book.module

<?php
/**
 * @file
 * Allows users to create and organize related content in an outline.
 */

/**
 * Implements hook_theme().
 */
function book_theme() {
  $base = array(
    'file' => 'book.theme.inc',
  );

  return array(
    'book_navigation' => array(
      'variables' => array('book_link' => NULL),
      'template' => 'templates/book-navigation',
    ) + $base,
    'book_admin_table' => array(
      'render element' => 'form',
    ) + $base,
    'book_title_link' => array(
      'variables' => array('link' => NULL),
    ) + $base,
    'book_all_books_block' => array(
      'render element' => 'book_menus',
      'template' => 'templates/book-all-books-block',
    ) + $base,
  );
}

/**
 * Implements hook_permission().
 */
function book_permission() {
  return array(
    'administer book outlines' => array(
      'title' => t('Administer book outlines'),
    ),
    'create new books' => array(
      'title' => t('Create new books'),
    ),
    'add content to books' => array(
      'title' => t('Add content and child pages to books'),
    ),
  );
}

/**
 * Implements hook_config_info().
 */
function book_config_info() {
  $prefixes['book.settings'] = array(
    'label' => t('Book settings'),
    'group' => t('Configuration'),
  );
  return $prefixes;
}

/**
 * Implements hook_views_api().
 */
function book_views_api() {
  return array(
    'api' => '3.0',
    'path' => backdrop_get_path('module', 'book') . '/views',
  );
}

/**
 * Implements hook_autoload_info().
 */
function book_autoload_info() {
  return array(
    'views_plugin_argument_default_book_root' => 'views/views_plugin_argument_default_book_root.inc',
  );
}

/**
 * Adds relevant book links to the node's links.
 *
 * @param Node $node
 *   The book page node to add links to.
 * @param $view_mode
 *   The display mode of the node.
 */
function book_node_view_link(Node $node, $view_mode) {
  $links = array();
  $config = config('book.settings');
  $link_options = $config->get('book_links');

  if (isset($node->book['depth'])) {
    if ($view_mode == 'full' && node_is_page($node)) {
      $child_type = $config->get('book_child_type');
      $admin_access = user_access('add content to books') || user_access('administer book outlines');
      $link_options = $config->get('book_links');
      $create_access = node_access('create', $child_type);
      $depth_allowed = $node->book['depth'] < MENU_MAX_DEPTH;
      $show_add_child_link = in_array('book_add_child', $link_options, TRUE);
      $show_reorder_link = in_array('book_reorder', $link_options, TRUE);
      if ($admin_access && $create_access && $node->status == 1 && $depth_allowed && $show_add_child_link) {
        $links['book_add_child'] = array(
          'title' => t('Add child page'),
          'href' => 'node/add/' . str_replace('_', '-', $child_type),
          'query' => array('parent' => $node->book['mlid']),
        );
      }
      if (user_access('administer book outlines') && $show_reorder_link) {
        $links['book_reorder'] = array(
          'title' => t('Reorder book'),
          'href' => 'admin/content/book/' . $node->book['bid'],
        );
      }
    }
  }

  if (!empty($links)) {
    $node->content['links']['book'] = array(
      '#theme' => 'links__node__book',
      '#links' => $links,
      '#attributes' => array('class' => array('links', 'inline')),
    );
  }
}

/**
 * Implements hook_menu().
 */
function book_menu() {
  $items['admin/content/book'] = array(
    'title' => 'Manage Books',
    'description' => "Manage your site's book outlines.",
    'page callback' => 'book_admin_overview',
    'access arguments' => array('administer book outlines'),
    'type' => MENU_LOCAL_TASK,
    'file' => 'book.admin.inc',
  );
  $items['admin/content/book/list'] = array(
    'title' => 'List',
    'type' => MENU_DEFAULT_LOCAL_TASK,
  );
  $items['admin/content/book/settings'] = array(
    'title' => 'Settings',
    'page callback' => 'backdrop_get_form',
    'page arguments' => array('book_admin_settings'),
    'access arguments' => array('administer site configuration'),
    'type' => MENU_LOCAL_TASK,
    'weight' => 8,
    'file' => 'book.admin.inc',
  );
  $items['admin/content/book/%node'] = array(
    'title' => 'Re-order book pages and change titles',
    'page callback' => 'backdrop_get_form',
    'page arguments' => array('book_admin_edit', 3),
    'access callback' => '_book_outline_access',
    'access arguments' => array(3),
    'file' => 'book.admin.inc',
  );
  $items['book'] = array(
    'title' => 'Books',
    'page callback' => 'book_render',
    'access arguments' => array('access content'),
    'type' => MENU_SUGGESTED_ITEM,
    'file' => 'book.pages.inc',
  );
  $items['node/%node/outline-remove'] = array(
    'title' => 'Remove from book outline',
    'page callback' => 'backdrop_get_form',
    'page arguments' => array('book_remove_form', 1),
    'access callback' => '_book_outline_remove_access',
    'access arguments' => array(1),
    'file' => 'book.pages.inc',
  );

  return $items;
}

/**
 * Access callback: Determines if the outline tab is accessible.
 *
 * Path:
 * - admin/content/book/%node
 * - node/%node/outline
 *
 * @param Node $node
 *   The node whose outline tab is to be viewed.
 *
 * @see book_menu()
 */
function _book_outline_access(Node $node) {
  return user_access('administer book outlines') && node_access('view', $node);
}

