/**
 * @file
 * Autocomplete based on jQuery UI.
 */

(function ($, Drupal) {
  let autocomplete;

  /**
   * Helper splitting terms from the autocomplete value.
   *
   * @function Drupal.autocomplete.splitValues
   *
   * @param {string} value
   *   The value being entered by the user.
   *
   * @return {Array}
   *   Array of values, split by comma.
   */
  function autocompleteSplitValues(value) {
    // We will match the value against comma-separated terms.
    const result = [];
    let quote = false;
    let current = '';
    const valueLength = value.length;
    let character;

    for (let i = 0; i < valueLength; i++) {
      character = value.charAt(i);
      if (character === '"') {
        current += character;
        quote = !quote;
      }
      else if (character === ',' && !quote) {
        result.push(current.trim());
        current = '';
      }
      else {
        current += character;
      }
    }
    if (value.length > 0) {
      result.push($.trim(current));
    }

    return result;
  }

  /**
   * Returns the last value of an multi-value textfield.
   *
   * @function Drupal.autocomplete.extractLastTerm
   *
   * @param {string} terms
   *   The value of the field.
   *
   * @return {string}
   *   The last value of the input field.
   */
  function extractLastTerm(terms) {
    return autocomplete.splitValues(terms).pop();
  }

  /**
   * The search handler is called before a search is performed.
   *
   * @function Drupal.autocomplete.options.search
   *
   * @param {object} event
   *   The event triggered.
   *
   * @return {bool}
   *   Whether to perform a search or not.
   */
  function searchHandler(event) {
    const options = autocomplete.options;

    if (options.isComposing) {
      return false;
    }

    const term = autocomplete.extractLastTerm(event.target.value);
    // Abort search if the first character is in firstCharacterBlacklist.
    if (term.length > 0 && options.firstCharacterBlacklist.indexOf(term[0]) !== -1) {
      return false;
    }
    // Only search when the term is at least the minimum length.
    return term.length >= options.minLength;
  }

  /**
   * JQuery UI autocomplete source callback.
   *
   * @param {object} request
   *   The request object.
   * @param {function} response
   *   The function to call with the response.
   */
  function sourceData(request, response) {
    const elementId = this.element.attr('id');

    if (!(elementId in autocomplete.cache)) {
      autocomplete.cache[elementId] = {};
    }

    /**
     * Filter through the suggestions removing all terms already tagged and
     * display the available terms to the user.
     *
     * @param {object} suggestions
     *   Suggestions returned by the server.
     */
    function showSuggestions(suggestions) {
      const tagged = autocomplete.splitValues(request.term);
      const il = tagged.length;
      for (let i = 0; i < il; i++) {
        const index = suggestions.indexOf(tagged[i]);
        if (index >= 0) {
          suggestions.splice(index, 1);
        }
      }
      response(suggestions);
    }

    /**
     * Transforms the data object into an array and update autocomplete results.
     *
     * @param {object} data
     *   The data sent back from the server.
     */
    function sourceCallbackHandler(data) {
      autocomplete.cache[elementId][term] = data;

      // Send the new string array of terms to the jQuery UI list.
      showSuggestions(data);
    }

    // Get the desired term and construct the autocomplete URL for it.
    const term = autocomplete.extractLastTerm(request.term);

    // Check if the term is already cached.
    if (autocomplete.cache[elementId].hasOwnProperty(term)) {
      showSuggestions(autocomplete.cache[elementId][term]);
    }
    else {
      const options = $.extend({ success: sourceCallbackHandler, data: { q: term } }, autocomplete.ajax);
      $.ajax(this.element.attr('data-autocomplete-path'), options);
    }
  }

  /**
   * Handles an autocompletefocus event.
   *
   * @return {bool}
   *   Always returns false.
   */
  function focusHandler() {
    return false;
  }

  /**
   * Handles an autocompleteselect event.
   *
   * @param {jQuery.Event} event
   *   The event triggered.
   * @param {object} ui
   *   The jQuery UI settings object.
   *
   * @return {bool}
   *   Returns false to indicate the event status.
   */
  function selectHandler(event, ui) {
    const terms = autocomplete.splitValues(event.target.value);
    // Remove the current input.
    terms.pop();
    // Add the selected item.
    terms.push(ui.item.value);

    event.target.value = terms.join(', ');
    // Return false to tell jQuery UI that we've filled in the value already.
    return false;
  }

  /**
   * Override jQuery UI _renderItem function to output HTML by default.
   *
   * @param {jQuery} ul
   *   jQuery collection of the ul element.
   * @param {object} item
   *   The list item to append.
   *
   * @return {jQuery}
   *   jQuery collection of the ul element.
   */
  function renderItem(ul, item) {
    return $('<li>')
      .append($('<a>').html(item.label))
      .appendTo(ul);
  }

  /**
   * Attaches the autocomplete behavior to all required fields.
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Attaches the autocomplete behaviors.
   * @prop {Drupal~behaviorDetach} detach
   *   Detaches the autocomplete behaviors.
   */
  Drupal.behaviors.autocomplete = {
    attach(context) {
      // Act on textfields with the "form-autocomplete" class.
      const $autocomplete = $(context).find('input.form-autocomplete').once('autocomplete');
      if ($autocomplete.length) {
        // Allow options to be overriden per instance.
        const blacklist = $autocomplete.attr('data-autocomplete-first-character-blacklist');
        $.extend(autocomplete.options, {
          firstCharacterBlacklist: (blacklist) || '',
        });
        // Use jQuery UI Autocomplete on the textfield.
        $autocomplete.autocomplete(autocomplete.options)
          .each(function () {
            $(this).data('ui-autocomplete')._renderItem = autocomplete.options.renderItem;
          });

        // Use CompositionEvent to handle IME inputs. It requests remote server on "compositionend" event only.
        $autocomplete.on('compositionstart.autocomplete', () => {
          autocomplete.options.isComposing = true;
        });
        $autocomplete.on('compositionend.autocomplete', () => {
          autocomplete.options.isComposing = false;
        });
      }
    },
    detach(context, settings, trigger) {
      if (trigger === 'unload') {
        $(context).find('input.form-autocomplete')
          .removeOnce('autocomplete')
          .autocomplete('destroy');
      }
    },
  };

  /**
   * Autocomplete object implementation.
   *
   * @namespace Drupal.autocomplete
   */
  autocomplete = {
    cache: {},
    // Exposes options to allow overriding by contrib.
    splitValues: autocompleteSplitValues,
    extractLastTerm,
    // jQuery UI autocomplete options.

    /**
     * JQuery UI option object.
     *
     * @name Drupal.autocomplete.options
     */
    options: {
      source: sourceData,
      focus: focusHandler,
      search: searchHandler,
      select: selectHandler,
      renderItem,
      minLength: 1,
      // Custom options, used by Drupal.autocomplete.
      firstCharacterBlacklist: '',
      // Custom options, indicate IME usage status.
      isComposing: false,
    },
    ajax: {
      dataType: 'json',
    },
  };

  Drupal.autocomplete = autocomplete;
}(jQuery, Drupal));