<?php

namespace App\Services;

use Brick\Math\BigInteger;

/** The site's legacy AzerothCore SRP format, independent of the game ticket. */
class AzerothCoreSrpService
{
    private const string MODULUS_HEX = '894B645E89E1535BBDAD5B8B290650530801B18EBFBF5E8FAB3C82872A3E9BB7';

    public function makeRegistrationData(string $username, string $password): array
    {
        $saltHex = strtoupper(bin2hex(random_bytes(32)));

        return [$saltHex, $this->makeVerifierHex($username, $password, $saltHex)];
    }

    public function makeVerifierHex(string $username, string $password, string $saltHex): string
    {
        $salt = hex2bin($saltHex);
        if ($salt === false || strlen($salt) !== 32) {
            throw new \InvalidArgumentException('Invalid site credential salt.');
        }

        $digest = hash('sha1', strtoupper(trim($username)).':'.strtoupper($password), true);
        $x = hash('sha1', $salt.$digest, true);
        $verifier = BigInteger::of(7)->modPow(
            BigInteger::fromBytes(strrev($x), false),
            BigInteger::fromBase(self::MODULUS_HEX, 16),
        );

        return strtoupper(bin2hex(strrev(str_pad($verifier->toBytes(false), 32, "\0", STR_PAD_LEFT))));
    }

    public function credentialsMatch(string $username, string $password, string $saltHex, string $verifierHex): bool
    {
        return hash_equals(strtoupper($verifierHex), $this->makeVerifierHex($username, $password, $saltHex));
    }
}