book.module

<?php
// $Id$

/**
 * @file
 * Allows users to collaboratively author a book.
 */

/**
 * Implementation of hook_node_info().
 */
function book_node_info() {
  return array('book' => array('name' => t('book page'), 'base' => 'book'));
}

/**
 * Implementation of hook_perm().
 */
function book_perm() {
    return array('create book pages', 'maintain books', 'edit own book pages', 'see printer-friendly version');
}

/**
 * Implementation of hook_access().
 */
function book_access($op, $node) {
  global $user;

  if ($op == 'create') {
    // Only registered users can create book pages.  Given the nature
    // of the book module this is considered to be a good/safe idea.
    return user_access('create book pages');
  }

  if ($op == 'update') {
    // Only registered users can update book pages.  Given the nature
    // of the book module this is considered to be a good/safe idea.
    // One can only update a book page if there are no suggested updates
    // of that page waiting for approval.  That is, only updates that
    // don't overwrite the current or pending information are allowed.

    if ((user_access('maintain books') && !$node->moderate) || ($node->uid == $user->uid && user_access('edit own book pages'))) {
      return TRUE;
    }
    else {
       // do nothing. node-access() will determine further access
    }
  }
}

/**
 * Implementation of hook_link().
 */
function book_link($type, $node = 0, $main = 0) {

  $links = array();

  if ($type == 'node' && isset($node->parent)) {
    if (!$main) {
      if (book_access('create', $node)) {
        $links[] = l(t('add child page'), "node/add/book/parent/$node->nid");
      }
      if (user_access('see printer-friendly version')) {
        $links[] = l(t('printer-friendly version'),
                     'book/export/html/'. $node->nid,
                     array('title' => t('Show a printer-friendly version of this book page and its sub-pages.')));
      }
    }
  }

  return $links;
}

/**
 * Implementation of hook_menu().
 */
function book_menu($may_cache) {
  $items = array();

  if ($may_cache) {
    $items[] = array(
      'path' => 'book',
      'title' => t('books'),
      'access' => user_access('access content'),
      'type' => MENU_NORMAL_ITEM,
      'weight' => 5);
    $items[] = array(
      'path' => 'node/add/book',
      'title' => t('book page'),
      'access' => user_access('create book pages'));
    $items[] = array(
      'path' => 'admin/node/book',
      'title' => t('books'),
      'callback' => 'book_admin',
      'access' => user_access('administer nodes'),
      'type' => MENU_LOCAL_TASK,
      'weight' => -1);
    $items[] = array(
      'path' => 'admin/node/book/list',
      'title' => t('list'),
      'type' => MENU_DEFAULT_LOCAL_TASK);
    $items[] = array(
      'path' => 'admin/node/book/orphan',
      'title' => t('orphan pages'),
      'callback' => 'book_admin_orphan',
      'type' => MENU_LOCAL_TASK,
      'weight' => 8);
    $items[] = array(
      'path' => 'book',
      'title' => t('books'),
      'callback' => 'book_render',
      'access' => user_access('access content'),
      'type' => MENU_SUGGESTED_ITEM);
    $items[] = array(
      'path' => 'book/export',
      'callback' => 'book_export',
      'access' => user_access('access content'),
      'type' => MENU_CALLBACK);
  }
  else {
    // To avoid SQL overhead, check whether we are on a node page and whether the
    // user is allowed to maintain books.
    if (arg(0) == 'node' && is_numeric(arg(1)) && user_access('maintain books')) {
      // Only add the outline-tab for non-book pages:
      $result = db_query(db_rewrite_sql("SELECT n.nid FROM {node} n WHERE n.nid = %d AND n.type != 'book'"), arg(1));
      if (db_num_rows($result) > 0) {
        $items[] = array(
          'path' => 'node/'. arg(1) .'/outline',
          'title' => t('outline'),
          'callback' => 'book_outline',
          'access' => user_access('maintain books'),
          'type' => MENU_LOCAL_TASK,
          'weight' => 2);
      }
    }
  }

  return $items;
}

/**
 * Implementation of hook_block().
 *
 * 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($op = 'list', $delta = 0) {
  $block = array();
  if ($op == 'list') {
    $block[0]['info'] = t('Book navigation');
    return $block;
  }
  else if ($op == 'view') {
    // Only display this block when the user is browsing a book:
    if (arg(0) == 'node' && is_numeric(arg(1))) {
      $result = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.parent FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.nid = %d'), arg(1));
      if (db_num_rows($result) > 0) {
        $node = db_fetch_object($result);

