bibcite_footnotes_2/footnotes.module

<?php

/**
 * @file
 * This file contains the hooks for Footnotes module.
 *
 * The Footnotes module is a filter that can be used to insert
 * automatically numbered footnotes into Drupal texts.
 */

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Url;

/**
 * Implements hook_help().
 */
function footnotes_help($route_name, RouteMatchInterface $route_match) {
  switch ($route_name) {
    case 'help.page.footnotes':
      return t("Insert automatically numbered footnotes using &lt;fn&gt; or [fn] tags. Enable the footnotes text filter <a href=':href'>here</a>", [
        ':href' => Url::fromRoute('filter.admin_overview')->toString(),
      ]);
  }
}

/**
 * Implements hook_theme().
 *
 * Thanks to emfabric for this implementation. http://drupal.org/node/221156
 */
function footnotes_theme() {
  return [
    'footnote_link' => [
      'variables' => [
        'fn'    => NULL,
      ],
    ],
    'footnote_list' => [
      'variables' => [
        'footnotes'=> NULL,
      ],
    ],
  ];
}


/**
 * Helper for other filters, check if Footnotes is present in your filter chain.
 *
 * Note: Due to changes in Filter API, the arguments to this function have
 * changed in Drupal 7.
 *
 * Other filters may leverage the Footnotes functionality in a simple way:
 * by outputting markup with <fn>...</fn> tags within.
 *
 * This creates a dependency, the Footnotes filter must be present later in
 * "Input format". By calling this helper function the other filters that
 * depend on Footnotes may check whether Footnotes is present later in the chain
 * of filters in the current Input format.
 *
 * If this function returns true, the caller may depend on Footnotes. Function
 * returns false if caller may not depend on Footnotes.
 *
 * You should also put "dependencies = footnotes" in your module.info file.
 *
 * Example usage:
 * <code>
 * _filter_example_process( $text, $filter, $format ) {
 *   ...
 *   if(footnotes_is_footnotes_later($format, $filter)) {
 *     //output markup which may include [fn] tags
 *   }
 *   else {
 *     // must make do without footnotes features
 *     // can also emit warning/error that user should install and configure
 *     // footnotes module
 *   }
 *   ...
 * }
 * </code>
 *
 * @param object $format
 *   The text format object caller is part of.
 * @param object $caller_filter
 *   The filter object representing the caller (in this text format).
 *
 * @return True
 *   If Footnotes is present after $caller in $format.
 */
function footnotes_is_footnotes_later($format, $caller_filter) {
  return $format['filter_footnotes']['weight'] > $caller_filter['weight'];
}