<?php
/**
 * Related-ID cache.
 *
 * Relationship queries are the expensive part of a related-content plugin, so the
 * resolved ID list for (display, source post) is stored in post meta and only
 * regenerated when the post, its terms, or the Display configuration change.
 *
 * @package Stunning_Related
 */

defined( 'ABSPATH' ) || exit;

/**
 * Cache layer.
 */
class SRPP_Cache {

	const META_PREFIX  = '_srpp_rel_';
	const VERSION_OPT  = 'srpp_cache_version';

	/**
	 * Hook invalidation events.
	 */
	public static function init() {
		add_action( 'save_post', array( __CLASS__, 'on_save_post' ), 20, 2 );
		add_action( 'deleted_post', array( __CLASS__, 'flush_post' ) );
		add_action( 'set_object_terms', array( __CLASS__, 'on_set_terms' ), 10, 4 );
		add_action( 'transition_post_status', array( __CLASS__, 'on_transition' ), 10, 3 );
		add_action( 'srpp_settings_saved', array( __CLASS__, 'flush_all' ) );
	}

	/**
	 * Current global cache version.
	 *
	 * @return int
	 */
	public static function version() {
		return (int) get_option( self::VERSION_OPT, 1 );
	}

	/**
	 * Bump the global version, invalidating every stored list at once.
	 */
	public static function flush_all() {
		update_option( self::VERSION_OPT, self::version() + 1, false );
	}

	/**
	 * Remove every cached list for one post.
	 *
	 * @param int $post_id Post ID.
	 */
	public static function flush_post( $post_id ) {
		global $wpdb;

		$post_id = absint( $post_id );
		if ( ! $post_id ) {
			return;
		}

		// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Bulk meta delete by key pattern has no core API; the post_meta cache is cleared right after.
		$wpdb->query(
			$wpdb->prepare(
				"DELETE FROM {$wpdb->postmeta} WHERE post_id = %d AND meta_key LIKE %s",
				$post_id,
				$wpdb->esc_like( self::META_PREFIX ) . '%'
			)
		);
		// phpcs:enable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching

		wp_cache_delete( $post_id, 'post_meta' );
	}

	/**
	 * Purge every cached list in the database.
	 */
	public static function purge_database() {
		global $wpdb;

		// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Bulk meta delete by key pattern has no core API; the object cache is flushed right after.
		$wpdb->query(
			$wpdb->prepare(
				"DELETE FROM {$wpdb->postmeta} WHERE meta_key LIKE %s",
				$wpdb->esc_like( self::META_PREFIX ) . '%'
			)
		);
		// phpcs:enable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching

		wp_cache_flush();
		self::flush_all();
	}

	/**
	 * Invalidate when a post is saved.
	 *
	 * @param int     $post_id Post ID.
	 * @param WP_Post $post    Post object.
	 */
	public static function on_save_post( $post_id, $post ) {
		if ( wp_is_post_revision( $post_id ) || wp_is_post_autosave( $post_id ) ) {
			return;
		}

		if ( SRPP_CPT === $post->post_type ) {
			self::flush_all();
			return;
		}

		self::flush_post( $post_id );
	}

	/**
	 * Terms changed — relatedness for other posts may change too.
	 *
	 * @param int    $object_id Object ID.
	 * @param array  $terms     Terms.
	 * @param array  $tt_ids    Term taxonomy IDs.
	 * @param string $taxonomy  Taxonomy.
	 */
	public static function on_set_terms( $object_id, $terms, $tt_ids, $taxonomy ) {
		unset( $terms, $tt_ids );

