<?php
declare(strict_types=1);
namespace KTXM\ServiceWopi\Host;

use phpseclib3\Crypt\RSA;
use phpseclib3\Math\BigInteger;

class ProofValidator
{
    public function valid(array $keys, string $token, string $url, string $timestamp, string $proof, string $oldProof, int $now): bool
    {
        if (!preg_match('/^[0-9]{1,18}$/D', $timestamp)) { return false; }
        $ticks = (int) $timestamp;
        // .NET ticks: 100 ns since 0001-01-01. Bound both stale and future requests.
        $seconds = intdiv($ticks, 10000000) - 62135596800;
        if (abs($seconds - $now) > 1200) { return false; }
        $url = strtoupper($url);
        $data = pack('N', strlen($token)) . $token . pack('N', strlen($url)) . $url
            . pack('N', 8) . pack('J', $ticks);
        return $this->verify($keys, '', $proof, $data)
            || $this->verify($keys, '', $oldProof, $data)
            || $this->verify($keys, 'old', $proof, $data);
    }

    private function verify(array $keys, string $prefix, string $signature, string $data): bool
    {
        $signature = base64_decode($signature, true);
        $modulus = base64_decode($keys[$prefix . 'modulus'] ?? '', true);
        $exponent = base64_decode($keys[$prefix . 'exponent'] ?? '', true);
        if (!$signature || !$modulus || !$exponent || strlen($modulus) > 1024 || strlen($exponent) > 8) { return false; }
        try {
            $key = RSA::loadPublicKey(['n' => new BigInteger($modulus, 256), 'e' => new BigInteger($exponent, 256)]);
            return $key->withPadding(RSA::SIGNATURE_PKCS1)->withHash('sha256')->verify($data, $signature);
        } catch (\Throwable) {
            return false;
        }
    }
}