<?php
/**
 * Page cache for embed responses.
 *
 * - fresh copy: transient `aoo_page_<md5>` for the TTL aoo sends (600 s) or the admin override
 * - stale copy: transient `aoo_stale_<md5>` kept 7 days — served (header `X-Aoo-Cache: stale`) when aoo
 *   is unreachable, and its ETag is used for a cheap conditional re-fetch (304 → renew)
 * - article cards (`embed/cards`, W4) share all of the above — index entry type 'cards'
 * - index option `aooshop_cache_index` lists every key ({type, slug, page, price?, sort?}) so purge from aoo / "ล้างแคช" can find them
 * - listing filters `price` / `sort` are part of the key only when set (unfiltered pages keep their 0.1 keys) — the
 *   router whitelists them first, so junk values never create entries
 * - listing pages (AooShop_Router::LISTING_TYPES) are always asked with `parts=1` (0.4 per-type templates —
 *   payload.parts {header, filters, grid, footer}); not part of the cache key since every 0.4 request is the same.
 *   A copy cached before the upgrade simply has no parts → renderer falls back (grid = whole html)
 * - after a network/5xx failure aoo is skipped for 60 s (circuit) so visitors don't each wait 8 s
 * - public data API (W2, `embed/data/*` — class-data-api.php) shares all of the above — index entry type 'data'
 *   (purged by every event via `aooshop_purge_list_types`) · `facets_unavailable` (503 before aoo's DB migration)
 *   is a feature answer, not an outage → never trips the circuit
 *
 * @package AooShop
 */

defined( 'ABSPATH' ) || exit;

class AooShop_Cache {

	// 0.7.0: was `aoo_page_` / `aoo_stale_` (too short a prefix for WordPress.org) — old rows expire on their own,
	// uninstall.php removes both spellings.
	const PREFIX       = 'aooshop_page_';
	const STALE_PREFIX = 'aooshop_stale_';
	const INDEX_OPTION = 'aooshop_cache_index';
	const DOWN_KEY     = 'aooshop_api_down';
	const REFRESH_HOOK = 'aooshop_refresh_page';
	const STALE_TTL    = 604800; // 7 days.
	const DEFAULT_TTL  = 600;
	const DOWN_TTL     = 60;
	const INDEX_MAX    = 5000;
	/** Listing filters carried in page queries (whitelisted by AooShop_Router::filters()). */
	const FILTER_KEYS = array( 'price', 'sort', 'on_sale' );

	/** @var AooShop_Settings */
	private $settings;
	/** @var AooShop_Api_Client */
	private $api;

	public function __construct( AooShop_Settings $settings, AooShop_Api_Client $api ) {
		$this->settings = $settings;
		$this->api      = $api;
	}

	public function hooks() {
		add_action( self::REFRESH_HOOK, array( $this, 'refresh' ), 10, 1 );
	}

	/** Normalized page query → cache key (md5). */
	public static function key( array $query ) {
		$norm = array(
			'type' => isset( $query['type'] ) ? (string) $query['type'] : '',
			'slug' => isset( $query['slug'] ) ? (string) $query['slug'] : '',
			'page' => isset( $query['page'] ) ? max( 1, (int) $query['page'] ) : 1,
			'q'    => isset( $query['q'] ) ? (string) $query['q'] : '',
		);
		foreach ( self::FILTER_KEYS as $k ) {
			if ( isset( $query[ $k ] ) && '' !== (string) $query[ $k ] ) {
				$norm[ $k ] = (string) $query[ $k ];
			}
		}
		return md5( wp_json_encode( $norm ) );
	}

	/** Normalized card args (AooShop_Cards::normalize()) → cache key — own namespace, never equal to a page key. */
	public static function cards_key( array $args ) {
		return md5( wp_json_encode( array( 'cards' => $args ) ) );
	}

	/** Data API endpoint + normalized args → cache key — own namespace. */
	public static function data_key( $endpoint, array $args ) {
		return md5( wp_json_encode( array( 'data' => (string) $endpoint, 'args' => $args ) ) );
	}