        $path = book_location($node);
        $path[] = $node;

        $expand = array();
        foreach ($path as $key => $node) {
          $expand[] = $node->nid;
        }

        $block['subject'] = check_plain($path[0]->title);
        $block['content'] = book_tree($expand[0], 5, $expand);
      }
    }

    return $block;
  }
}

/**
 * Implementation of hook_load().
 */
function book_load($node) {
  global $user;

  $book = db_fetch_object(db_query('SELECT parent, weight FROM {book} WHERE vid = %d', $node->vid));

  if (arg(2) == 'edit' && !user_access('administer nodes')) {
    // If a user is about to update a book page, we overload some
    // fields to reflect the changes.
    if ($user->uid) {
      $book->uid = $user->uid;
      $book->name = $user->name;
    }
    else {
      $book->uid = 0;
      $book->name = '';
    }
  }

  return $book;
}

/**
 * Implementation of hook_insert().
 */
function book_insert($node) {
  db_query("INSERT INTO {book} (nid, vid, parent, weight) VALUES (%d, %d, %d, %d)", $node->nid, $node->vid, $node->parent, $node->weight);
}

/**
 * Implementation of hook_update().
 */
function book_update($node) {
  if ($node->revision) {
    db_query("INSERT INTO {book} (nid, vid, parent, weight) VALUES (%d, %d, %d, %d)", $node->nid, $node->vid, $node->parent, $node->weight);
  }
  else {
    db_query("UPDATE {book} SET parent = %d, weight = %d WHERE vid = %d", $node->parent, $node->weight, $node->vid);
  }
}

/**
 * Implementation of hook_delete().
 */
function book_delete(&$node) {
  db_query('DELETE FROM {book} WHERE nid = %d', $node->nid);
}

/**
 * Implementation of hook_submit().
 */
function book_submit(&$node) {
  // Set default values for non-administrators.
  if (!user_access('administer nodes')) {
    $node->weight = 0;
    $node->revision = 1;
  }
}

/**
 * Implementation of hook_validate().
 */
function book_validate($node) {
  node_validate_title($node);
}

/**
 * Implementation of hook_form().
 */
function book_form(&$node) {
  $form['parent'] = array(
    '#type' => 'select', '#title' => t('Parent'), '#default_value' => ($node->parent ? $node->parent : arg(4)), '#options' => book_toc($node->nid), '#weight' => -4,
    '#description' => t('The parent that this page belongs in. Note that pages whose parent is &lt;top-level&gt; are regarded as independent, top-level books.')
  );

  $form['title'] = array('#type' => 'textfield', '#title' => t('Title'), '#required' => TRUE, '#default_value' => $node->title, '#weight' => -5);
  $form['body_filter']['body'] = array('#type' => 'textarea', '#title' => t('Body'), '#default_value' => $node->body, '#rows' => 20, '#required' => TRUE);
  $form['body_filter']['format'] = filter_form($node->format);

  $form['log'] = array(
    '#type' => 'textarea', '#title' => t('Log message'), '#default_value' => $node->log, '#weight' => 5,
    '#description' => t('An explanation of the additions or updates being made to help other authors understand your motivations.')
  );

  if (user_access('administer nodes')) {
    $form['weight'] = array(
        '#type' => 'weight', '#title' => t('Weight'), '#default_value' => $node->weight, '#delta' => 15, '#weight' => 5,
        '#description' => t('Pages at a given level are ordered first by weight and then by title.')
    );
  }
  else {
    // If a regular user updates a book page, we create a new revision
    // authored by that user:
    $form['revision'] = array('#type' => 'hidden', '#value' => 1);
  }

  return $form;
}

/**
 * Implementation of function book_outline()
 * Handles all book outline operations.
 */
function book_outline() {

