<?php

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

// phpcs:disable WordPress.DB.DirectDatabaseQuery -- A backup must read live, uncached data (and take locks); caching would be wrong here.

/**
 * Makes sure only one worker processes the backup job at a time.
 *
 * Prefers MySQL GET_LOCK: it is released automatically if PHP is killed mid-request,
 * so a crashed worker never leaves a stuck lock behind. Falls back to an expiring
 * option-based lock on databases without GET_LOCK.
 */
final class SWPB_Lock
{
    private const FALLBACK_OPTION = 'swpb_worker_lock';

    private string $name;
    private string $mode = '';
    private string $token = '';

    public function __construct()
    {
        global $wpdb;
        $this->name = 'swpb_' . md5(DB_NAME . '|' . $wpdb->prefix);
    }

    public function acquire(int $fallback_ttl = 180): bool
    {
        global $wpdb;

        $got = $wpdb->get_var($wpdb->prepare('SELECT GET_LOCK(%s, 0)', $this->name));
        if ($got !== null && $wpdb->last_error === '') {
            if ((int)$got === 1) {
                $this->mode = 'mysql';
                return true;
            }
            return false;
        }

        // Fallback: atomic insert of an option that expires.
        $this->token = wp_generate_password(20, false, false);
        $value = time() + $fallback_ttl . '|' . $this->token;
        if (add_option(self::FALLBACK_OPTION, $value, '', false)) {
            $this->mode = 'option';
            return true;
        }
        $current = (string)get_option(self::FALLBACK_OPTION, '');
        $expires = (int)strtok($current, '|');
        if ($expires > 0 && $expires < time()) {
            delete_option(self::FALLBACK_OPTION);
            if (add_option(self::FALLBACK_OPTION, $value, '', false)) {
                $this->mode = 'option';
                return true;
            }
        }
        return false;
    }

    public function release(): void
    {
        global $wpdb;
        if ($this->mode === 'mysql') {
            $wpdb->query($wpdb->prepare('SELECT RELEASE_LOCK(%s)', $this->name));
        } elseif ($this->mode === 'option') {
            wp_cache_delete(self::FALLBACK_OPTION, 'options');
            $current = (string)get_option(self::FALLBACK_OPTION, '');
            if (substr($current, -strlen($this->token)) === $this->token) {
                delete_option(self::FALLBACK_OPTION);
            }
        }
        $this->mode = '';
    }
}