		$tax = get_taxonomy( $taxonomy );
		if ( ! $tax || ! $tax->public ) {
			return;
		}

		self::flush_post( $object_id );
		self::flush_all();
	}

	/**
	 * Publish/unpublish changes candidate pools.
	 *
	 * @param string  $new New status.
	 * @param string  $old Old status.
	 * @param WP_Post $post Post.
	 */
	public static function on_transition( $new, $old, $post ) {
		if ( $new === $old || SRPP_CPT === $post->post_type ) {
			return;
		}

		if ( 'publish' === $new || 'publish' === $old ) {
			self::flush_all();
		}
	}

	/**
	 * Signature of a Display's relevant configuration.
	 *
	 * @param SRPP_Display $display Display.
	 * @return string
	 */
	public static function signature( $display ) {
		$relevant = array(
			$display->opt( 'target_types' ),
			$display->opt( 'selection_mode' ),
			$display->opt( 'manual_ids' ),
			$display->opt( 'relate_by' ),
			$display->opt( 'engine' ),
			$display->opt( 'weights' ),
			$display->opt( 'recency_days' ),
			$display->opt( 'fallback' ),
			$display->opt( 'cross_match' ),
			$display->opt( 'order' ),
			$display->opt( 'items' ),
			$display->opt( 'ex_current' ),
			$display->opt( 'ex_password' ),
			$display->opt( 'ex_private' ),
			$display->opt( 'ex_noindex' ),
			$display->opt( 'ex_outofstock' ),
			$display->opt( 'ex_terms' ),
			$display->opt( 'ex_authors' ),
			$display->opt( 'ex_ids' ),
		);

		return substr( md5( wp_json_encode( $relevant ) ), 0, 12 );
	}

	/**
	 * Read a cached ID list.
	 *
	 * @param SRPP_Display $display   Display.
	 * @param int          $source_id Source post ID.
	 * @return array|false
	 */
	public static function get( $display, $source_id ) {
		if ( ! srpp_get_option( 'cache_enabled', 1 ) ) {
			return false;
		}

		$ttl = (int) $display->opt( 'cache_ttl', DAY_IN_SECONDS );
		if ( $ttl <= 0 ) {
			return false;
		}

		$entry = get_post_meta( $source_id, self::META_PREFIX . $display->id, true );

		if ( ! is_array( $entry ) || ! isset( $entry['ids'], $entry['h'], $entry['t'], $entry['v'] ) ) {
			return false;
		}

		if ( (int) $entry['v'] !== self::version() ) {
			return false;
		}

		if ( $entry['h'] !== self::signature( $display ) ) {
			return false;
		}

		if ( ( time() - (int) $entry['t'] ) > $ttl ) {
			return false;
		}

		return array_map( 'absint', (array) $entry['ids'] );
	}

	/**
	 * Store an ID list.
	 *
	 * @param SRPP_Display $display   Display.
	 * @param int          $source_id Source post ID.
	 * @param array        $ids       Resolved IDs.
	 */
	public static function set( $display, $source_id, $ids ) {
		if ( ! srpp_get_option( 'cache_enabled', 1 ) || (int) $display->opt( 'cache_ttl' ) <= 0 ) {
			return;
		}

		update_post_meta(
			$source_id,
			self::META_PREFIX . $display->id,
			array(
				'v'   => self::version(),
				'h'   => self::signature( $display ),
				't'   => time(),
				'ids' => array_map( 'absint', $ids ),
			)
		);
	}

	/**
	 * How many cached rows exist (for the Tools screen).
	 *
	 * @return int
	 */
	public static function count_rows() {
		global $wpdb;

		$key   = 'srpp_cached_rows';
		$count = wp_cache_get( $key, 'srpp' );

		if ( false !== $count ) {
			return (int) $count;
		}

		// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Counting meta by key pattern has no core API; the result is cached below.
		$count = (int) $wpdb->get_var(
			$wpdb->prepare(
				"SELECT COUNT(*) FROM {$wpdb->postmeta} WHERE meta_key LIKE %s",
				$wpdb->esc_like( self::META_PREFIX ) . '%'
			)
		);
		// phpcs:enable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching

		wp_cache_set( $key, $count, 'srpp', 5 * MINUTE_IN_SECONDS );

		return $count;
	}
}