<?php
namespace Consiva\Consent\Support;

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

/**
 * An atomic lock held in wp_options (no object cache involved, so it works across servers).
 *
 * WordPress's add_option() is not atomic: core runs INSERT … ON DUPLICATE KEY UPDATE, so two requests can both
 * "add" the same option and both think they won. Here the database decides: INSERT IGNORE inserts at
 * most one row, and a stale lock is taken over with a single UPDATE that only one request can match.
 * Found in the 9.6 security review: two token refreshes at once spent the same refresh token, the
 * second got 401, and the site was disconnected.
 */
final class Lock {

	/**
	 * @param string $name Option name.
	 * @param int    $ttl  Seconds before the lock counts as abandoned.
	 * @return bool Whether this request holds the lock.
	 */
	public static function acquire( $name, $ttl ) {
		global $wpdb;
		$now   = time();
		$until = (string) ( $now + (int) $ttl );
		// phpcs:disable WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- the point is to bypass caches.
		$inserted = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO {$wpdb->options} (option_name, option_value, autoload) VALUES (%s, %s, 'no')", $name, $until ) );
		if ( 1 !== $inserted ) {
			// Held by someone. Take it over only if it has expired; if two requests try, one UPDATE matches.
			$taken = $wpdb->query( $wpdb->prepare( "UPDATE {$wpdb->options} SET option_value = %s WHERE option_name = %s AND CAST(option_value AS UNSIGNED) < %d", $until, $name, $now ) );
		}
		// phpcs:enable
		self::forget_cached( $name );
		return 1 === $inserted || ( isset( $taken ) && 1 === $taken );
	}

	/**
	 * @param string $name Option name.
	 * @return void
	 */
	public static function release( $name ) {
		delete_option( $name );
		self::forget_cached( $name );
	}

	/**
	 * @param string $name Option name.
	 * @return void
	 */
	private static function forget_cached( $name ) {
		wp_cache_delete( $name, 'options' );
		$missing = wp_cache_get( 'notoptions', 'options' );
		if ( is_array( $missing ) && isset( $missing[ $name ] ) ) {
			unset( $missing[ $name ] );
			wp_cache_set( 'notoptions', $missing, 'options' );
		}
	}
}