<?php

namespace Drupal\search_api\Contrib;

use Drupal\search_api\Query\QueryInterface;
use Drupal\search_api\Backend\BackendInterface;
use Drupal\search_api_autocomplete\SearchInterface;

/**
 * Describes the method a backend plugin has to add to support autocompletion.
 *
 * In addition, the backend has to include "search_api_autocomplete" in the
 * return value of its getSupportedFeatures() implementation.
 *
 * This interface is present on behalf of the Search API Autocomplete
 * (search_api_autocomplete) module.
 */
interface AutocompleteBackendInterface extends BackendInterface {

  /**
   * Retrieves autocompletion suggestions for some user input.
   *
   * @param \Drupal\search_api\Query\QueryInterface $query
   *   A query representing the base search, with all completely entered words
   *   in the user input so far as the search keys.
   * @param \Drupal\search_api_autocomplete\SearchInterface $search
   *   An object containing details about the search the user is on, and
   *   settings for the autocompletion. See the class documentation for details.
   *   Especially $search->getOptions() should be checked for settings, like
   *   whether to try and estimate result counts for returned suggestions.
   * @param string $incomplete_key
   *   The start of another fulltext keyword for the search, which should be
   *   completed. Might be empty, in which case all user input up to now was
   *   considered completed. Then, additional keywords for the search could be
   *   suggested.
   * @param string $user_input
   *   The complete user input for the fulltext search keywords so far.
   *
   * @return \Drupal\search_api_autocomplete\Suggestion\SuggestionInterface[]
   *   An array of autocomplete suggestions.
   */
  public function getAutocompleteSuggestions(QueryInterface $query, SearchInterface $search, string $incomplete_key, string $user_input): array;

}