function book_prev

Fetches the menu link for the previous page of the book.

Parameters

$book_link: A fully loaded menu link that is part of the book hierarchy.

Return value

A fully loaded menu link for the page before the one represented in $book_link.

File

modules/book/book.module, line 765

Code

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;
        }
    }
}