/*
 * 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/ByteBuffer.h>
#include <AK/String.h>
#include <AK/StringBuilder.h>
#include <AK/StringView.h>
#include <AK/Types.h>
#include <AK/Vector.h>

constexpr static auto IPAD = 0x36;
constexpr static auto OPAD = 0x5c;

namespace Crypto {
namespace Authentication {

template<typename HashT>
class HMAC {
public:
    using HashType = HashT;
    using TagType = typename HashType::DigestType;

    size_t digest_size() const { return m_inner_hasher.digest_size(); }

    template<typename KeyBufferType, typename... Args>
    HMAC(KeyBufferType key, Args... args)
        : m_inner_hasher(args...)
        , m_outer_hasher(args...)
    {
        derive_key(key);
        reset();
    }

    TagType process(const u8* message, size_t length)
    {
        reset();
        update(message, length);
        return digest();
    }

    void update(const u8* message, size_t length)
    {
        m_inner_hasher.update(message, length);
    }

    TagType process(const ByteBuffer& buffer) { return process(buffer.data(), buffer.size()); }
    TagType process(const StringView& string) { return process((const u8*)string.characters_without_null_termination(), string.length()); }
    void update(const ByteBuffer& buffer) { return update(buffer.data(), buffer.size()); }
    void update(const StringView& string) { return update((const u8*)string.characters_without_null_termination(), string.length()); }

    TagType digest()
    {
        m_outer_hasher.update(m_inner_hasher.digest().immutable_data(), m_inner_hasher.digest_size());
        auto result = m_outer_hasher.digest();
        reset();
        return result;
    }

    void reset()
    {
        m_inner_hasher.reset();
        m_outer_hasher.reset();
        m_inner_hasher.update(m_key_data, m_inner_hasher.block_size());
        m_outer_hasher.update(m_key_data + m_inner_hasher.block_size(), m_outer_hasher.block_size());
    }

    String class_name() const
    {
        StringBuilder builder;
        builder.append("HMAC-");
        builder.append(m_inner_hasher.class_name());
        return builder.build();
    }

private:
    void derive_key(const u8* key, size_t length)
    {
        auto block_size = m_inner_hasher.block_size();
        u8 v_key[block_size];
        __builtin_memset(v_key, 0, block_size);
        ByteBuffer key_buffer = ByteBuffer::wrap(v_key, block_size);
        // m_key_data is zero'd, so copying the data in
        // the first few bytes leaves the rest zero, which
        // is exactly what we want (zero padding)
        if (length > block_size) {
            m_inner_hasher.update(key, length);
            auto digest = m_inner_hasher.digest();
            // FIXME: should we check if the hash function creates more data than its block size?
            key_buffer.overwrite(0, digest.immutable_data(), m_inner_hasher.digest_size());
        } else {
            key_buffer.overwrite(0, key, length);
        }

        // fill out the inner and outer padded keys
        auto* i_key = m_key_data;
        auto* o_key = m_key_data + block_size;
        for (size_t i = 0; i < block_size; ++i) {
            auto key_byte = key_buffer[i];
            i_key[i] = key_byte ^ IPAD;
            o_key[i] = key_byte ^ OPAD;
        }
    }

    void derive_key(const ByteBuffer& key) { derive_key(key.data(), key.size()); }
    void derive_key(const StringView& key) { derive_key((const u8*)key.characters_without_null_termination(), key.length()); }

    HashType m_inner_hasher, m_outer_hasher;
    u8 m_key_data[2048];
};

}
}