<?php
/**
 * Atomic, self-expiring locks stored in the options table.
 *
 * @package SiteAuditHub
 */

namespace SiteAuditHub;

defined( 'ABSPATH' ) || exit;

/**
 * Prevents overlapping workers and duplicate job creation.
 */
class Lock {

	const PREFIX = 'siteaudithub_lock_';

	/**
	 * Try to acquire a lock.
	 *
	 * @param string $name Lock name.
	 * @param int    $ttl  Seconds after which a stale lock may be broken.
	 * @return string|false Token on success.
	 */
	public static function acquire( $name, $ttl = 120 ) {
		global $wpdb;
		$option = self::PREFIX . sanitize_key( $name );
		$token  = wp_generate_password( 20, false, false );
		$value  = ( time() + (int) $ttl ) . '|' . $token;

		// INSERT IGNORE is atomic thanks to the unique option_name key.
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$inserted = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO %i (option_name, option_value, autoload) VALUES (%s, %s, 'no')", $wpdb->options, $option, $value ) );
		if ( $inserted ) {
			wp_cache_delete( $option, 'options' );
			wp_cache_delete( 'notoptions', 'options' );
			return $token;
		}

		// Break stale lock.
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$current = $wpdb->get_var( $wpdb->prepare( 'SELECT option_value FROM %i WHERE option_name = %s', $wpdb->options, $option ) );
		if ( is_string( $current ) ) {
			$parts = explode( '|', $current, 2 );
			if ( (int) $parts[0] < time() ) {
				// Compare-and-swap so two workers cannot both break the same stale lock.
				// phpcs:ignore WordPress.DB.DirectDatabaseQuery
				$updated = $wpdb->query( $wpdb->prepare( 'UPDATE %i SET option_value = %s WHERE option_name = %s AND option_value = %s', $wpdb->options, $value, $option, $current ) );
				if ( $updated ) {
					wp_cache_delete( $option, 'options' );
					return $token;
				}
			}
		}
		return false;
	}

	/**
	 * Release a lock if we still own it.
	 *
	 * @param string $name  Lock name.
	 * @param string $token Token from acquire().
	 */
	public static function release( $name, $token ) {
		global $wpdb;
		$option = self::PREFIX . sanitize_key( $name );
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$wpdb->query( $wpdb->prepare( 'DELETE FROM %i WHERE option_name = %s AND option_value LIKE %s', $wpdb->options, $option, '%|' . $wpdb->esc_like( $token ) ) );
		wp_cache_delete( $option, 'options' );
	}

	/**
	 * Remove all plugin locks (deactivation/uninstall).
	 */
	public static function release_all() {
		global $wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery
		$wpdb->query( $wpdb->prepare( 'DELETE FROM %i WHERE option_name LIKE %s', $wpdb->options, $wpdb->esc_like( self::PREFIX ) . '%' ) );
	}
}