(function ($, Drupal, drupalSettings) {

  "use strict";

  /**
   * Attach the machine-readable name form element behavior.
   */
  Drupal.behaviors.machineName = {
    /**
     * Attaches the behavior.
     *
     * @param settings.machineName
     *   A list of elements to process, keyed by the HTML ID of the form element
     *   containing the human-readable value. Each element is an object defining
     *   the following properties:
     *   - target: The HTML ID of the machine name form element.
     *   - suffix: The HTML ID of a container to show the machine name preview in
     *     (usually a field suffix after the human-readable name form element).
     *   - label: The label to show for the machine name preview.
     *   - replace_pattern: A regular expression (without modifiers) matching
     *     disallowed characters in the machine name; e.g., '[^a-z0-9]+'.
     *   - replace: A character to replace disallowed characters with; e.g., '_'
     *     or '-'.
     *   - standalone: Whether the preview should stay in its own element rather
     *     than the suffix of the source element.
     *   - field_prefix: The #field_prefix of the form element.
     *   - field_suffix: The #field_suffix of the form element.
     */
    attach: function (context, settings) {
      var self = this;
      var $context = $(context);
      var timeout = null;
      var xhr = null;

      function clickEditHandler(e) {
        var data = e.data;
        e.preventDefault();
        data.$wrapper.show();
        data.$target.trigger('focus');
        data.$suffix.hide();
        data.$source.off('.machineName');
      }

      function machineNameHandler(e) {
        var data = e.data;
        var options = data.options;
        var baseValue = $(e.target).val();

        var rx = new RegExp(options.replace_pattern, 'g');
        var expected = baseValue.toLowerCase().replace(rx, options.replace).substr(0, options.maxlength);

        // Abort the last pending request because the label has changed and it
        // is no longer valid.
        if (xhr && xhr.readystate !== 4) {
          xhr.abort();
          xhr = null;
        }

        // Wait 300 milliseconds since the last event to update the machine name
        // i.e., after the user has stopped typing.
        if (timeout) {
          clearTimeout(timeout);
          timeout = null;
        }
        timeout = setTimeout(function () {
          if (baseValue.toLowerCase() !== expected) {
            xhr = self.transliterate(baseValue, options).done(function (machine) {
              self.showMachineName(machine.substr(0, options.maxlength), data);
            });
          }
          else {
            self.showMachineName(expected, data);
          }
        }, 300);
      }

      Object.keys(settings.machineName).forEach(function (source_id) {
        var machine, eventData;
        var options = settings.machineName[source_id];

        var $source = $context.find(source_id).addClass('machine-name-source').once('machine-name');
        var $target = $context.find(options.target).addClass('machine-name-target');
        var $suffix = $context.find(options.suffix);
        var $wrapper = $target.closest('.form-item');
        // All elements have to exist.
        if (!$source.length || !$target.length || !$suffix.length || !$wrapper.length) {
          return;
        }
        // Skip processing upon a form validation error on the machine name.
        if ($target.hasClass('error')) {
          return;
        }
        // Figure out the maximum length for the machine name.
        options.maxlength = $target.attr('maxlength');
        // Hide the form item container of the machine name form element.
        $wrapper.hide();
        // Determine the initial machine name value. Unless the machine name form
        // element is disabled or not empty, the initial default value is based on
        // the human-readable form element value.
        if ($target.is(':disabled') || $target.val() !== '') {
          machine = $target.val();
        }
        else {
          machine = self.transliterate($source.val(), options);
        }
        // Append the machine name preview to the source field.
        var $preview = $('<span class="machine-name-value">' + options.field_prefix + Drupal.checkPlain(machine) + options.field_suffix + '</span>');
        $suffix.empty();
        if (options.label) {
          $suffix.append('<span class="machine-name-label">' + options.label + ': </span>');
        }
        $suffix.append($preview);

        // If the machine name cannot be edited, stop further processing.
        if ($target.is(':disabled')) {
          return;
        }

        eventData = {
          $source: $source,
          $target: $target,
          $suffix: $suffix,
          $wrapper: $wrapper,
          $preview: $preview,
          options: options
        };
        // If it is editable, append an edit link.
        var $link = $('<span class="admin-link"><button type="button" class="link">' + Drupal.t('Edit') + '</button></span>').on('click', eventData, clickEditHandler);
        $suffix.append($link);

        // Preview the machine name in realtime when the human-readable name
        // changes, but only if there is no machine name yet; i.e., only upon
        // initial creation, not when editing.
        if ($target.val() === '') {
          $source.on('keyup.machineName change.machineName input.machineName', eventData, machineNameHandler)
            // Initialize machine name preview.
            .trigger('keyup');
        }
      });
    },

    showMachineName: function (machine, data) {
      var settings = data.options;
      // Set the machine name to the transliterated value.
      if (machine !== '') {
        if (machine !== settings.replace) {
          data.$target.val(machine);
          data.$preview.html(settings.field_prefix + Drupal.checkPlain(machine) + settings.field_suffix);
        }
        data.$suffix.show();
      }
      else {
        data.$suffix.hide();
        data.$target.val(machine);
        data.$preview.empty();
      }
    },

    /**
     * Transliterate a human-readable name to a machine name.
     *
     * @param source
     *   A string to transliterate.
     * @param settings
     *   The machine name settings for the corresponding field, containing:
     *   - replace_pattern: A regular expression (without modifiers) matching
     *     disallowed characters in the machine name; e.g., '[^a-z0-9]+'.
     *   - replace: A character to replace disallowed characters with; e.g., '_'
     *     or '-'.
     *   - maxlength: The maximum length of the machine name.
     *
     * @return
     *   The transliterated source string.
     */
    transliterate: function (source, settings) {
      return $.get(Drupal.url('machine_name/transliterate'), {
        text: source,
        langcode: drupalSettings.langcode,
        replace_pattern: settings.replace_pattern,
        replace: settings.replace,
        lowercase: true
      });
    }
  };

})(jQuery, Drupal, drupalSettings);