/**
 * @file
 * Form features.
 */

/**
 * Triggers when a value in the form changed.
 *
 * The event triggers when content is typed or pasted in a text field, before
 * the change event triggers.
 *
 * @event formUpdated
 */

(function ($, Drupal, debounce) {

  'use strict';

  /**
   * Retrieves the summary for the first element.
   *
   * @return {string}
   */
  $.fn.drupalGetSummary = function () {
    var callback = this.data('summaryCallback');
    return (this[0] && callback) ? $.trim(callback(this[0])) : '';
  };

  /**
   * Sets the summary for all matched elements.
   *
   * @param {function} callback
   *   Either a function that will be called each time the summary is
   *   retrieved or a string (which is returned each time).
   *
   * @return {jQuery}
   *
   * @fires event:summaryUpdated
   *
   * @listens event:formUpdated
   */
  $.fn.drupalSetSummary = function (callback) {
    var self = this;

    // To facilitate things, the callback should always be a function. If it's
    // not, we wrap it into an anonymous function which just returns the value.
    if (typeof callback !== 'function') {
      var val = callback;
      callback = function () { return val; };
    }

    return this
      .data('summaryCallback', callback)
      // To prevent duplicate events, the handlers are first removed and then
      // (re-)added.
      .off('formUpdated.summary')
      .on('formUpdated.summary', function () {
        self.trigger('summaryUpdated');
      })
      // The actual summaryUpdated handler doesn't fire when the callback is
      // changed, so we have to do this manually.
      .trigger('summaryUpdated');
  };

  /**
   * Prevents consecutive form submissions of identical form values.
   *
   * Repetitive form submissions that would submit the identical form values
   * are prevented, unless the form values are different to the previously
   * submitted values.
   *
   * This is a simplified re-implementation of a user-agent behavior that
   * should be natively supported by major web browsers, but at this time, only
   * Firefox has a built-in protection.
   *
   * A form value-based approach ensures that the constraint is triggered for
   * consecutive, identical form submissions only. Compared to that, a form
   * button-based approach would (1) rely on [visible] buttons to exist where
   * technically not required and (2) require more complex state management if
   * there are multiple buttons in a form.
   *
   * This implementation is based on form-level submit events only and relies
   * on jQuery's serialize() method to determine submitted form values. As such,
   * the following limitations exist:
   *
   * - Event handlers on form buttons that preventDefault() do not receive a
   *   double-submit protection. That is deemed to be fine, since such button
   *   events typically trigger reversible client-side or server-side
   *   operations that are local to the context of a form only.
   * - Changed values in advanced form controls, such as file inputs, are not
   *   part of the form values being compared between consecutive form submits
   *   (due to limitations of jQuery.serialize()). That is deemed to be
   *   acceptable, because if the user forgot to attach a file, then the size of
   *   HTTP payload will most likely be small enough to be fully passed to the
   *   server endpoint within (milli)seconds. If a user mistakenly attached a
   *   wrong file and is technically versed enough to cancel the form submission
   *   (and HTTP payload) in order to attach a different file, then that
   *   edge-case is not supported here.
   *
   * Lastly, all forms submitted via HTTP GET are idempotent by definition of
   * HTTP standards, so excluded in this implementation.
   *
   * @type {Drupal~behavior}
   */
  Drupal.behaviors.formSingleSubmit = {
    attach: function () {
      function onFormSubmit(e) {
        var $form = $(e.currentTarget);
        var formValues = $form.serialize();
        var previousValues = $form.attr('data-drupal-form-submit-last');
        if (previousValues === formValues) {
          e.preventDefault();
        }
        else {
          $form.attr('data-drupal-form-submit-last', formValues);
        }
      }

      $('body').once('form-single-submit')
        .on('submit.singleSubmit', 'form:not([method~="GET"])', onFormSubmit);
    }
  };

  /**
   * Sends a 'formUpdated' event each time a form element is modified.
   *
   * @param {HTMLElement} element
   *
   * @fires event:formUpdated
   */
  function triggerFormUpdated(element) {
    $(element).trigger('formUpdated');
  }

  /**
   * Collects the IDs of all form fields in the given form.
   *
   * @param {HTMLFormElement} form
   *
   * @return {Array}
   */
  function fieldsList(form) {
    var $fieldList = $(form).find('[name]').map(function (index, element) {
      // We use id to avoid name duplicates on radio fields and filter out
      // elements with a name but no id.
      return element.getAttribute('id');
    });
    // Return a true array.
    return $.makeArray($fieldList);
  }

  /**
   * Triggers the 'formUpdated' event on form elements when they are modified.
   *
   * @type {Drupal~behavior}
   *
   * @fires event:formUpdated
   */
  Drupal.behaviors.formUpdated = {
    attach: function (context) {
      var $context = $(context);
      var contextIsForm = $context.is('form');
      var $forms = (contextIsForm ? $context : $context.find('form')).once('form-updated');
      var formFields;

      if ($forms.length) {
        // Initialize form behaviors, use $.makeArray to be able to use native
        // forEach array method and have the callback parameters in the right
        // order.
        $.makeArray($forms).forEach(function (form) {
          var events = 'change.formUpdated input.formUpdated ';
          var eventHandler = debounce(function (event) { triggerFormUpdated(event.target); }, 300);
          formFields = fieldsList(form).join(',');

          form.setAttribute('data-drupal-form-fields', formFields);
          $(form).on(events, eventHandler);
        });
      }
      // On ajax requests context is the form element.
      if (contextIsForm) {
        formFields = fieldsList(context).join(',');
        // @todo replace with form.getAttribute() when #1979468 is in.
        var currentFields = $(context).attr('data-drupal-form-fields');
        // If there has been a change in the fields or their order, trigger
        // formUpdated.
        if (formFields !== currentFields) {
          triggerFormUpdated(context);
        }
      }

    },
    detach: function (context, settings, trigger) {
      var $context = $(context);
      var contextIsForm = $context.is('form');
      if (trigger === 'unload') {
        var $forms = (contextIsForm ? $context : $context.find('form')).removeOnce('form-updated');
        if ($forms.length) {
          $.makeArray($forms).forEach(function (form) {
            form.removeAttribute('data-drupal-form-fields');
            $(form).off('.formUpdated');
          });
        }
      }
    }
  };

  /**
   * Prepopulate form fields with information from the visitor browser.
   *
   * @type {Drupal~behavior}
   */
  Drupal.behaviors.fillUserInfoFromBrowser = {
    attach: function (context, settings) {
      var userInfo = ['name', 'mail', 'homepage'];
      var $forms = $('[data-user-info-from-browser]').once('user-info-from-browser');
      if ($forms.length) {
        userInfo.map(function (info) {
          var $element = $forms.find('[name=' + info + ']');
          var browserData = localStorage.getItem('Drupal.visitor.' + info);
          var emptyOrDefault = ($element.val() === '' || ($element.attr('data-drupal-default-value') === $element.val()));
          if ($element.length && emptyOrDefault && browserData) {
            $element.val(browserData);
          }
        });
      }
      $forms.on('submit', function () {
        userInfo.map(function (info) {
          var $element = $forms.find('[name=' + info + ']');
          if ($element.length) {
            localStorage.setItem('Drupal.visitor.' + info, $element.val());
          }
        });
      });
    }
  };

})(jQuery, Drupal, Drupal.debounce);