/**
 * Access callback: Determines if the user can remove nodes from the outline.
 *
 * @param Node $node
 *   The node to remove from the outline.
 *
 * @see book_menu()
 */
function _book_outline_remove_access(Node $node) {
  return _book_node_is_removable($node) && _book_outline_access($node);
}

/**
 * Determines if a node can be removed from the book.
 *
 * A node can be removed from a book if it is actually in a book and it either
 * is not a top-level page or is a top-level page with no children.
 *
 * @param $node
 *   The node to remove from the outline.
 */
function _book_node_is_removable($node) {
  return (!empty($node->book['bid']) && (($node->book['bid'] != $node->nid) || !$node->book['has_children']));
}

/**
 * Implements hook_admin_paths().
 */
function book_admin_paths() {
  if (config_get('system.core', 'node_admin_theme')) {
    $paths = array(
      'node/*/outline-remove' => TRUE,
    );
    return $paths;
  }
}

/**
 * Implements hook_entity_info_alter().
 */
function book_entity_info_alter(&$info) {
  // Add the 'Print' display mode for nodes.
  $info['node']['view modes'] += array(
    'print' => array(
      'label' => t('Print'),
      'custom settings' => FALSE,
    ),
  );
}

/**
 * Implements hook_block_info().
 */
function book_block_info() {
  $blocks['navigation'] = array(
    'info' => t('Book navigation'),
    'description' => t('Shows the table of contents expanded to the current page if viewing book content.'),
    'cache' =>  BACKDROP_CACHE_PER_PAGE | BACKDROP_CACHE_PER_ROLE,
  );

  return $blocks;
}

/**
 * Implements hook_block_view().
 *
 * Displays the book table of contents in a block when the current page is a
 * single-node view of a book node.
 */
function book_block_view($delta = '', $settings = array()) {
  $block = array();
  $current_bid = 0;
  if ($node = menu_get_object()) {
    $current_bid = empty($node->book['bid']) ? 0 : $node->book['bid'];
  }

  if ($settings['book_mode'] == 'all pages') {
    $block['subject'] = t('Book navigation');
    $book_menus = array();
    $pseudo_tree = array(0 => array('below' => FALSE));
    foreach (book_get_books() as $book_id => $book) {
      if ($book['bid'] == $current_bid) {
        // If the current page is a node associated with a book, the menu
        // needs to be retrieved.
        $book_menus[$book_id] = menu_tree_output(menu_tree_all_data($node->book['menu_name'], $node->book));
      }
      else {
        // Since we know we will only display a link to the top node, there
        // is no reason to run an additional menu tree query for each book.
        $book['in_active_trail'] = FALSE;
        // Check whether user can access the book link.
        $book_node = node_load($book['nid']);
        $book['access'] = node_access('view', $book_node);
        $pseudo_tree[0]['link'] = $book;
        $book_menus[$book_id] = menu_tree_output($pseudo_tree);
      }
    }
    if ($block['content'] = $book_menus) {
      $book_menus['#theme'] = 'book_all_books_block';
    }
  }
  elseif ($current_bid) {
    // Only display this block when the user is browsing a book.
  $select = db_select('node', 'n')
    ->fields('n', array('title'))
    ->condition('n.nid', $node->book['bid'])
    ->addTag('node_access');
    $title = $select->execute()->fetchField();
    // Only show the block if the user has view access for the top-level node.
    if ($title) {
      $tree = menu_tree_all_data($node->book['menu_name'], $node->book);
      // There should only be one element at the top level.
      $data = array_shift($tree);
      $block['subject'] = l($data['link']['link_title'], $data['link']['link_path'], array('attributes' => array('class' => array('book-title'))));
      $block['content'] = ($data['below']) ? menu_tree_output($data['below']) : '';
    }
  }

  return $block;
}

/**
 * Implements hook_block_configure().
 */
function book_block_configure($delta = '', $settings = array()) {
  $settings += array(
    'book_mode' => 'all pages',
  );
  $options = array(
    'all pages' => t('Show block on all pages'),
    'book pages' => t('Show block only on book pages'),
  );
  $form['book_mode'] = array(
    '#type' => 'radios',
    '#title' => t('Book navigation block display'),
    '#options' => $options,
    '#default_value' => $settings['book_mode'],
  );
  $form['book_mode']['all pages']['#description'] = t("The block will contain the automatically generated menus for all of the site's books.");
  $form['book_mode']['book pages']['#description'] = t("The block will contain only the one menu corresponding to the current page's book. If the current page is not in a book, no block will be displayed.");

  return $form;
}

/**
 * Returns an array of all books.
 *
 * This list may be used for generating a list of all the books, or for building
 * the options for a form select.
 *
 * @return
 *   An array of all books.
 */
function book_get_books() {
  $all_books = &backdrop_static(__FUNCTION__);

  if (!isset($all_books)) {
    $all_books = array();
    $nids = db_query("SELECT DISTINCT(bid) FROM {book}")->fetchCol();

