<?php
/**
 * Grouped transient cache.
 *
 * @package TurtleReport
 */

namespace TurtleReport\Support;

defined( 'ABSPATH' ) || exit;

/**
 * Caches Google responses in transients, in named groups.
 *
 * Each group (for example "site:abc123") has a version number. Flushing a
 * group bumps its version, so old entries are never read again and expire on
 * their own. This avoids slow LIKE queries on the options table and works the
 * same with a persistent object cache.
 */
final class Cache {

	const VERSIONS_OPTION = 'turtlereport_cache_versions';

	/**
	 * Returns the cached value, or computes and stores it.
	 *
	 * @param string   $group    Cache group.
	 * @param string   $key      Unique key within the group.
	 * @param int      $ttl      Lifetime in seconds. 0 disables caching.
	 * @param callable $callback Produces the value on a miss.
	 * @return mixed
	 */
	public function remember( $group, $key, $ttl, callable $callback ) {
		if ( $ttl <= 0 ) {
			return $callback();
		}
		$name   = $this->name( $group, $key );
		$cached = get_transient( $name );
		if ( is_array( $cached ) && array_key_exists( 'v', $cached ) ) {
			return $cached['v'];
		}
		$value = $callback();
		TransientStore::set( $name, array( 'v' => $value ), $ttl );
		return $value;
	}

	/**
	 * Invalidates every entry in a group.
	 *
	 * @param string $group Cache group.
	 * @return void
	 */
	public function flush( $group ) {
		OptionUpdate::change(
			self::VERSIONS_OPTION,
			static function ( array $versions ) use ( $group ) {
				$versions[ $group ] = isset( $versions[ $group ] ) ? (int) $versions[ $group ] + 1 : 2;
				return $versions;
			}
		);
	}

	/**
	 * Builds the transient name. Transient names must stay under 172 characters.
	 *
	 * @param string $group Cache group.
	 * @param string $key   Key within the group.
	 * @return string
	 */
	private function name( $group, $key ) {
		$versions = $this->versions();
		$version  = isset( $versions[ $group ] ) ? (int) $versions[ $group ] : 1;
		return 'tly_' . md5( $group . '|' . $version . '|' . $key );
	}

	/**
	 * Current group versions.
	 *
	 * @return array<string,int>
	 */
	private function versions() {
		$versions = get_option( self::VERSIONS_OPTION, array() );
		return is_array( $versions ) ? $versions : array();
	}
}