class BBP_Skip_Children {

	/**
	 * @var int Post ID being updated
	 */
	private $updating_post = 0;

	/**
	 * @var bool The original value of $_wp_suspend_cache_invalidation global
	 */
	private $original_cache_invalidation = false;

	/** Methods ***************************************************************/

	/**
	 * Hook into the 'pre_post_update' action.
	 *
	 * @since 2.1.0 bbPress (r4011)
	 */
	public function __construct() {
		add_action( 'pre_post_update', array( $this, 'pre_post_update' ) );
	}

	/**
	 * Only clean post caches for main bbPress posts.
	 *
	 * Check that the post being updated is a bbPress post type, saves the
	 * post ID to be used later, and adds an action to 'clean_post_cache' that
	 * prevents child post caches from being cleared.
	 *
	 * @since 2.1.0 bbPress (r4011)
	 *
	 * @param int $post_id The post ID being updated
	 * @return If invalid post data
	 */
	public function pre_post_update( $post_id = 0 ) {

		// Bail if post ID is not a bbPress post type
		if ( empty( $post_id ) || ! bbp_is_custom_post_type( $post_id ) ) {
			return;
		}

		// Store the $post_id
		$this->updating_post = $post_id;

		// Skip related post cache invalidation. This prevents invalidating the
		// caches of the child posts when there is no reason to do so.
		add_action( 'clean_post_cache', array( $this, 'skip_related_posts' ) );
	}

	/**
	 * Skip cache invalidation of related posts if the post ID being invalidated
	 * is not the one that was just updated.
	 *
	 * @since 2.1.0 bbPress (r4011)
	 *
	 * @param int $post_id The post ID of the cache being invalidated
	 * @return If invalid post data
	 */
	public function skip_related_posts( $post_id = 0 ) {

		// Bail if this post is not the current bbPress post
		if ( empty( $post_id ) || ( $this->updating_post !== $post_id ) ) {
			return;
		}

		// Stash the current cache invalidation value in a variable, so we can
		// restore back to it nicely in the future.
		global $_wp_suspend_cache_invalidation;

		$this->original_cache_invalidation = $_wp_suspend_cache_invalidation;

		// Turn off cache invalidation
		wp_suspend_cache_invalidation( true );

		// Restore cache invalidation
		add_action( 'wp_insert_post', array( $this, 'restore_cache_invalidation' ) );
	}

	/**
	 * Restore the cache invalidation to its previous value.
	 *
	 * @since 2.1.0 bbPress (r4011)
	 */
	public function restore_cache_invalidation() {
		wp_suspend_cache_invalidation( $this->original_cache_invalidation );
	}
}