    if ($nids) {
      $query = db_select('book', 'b', array('fetch' => PDO::FETCH_ASSOC));
      $query->join('node', 'n', 'b.nid = n.nid');
      $query->join('menu_links', 'ml', 'b.mlid = ml.mlid');
      $query->addField('n', 'type', 'type');
      $query->addField('n', 'title', 'title');
      $query->fields('b');
      $query->fields('ml');
      $query->condition('n.nid', $nids, 'IN');
      $query->condition('n.status', 1);
      $query->orderBy('ml.weight');
      $query->orderBy('ml.link_title');
      $query->addTag('node_access');
      $result2 = $query->execute();
      foreach ($result2 as $link) {
        $link['href'] = $link['link_path'];
        $link['options'] = unserialize($link['options']);
        $all_books[$link['bid']] = $link;
      }
    }
  }

  return $all_books;
}

/**
 * Implements hook_form_BASE_FORM_ID_alter().
 *
 * Adds the book fieldset to the node form.
 *
 * @see book_pick_book_nojs_submit()
 */
function book_form_node_form_alter(&$form, &$form_state, $form_id) {
  $node = $form['#node'];
  $access = book_all_types_allowed();
  if (!$access) {
    if (user_access('add content to books') && ((!empty($node->book['mlid']) && !empty($node->nid)) || book_type_is_allowed($node->type))) {
      // Already in the book hierarchy, or this node type is allowed.
      $access = TRUE;
    }
  }

  if ($access) {
    _book_add_form_elements($form, $form_state, $node);
    // Since the "Book" dropdown can't trigger a form submission when
    // JavaScript is disabled, add a submit button to do that. book.admin.css hides
    // this button when JavaScript is enabled.
    $form['book']['pick-book'] = array(
      '#type' => 'submit',
      '#value' => t('Change book (update list of parents)'),
      '#submit' => array('book_pick_book_nojs_submit'),
      '#weight' => 20,
      '#attached' => array(
        'css' => array(backdrop_get_path('module', 'book') . '/css/book.admin.css'),
      ),
    );
    if (!empty($node->nid)) {
      $form['book']['actions'] = array(
        '#theme' => 'links',
        '#links' => array(),
        '#attributes' => array('class' => array('links', 'inline')),
        '#weight' => 40,
      );
      if (_book_outline_remove_access($node)) {
        $form['book']['actions']['#links']['remove'] = array(
          'title' => t('Remove from book outline'),
          'href' => 'node/' . $node->nid . '/outline-remove',
        );
      }
      if (!empty($node->book['bid']) && _book_outline_access($node)) {
        $form['book']['actions']['#links']['reorder'] = array(
          'title' => t('Reorder book pages'),
          'href' => 'admin/content/book/' . $node->book['bid'],
        );
      }
    }
  }
}

/**
 * Form submission handler for node_form().
 *
 * This handler is run when JavaScript is disabled. It triggers the form to
 * rebuild so that the "Parent item" options are changed to reflect the newly
 * selected book. When JavaScript is enabled, the submit button that triggers
 * this handler is hidden, and the "Book" dropdown directly triggers the
 * book_form_update() Ajax callback instead.
 *
 * @see book_form_update()
 * @see book_form_node_form_alter()
 */
function book_pick_book_nojs_submit($form, &$form_state) {
  $form_state['node']->book = $form_state['values']['book'];
  $form_state['rebuild'] = TRUE;
}

/**
 * Builds the parent selection form element for the node form or outline tab.
 *
 * This function is also called when generating a new set of options during the
 * Ajax callback, so an array is returned that can be used to replace an
 * existing form element.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   A parent selection form element.
 */
function _book_parent_select($book_link) {
  // Offer a message or a drop-down to choose a different parent page.
  $form = array(
    '#type' => 'hidden',
    '#value' => -1,
    '#prefix' => '<div id="edit-book-plid-wrapper">',
    '#suffix' => '</div>',
  );

  if ($book_link['nid'] === $book_link['bid']) {
    // This is a book - at the top level.
    if ($book_link['original_bid'] === $book_link['bid']) {
      $form['#prefix'] .= '<em>' . t('This is the top-level page in this book.') . '</em>';
    }
    else {
      $form['#prefix'] .= '<em>' . t('This will be the top-level page in this book.') . '</em>';
    }
  }
  elseif (!$book_link['bid']) {
    $form['#prefix'] .= '<em>' . t('No book selected.') . '</em>';
  }
  else {
    $form = array(
      '#type' => 'select',
      '#title' => t('Parent item'),
      '#default_value' => $book_link['plid'],
      '#description' => t('The parent page in the book. The maximum depth for a book and all child pages is !maxdepth. Some pages in the selected book may not be available as parents if selecting them would exceed this limit.', array('!maxdepth' => MENU_MAX_DEPTH)),
      '#options' => book_toc($book_link['bid'], $book_link['parent_depth_limit'], array($book_link['mlid'])),
      '#attributes' => array('class' => array('book-title-select')),
      '#prefix' => '<div id="edit-book-plid-wrapper">',
      '#suffix' => '</div>',
    );
  }

  return $form;
}

/**
 * Builds the common elements of the book form for the node and outline forms.
 *
 * @param Node $node
 *   The node whose form is being viewed.
 */
function _book_add_form_elements(&$form, &$form_state, Node $node) {
  // If the form is being processed during the Ajax callback of our book bid
  // dropdown, then $form_state will hold the value that was selected.
  if (isset($form_state['values']['book'])) {
    $node->book = $form_state['values']['book'];
  }