  $op = $_POST['op'];
  $edit = $_POST['edit'];
  $node = node_load(arg(1));

  if ($node->nid) {
    switch ($op) {
      case t('Add to book outline'):
        db_query('INSERT INTO {book} (nid, vid, parent, weight) VALUES (%d, %d, %d, %d)', $node->nid, $node->vid, $edit['parent'], $edit['weight']);
        db_query("UPDATE {node_revisions} SET log = '%s' WHERE vid = %d", $edit['log'], $node->vid);
        drupal_set_message(t('The post has been added to the book.'));
        drupal_goto("node/$node->nid");
        break;

      case t('Update book outline'):
        db_query('UPDATE {book} SET parent = %d, weight = %d WHERE vid = %d', $edit['parent'], $edit['weight'], $node->vid);
        db_query("UPDATE {node_revisions} SET log = '%s' WHERE vid = %d", $edit['log'], $node->vid);
        drupal_set_message(t('The book outline has been updated.'));
        drupal_goto("node/$node->nid");
        break;

      case t('Remove from book outline'):
        db_query('DELETE FROM {book} WHERE nid = %d', $node->nid);
        drupal_set_message(t('The post has been removed from the book.'));
        drupal_goto("node/$node->nid");
        break;

      default:
        $page = db_fetch_object(db_query('SELECT * FROM {book} WHERE vid = %d', $node->vid));

        $form['parent'] = array(
          '#type' => 'select', '#title' => t('Parent'), '#default_value' => $page->parent,
          '#options' => book_toc($node->nid), '#description' => t('The parent page in the book.')
        );

        $form['weight'] = array(
          '#type' => 'weight', '#title' => t('Weight'), '#default_value' => $page->weight, '#delta' => 15,
          '#description' => t('Pages at a given level are ordered first by weight and then by title.')
        );

        $form['log'] = array(
          '#type' => 'textarea', '#title' => t('Log message'),
          '#default_value' => $node->log, '#description' => t('An explanation to help other authors understand your motivations to put this post into the book.')
        );

        if ($page->nid) {
          $form['update'] = array('#type' => 'submit', '#value' => t('Update book outline'));
          $form['remove'] = array('#type' => 'submit', '#value' => t('Remove from book outline'));
        }
        else {
          $form['add'] = array('#type' => 'submit', '#value' => t('Add to book outline'));
        }

        drupal_set_title(check_plain($node->title));
        return drupal_get_form('book_outline', $form);
    }
  }
}

/**
 * Return the path (call stack) to a certain book page.
 */
function book_location($node, $nodes = array()) {
  $parent = db_fetch_object(db_query(db_rewrite_sql('SELECT n.nid, n.title, b.parent, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.nid = %d'), $node->parent));
  if ($parent->title) {
    $nodes = book_location($parent, $nodes);
    array_push($nodes, $parent);
  }
  return $nodes;
}

/**
 * Accumulates the nodes up to the root of the book from the given node in the $nodes array.
 */
function book_location_down($node, $nodes = array()) {
  $last_direct_child = db_fetch_object(db_query(db_rewrite_sql('SELECT n.nid, n.title, b.parent, b.weight FROM {node} n INNER JOIN {book} b ON n.nid = b.nid WHERE n.status = 1 AND b.parent = %d ORDER BY b.weight DESC, n.title DESC'), $node->nid));
  if ($last_direct_child) {
    array_push($nodes, $last_direct_child);
    $nodes = book_location_down($last_direct_child, $nodes);
  }
  return $nodes;
}

