/*
 * Copyright (c) 2020, Ali Mohammad Pur <ali.mpfard@gmail.com>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#pragma once

#include <AK/OwnPtr.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/StringView.h>
#include <LibCrypto/Authentication/GHash.h>
#include <LibCrypto/Cipher/Mode/CTR.h>
#include <LibCrypto/Verification.h>

namespace Crypto {
namespace Cipher {

using IncrementFunction = IncrementInplace;

template<typename T>
class GCM : public CTR<T, IncrementFunction> {
public:
    constexpr static size_t IVSizeInBits = 128;

    virtual ~GCM() { }

    template<typename... Args>
    explicit constexpr GCM<T>(Args... args)
        : CTR<T>(args...)
    {
        static_assert(T::BlockSizeInBits == 128u, "GCM Mode is only available for 128-bit Ciphers");

        __builtin_memset(m_auth_key_storage, 0, block_size);
        typename T::BlockType key_block(m_auth_key_storage, block_size);
        this->cipher().encrypt_block(key_block, key_block);
        key_block.bytes().copy_to(m_auth_key);

        m_ghash = make<Authentication::GHash>(m_auth_key);
    }

    virtual String class_name() const override
    {
        StringBuilder builder;
        builder.append(this->cipher().class_name());
        builder.append("_GCM");
        return builder.build();
    }

    virtual size_t IV_length() const override { return IVSizeInBits / 8; }

    // FIXME: This overload throws away the auth stuff, think up a better way to return more than a single bytebuffer.
    virtual void encrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}, Bytes* = nullptr) override
    {
        VERIFY(!ivec.is_empty());

        static ByteBuffer dummy;

        encrypt(in, out, ivec, dummy, dummy);
    }
    virtual void decrypt(ReadonlyBytes in, Bytes& out, ReadonlyBytes ivec = {}) override
    {
        encrypt(in, out, ivec);
    }

    void encrypt(const ReadonlyBytes& in, Bytes out, const ReadonlyBytes& iv_in, const ReadonlyBytes& aad, Bytes tag)
    {
        auto iv_buf = ByteBuffer::copy(iv_in.data(), iv_in.size());
        auto iv = iv_buf.bytes();

        // Increment the IV for block 0
        CTR<T>::increment(iv);
        typename T::BlockType block0;
        block0.overwrite(iv);
        this->cipher().encrypt_block(block0, block0);

        // Skip past block 0
        CTR<T>::increment(iv);

        if (in.is_empty())
            CTR<T>::key_stream(out, iv);
        else
            CTR<T>::encrypt(in, out, iv);

        auto auth_tag = m_ghash->process(aad, out);
        block0.apply_initialization_vector(auth_tag.data);
        block0.bytes().copy_to(tag);
    }

    VerificationConsistency decrypt(ReadonlyBytes in, Bytes out, ReadonlyBytes iv_in, ReadonlyBytes aad, ReadonlyBytes tag)
    {
        auto iv_buf = ByteBuffer::copy(iv_in.data(), iv_in.size());
        auto iv = iv_buf.bytes();

        // Increment the IV for block 0
        CTR<T>::increment(iv);
        typename T::BlockType block0;
        block0.overwrite(iv);
        this->cipher().encrypt_block(block0, block0);

        // Skip past block 0
        CTR<T>::increment(iv);

        auto auth_tag = m_ghash->process(aad, in);
        block0.apply_initialization_vector(auth_tag.data);

        auto test_consistency = [&] {
            if (block0.block_size() != tag.size() || __builtin_memcmp(block0.bytes().data(), tag.data(), tag.size()) != 0)
                return VerificationConsistency::Inconsistent;

            return VerificationConsistency::Consistent;
        };
        // FIXME: This block needs constant-time comparisons.

        if (in.is_empty()) {
            out = {};
            return test_consistency();
        }

        CTR<T>::encrypt(in, out, iv);
        return test_consistency();
    }

private:
    static constexpr auto block_size = T::BlockType::BlockSizeInBits / 8;
    u8 m_auth_key_storage[block_size];
    Bytes m_auth_key { m_auth_key_storage, block_size };
    OwnPtr<Authentication::GHash> m_ghash;
};

}

}