  $form['book'] = array(
    '#type' => 'fieldset',
    '#title' => t('Book outline'),
    '#weight' => 10,
    '#collapsible' => TRUE,
    '#collapsed' => TRUE,
    '#group' => 'additional_settings',
    '#attributes' => array(
      'class' => array('book-outline-form'),
    ),
    '#attached' => array(
      'js' => array(backdrop_get_path('module', 'book') . '/js/book.js'),
    ),
    '#tree' => TRUE,
  );
  foreach (array('menu_name', 'mlid', 'nid', 'router_path', 'has_children', 'options', 'module', 'original_bid', 'parent_depth_limit') as $key) {
    $form['book'][$key] = array(
      '#type' => 'value',
      '#value' => $node->book[$key],
    );
  }

  $form['book']['plid'] = _book_parent_select($node->book);

  // @see _book_admin_table_tree(). The weight may be larger than 15.
  $form['book']['weight'] = array(
    '#type' => 'number',
    '#title' => t('Weight'),
    '#default_value' => $node->book['weight'],
    '#weight' => 5,
    '#description' => t('Pages at a given level are ordered first by weight and then by title.'),
  );
  $options = array();
  $nid = isset($node->nid) ? $node->nid : 'new';

  if (isset($node->nid) && ($nid == $node->book['original_bid']) && ($node->book['parent_depth_limit'] == 0)) {
    // This is the top level node in a maximum depth book and thus cannot be moved.
    $options[$node->nid] = $node->title;
  }
  else {
    foreach (book_get_books() as $book) {
      $options[$book['nid']] = $book['title'];
    }
  }

  if (user_access('create new books') && ($nid == 'new' || ($nid != $node->book['original_bid']))) {
    // The node can become a new book, if it is not one already.
    $options = array($nid => '<' . t('create a new book') . '>') + $options;
  }
  if (!$node->book['mlid']) {
    // The node is not currently in the hierarchy.
    $options = array(0 => '<' . t('none') . '>') + $options;
  }

  // Add a drop-down to select the destination book.
  $form['book']['bid'] = array(
    '#type' => 'select',
    '#title' => t('Book'),
    '#default_value' => $node->book['bid'],
    '#options' => $options,
    '#access' => (bool) $options,
    '#description' => t('Your page will be a part of the selected book.'),
    '#weight' => -5,
    '#attributes' => array('class' => array('book-title-select')),
    '#ajax' => array(
      'callback' => 'book_form_update',
      'wrapper' => 'edit-book-plid-wrapper',
      'effect' => 'fade',
      'speed' => 'fast',
    ),
  );
}

/**
 * Renders a new parent page select element when the book selection changes.
 *
 * This function is called via Ajax when the selected book is changed on a node
 * or book outline form.
 *
 * @return
 *   The rendered parent page select element.
 */
function book_form_update($form, $form_state) {
  return $form['book']['plid'];
}

/**
 * Handles additions and updates to the book outline.
 *
 * This common helper function performs all additions and updates to the book
 * outline through node addition, node editing, node deletion, or the outline
 * tab.
 *
 * @param Node $node
 *   The node that is being saved, added, deleted, or moved.
 *
 * @return
 *   TRUE if the menu link was saved; FALSE otherwise.
 */
function _book_update_outline(Node $node) {
  if (empty($node->book['bid'])) {
    return FALSE;
  }
  $new = empty($node->book['mlid']);

  $node->book['link_path'] = 'node/' . $node->nid;
  $node->book['link_title'] = $node->title;
  $node->book['parent_mismatch'] = FALSE; // The normal case.

  if ($node->book['bid'] == $node->nid) {
    $node->book['plid'] = 0;
    $node->book['menu_name'] = book_menu_name($node->nid);
  }
  else {
    // Check in case the parent is not is this book; the book takes precedence.
    if (!empty($node->book['plid'])) {
      $parent = db_query("SELECT * FROM {book} WHERE mlid = :mlid", array(
        ':mlid' => $node->book['plid'],
      ))->fetchAssoc();
    }
    if (empty($node->book['plid']) || !$parent || $parent['bid'] != $node->book['bid']) {
      $node->book['plid'] = db_query("SELECT mlid FROM {book} WHERE nid = :nid", array(
        ':nid' => $node->book['bid'],
      ))->fetchField();
      $node->book['parent_mismatch'] = TRUE; // Likely when JS is disabled.
    }
  }

