<?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';
        $handle = fopen($file, 'c+');
        if ($handle === false) {
            throw new RuntimeException('Cannot open rate limit bucket');
        }
        if (!flock($handle, LOCK_EX)) {
            fclose($handle);
            throw new RuntimeException('Cannot lock rate limit bucket');
        }
        $now = time();
        $events = [];
        $contents = stream_get_contents($handle);
        $decoded = json_decode(is_string($contents) ? $contents : '', true);
        if (is_array($decoded)) {
            foreach ($decoded as $event) {
                if (is_int($event) && $event > $now - $windowSeconds) {
                    $events[] = $event;
                }
            }
        }
        if (count($events) >= $limit) {
            flock($handle, LOCK_UN);
            fclose($handle);
            throw new RuntimeException('Rate limit exceeded');
        }
        $events[] = $now;
        ftruncate($handle, 0);
        rewind($handle);
        fwrite($handle, json_encode($events) ?: '[]');
        fflush($handle);
        flock($handle, LOCK_UN);
        fclose($handle);
        @chmod($file, 0600);
    }
}