<?php
/**
 * Object Cache integration layer for Zone C (Cold) data.
 *
 * @package WP_Data_Optimizer
 */

declare(strict_types=1);

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Object Cache integration layer for Zone C (Cold) data.
 *
 * Provides a unified API for cache operations across all cold post types,
 * with bulk prefetch support for reducing DB queries on archive pages.
 *
 * This class sits on top of TMDO_Zone_Cold and adds:
 *   - Bulk prefetch for multiple posts (archive/search result pages)
 *   - Cache warming on post save
 *   - Cache statistics for admin dashboard
 *   - Group-level cache flush
 */
class TMDO_Cache_Layer {

	/**
	 * Prefetch cold data for multiple posts into Object Cache.
	 *
	 * Call this early on archive/search pages to batch-load cold blobs
	 * in a single query instead of N+1 queries per post.
	 *
	 * @param int[]  $post_ids  Array of post IDs to prefetch.
	 * @param string $post_type Post type.
	 */
	public static function prefetch( array $post_ids, string $post_type ): void {
		if ( empty( $post_ids ) ) {
			return;
		}

		$cold_keys = TMDO_Schema_Registry::instance()->get_cold_meta_keys( $post_type );
		if ( empty( $cold_keys ) ) {
			return;
		}

		$group = 'wpdo_cold_' . sanitize_key( $post_type );

		// Check which IDs are already cached.
		$uncached = array();
		foreach ( $post_ids as $pid ) {
			$cached = wp_cache_get( "cold_{$pid}", $group );
			if ( false === $cached ) {
				$uncached[] = (int) $pid;
			}
		}

		if ( empty( $uncached ) ) {
			return;
		}

		// Bulk fetch from cold table.
		global $wpdb;
		$table        = TMDO_Zone_Cold::table( $post_type );
		$placeholders = implode( ',', array_fill( 0, count( $uncached ), '%d' ) );

		// phpcs:disable WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare -- Table from TMDO_Zone_Cold::table(); $placeholders built from array_fill with %d.
		$rows = $wpdb->get_results(
			$wpdb->prepare(
				"SELECT post_id, data FROM `{$table}` WHERE post_id IN ({$placeholders})",
				...$uncached
			),
			ARRAY_A
		);
		// phpcs:enable WordPress.DB.PreparedSQL.InterpolatedNotPrepared,WordPress.DB.PreparedSQLPlaceholders.UnfinishedPrepare

		// Get cache TTL from registry.
		$fields = TMDO_Schema_Registry::instance()->get_zone_fields_for_type( 'cold', $post_type );
		$ttl    = HOUR_IN_SECONDS;
		foreach ( $fields as $field ) {
			if ( ! empty( $field['cache_ttl'] ) ) {
				$ttl = (int) $field['cache_ttl'];
				break;
			}
		}

		// Index fetched rows by post_id.
		$fetched = array();
		foreach ( $rows ?: array() as $row ) {
			$data                             = json_decode( $row['data'], true );
			$fetched[ (int) $row['post_id'] ] = is_array( $data ) ? $data : array();
		}

		// Cache all results (including empty arrays for posts with no cold data).
		foreach ( $uncached as $pid ) {
			$data = $fetched[ $pid ] ?? array();
			wp_cache_set( "cold_{$pid}", $data, $group, $ttl );
		}
	}

	/**
	 * Warm the cache for a single post after it's saved/updated.
	 *
	 * Hooked to 'save_post' to ensure fresh data is in cache.
	 *
	 * @param int    $post_id   Post ID.
	 * @param string $post_type Post type.
	 */
	public static function warm_post( int $post_id, string $post_type ): void {
		$cold_keys = TMDO_Schema_Registry::instance()->get_cold_meta_keys( $post_type );
		if ( empty( $cold_keys ) ) {
			return;
		}

		// Force a fresh read from DB (bypasses cache).
		$group = 'wpdo_cold_' . sanitize_key( $post_type );
		wp_cache_delete( "cold_{$post_id}", $group );

		// Re-read will populate cache.
		TMDO_Zone_Cold::get_blob( $post_id, $post_type );
	}

	/**
	 * Flush all cold cache for a post type.
	 *
	 * Useful after bulk imports or schema changes.
	 *
	 * @param string $post_type Post type to flush.
	 */
	public static function flush_group( string $post_type ): void {
		$group = 'wpdo_cold_' . sanitize_key( $post_type );

		if ( function_exists( 'wp_cache_flush_group' ) ) {
			wp_cache_flush_group( $group );
		}
		// If wp_cache_flush_group is not available (older WP or no object cache),
		// individual entries will expire via TTL.
	}

	/**
	 * Get cache statistics for the admin dashboard.
	 *
	 * @return array{groups: array, prefetch_support: bool}
	 */
	public static function get_stats(): array {
		$registry   = TMDO_Schema_Registry::instance();
		$cold_types = $registry->get_cold_post_types();
		$groups     = array();

		foreach ( $cold_types as $pt ) {
			$group  = 'wpdo_cold_' . sanitize_key( $pt );
			$keys   = $registry->get_cold_meta_keys( $pt );
			$fields = $registry->get_zone_fields_for_type( 'cold', $pt );
			$ttl    = HOUR_IN_SECONDS;
			foreach ( $fields as $field ) {
				if ( ! empty( $field['cache_ttl'] ) ) {
					$ttl = (int) $field['cache_ttl'];
					break;
				}
			}

			$groups[] = array(
				'post_type' => $pt,
				'group'     => $group,
				'meta_keys' => $keys,
				'ttl'       => $ttl,
			);
		}

		return array(
			'groups'           => $groups,
			'prefetch_support' => true,
			'flush_support'    => function_exists( 'wp_cache_flush_group' ),
		);
	}

	/**
	 * Register WordPress hooks for cache warming.
	 */
	public static function register_hooks(): void {
		add_action( 'save_post', array( __CLASS__, 'on_save_post' ), 99, 2 );

		// Prefetch on HivePress archive pages.
		add_action( 'loop_start', array( __CLASS__, 'on_loop_start' ), 10, 1 );
	}

	/**
	 * Warm cache after post save.
	 *
	 * @param int      $post_id Post ID.
	 * @param \WP_Post $post    Post object.
	 * @return void
	 */
	public static function on_save_post( int $post_id, \WP_Post $post ): void {
		if ( wp_is_post_revision( $post_id ) || wp_is_post_autosave( $post_id ) ) {
			return;
		}

		$cold_keys = TMDO_Schema_Registry::instance()->get_cold_meta_keys( $post->post_type );
		if ( ! empty( $cold_keys ) ) {
			self::warm_post( $post_id, $post->post_type );
		}
	}

	/**
	 * Prefetch cold data at the start of a main query loop.
	 *
	 * @param \WP_Query $query The current WP_Query object.
	 * @return void
	 */
	public static function on_loop_start( \WP_Query $query ): void {
		if ( ! $query->is_main_query() || is_admin() ) {
			return;
		}

		$posts = $query->posts;
		if ( empty( $posts ) ) {
			return;
		}

		$post_type = $query->get( 'post_type' );
		if ( is_array( $post_type ) ) {
			$post_type = reset( $post_type );
		}

		if ( ! $post_type ) {
			return;
		}

		$cold_keys = TMDO_Schema_Registry::instance()->get_cold_meta_keys( $post_type );
		if ( empty( $cold_keys ) ) {
			return;
		}

		$post_ids = wp_list_pluck( $posts, 'ID' );
		self::prefetch( $post_ids, $post_type );
	}
}