  if (menu_link_save($node->book)) {
    if ($new) {
      // Insert new.
      db_insert('book')
        ->fields(array(
          'nid' => $node->nid,
          'mlid' => $node->book['mlid'],
          'bid' => $node->book['bid'],
        ))
        ->execute();
      // Reset the cache of stored books.
      backdrop_static_reset('book_get_books');
    }
    else {
      if ($node->book['bid'] != db_query("SELECT bid FROM {book} WHERE nid = :nid", array(
          ':nid' => $node->nid,
        ))->fetchField()) {
        // Update the bid for this page and all children.
        book_update_bid($node->book);
        // Reset the cache of stored books.
        backdrop_static_reset('book_get_books');
      }
    }
    // Get all nodes that are part of this book and flush their caches.
    $affected_nids = db_query("SELECT nid FROM {book} WHERE bid = :bid", array(
      ':bid' => $node->book['bid'],
    ))->fetchAllAssoc('nid');
    entity_get_controller('node')->resetCache(array_keys($affected_nids));

    return TRUE;
  }

  // Failed to save the menu link.
  return FALSE;
}

/**
 * Updates the book ID of a page and its children when it moves to a new book.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 */
function book_update_bid($book_link) {
  $query = db_select('menu_links');
  $query->addField('menu_links', 'mlid');
  for ($i = 1; $i <= MENU_MAX_DEPTH && $book_link["p$i"]; $i++) {
    $query->condition("p$i", $book_link["p$i"]);
  }
  $mlids = $query->execute()->fetchCol();

  if ($mlids) {
    db_update('book')
      ->fields(array('bid' => $book_link['bid']))
      ->condition('mlid', $mlids, 'IN')
      ->execute();
  }
}

/**
 * Gets the book menu tree for a page and returns it as a linear array.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   A linear array of menu links in the order that the links are shown in the
 *   menu, so the previous and next pages are the elements before and after the
 *   element corresponding to the current node. The children of the current node
 *   (if any) will come immediately after it in the array, and links will only
 *   be fetched as deep as one level deeper than $book_link.
 */
function book_get_flat_menu($book_link) {
  $flat = &backdrop_static(__FUNCTION__, array());

  if (!isset($flat[$book_link['mlid']])) {
    // Call menu_tree_all_data() to take advantage of the menu system's caching.
    $tree = menu_tree_all_data($book_link['menu_name'], $book_link, $book_link['depth'] + 1);
    $flat[$book_link['mlid']] = array();
    _book_flatten_menu($tree, $flat[$book_link['mlid']]);
  }

  return $flat[$book_link['mlid']];
}

/**
 * Recursively converts a tree of menu links to a flat array.
 *
 * @param $tree
 *   A tree of menu links in an array.
 * @param $flat
 *   A flat array of the menu links from $tree, passed by reference.
 *
 * @see book_get_flat_menu().
 */
function _book_flatten_menu($tree, &$flat) {
  foreach ($tree as $data) {
    if (!$data['link']['hidden']) {
      $flat[$data['link']['mlid']] = $data['link'];
      if ($data['below']) {
        _book_flatten_menu($data['below'], $flat);
      }
    }
  }
}

/**
 * Fetches the menu link for the previous page of the book.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   A fully loaded menu link for the page before the one represented in
 *   $book_link.
 */
function book_prev($book_link) {
  // If the parent is zero, we are at the start of a book.
  if ($book_link['plid'] == 0) {
    return NULL;
  }
  $flat = book_get_flat_menu($book_link);
  reset($flat);
  $curr = NULL;
  do {
    $prev = $curr;
    $curr = current($flat);
    $key = key($flat);
    next($flat);
  } while ($key && $key != $book_link['mlid']);

  if ($key == $book_link['mlid']) {
    // The previous page in the book may be a child of the previous visible link.
    if ($prev['depth'] == $book_link['depth'] && $prev['has_children']) {
      // The subtree will have only one link at the top level - get its data.
      $tree = book_menu_subtree_data($prev);
      $data = array_shift($tree);
      // The link of interest is the last child - iterate to find the deepest one.
      while ($data['below']) {
        $data = end($data['below']);
      }

      return $data['link'];
    }
    else {
      return $prev;
    }
  }
}

/**
 * Fetches the menu link for the next page of the book.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   A fully loaded menu link for the page after the one represented in
 *   $book_link.
 */
function book_next($book_link) {
  $flat = book_get_flat_menu($book_link);
  reset($flat);
  do {
    $key = key($flat);
    next($flat);
  }
  while ($key && $key != $book_link['mlid']);

  if ($key == $book_link['mlid']) {
    return current($flat);
  }
}

/**
 * Formats the menu links for the child pages of the current page.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   HTML for the links to the child pages of the current page.
 */
function book_children($book_link) {
  $flat = book_get_flat_menu($book_link);

  $children = array();

  if ($book_link['has_children']) {
    // Walk through the array until we find the current page.
    do {
      $link = array_shift($flat);
    }
    while ($link && ($link['mlid'] != $book_link['mlid']));
    // Continue though the array and collect the links whose parent is this page.
    while (($link = array_shift($flat)) && $link['plid'] == $book_link['mlid']) {
      $data['link'] = $link;
      $data['below'] = '';
      $children[] = $data;
    }
  }

  if ($children) {
    $elements = menu_tree_output($children);
    return backdrop_render($elements);
  }
  return '';
}