/**
 * Fetches the node object of the previous page of the book.
 */
function book_prev($node) {
  // If the parent is zero, we are at the start of a book so there is no previous.
  if ($node->parent == 0) {
    return NULL;
  }

  // Previous on the same level:
  $direct_above = db_fetch_object(db_query(db_rewrite_sql("SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE b.parent = %d AND n.status = 1 AND n.moderate = 0 AND (b.weight < %d OR (b.weight = %d AND n.title < '%s')) ORDER BY b.weight DESC, n.title DESC"), $node->parent, $node->weight, $node->weight, $node->title));
  if ($direct_above) {
    // Get last leaf of $above.
    $path = book_location_down($direct_above);

    return $path ? (count($path) > 0 ? array_pop($path) : NULL) : $direct_above;
  }
  else {
    // Direct parent:
    $prev = db_fetch_object(db_query(db_rewrite_sql('SELECT n.nid, n.title FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.nid = %d AND n.status = 1 AND n.moderate = 0'), $node->parent));
    return $prev;
  }
}

/**
 * Fetches the node object of the next page of the book.
 */
function book_next($node) {
  // get first direct child
  $child = db_fetch_object(db_query(db_rewrite_sql('SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE b.parent = %d AND n.status = 1 AND n.moderate = 0 ORDER BY b.weight ASC, n.title ASC'), $node->nid));
  if ($child) {
    return $child;
  }

  // No direct child: get next for this level or any parent in this book.
  array_push($path = book_location($node), $node); // Path to top-level node including this one.

  while (($leaf = array_pop($path)) && count($path)) {
    $next = db_fetch_object(db_query(db_rewrite_sql("SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE b.parent = %d AND n.status = 1 AND n.moderate = 0 AND (b.weight > %d OR (b.weight = %d AND n.title > '%s')) ORDER BY b.weight ASC, n.title ASC"), $leaf->parent, $leaf->weight, $leaf->weight, $leaf->title));
    if ($next) {
      return $next;
    }
  }
}

/**
 * Returns the content of a given node.  If $teaser if true, returns
 * the teaser rather than full content.  Displays the most recently
 * approved revision of a node (if any) unless we have to display this
 * page in the context of the moderation queue.
 */
function book_content($node, $teaser = FALSE) {
  $op = $_POST['op'];

  // Extract the page body.
  $node = node_prepare($node, $teaser);

  return $node;
}

/**
 * Implementation of hook_view().
 *
 * If not displayed on the main page, we render the node as a page in the
 * book with extra links to the previous and next pages.
 */
function book_view(&$node, $teaser = FALSE, $page = FALSE) {
  $node = book_content($node, $teaser);
}

/**
 * Implementation of hook_nodeapi().
 *
 * Appends book navigation to all nodes in the book.
 */
function book_nodeapi(&$node, $op, $teaser, $page) {
  switch ($op) {
    case 'view':
      if (!$teaser) {
        $book = db_fetch_array(db_query('SELECT * FROM {book} WHERE vid = %d', $node->vid));
        if ($book) {
          if ($node->moderate && user_access('administer nodes')) {
            drupal_set_message(t("The post has been submitted for moderation and won't be accessible until it has been approved."));
          }

          foreach ($book as $key => $value) {
            $node->$key = $value;
          }

          $path = book_location($node);
          // Construct the breadcrumb:
          $node->breadcrumb = array(); // Overwrite the trail with a book trail.
          foreach ($path as $level) {
            $node->breadcrumb[] = array('path' => 'node/'. $level->nid, 'title' =>  $level->title);
          }
          $node->breadcrumb[] = array('path' => 'node/'. $node->nid);

          $node->body .= theme('book_navigation', $node);

          if ($page) {
            menu_set_location($node->breadcrumb);
          }
        }
      }
      break;
    case 'delete revision':
      db_query('DELETE FROM {book} WHERE vid = %d', $node->vid);
      break;
  }
}