	/**
	 * Public data API payload (`embed/data/{products,facets,collections,suggest}`) — args already whitelisted by
	 * AooShop_Data_Api::normalize_*() (only scalar values; '' / null are not sent).
	 *
	 * @param string $endpoint 'data/products' | 'data/facets' | 'data/collections' | 'data/suggest'.
	 * @param array  $args     Normalized args.
	 * @param bool   $force    Skip the fresh copy (refresh event).
	 * @return array{payload:array, source:string}|WP_Error
	 */
	public function get_data( $endpoint, array $args, $force = false ) {
		return $this->remember(
			self::data_key( $endpoint, $args ),
			$endpoint,
			$args,
			array( 'type' => 'data', 'slug' => '', 'endpoint' => (string) $endpoint, 'args' => $args ),
			'is_array',
			__( 'Incomplete data from AOO.', 'aoo-shop' ),
			$force
		);
	}

	/**
	 * Page payload for a route query.
	 *
	 * @param array $query {type, slug?, page?, q?}.
	 * @param bool  $force Skip the fresh copy (refresh event).
	 * @return array{payload:array, source:string}|WP_Error  source: hit | miss | revalidated | stale
	 */
	public function get_page( array $query, $force = false ) {
		$api_query = array(
			'type' => $query['type'],
			'slug' => isset( $query['slug'] ) ? $query['slug'] : null,
			'page' => ( isset( $query['page'] ) && (int) $query['page'] > 1 ) ? (int) $query['page'] : null,
			'q'    => isset( $query['q'] ) ? $query['q'] : null,
		);
		foreach ( self::FILTER_KEYS as $k ) {
			$api_query[ $k ] = isset( $query[ $k ] ) && '' !== (string) $query[ $k ] ? (string) $query[ $k ] : null;
		}
		if ( in_array( (string) $query['type'], AooShop_Router::LISTING_TYPES, true ) ) {
			$api_query['parts'] = 1;
		}
		return $this->remember(
			self::key( $query ),
			'page',
			$api_query,
			$query,
			function ( $payload ) {
				return isset( $payload['status'], $payload['html'] );
			},
			__( 'Incomplete page data from AOO.', 'aoo-shop' ),
			$force
		);
	}

	/**
	 * Article product cards (`embed/cards`) — same fresh/stale/circuit rules as pages, same index (so "ล้างแคช"
	 * and purge from aoo clear them: index entry type = 'cards'; W6 should purge every 'cards' entry on any
	 * product change since a card list can hold any product).
	 *
	 * @param array $args  Normalized args (AooShop_Cards::normalize() — api keys only).
	 * @param bool  $force Skip the fresh copy (refresh event).
	 * @return array{payload:array, source:string}|WP_Error
	 */
	public function get_cards( array $args, $force = false ) {
		$api_query = $args;
		foreach ( array( 'ids', 'slugs' ) as $list ) {
			$api_query[ $list ] = ! empty( $args[ $list ] ) ? implode( ',', (array) $args[ $list ] ) : null;
		}
		return $this->remember(
			self::cards_key( $args ),
			'cards',
			$api_query,
			array( 'type' => 'cards', 'slug' => '', 'args' => $args ),
			function ( $payload ) {
				return isset( $payload['html'] ) && is_string( $payload['html'] ) && isset( $payload['products'] ) && is_array( $payload['products'] );
			},
			__( 'Incomplete product card data from AOO.', 'aoo-shop' ),
			$force
		);
	}