/**
 * Generates the corresponding menu name from a book ID.
 *
 * @param $bid
 *   The book ID for which to make a menu name.
 *
 * @return
 *   The menu name.
 */
function book_menu_name($bid) {
  return 'book-toc-' . $bid;
}

/**
 * Implements hook_node_load().
 */
function book_node_load($nodes, $types) {
  $result = db_query("SELECT * FROM {book} b INNER JOIN {menu_links} ml ON b.mlid = ml.mlid WHERE b.nid IN (:nids)", array(':nids' =>  array_keys($nodes)), array('fetch' => PDO::FETCH_ASSOC));
  foreach ($result as $record) {
    $nodes[$record['nid']]->book = $record;
    $nodes[$record['nid']]->book['href'] = $record['link_path'];
    $nodes[$record['nid']]->book['title'] = $record['link_title'];
    $nodes[$record['nid']]->book['options'] = unserialize($record['options']);
  }
}

/**
 * Implements hook_node_view().
 */
function book_node_view(Node $node, $view_mode) {
  if ($view_mode == 'full') {
    if (!empty($node->book['bid']) && empty($node->in_preview) && config_get('book.settings', 'book_navigation')) {
      $node->content['book_navigation'] = array(
        '#markup' => theme('book_navigation', array('book_link' => $node->book)),
        '#weight' => 100,
        '#attached' => array(
          'css' => array(
            backdrop_get_path('module', 'book') . '/css/book.theme.css',
          ),
        ),
      );
    }
  }

  if ($view_mode != 'rss') {
    book_node_view_link($node, $view_mode);
  }
}

/**
 * Implements hook_init().
 *
 * Adds the book menu to the list of menus used to build the active trail when
 * viewing a book page.
 */
function book_init() {
  if (($node = menu_get_object()) && !empty($node->book['bid'])) {
    $active_menus = menu_get_active_menu_names();
    $active_menus[] = $node->book['menu_name'];
    menu_set_active_menu_names($active_menus);
  }
}

/**
 * Implements hook_node_presave().
 */
function book_node_presave(Node $node) {
  // Always save a revision for non-administrators.
  if (!empty($node->book['bid']) && !user_access('administer nodes')) {
    $node->revision = 1;
  }
  // Make sure a new node gets a new menu link.
  if (empty($node->nid)) {
    $node->book['mlid'] = NULL;
  }
}

/**
 * Implements hook_node_insert().
 */
function book_node_insert(Node $node) {
  if (!empty($node->book['bid'])) {
    if ($node->book['bid'] == 'new') {
      // New nodes that are their own book.
      $node->book['bid'] = $node->nid;
    }
    $node->book['nid'] = $node->nid;
    $node->book['menu_name'] = book_menu_name($node->book['bid']);
    _book_update_outline($node);
    $destination = backdrop_get_destination();
    if ($destination['destination'] != 'admin/content/book/' . $node->book['bid'] && _book_outline_access($node)) {
      backdrop_set_message(t('Reorder book pages from the <a href="@url">book outline</a>.', array('@url' => url('admin/content/book/' . $node->book['bid']))));
    }
  }
}

/**
 * Implements hook_node_update().
 */
function book_node_update(Node $node) {
  if (!empty($node->book['bid'])) {
    if ($node->book['bid'] == 'new') {
      // New nodes that are their own book.
      $node->book['bid'] = $node->nid;
    }
    $node->book['nid'] = $node->nid;
    $node->book['menu_name'] = book_menu_name($node->book['bid']);
    _book_update_outline($node);
    $destination = backdrop_get_destination();
    if ($destination['destination'] != 'admin/content/book/' . $node->book['bid'] && _book_outline_access($node)) {
      backdrop_set_message(t('Reorder book pages from the <a href="@url">book outline</a>.', array('@url' => url('admin/content/book/' . $node->book['bid']))));
    }
  }
}

/**
 * Implements hook_node_predelete().
 */
function book_node_predelete(Node $node) {
  if (!empty($node->book['bid'])) {
    if ($node->nid == $node->book['bid']) {
      // Handle deletion of a top-level post.
      $result = db_query("SELECT b.nid FROM {menu_links} ml INNER JOIN {book} b on b.mlid = ml.mlid WHERE ml.plid = :plid", array(
        ':plid' => $node->book['mlid']
      ));
      foreach ($result as $child) {
        $child_node = node_load($child->nid);
        $child_node->book['bid'] = $child_node->nid;
        _book_update_outline($child_node);
      }
    }
    menu_link_delete($node->book['mlid']);
    db_delete('book')
      ->condition('mlid', $node->book['mlid'])
      ->execute();
    backdrop_static_reset('book_get_books');
  }
}