/**
 * Prepares both the custom breadcrumb trail and the forward/backward
 * navigation for a node presented as a book page.
 *
 * @ingroup themeable
 */
function theme_book_navigation($node) {
  if ($node->nid) {
    $output .= '<div class="book">';

    if ($tree = book_tree($node->nid)) {
      $output .= '<div class="tree">'. $tree .'</div>';
    }

    if ($prev = book_prev($node)) {
      drupal_add_link(array('rel' => 'prev', 'href' => url('node/'. $prev->nid)));
      $links .= '<div class="prev">';
      $links .= l(t('previous'), 'node/'. $prev->nid, array('title' => t('View the previous page.')));
      $links .= '</div>';
      $titles .= '<div class="prev">'. check_plain($prev->title) .'</div>';
    }
    else {
      $links .= '<div class="prev">&nbsp;</div>'; // Make an empty div to fill the space.
    }
    if ($next = book_next($node)) {
      drupal_add_link(array('rel' => 'next', 'href' => url('node/'. $next->nid)));
      $links .= '<div class="next">';
      $links .= l(t('next'), 'node/'. $next->nid, array('title' => t('View the next page.')));
      $links .= '</div>';
      $titles .= '<div class="next">'. check_plain($next->title) .'</div>';
    }
    else {
      $links .= '<div class="next">&nbsp;</div>'; // Make an empty div to fill the space.
    }
    if ($node->parent) {
      drupal_add_link(array('rel' => 'index', 'href' => url('node/'. $node->parent)));
      $links .= '<div class="up">';
      $links .= l(t('up'), 'node/'. $node->parent, array('title' => t('View this page\'s parent section.')));
      $links .= '</div>';
    }

    $output .= '<div class="nav">';
    $output .= ' <div class="links">'. $links .'</div>';
    $output .= ' <div class="titles">'. $titles .'</div>';
    $output .= '</div>';
    $output .= '</div>';
  }

  return $output;
}

/**
 * This is a helper function for book_toc().
 */
function book_toc_recurse($nid, $indent, $toc, $children, $exclude) {
  if ($children[$nid]) {
    foreach ($children[$nid] as $foo => $node) {
      if (!$exclude || $exclude != $node->nid) {
        $toc[$node->nid] = $indent .' '. $node->title;
        $toc = book_toc_recurse($node->nid, $indent .'--', $toc, $children, $exclude);
      }
    }
  }

  return $toc;
}

/**
 * Returns an array of titles and nid entries of book pages in table of contents order.
 */
function book_toc($exclude = 0) {
  $result = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.parent, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.status = 1 ORDER BY b.weight, n.title'));

  while ($node = db_fetch_object($result)) {
    if (!$children[$node->parent]) {
      $children[$node->parent] = array();
    }
    array_push($children[$node->parent], $node);
  }

  $toc = array();

  // If the user is an administrator, add the top-level book page;
  // only administrators can start new books.
  if (user_access('administer nodes')) {
    $toc[0] = '<'. t('top-level') .'>';
  }

  $toc = book_toc_recurse(0, '', $toc, $children, $exclude);

  return $toc;
}

/**
 * This is a helper function for book_tree()
 */
function book_tree_recurse($nid, $depth, $children, $unfold = array()) {
  if ($depth > 0) {
    if ($children[$nid]) {
      foreach ($children[$nid] as $foo => $node) {
        if (in_array($node->nid, $unfold)) {
          if ($tree = book_tree_recurse($node->nid, $depth - 1, $children, $unfold)) {
            $output .= '<li class="expanded">';
            $output .= l($node->title, 'node/'. $node->nid);
            $output .= '<ul>'. $tree .'</ul>';
            $output .= '</li>';
          }
          else {
            $output .= '<li class="leaf">'. l($node->title, 'node/'. $node->nid) .'</li>';
          }
        }
        else {
          if ($tree = book_tree_recurse($node->nid, 1, $children)) {
            $output .= '<li class="collapsed">'. l($node->title, 'node/'. $node->nid) .'</li>';
          }
          else {
            $output .= '<li class="leaf">'. l($node->title, 'node/'. $node->nid) .'</li>';
          }
        }
      }
    }
  }

