<?php
declare(strict_types=1);

final class RateLimiter
{
    public function __construct(private string $dir)
    {
    }

    public function assertAllowed(string $bucket, int $limit, int $windowSeconds): void
    {
        if ($limit < 1) {
            throw new RuntimeException('Rate limit is invalid');
        }
        if (!is_dir($this->dir)) {
            mkdir($this->dir, 0700, true);
        }
        $file = $this->dir . '/' . preg_replace('/[^A-Za-z0-9._-]/', '_', $bucket) . '.json';
        $now = time();
        $events = [];
        if (is_file($file)) {
            $decoded = json_decode((string)file_get_contents($file), true);
            if (is_array($decoded)) {
                foreach ($decoded as $event) {
                    if (is_int($event) && $event > $now - $windowSeconds) {
                        $events[] = $event;
                    }
                }
            }
        }
        if (count($events) >= $limit) {
            throw new RuntimeException('Rate limit exceeded');
        }
        $events[] = $now;
        file_put_contents($file, json_encode($events), LOCK_EX);
        @chmod($file, 0600);
    }
}