/**
 * Implements hook_node_prepare().
 */
function book_node_prepare(Node $node) {
  // Prepare defaults for the add/edit form.
  if (empty($node->book) && (user_access('add content to books') || user_access('administer book outlines'))) {
    $node->book = array();

    if (empty($node->nid) && isset($_GET['parent']) && is_numeric($_GET['parent'])) {
      // Handle "Add child page" links:
      $parent = book_link_load($_GET['parent']);

      if ($parent && $parent['access']) {
        $node->book['bid'] = $parent['bid'];
        $node->book['plid'] = $parent['mlid'];
        $node->book['menu_name'] = $parent['menu_name'];
      }
    }
    // Set defaults.
    $node->book += _book_link_defaults(!empty($node->nid) ? $node->nid : 'new');
  }
  else {
    if (isset($node->book['bid']) && !isset($node->book['original_bid'])) {
      $node->book['original_bid'] = $node->book['bid'];
    }
  }
  // Find the depth limit for the parent select.
  if (isset($node->book['bid']) && !isset($node->book['parent_depth_limit'])) {
    $node->book['parent_depth_limit'] = _book_parent_depth_limit($node->book);
  }
}

/**
 * Finds the depth limit for items in the parent select.
 *
 * @param $book_link
 *   A fully loaded menu link that is part of the book hierarchy.
 *
 * @return
 *   The depth limit for items in the parent select.
 */
function _book_parent_depth_limit($book_link) {
  return MENU_MAX_DEPTH - 1 - (($book_link['mlid'] && $book_link['has_children']) ? menu_link_children_relative_depth($book_link) : 0);
}

/**
 * Implements hook_form_FORM_ID_alter().
 *
 * Alters the confirm form for a single node deletion.
 *
 * @see node_delete_confirm()
 */
function book_form_node_delete_confirm_alter(&$form, $form_state) {
  $node = node_load($form['nid']['#value']);

  if (isset($node->book) && $node->book['has_children']) {
    $form['book_warning'] = array(
      '#type' => 'help',
      '#markup' => t('%title is part of a book outline, and has associated child pages. If you proceed with deletion, the child pages will be relocated automatically.', array('%title' => $node->title)),
      '#weight' => -10,
    );
  }
}

/**
 * Returns an array with default values for a book page's menu link.
 *
 * @param $nid
 *   The ID of the node whose menu link is being created.
 *
 * @return
 *   The default values for the menu link.
 */
function _book_link_defaults($nid) {
  return array('original_bid' => 0, 'menu_name' => '', 'nid' => $nid, 'bid' => 0, 'router_path' => 'node/%', 'plid' => 0, 'mlid' => 0, 'has_children' => 0, 'weight' => 0, 'module' => 'book', 'options' => array());
}

 /**
 * Implements hook_preprocess_block().
 */
function book_preprocess_block(&$variables) {
  if ($variables['block']->module == 'book') {
    $variables['attributes']['role'] = 'navigation';
  }
}

/**
 * Recursively processes and formats menu items for book_toc().
 *
 * This helper function recursively modifies the table of contents array for
 * each item in the menu tree, ignoring items in the exclude array or at a depth
 * greater than the limit. Truncates titles over thirty characters and appends
 * an indentation string incremented by depth.
 *
 * @param $tree
 *   The data structure of the book's menu tree. Includes hidden links.
 * @param $indent
 *   A string appended to each menu item title. Increments by '--' per depth
 *   level.
 * @param $toc
 *   Reference to the table of contents array. This is modified in place, so the
 *   function does not have a return value.
 * @param $exclude
 *   (optional) An array of menu link ID values. Any link whose menu link ID is
 *   in this array will be excluded (along with its children). Defaults to an
 *   empty array.
 * @param $depth_limit
 *   Any link deeper than this value will be excluded (along with its children).
 */
function _book_toc_recurse($tree, $indent, &$toc, $exclude, $depth_limit) {
  foreach ($tree as $data) {
    if ($data['link']['depth'] > $depth_limit) {
      // Don't iterate through any links on this level.
      break;
    }

    if (!in_array($data['link']['mlid'], $exclude)) {
      $toc[$data['link']['mlid']] = $indent . ' ' . truncate_utf8($data['link']['title'], 30, TRUE, TRUE);
      if ($data['below']) {
        _book_toc_recurse($data['below'], $indent . '--', $toc, $exclude, $depth_limit);
      }
    }
  }
}

/**
 * Returns an array of book pages in table of contents order.
 *
 * @param $bid
 *   The ID of the book whose pages are to be listed.
 * @param $depth_limit
 *   Any link deeper than this value will be excluded (along with its children).
 * @param $exclude
 *   Optional array of menu link ID values. Any link whose menu link ID is in
 *   this array will be excluded (along with its children).
 *
 * @return
 *   An array of (menu link ID, title) pairs for use as options for selecting a
 *   book page.
 */
function book_toc($bid, $depth_limit, $exclude = array()) {
  $tree = menu_tree_all_data(book_menu_name($bid));
  $toc = array();
  _book_toc_recurse($tree, '', $toc, $exclude, $depth_limit);

  return $toc;
}

/**
 * Determine if a given node type is in the list of types allowed for books.
 *
 * @param $type
 *   A node type.
 *
 * @return
 *   A Boolean TRUE if the node type can be included in books; otherwise, FALSE.
 */
function book_type_is_allowed($type) {
  $book_allowed_types = array_filter(config_get('book.settings', 'book_allowed_types'));
  return in_array($type, $book_allowed_types);
}