  return $output;
}

/**
 * Returns an HTML nested list (wrapped in a menu-class div) representing the book nodes
 * as a tree.
 */
function book_tree($parent = 0, $depth = 3, $unfold = array()) {
  $result = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.parent, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.status = 1 AND n.moderate = 0 ORDER BY b.weight, n.title'));

  while ($node = db_fetch_object($result)) {
    $list = $children[$node->parent] ? $children[$node->parent] : array();
    array_push($list, $node);
    $children[$node->parent] = $list;
  }

  if ($tree = book_tree_recurse($parent, $depth, $children, $unfold)) {
    return '<ul class="menu">'. $tree .'</ul>';
  }
}

/**
 * Menu callback; prints a listing of all books.
 */
function book_render() {
  $result = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE b.parent = 0 AND n.status = 1 AND n.moderate = 0 ORDER BY b.weight, n.title'));

  $books = array();
  while ($node = db_fetch_object($result)) {
    $books[] = l($node->title, 'node/'. $node->nid);
  }

  return theme('item_list', $books);
}

/**
 * Menu callback; Generates various representation of a book page with
 * all descendants and prints the requested representation to output.
 *
 * The function delegates the generation of output to helper functions.
 * The function name is derived by prepending 'book_export_' to the
 * given output type.  So, e.g., a type of 'html' results in a call to
 * the function book_export_html().
 *
 * @param type
 *   - a string encoding the type of output requested.
 *       The following types are currently supported in book module
 *          html: HTML (printer friendly output)
 *       Other types are supported in contributed modules.
 * @param nid
 *   - an integer representing the node id (nid) of the node to export
 *
 */
function book_export($type = 'html', $nid = 0) {
  $type = drupal_strtolower($type);
  $depth = _book_get_depth($nid);
  $export_function = 'book_export_' . $type;

  if (function_exists($export_function)) {
    print call_user_func($export_function, $nid, $depth);
  }
  else {
    drupal_set_message('Unknown export format');
    drupal_not_found();
  }
}

/**
 * This function is called by book_export() to generate HTML for export.
 *
 * The given node is /embedded to its absolute depth in a top level
 * section/.  For example, a child node with depth 2 in the hierarchy
 * is contained in (otherwise empty) &lt;div&gt; elements
 * corresponding to depth 0 and depth 1.  This is intended to support
 * WYSIWYG output - e.g., level 3 sections always look like level 3
 * sections, no matter their depth relative to the node selected to be
 * exported as printer-friendly HTML.
 *
 * @param nid
 *   - an integer representing the node id (nid) of the node to export
 * @param depth
 * - an integer giving the depth in the book hierarchy of the node
       which is to be exported
 * @return
 * - string containing HTML representing the node and its children in
       the book hierarchy
*/
function book_export_html($nid, $depth) {
  if (user_access('see printer-friendly version')) {
    global $base_url;
    for ($i = 1; $i < $depth; $i++) {
      $output .= "<div class=\"section-$i\">\n";
    }
    $output .= book_recurse($nid, $depth, 'book_node_visitor_html_pre', 'book_node_visitor_html_post');
    for ($i = 1; $i < $depth; $i++) {
      $output .= "</div>\n";

    }
    $html = "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\n";
    $html .= '<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">';
    $html .= "<head>\n<title>". check_plain($node->title) ."</title>\n";
    $html .= '<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />';
    $html .= '<base href="'. $base_url .'/" />' . "\n";
    $html .= "<style type=\"text/css\">\n@import url(misc/print.css);\n</style>\n";
    $html .= "</head>\n<body>\n". $output . "\n</body>\n</html>\n";
    return $html;
  }
  else {
    drupal_access_denied();
  }
}

