<?php

declare(strict_types=1);

namespace WordPress\CloudflareWorkersAiProvider;

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

/**
 * One-at-a-time locks for background jobs (backfill, embeddings, usage writes).
 *
 * On MySQL/MariaDB: named locks (GET_LOCK). They belong to the DB connection, so a
 * PHP process that dies mid-run releases its lock and nothing is left stale.
 *
 * Elsewhere (the SQLite integration answers GET_LOCK with the string '1=1', i.e.
 * no real lock): an option row, created atomically by add_option() on its unique
 * key. A process that dies leaves the row behind, so a lock older than STALE
 * seconds is taken over.
 */
final class Lock
{
    private const STALE = 600;

    /** @var array<string, true> Locks this request holds as options. */
    private static array $optionLocks = [];

    public static function acquire(string $name, int $timeout = 0): bool
    {
        if (!self::namedLocks()) {
            return self::acquireOption($name, $timeout);
        }
        global $wpdb;
        $got = $wpdb->get_var($wpdb->prepare('SELECT GET_LOCK(%s, %d)', self::key($name), $timeout)); // phpcs:ignore WordPress.DB.DirectDatabaseQuery
        if ($got === '1' || $got === 1) {
            return true;
        }
        if ($got === '0' || $got === 0) {
            return false; // held by another connection
        }
        // NULL or anything unexpected: this database does not do named locks after all.
        return self::acquireOption($name, $timeout);
    }

    public static function release(string $name): void
    {
        if (isset(self::$optionLocks[$name])) {
            unset(self::$optionLocks[$name]);
            delete_option(self::optionKey($name));
            return;
        }
        global $wpdb;
        $wpdb->query($wpdb->prepare('SELECT RELEASE_LOCK(%s)', self::key($name))); // phpcs:ignore WordPress.DB.DirectDatabaseQuery
    }

    /**
     * Whether the database has real named locks (MySQL, MariaDB).
     */
    public static function namedLocks(): bool
    {
        global $wpdb;
        $sqlite = (defined('DB_ENGINE') && DB_ENGINE === 'sqlite') || (is_object($wpdb) && stripos(get_class($wpdb), 'sqlite') !== false);
        return (bool) apply_filters('aipcf_named_locks', !$sqlite);
    }

    private static function acquireOption(string $name, int $timeout): bool
    {
        $key      = self::optionKey($name);
        $deadline = time() + max(0, $timeout);
        do {
            // add_option() inserts only when the row does not exist yet (unique option_name).
            if (add_option($key, (string) time(), '', false)) {
                self::$optionLocks[$name] = true;
                return true;
            }
            wp_cache_delete($key, 'options');
            $since = (int) get_option($key, 0);
            if ($since > 0 && $since < time() - self::STALE) {
                // Left by a process that died: take it over.
                delete_option($key);
                continue;
            }
            if (time() >= $deadline) {
                return false;
            }
            usleep(250000);
        } while (true);
    }

    private static function optionKey(string $name): string
    {
        return 'aipcf_lock_' . $name;
    }

    private static function key(string $name): string
    {
        global $wpdb;
        // Named locks are server-wide; scope them to this site's tables.
        return substr('aipcf_' . $wpdb->prefix . $name, 0, 64);
    }
}