/**
 * Determine if users are allowed to add any content type to books.
 *
 * @return bool
 *   A Boolean TRUE if all node types can be included in books for this user;
 *   otherwise, FALSE.
 */
function book_all_types_allowed() {
  return user_access('administer book outlines') && config_get('book.settings', 'book_admin_allowed_all');
}

/**
 * Implements hook_node_type_update().
 *
 * Updates the Book module's persistent variables if the machine-readable name
 * of a node type is changed.
 */
function book_node_type_update($type) {
  if (!empty($type->old_type) && $type->old_type != $type->type) {
    $config = config('book.settings');
    // Update the list of node types that are allowed to be added to books.
    $allowed_types = $config->get('book_allowed_types');
    $key = array_search($type->old_type, $allowed_types);

    if ($key !== FALSE) {
      $allowed_types[$type->type] = $allowed_types[$key] ? $type->type : 0;
      unset($allowed_types[$key]);
      $config->set('book_allowed_types', $allowed_types);
    }

    // Update the setting for the "Add child page" link.
    if ($config->get('book_child_type') == $type->old_type) {
      $config->set('book_child_type', $type->type);
    }
    $config->save();
  }
}

/**
 * Get a translated book menu link by its menu link ID.
 *
 * Like menu_link_load(), but adds additional data from the {book} table.
 *
 * Do not call when loading a node, since this function may call node_load().
 *
 * @param $mlid
 *   The menu link ID of the book menu item.
 *
 * @return
 *   A menu link, with the link translated for rendering and data added from the
 *   {book} table. EMPTY if there is no item. FALSE if there is an error.
 *
 * @see _menu_link_translate()
 */
function book_link_load($mlid, $skip_access_check = FALSE) {
  $cache = &backdrop_static(__FUNCTION__, array());

  if (!is_numeric($mlid)) {
    return FALSE;
  }

  if (!isset($cache[$mlid])) {
    $item = db_query("SELECT * FROM {menu_links} ml INNER JOIN {book} b ON b.mlid = ml.mlid LEFT JOIN {menu_router} m ON m.path = ml.router_path WHERE ml.mlid = :mlid", array(':mlid' => $mlid))->fetchAssoc();
    if (!empty($item)) {
      if ($skip_access_check) {
        $item['access'] = TRUE;
      }
      _menu_link_translate($item);
    }
    $cache[$mlid] = $item;
  }

  return $cache[$mlid];
}

/**
 * Gets the data representing a subtree of the book hierarchy.
 *
 * The root of the subtree will be the link passed as a parameter, so the
 * returned tree will contain this item and all its descendants in the menu
 * tree.
 *
 * @param $link
 *   A fully loaded menu link.
 *
 * @return
 *   A subtree of menu links in an array, in the order they should be rendered.
 */
function book_menu_subtree_data($link) {
  $tree = &backdrop_static(__FUNCTION__, array());

  // Generate a cache ID (cid) specific for this $menu_name and $link.
  $cid = 'links:' . $link['menu_name'] . ':subtree-cid:' . $link['mlid'];

  if (!isset($tree[$cid])) {
    $cache = cache('menu')->get($cid);

    if ($cache && isset($cache->data)) {
      // If the cache entry exists, it will just be the cid for the actual data.
      // This avoids duplication of large amounts of data.
      $cache = cache('menu')->get($cache->data);

      if ($cache && isset($cache->data)) {
        $data = $cache->data;
      }
    }

    // If the subtree data was not in the cache, $data will be NULL.
    if (!isset($data)) {
      $query = db_select('menu_links', 'ml', array('fetch' => PDO::FETCH_ASSOC));
      $query->join('menu_router', 'm', 'm.path = ml.router_path');
      $query->join('book', 'b', 'ml.mlid = b.mlid');
      $query->fields('b');
      $query->fields('m', array('load_functions', 'to_arg_functions', 'access_callback', 'access_arguments', 'page_callback', 'page_arguments', 'delivery_callback', 'title', 'title_callback', 'title_arguments', 'type'));
      $query->fields('ml');
      $query->condition('menu_name', $link['menu_name']);
      for ($i = 1; $i <= MENU_MAX_DEPTH && $link["p$i"]; ++$i) {
        $query->condition("p$i", $link["p$i"]);
      }
      for ($i = 1; $i <= MENU_MAX_DEPTH; ++$i) {
        $query->orderBy("p$i");
      }
      $links = array();
      foreach ($query->execute() as $item) {
        $links[] = $item;
      }
      $data['tree'] = menu_tree_data($links, array(), $link['depth']);
      $data['node_links'] = array();
      menu_tree_collect_node_links($data['tree'], $data['node_links']);
      // Compute the real cid for book subtree data.
      $tree_cid = 'links:' . $item['menu_name'] . ':subtree-data:' . hash('sha256', serialize($data));
      // Cache the data, if it is not already in the cache.

      if (!cache('menu')->get($tree_cid)) {
        cache('menu')->set($tree_cid, $data);
      }
      // Cache the cid of the (shared) data using the menu and item-specific cid.
      cache('menu')->set($cid, $tree_cid);
    }
    // Check access for the current user to each item in the tree.
    menu_tree_check_access($data['tree'], $data['node_links']);
    $tree[$cid] = $data['tree'];
  }

  return $tree[$cid];
}