#include "CryptoUtils.h"
#include "crypto/tiny_aes.hpp"

namespace {
QByteArray removePkcs7Padding(const QByteArray &data)
{
    if (data.isEmpty()) {
        return {};
    }

    const int padding = static_cast<unsigned char>(data.back());
    if (padding < 1 || padding > AES_BLOCKLEN || padding > data.size()) {
        return data;
    }

    for (int i = data.size() - padding; i < data.size(); ++i) {
        if (static_cast<unsigned char>(data.at(i)) != padding) {
            return data;
        }
    }

    return data.left(data.size() - padding);
}
}

QByteArray CryptoUtils::decryptAes128CbcBase64(const QByteArray &encryptedBase64)
{
    static const uint8_t key[AES_KEYLEN] = {
        0x2b, 0x7e, 0x15, 0x16, 0x28, 0xae, 0xd2, 0xa6,
        0xab, 0xf7, 0x15, 0x88, 0x09, 0xcf, 0x4f, 0x3c
    };

    static const uint8_t iv[AES_BLOCKLEN] = {
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
        0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
    };

    const QByteArray encrypted = QByteArray::fromBase64(encryptedBase64);
    if (encrypted.isEmpty() || (encrypted.size() % AES_BLOCKLEN) != 0) {
        return {};
    }

    QByteArray buffer = encrypted;
    AES_ctx ctx;
    AES_init_ctx_iv(&ctx, key, iv);
    AES_CBC_decrypt_buffer(&ctx, reinterpret_cast<uint8_t*>(buffer.data()), static_cast<size_t>(buffer.size()));
    return removePkcs7Padding(buffer);
}