/**
 * How the book's HTML export should be themed
 *
 * @ingroup themeable
 */
function theme_book_export_html($title, $content) {
  global $base_url;
  $html = "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">\n";
  $html .= '<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">';
  $html .= "<head>\n<title>". $title ."</title>\n";
  $html .= '<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />';
  $html .= '<base href="'. $base_url .'/" />' . "\n";
  $html .= "<style type=\"text/css\">\n@import url(misc/print.css);\n</style>\n";
  $html .= "</head>\n<body>\n". $content . "\n</body>\n</html>\n";
  return $html;
}

/**
 * Given a node, this function returns the depth of the node in its hierarchy.
 * A root node has depth 1, and children of a node of depth n have depth (n+1).
 *
 * @param nid
 *   - the nid of the node whose depth to compute.
 * @return
 *   - the depth of the given node in its hierarchy.  Returns 0 if the node
 *  does not exist or is not part of a book hierarchy.
 */
function _book_get_depth($nid) {
  $depth = 0;
  if ($nid) {
    while ($nid) {
      $result = db_query(db_rewrite_sql('SELECT b.parent FROM {book} b WHERE b.nid = %d'), $nid);
      $obj =  db_fetch_object($result);
      $parent = $obj->parent;
      if ($nid == $parent->parent) {
        $nid = 0;
      }
      else {
        $nid = $parent;
      }
      $depth++;
    }
    return $depth;
  }
  else {
    return 0;
  }
}

/**
 * Traverses the book tree.  Applies the $visit_pre() callback to each
 * node, is called recursively for each child of the node (in weight,
 * title order).  Finally appends the output of the $visit_post()
 * callback to the output before returning the generated output.
 *
 * @param nid
 *  - the node id (nid) of the root node of the book hierarchy.
 * @param depth
 *  - the depth of the given node in the book hierarchy.
 * @param visit_pre
 *  - a function callback to be called upon visiting a node in the tree
 * @param visit_post
 *  - a function callback to be called after visiting a node in the tree,
 *    but before recursively visiting children.
 * @return
 *  - the output generated in visiting each node
 */
function book_recurse($nid = 0, $depth = 1, $visit_pre, $visit_post) {
  $result = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.status = 1 AND n.nid = %d AND n.moderate = 0 ORDER BY b.weight, n.title'), $nid);
  while ($page = db_fetch_object($result)) {
    // Load the node:
    $node = node_load($page->nid);

    if ($node) {
      if (function_exists($visit_pre)) {
        $output .= call_user_func($visit_pre, $node, $depth, $nid);
      }
      else {
        $output .= book_node_visitor_html_pre($node, $depth, $nid);
      }

      $children = db_query(db_rewrite_sql('SELECT n.nid, n.title, b.weight FROM {node} n INNER JOIN {book} b ON n.vid = b.vid WHERE n.status = 1 AND b.parent = %d AND n.moderate = 0 ORDER BY b.weight, n.title'), $node->nid);
      while ($childpage = db_fetch_object($children)) {
          $childnode = node_load($childpage->nid);
          if ($childnode->nid != $node->nid) {
              $output .= book_recurse($childnode->nid, $depth + 1, $visit_pre, $visit_post);
          }
      }
      if (function_exists($visit_post)) {
        $output .= call_user_func($visit_post, $node, $depth);
      }
      else {
        # default
        $output .= book_node_visitor_html_post($node, $depth);
      }
    }
  }

  return $output;
}

/**
 * Generates printer-friendly HTML for a node.  This function
 * is a 'pre-node' visitor function for book_recurse().
 *
 * @param $node
 *   - the node to generate output for.
 * @param $depth
 *   - the depth of the given node in the hierarchy. This
 *   is used only for generating output.
 * @param $nid
 *   - the node id (nid) of the given node. This
 *   is used only for generating output.
 * @return
 *   - the HTML generated for the given node.
 */
function book_node_visitor_html_pre($node, $depth, $nid) {
  // Output the content:
  if (node_hook($node, 'content')) {
    $node = node_invoke($node, 'content');
  }
  // Allow modules to change $node->body before viewing.
  node_invoke_nodeapi($node, 'print', $node->