<?php
/**
 * Comment query router for HivePress comment-type models.
 *
 * Rewrites `WP_Comment_Query` SQL clauses to JOIN the per-addon shadow tables
 * built by Sprint 2 adapters. Currently handles four `comment_type` values:
 *
 *   hp_message  → wp_wpdo_comment_hp_message    (recipient_id, is_read indexed)
 *   hp_favorite → wp_wpdo_comment_hp_favorite   (UNIQUE user_id+listing_id)
 *   hp_offer    → wp_wpdo_comment_hp_offer      (request_id, approved indexed)
 *   hp_review   → wp_wpdo_comment_hp_review     (managed by entity-bridge)
 *
 * Disabled by default. Operator opts in via:
 *
 *   wp option update wpdo_hivepress_comment_router_enabled 1
 *
 * Once enabled, comment queries with `type` matching one of the above gain a
 * shadow-table LEFT JOIN at `comments_clauses` filter time. The JOIN is
 * deliberately LEFT so missing shadow rows (during dual_write phase before
 * backfill completes) don't drop legitimate comments.
 *
 * Per Karpathy guideline: this router only handles the four comment_types
 * Sprint 2 actually needs — no extension hooks for "future addons".
 *
 * @package WP_Data_Optimizer
 * @since   3.0.0
 */

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

if ( ! class_exists( 'TMDO_HivePress_Comment_Router' ) ) {

	/**
	 * Comment query rewriter.
	 *
	 * Single-instance, registered via static `register()`. Stateless apart from
	 * the option-cached enabled flag.
	 */
	final class TMDO_HivePress_Comment_Router {

		/** Option key controlling the rewriter. */
		public const OPTION_ENABLED = 'wpdo_hivepress_comment_router_enabled';

		/**
		 * Map of comment_type → shadow table (without wpdb prefix).
		 *
		 * @var array<string,string>
		 */
		private const SHADOW_MAP = array(
			'hp_message'  => 'wpdo_comment_hp_message',
			'hp_favorite' => 'wpdo_comment_hp_favorite',
			'hp_offer'    => 'wpdo_comment_hp_offer',
			'hp_review'   => 'wpdo_comment_hp_review',
		);

		/**
		 * Whether the router is bound this request.
		 *
		 * @var bool
		 */
		private static bool $bound = false;

		/**
		 * Bind the comments_clauses filter (idempotent).
		 *
		 * Bootstrap calls this from each adapter's on_register_query_hooks()
		 * so router activation follows the same gate as adapter binding.
		 */
		public static function register(): void {
			if ( self::$bound ) {
				return;
			}
			if ( ! self::is_enabled() ) {
				return;
			}
			add_filter( 'comments_clauses', array( __CLASS__, 'rewrite' ), 20, 2 );
			self::$bound = true;
		}

		/**
		 * Reset internal state (test only).
		 *
		 * @internal
		 */
		public static function reset_for_tests(): void {
			self::$bound = false;
		}

		/**
		 * Whether router is enabled via the operator option.
		 */
		public static function is_enabled(): bool {
			if ( ! function_exists( 'get_option' ) ) {
				return false;
			}
			return (bool) (int) get_option( self::OPTION_ENABLED, 0 );
		}

		/**
		 * Filter callback: rewrite comments_clauses for known hp comment types.
		 *
		 * @param array             $clauses  SQL clauses (join, where, fields, ...).
		 * @param \WP_Comment_Query $query    The query object.
		 * @return array Possibly-modified clauses.
		 */
		public static function rewrite( array $clauses, $query ): array {
			$type = self::query_comment_type( $query );
			if ( '' === $type || ! isset( self::SHADOW_MAP[ $type ] ) ) {
				return $clauses;
			}

			global $wpdb;
			$shadow = $wpdb->prefix . self::SHADOW_MAP[ $type ];
			$alias  = 'wpdo_shadow';

			// LEFT JOIN keeps row visibility when shadow lags (during backfill).
			$join = ( $clauses['join'] ?? '' ) . " LEFT JOIN `{$shadow}` AS {$alias} ON {$alias}.comment_id = {$wpdb->comments}.comment_ID";

			// Filter pushdown: hp_message recipient lookup uses comment_karma in HP.
			// We rewrite WHERE clauses that filter by comment_karma (= recipient hack)
			// to use the indexed shadow column.
			$where = (string) ( $clauses['where'] ?? '' );
			if ( 'hp_message' === $type && '' !== $where ) {
				$where = preg_replace(
					'/' . preg_quote( $wpdb->comments, '/' ) . '\.comment_karma\s*=\s*(\d+)/',
					$alias . '.recipient_id = $1',
					$where
				);
			}

			$clauses['join']  = $join;
			$clauses['where'] = $where;

			/**
			 * Filter: wpdo_hivepress_comment_router_clauses
			 *
			 * Allows fine-grained tweaks per comment_type. Intended for adapter
			 * tests + future custom-column lookups.
			 *
			 * @param array  $clauses Modified clauses.
			 * @param string $type    Matched comment_type.
			 * @param string $alias   Shadow table alias.
			 */
			return apply_filters( 'wpdo_hivepress_comment_router_clauses', $clauses, $type, $alias );
		}

		/**
		 * Extract the comment_type from a WP_Comment_Query.
		 *
		 * @param \WP_Comment_Query $query Query object.
		 */
		private static function query_comment_type( $query ): string {
			if ( ! is_object( $query ) || ! isset( $query->query_vars ) ) {
				return '';
			}
			$type = $query->query_vars['type'] ?? '';
			if ( is_array( $type ) ) {
				$type = reset( $type );
			}
			return is_string( $type ) ? $type : '';
		}
	}

} // end if ( ! class_exists )