<?php

class ComicPressDBInterface {
  var $_non_comic_categories, $_all_categories;

  function ComicPressDBInterface() {}
  
  function get_instance() {
    static $instance;
    
    if (!isset($instance)) { $instance = new ComicPressDBInterface(); }
    return $instance;
  }

  function _get_categories() { return get_categories("hide_empty=0"); }

  /**
   * Set the comic categories for the current run of ComicPress.
   */
  function set_comic_categories($categories) {
    $this->_all_categories       = get_all_category_ids();
    $this->_non_comic_categories = array_values(array_diff($this->_all_categories, $categories));
  }

  function _get_categories_to_exclude($category = null) {
    return (is_null($category)) ? $this->_non_comic_categories : array_values(array_diff($this->_all_categories, array($category)));
  }
  
  /**
   * Find the terminal post in a specific category.
   */
  function get_terminal_post_in_category($category_id, $first = true) {
    $this->_prepare_wp_query();
    
    $sort_order = $first ? "asc" : "desc";
    $terminal_comic_query = new WP_Query();
    $terminal_comic_query->query("showposts=1&order=${sort_order}&cat=${category_id}&status=publish");
    $post = false;
    if ($terminal_comic_query->have_posts()) {
      $post = reset($terminal_comic_query->posts);
    }

    $this->_reset_wp_query();
    return $post;
  }
  
  /**
   * Get the first comic in a category.
   */
  function get_first_comic($category_id) {
    return $this->get_terminal_post_in_category($category_id);
  }
  
  /**
   * Get the last comic in a category.
   */
  function get_last_comic($category_id) {
    return $this->get_terminal_post_in_category($category_id, false);  
  }

  /**
   * Get the comic post adjacent to the current comic.
   * Wrapper around get_adjacent_post(). Don't unit test this method.
   */
  function get_adjacent_comic($category, $next = false, $override_post = null) {
    global $post;

    $this->_prepare_wp_query();
    if (!is_null($override_post)) { $temp_post = $post; $post = $override_post; }
    
    $result = get_adjacent_post(false, implode(" and ", $this->_get_categories_to_exclude($category)), !$next);

    $this->_reset_wp_query();
    if (!is_null($override_post)) { $post = $temp_post; }

    return empty($result) ? false : $result;
  }

  function _prepare_wp_query() {
    global $wp_query;

    $this->is_single = $wp_query->is_single;
    $this->in_the_loop = $wp_query->in_the_loop;

    $wp_query->is_single = $wp_query->in_the_loop = true;
  }

  function _reset_wp_query() {
    global $wp_query;

    $wp_query->is_single = $this->is_single;
    $wp_query->in_the_loop = $this->in_the_loop;
  }
  
  /**
   * Get the previous comic from the current one.
   */
  function get_previous_comic($category = null, $override_post = null) { return $this->get_adjacent_comic($category, false, $override_post); }

  /**
   * Get the next comic from the current one.
   */
  function get_next_comic($category = null, $override_post = null) { return $this->get_adjacent_comic($category, true, $override_post); }
}

?>