<?php
// partials/proxy_helpers.php — small shared helpers for the *-proxy.php endpoints.
//
// - lastfm_api_key():       read LASTFM_API_KEY from env (with legacy fallback).
// - proxy_host_is_safe():   reject hosts that resolve to private/reserved IPs (SSRF guard).
// - proxy_rate_limit():     simple per-IP sliding-window limit, file-backed.

if (!function_exists('lastfm_api_key')) {
    function lastfm_api_key(): string {
        $env = getenv('LASTFM_API_KEY');
        if (is_string($env) && $env !== '') return $env;
        throw new RuntimeException('LASTFM_API_KEY is not set in the php-fpm environment');
    }
}

if (!function_exists('proxy_host_is_safe')) {
    function proxy_host_is_safe(string $host): bool {
        if ($host === '') return false;
        // Reject anything that looks like a literal IPv6 with brackets stripped earlier.
        $records = @dns_get_record($host, DNS_A | DNS_AAAA);
        $ips = [];
        if (is_array($records)) {
            foreach ($records as $r) {
                if (!empty($r['ip']))    $ips[] = $r['ip'];
                if (!empty($r['ipv6']))  $ips[] = $r['ipv6'];
            }
        }
        // Also check if the host is itself an IP literal.
        if (filter_var($host, FILTER_VALIDATE_IP)) {
            $ips[] = $host;
        }
        if (!$ips) return false; // unresolvable -> deny
        foreach ($ips as $ip) {
            $ok = filter_var(
                $ip,
                FILTER_VALIDATE_IP,
                FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE
            );
            if ($ok === false) return false;
        }
        return true;
    }
}

if (!function_exists('proxy_rate_limit')) {
    /**
     * Returns true if the request is allowed. Uses a tiny file per
     * (endpoint, client IP) holding recent unix timestamps.
     */
    function proxy_rate_limit(string $endpoint, int $max = 30, int $windowSec = 60): bool {
        $ip   = $_SERVER['REMOTE_ADDR'] ?? '0.0.0.0';
        $key  = preg_replace('/[^A-Za-z0-9._-]/', '_', $endpoint . '_' . $ip);
        $dir  = sys_get_temp_dir() . '/sillylaird_ratelimit';
        if (!is_dir($dir)) @mkdir($dir, 0700, true);
        $file = $dir . '/' . $key;

        $now    = time();
        $cutoff = $now - $windowSec;

        $fp = @fopen($file, 'c+');
        if (!$fp) return true; // fail-open: don't block legit traffic on disk error
        try {
            flock($fp, LOCK_EX);
            $data = stream_get_contents($fp);
            $stamps = $data === '' ? [] : array_map('intval', explode("\n", trim($data)));
            $stamps = array_values(array_filter($stamps, fn($t) => $t >= $cutoff));
            if (count($stamps) >= $max) {
                return false;
            }
            $stamps[] = $now;
            ftruncate($fp, 0);
            rewind($fp);
            fwrite($fp, implode("\n", $stamps));
            return true;
        } finally {
            flock($fp, LOCK_UN);
            fclose($fp);
        }
    }
}