<?php

declare(strict_types=1);

/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2014-2018 Spomky-Labs
 *
 * This software may be modified and distributed under the terms
 * of the MIT license.  See the LICENSE file for details.
 */

namespace Jose\Component\Core\Util;

/**
 * @internal
 */
class ECSignature
{
    public static function toDER(string $signature, int $partLength): string
    {
        $signature = \unpack('H*', $signature)[1];
        if (\mb_strlen($signature, '8bit') !== 2 * $partLength) {
            throw new \InvalidArgumentException('Invalid length.');
        }
        $R = \mb_substr($signature, 0, $partLength, '8bit');
        $S = \mb_substr($signature, $partLength, null, '8bit');

        $R = self::preparePositiveInteger($R);
        $Rl = \mb_strlen($R, '8bit') / 2;
        $S = self::preparePositiveInteger($S);
        $Sl = \mb_strlen($S, '8bit') / 2;
        $der = \pack('H*',
            '30'.($Rl + $Sl + 4 > 128 ? '81' : '').\dechex($Rl + $Sl + 4)
            .'02'.\dechex($Rl).$R
            .'02'.\dechex($Sl).$S
        );

        return $der;
    }

    public static function fromDER(string $der, int $partLength): string
    {
        $hex = \unpack('H*', $der)[1];
        if ('30' !== \mb_substr($hex, 0, 2, '8bit')) { // SEQUENCE
            throw new \RuntimeException();
        }
        if ('81' === \mb_substr($hex, 2, 2, '8bit')) { // LENGTH > 128
            $hex = \mb_substr($hex, 6, null, '8bit');
        } else {
            $hex = \mb_substr($hex, 4, null, '8bit');
        }
        if ('02' !== \mb_substr($hex, 0, 2, '8bit')) { // INTEGER
            throw new \RuntimeException();
        }

        $Rl = \hexdec(\mb_substr($hex, 2, 2, '8bit'));
        $R = self::retrievePositiveInteger(\mb_substr($hex, 4, $Rl * 2, '8bit'));
        $R = \str_pad($R, $partLength, '0', STR_PAD_LEFT);

        $hex = \mb_substr($hex, 4 + $Rl * 2, null, '8bit');
        if ('02' !== \mb_substr($hex, 0, 2, '8bit')) { // INTEGER
            throw new \RuntimeException();
        }
        $Sl = \hexdec(\mb_substr($hex, 2, 2, '8bit'));
        $S = self::retrievePositiveInteger(\mb_substr($hex, 4, $Sl * 2, '8bit'));
        $S = \str_pad($S, $partLength, '0', STR_PAD_LEFT);

        return \pack('H*', $R.$S);
    }

    private static function preparePositiveInteger(string $data): string
    {
        if (\mb_substr($data, 0, 2, '8bit') > '7f') {
            return '00'.$data;
        }
        while ('00' === \mb_substr($data, 0, 2, '8bit') && \mb_substr($data, 2, 2, '8bit') <= '7f') {
            $data = \mb_substr($data, 2, null, '8bit');
        }

        return $data;
    }

    private static function retrievePositiveInteger(string $data): string
    {
        while ('00' === \mb_substr($data, 0, 2, '8bit') && \mb_substr($data, 2, 2, '8bit') > '7f') {
            $data = \mb_substr($data, 2, null, '8bit');
        }

        return $data;
    }
}