	/**
	 * Fresh copy → conditional fetch (ETag of the stale copy) → stale fallback.
	 *
	 * @param string   $key       Cache key.
	 * @param string   $endpoint  Embed endpoint.
	 * @param array    $api_query Query sent to aoo.
	 * @param array    $query     What the index / refresh event remember ({type, slug, …}).
	 * @param callable $valid     fn(array $payload): bool.
	 * @param string   $invalid   Error message for an invalid payload.
	 * @param bool     $force     Skip the fresh copy.
	 */
	private function remember( $key, $endpoint, array $api_query, array $query, $valid, $invalid, $force ) {
		if ( ! $force ) {
			$fresh = get_transient( self::PREFIX . $key );
			if ( is_array( $fresh ) && isset( $fresh['payload'] ) ) {
				return array( 'payload' => $fresh['payload'], 'source' => 'hit' );
			}
		}

		$stale = get_transient( self::STALE_PREFIX . $key );
		$stale = ( is_array( $stale ) && isset( $stale['payload'] ) ) ? $stale : null;

		if ( get_transient( self::DOWN_KEY ) ) {
			return $this->fallback( $key, $query, $stale, new WP_Error( 'aoo_down', __( 'AOO is not responding (requests paused for now).', 'aoo-shop' ) ) );
		}

		$res = $this->api->get( $endpoint, $api_query, $stale ? $stale['etag'] : null );

		if ( is_wp_error( $res ) ) {
			$data = $res->get_error_data();
			// `facets_unavailable` = aoo is up but its DB lacks the facets RPC yet — not an outage.
			if ( is_array( $data ) && ! empty( $data['retryable'] ) && 'aoo_facets_unavailable' !== $res->get_error_code() ) {
				set_transient( self::DOWN_KEY, 1, self::DOWN_TTL );
			}
			return $this->fallback( $key, $query, $stale, $res );
		}

		if ( 304 === $res['code'] && $stale ) {
			$this->store( $key, $query, $stale['payload'], $res['etag'] ? $res['etag'] : $stale['etag'] );
			return array( 'payload' => $stale['payload'], 'source' => 'revalidated' );
		}

		$payload = is_array( $res['data'] ) ? $res['data'] : null;
		if ( ! $payload || ! call_user_func( $valid, $payload ) ) {
			return $this->fallback( $key, $query, $stale, new WP_Error( 'aoo_bad_payload', $invalid ) );
		}

		$etag = $res['etag'] ? $res['etag'] : ( isset( $payload['cache']['etag'] ) ? (string) $payload['cache']['etag'] : '' );
		$this->store( $key, $query, $payload, $etag );
		return array( 'payload' => $payload, 'source' => 'miss' );
	}

	/** Refresh event (scheduled when a stale copy was served). */
	public function refresh( $query ) {
		if ( ! is_array( $query ) || empty( $query['type'] ) ) {
			return;
		}
		delete_transient( self::DOWN_KEY );
		if ( 'cards' === $query['type'] ) {
			if ( isset( $query['args'] ) && is_array( $query['args'] ) ) {
				$this->get_cards( $query['args'], true );
			}
			return;
		}
		if ( 'data' === $query['type'] ) {
			if ( ! empty( $query['endpoint'] ) && isset( $query['args'] ) && is_array( $query['args'] ) ) {
				$this->get_data( (string) $query['endpoint'], $query['args'], true );
			}
			return;
		}
		$this->get_page( $query, true );
	}

	private function fallback( $key, array $query, $stale, WP_Error $error ) {
		if ( $stale ) {
			if ( ! wp_next_scheduled( self::REFRESH_HOOK, array( $query ) ) ) {
				wp_schedule_single_event( time() + self::DOWN_TTL + 5, self::REFRESH_HOOK, array( $query ) );
			}
			return array( 'payload' => $stale['payload'], 'source' => 'stale' );
		}
		return $error;
	}

	private function ttl_for( array $payload ) {
		$ttl = isset( $payload['cache']['ttl'] ) ? (int) $payload['cache']['ttl'] : self::DEFAULT_TTL;
		return max( 60, $ttl > 0 ? $ttl : self::DEFAULT_TTL );
	}

