<?php
/**
 * Database-backed mutex with expiry.
 *
 * @package OrbitstemSEO
 */

namespace Orbitstem\SEO\Core;

defined( 'ABSPATH' ) || exit;

/**
 * Uses INSERT IGNORE on the options table, which succeeds for exactly one
 * request. add_option() is not usable here: it upserts with ON DUPLICATE KEY
 * UPDATE, so two requests could both believe they hold the lock.
 */
class Lock {

	/**
	 * Tries to take the lock.
	 *
	 * @param string $name Option name of the lock.
	 * @param int    $ttl  Seconds after which a held lock is considered stale.
	 * @return bool
	 */
	public static function acquire( $name, $ttl ) {
		if ( self::insert( $name ) ) {
			return true;
		}
		global $wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- lock state must bypass the object cache.
		$held_since = (int) $wpdb->get_var( $wpdb->prepare( "SELECT option_value FROM {$wpdb->options} WHERE option_name = %s", $name ) );
		if ( time() - $held_since < (int) $ttl ) {
			return false;
		}
		// Stale: delete only the exact stale row, then race for the lock once more.
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$wpdb->query( $wpdb->prepare( "DELETE FROM {$wpdb->options} WHERE option_name = %s AND option_value = %s", $name, (string) $held_since ) );
		return self::insert( $name );
	}

	/**
	 * Releases the lock.
	 *
	 * @param string $name Option name of the lock.
	 */
	public static function release( $name ) {
		global $wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$wpdb->delete( $wpdb->options, array( 'option_name' => $name ) );
		self::flush_cache( $name );
	}

	/**
	 * Atomic insert of the lock row.
	 *
	 * @param string $name Option name.
	 * @return bool Whether this request created the row.
	 */
	private static function insert( $name ) {
		global $wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$inserted = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO {$wpdb->options} (option_name, option_value, autoload) VALUES (%s, %s, 'no')", $name, (string) time() ) );
		self::flush_cache( $name );
		return 1 === (int) $inserted;
	}

	/**
	 * Keeps the options cache consistent with the direct queries.
	 *
	 * @param string $name Option name.
	 */
	private static function flush_cache( $name ) {
		wp_cache_delete( $name, 'options' );
		wp_cache_delete( 'notoptions', 'options' );
	}
}