajax object has been created through drupalSettings.ajax
          // it will have a selector. When there is no selector the object
          // has been initialized with a special class name picked up by the
          // Ajax behavior.

          if (instance.selector) {
            const selector = instance.selector.replace('#', '');
            if (selector in ajaxSettings) {
              delete ajaxSettings[selector];
            }
          }
        });
      }

      if (response.merge) {
        $.extend(true, drupalSettings, response.settings);
      }
      else {
        ajax.settings = response.settings;
      }
    },

    /**
     * Command to attach data using jQuery's data API.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.name
     *   The name or key (in the key value pair) of the data attached to this
     *   selector.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {string|object} response.value
     *   The value of to be attached.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    data(ajax, response, status) {
      $(response.selector).data(response.name, response.value);
    },

    /**
     * Command to apply a jQuery method.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {Array} response.args
     *   An array of arguments to the jQuery method, if any.
     * @param {string} response.method
     *   The jQuery method to invoke.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    invoke(ajax, response, status) {
      const $element = $(response.selector);
      $element[response.method](...response.args);
    },

    /**
     * Command to restripe a table.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.selector
     *   A jQuery selector string.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    restripe(ajax, response, status) {
      // :even and :odd are reversed because jQuery counts from 0 and
      // we count from 1, so we're out of sync.
      // Match immediate children of the parent element to allow nesting.
      $(response.selector).find('> tbody > tr:visible, > tr:visible')
        .removeClass('odd even')
        .filter(':even').addClass('odd').end()
        .filter(':odd').addClass('even');
    },

    /**
     * Command to update a form's build ID.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.old
     *   The old form build ID.
     * @param {string} response.new
     *   The new form build ID.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    update_build_id(ajax, response, status) {
      $(`input[name="form_build_id"][value="${response.old}"]`).val(response.new);
    },

    /**
     * Command to add css.
     *
     * Uses the proprietary addImport method if available as browsers which
     * support that method ignore @import statements in dynamically added
     * stylesheets.
     *
     * @param {Drupal.Ajax} [ajax]
     *   {@link Drupal.Ajax} object created by {@link Drupal.ajax}.
     * @param {object} response
     *   The response from the Ajax request.
     * @param {string} response.data
     *   A string that contains the styles to be added.
     * @param {number} [status]
     *   The XMLHttpRequest status.
     */
    add_css(ajax, response, status) {
      // Add the styles in the normal way.
      $('head').prepend(response.data);
      // Add imports in the styles using the addImport method if available.
      let match;
      const importMatch = /^@import url\("(.*)"\);$/igm;
      if (document.styleSheets[0].addImport && importMatch.test(response.data)) {
        importMatch.lastIndex = 0;
        do {
          match = importMatch.exec(response.data);
          document.styleSheets[0].addImport(match[1]);
        } while (match);
      }
    },
  };
}(jQuery, window, Drupal, drupalSettings));