	private function store( $key, array $query, array $payload, $etag ) {
		$entry = array(
			'payload' => $payload,
			'etag'    => (string) $etag,
			'at'      => time(),
		);
		set_transient( self::PREFIX . $key, $entry, $this->ttl_for( $payload ) );
		set_transient( self::STALE_PREFIX . $key, $entry, self::STALE_TTL );
		$this->index_add( $key, $query );
	}

	private function index_add( $key, array $query ) {
		$index = get_option( self::INDEX_OPTION, array() );
		if ( ! is_array( $index ) ) {
			$index = array();
		}
		if ( isset( $index[ $key ] ) ) {
			return; // Avoid an option write on every miss of a known page.
		}
		$entry = array(
			'type' => (string) $query['type'],
			'slug' => isset( $query['slug'] ) ? (string) $query['slug'] : '',
			'page' => isset( $query['page'] ) ? max( 1, (int) $query['page'] ) : 1, // Purge → exact URL for page caches.
		);
		foreach ( self::FILTER_KEYS as $k ) {
			if ( isset( $query[ $k ] ) && '' !== (string) $query[ $k ] ) {
				$entry[ $k ] = (string) $query[ $k ]; // Purge → URL with the same query string.
			}
		}
		$index[ $key ] = $entry;
		if ( count( $index ) > self::INDEX_MAX ) {
			$drop = array_slice( array_keys( $index ), 0, count( $index ) - self::INDEX_MAX );
			foreach ( $drop as $old ) {
				$this->delete_key( $old );
				unset( $index[ $old ] );
			}
		}
		update_option( self::INDEX_OPTION, $index, false );
	}

	private function delete_key( $key ) {
		delete_transient( self::PREFIX . $key );
		delete_transient( self::STALE_PREFIX . $key );
	}

	/**
	 * Action `aooshop_after_purge( $count, $match, $targets )` — plus the pre-rename `aoo_after_purge` on sites with the
	 * legacy-names flag (theme / mu-plugin code may listen to it).
	 *
	 * @param int           $count   Pages dropped.
	 * @param callable|null $match   Matcher used.
	 * @param array|null    $targets null = everything, else ['urls' => [...]].
	 */
	public static function fire_after_purge( $count, $match, $targets ) {
		do_action( 'aooshop_after_purge', $count, $match, $targets );
	}

	/**
	 * Drop cached pages. `$keep_stale` = only expire the fresh copy (next view re-fetches but a stale copy
	 * still covers an aoo outage) — what purge from aoo uses (class-purge.php). The admin button drops everything.
	 * Fires `aooshop_after_purge( $count, $match, null )` (null targets = "everything" for page caches —
	 * class-host-cache.php) unless `$notify` is false (class-purge.php fires it itself with exact URLs).
	 *
	 * @param callable|null $match      fn(array $entry{type, slug, page?}): bool — null = all.
	 * @param bool          $keep_stale Keep the 7-day stale copies (and their index entries).
	 * @param bool          $notify     Fire `aooshop_after_purge`.
	 * @return int Number of pages dropped.
	 */
	public function purge( $match = null, $keep_stale = false, $notify = true ) {
		$index = get_option( self::INDEX_OPTION, array() );
		if ( ! is_array( $index ) ) {
			return 0;
		}
		$count = 0;
		foreach ( $index as $key => $entry ) {
			if ( $match && ! call_user_func( $match, $entry ) ) {
				continue;
			}
			delete_transient( self::PREFIX . $key );
			if ( ! $keep_stale ) {
				delete_transient( self::STALE_PREFIX . $key );
				unset( $index[ $key ] );
			}
			$count++;
		}
		update_option( self::INDEX_OPTION, $index, false );
		delete_transient( self::DOWN_KEY );
		if ( $notify ) {
			AooShop_Cache::fire_after_purge( $count, $match, null );
		}
		return $count;
	}

	public function stats() {
		$index = get_option( self::INDEX_OPTION, array() );
		return array(
			'entries'  => is_array( $index ) ? count( $index ) : 0,
			'api_down' => (bool) get_transient( self::DOWN_KEY ),
		);
	}
}