<?php
/**
 * Object cache for docs data (tree, popular lists).
 *
 * @package KarmaDocs
 */

namespace KarmaDocs;

defined( 'ABSPATH' ) || exit;

/**
 * Cached values are keyed on a docs-specific "last changed" version that is bumped
 * only when docs structure or display data changes.
 *
 * WordPress' own posts last-changed key is not used on purpose: it changes on every
 * post meta update, and the view counter writes post meta on every page view, which
 * would invalidate the cache constantly.
 *
 * With a persistent object cache (Redis, Memcached) entries survive across requests;
 * without one they still dedupe work within a request.
 */
class Cache {

	/**
	 * Cache group.
	 */
	const GROUP = 'kdocs';

	/**
	 * Post meta keys that affect cached output (icons, access, ordering hints).
	 */
	const POST_META = array( '_kdocs_icon', '_kdocs_access', '_kdocs_roles', '_kdocs_featured' );

	/**
	 * Hooks that invalidate.
	 */
	public function register() {
		add_action( 'save_post_' . PostTypes::ARTICLE, array( __CLASS__, 'flush' ) );
		add_action( 'deleted_post', array( $this, 'on_post_change' ) );
		add_action( 'trashed_post', array( $this, 'on_post_change' ) );
		add_action( 'untrashed_post', array( $this, 'on_post_change' ) );
		add_action( 'transition_post_status', array( $this, 'on_transition' ), 10, 3 );
		add_action( 'set_object_terms', array( $this, 'on_set_terms' ), 10, 4 );

		foreach ( array( Taxonomies::KB, Taxonomies::CATEGORY ) as $taxonomy ) {
			add_action( 'created_' . $taxonomy, array( __CLASS__, 'flush' ) );
			add_action( 'edited_' . $taxonomy, array( __CLASS__, 'flush' ) );
			add_action( 'delete_' . $taxonomy, array( __CLASS__, 'flush' ) );
		}
		foreach ( array( 'added_term_meta', 'updated_term_meta', 'deleted_term_meta' ) as $hook ) {
			add_action( $hook, array( $this, 'on_term_meta' ), 10, 3 );
		}
		foreach ( array( 'added_post_meta', 'updated_post_meta', 'deleted_post_meta' ) as $hook ) {
			add_action( $hook, array( $this, 'on_post_meta' ), 10, 3 );
		}

		add_action( 'kdocs_tree_saved', array( __CLASS__, 'flush' ) );
		add_action( 'update_option_' . Settings::OPTION, array( __CLASS__, 'flush' ) );
		add_action( 'update_option_permalink_structure', array( __CLASS__, 'flush' ) );
	}

	/**
	 * Current docs data version.
	 *
	 * @return string
	 */
	public static function version() {
		return wp_cache_get_last_changed( self::GROUP );
	}

	/**
	 * Invalidates every cached docs value.
	 */
	public static function flush() {
		wp_cache_set_last_changed( self::GROUP );
	}

	/**
	 * Reads a value cached for the current docs version.
	 *
	 * @param string $key Key (without version).
	 * @return mixed|false
	 */
	public static function get( $key ) {
		return wp_cache_get( self::key( $key ), self::GROUP );
	}

	/**
	 * Stores a value for the current docs version.
	 *
	 * @param string $key    Key (without version).
	 * @param mixed  $value  Value.
	 * @param int    $expire Seconds (0 = until the version changes).
	 */
	public static function set( $key, $value, $expire = 0 ) {
		wp_cache_set( self::key( $key ), $value, self::GROUP, $expire );
	}

	/**
	 * Returns a cached value or computes and stores it.
	 *
	 * @param string   $key      Key (without version).
	 * @param callable $callback Producer.
	 * @param int      $expire   Seconds (0 = until the version changes).
	 * @return mixed
	 */
	public static function remember( $key, callable $callback, $expire = 0 ) {
		$value = self::get( $key );
		if ( false === $value ) {
			$value = $callback();
			self::set( $key, $value, $expire );
		}
		return $value;
	}

	/**
	 * Versioned key.
	 *
	 * @param string $key Key.
	 * @return string
	 */
	private static function key( $key ) {
		return $key . ':' . self::version();
	}

	/**
	 * Post deleted / trashed / restored.
	 *
	 * @param int $post_id Post.
	 */
	public function on_post_change( $post_id ) {
		if ( PostTypes::ARTICLE === get_post_type( $post_id ) ) {
			self::flush();
		}
	}

	/**
	 * Status changes (publish / unpublish).
	 *
	 * @param string   $new_status New.
	 * @param string   $old_status Old.
	 * @param \WP_Post $post       Post.
	 */
	public function on_transition( $new_status, $old_status, $post ) {
		if ( $new_status !== $old_status && PostTypes::ARTICLE === $post->post_type ) {
			self::flush();
		}
	}

	/**
	 * KB / category assignments.
	 *
	 * @param int    $object_id Object.
	 * @param array  $terms     Terms.
	 * @param array  $tt_ids    Term taxonomy ids.
	 * @param string $taxonomy  Taxonomy.
	 */
	public function on_set_terms( $object_id, $terms, $tt_ids, $taxonomy ) {
		if ( in_array( $taxonomy, array( Taxonomies::KB, Taxonomies::CATEGORY ), true ) ) {
			self::flush();
		}
	}

	/**
	 * Term meta (order, icon, color, KB assignment).
	 *
	 * @param int|array $meta_id   Meta id(s).
	 * @param int       $object_id Term.
	 * @param string    $meta_key  Key.
	 */
	public function on_term_meta( $meta_id, $object_id, $meta_key ) {
		if ( 0 === strpos( (string) $meta_key, 'kdocs_' ) ) {
			self::flush();
		}
	}

	/**
	 * Post meta that changes how articles are listed (not views / votes).
	 *
	 * @param int|array $meta_id   Meta id(s).
	 * @param int       $object_id Post.
	 * @param string    $meta_key  Key.
	 */
	public function on_post_meta( $meta_id, $object_id, $meta_key ) {
		if ( in_array( $meta_key, self::POST_META, true ) ) {
			self::flush();
		}
	}
}