// This file Copyright © Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.

#include <algorithm>
#include <array>
#include <cctype>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <optional>
#include <random>
#include <string>
#include <string_view>
#include <vector>

extern "C"
{
#include <b64/cdecode.h>
#include <b64/cencode.h>
}

#include <fmt/core.h>

#include "libtransmission/crypto-utils.h"
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-macros.h"
#include "libtransmission/utils.h"

using namespace std::literals;

// ---

namespace
{
constexpr auto TrSha1DigestStrlen = size_t{ 40 };

constexpr auto TrSha256DigestStrlen = size_t{ 64 };

namespace ssha1_impl
{

auto constexpr DigestStringSize = TrSha1DigestStrlen;
auto constexpr SaltedPrefix = "{"sv;

std::string tr_salt(std::string_view plaintext, std::string_view salt)
{
    static_assert(DigestStringSize == 40);

    // build a sha1 digest of the original content and the salt
    auto const digest = tr_sha1::digest(plaintext, salt);

    // convert it to a string. string holds three parts:
    // DigestPrefix, stringified digest of plaintext + salt, and the salt.
    return fmt::format("{:s}{:s}{:s}", SaltedPrefix, tr_sha1_to_string(digest), salt);
}

} // namespace ssha1_impl
} // namespace

std::string tr_ssha1(std::string_view plaintext)
{
    using namespace ssha1_impl;

    // build an array of random Salter chars
    auto constexpr Salter = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ./"sv;
    static_assert(std::size(Salter) == 64);
    auto constexpr SaltSize = size_t{ 8 };
    auto salt = tr_rand_obj<std::array<char, SaltSize>>();
    std::transform(
        std::begin(salt),
        std::end(salt),
        std::begin(salt),
        [&Salter](auto ch) { return Salter[ch % std::size(Salter)]; });

    return tr_salt(plaintext, std::string_view{ std::data(salt), std::size(salt) });
}

bool tr_ssha1_test(std::string_view text)
{
    using namespace ssha1_impl;

    return tr_strv_starts_with(text, SaltedPrefix) && std::size(text) >= std::size(SaltedPrefix) + DigestStringSize;
}

bool tr_ssha1_matches(std::string_view ssha1, std::string_view plaintext)
{
    using namespace ssha1_impl;

    if (!tr_ssha1_test(ssha1))
    {
        return false;
    }

    auto const salt = ssha1.substr(std::size(SaltedPrefix) + DigestStringSize);
    return tr_salt(plaintext, salt) == ssha1;
}

// ---

namespace
{
namespace base64_impl
{

constexpr size_t base64AllocSize(std::string_view input)
{
    size_t ret_length = 4 * ((std::size(input) + 2) / 3); // NOLINT misc-const-correctness
#ifdef USE_SYSTEM_B64
    // Additional space is needed for newlines if we're using unpatched libb64
    ret_length += ret_length / 72 + 1;
#endif
    return ret_length * 8;
}

} // namespace base64_impl
} // namespace

std::string tr_base64_encode(std::string_view input)
{
    using namespace base64_impl;

    auto buf = std::vector<char>(base64AllocSize(input));
    auto state = base64_encodestate{};
    base64_init_encodestate(&state);
    size_t len = base64_encode_block(std::data(input), std::size(input), std::data(buf), &state);
    len += base64_encode_blockend(std::data(buf) + len, &state);
    auto str = std::string{};
    std::copy_if(
        std::data(buf),
        std::data(buf) + len,
        std::back_inserter(str),
        [](auto ch) { return !tr_strv_contains("\r\n"sv, ch); });
    return str;
}

std::string tr_base64_decode(std::string_view input)
{
    auto buf = std::vector<char>(std::size(input) + 8);
    auto state = base64_decodestate{};
    base64_init_decodestate(&state);
    size_t const len = base64_decode_block(std::data(input), std::size(input), std::data(buf), &state);
    return std::string{ std::data(buf), len };
}

// ---

namespace
{
namespace hex_impl
{

template<typename InIt, typename OutIt>
constexpr void tr_binary_to_hex(InIt begin, InIt end, OutIt out)
{
    auto constexpr Hex = "0123456789abcdef"sv;

    while (begin != end)
    {
        auto const val = static_cast<unsigned int>(*begin++);
        *out++ = Hex[val >> 4];
        *out++ = Hex[val & 0xF];
    }
}

constexpr void tr_hex_to_binary(char const* input, void* voutput, size_t byte_length)
{
    auto constexpr Hex = "0123456789abcdef"sv;

    auto* output = static_cast<uint8_t*>(voutput);

    for (size_t i = 0; i < byte_length; ++i)
    {
        auto const upper_nibble = Hex.find(std::tolower(*input++));
        auto const lower_nibble = Hex.find(std::tolower(*input++));
        *output++ = (uint8_t)((upper_nibble << 4) | lower_nibble);
    }
}

} // namespace hex_impl
} // namespace

tr_sha1_string tr_sha1_to_string(tr_sha1_digest_t const& digest)
{
    using namespace hex_impl;

    auto str = tr_sha1_string{};
    tr_binary_to_hex(std::begin(digest), std::end(digest), std::back_inserter(str));
    TR_ASSERT(std::size(str) == TrSha1DigestStrlen);
    return str;
}

tr_sha256_string tr_sha256_to_string(tr_sha256_digest_t const& digest)
{
    using namespace hex_impl;

    auto str = tr_sha256_string{};
    tr_binary_to_hex(std::begin(digest), std::end(digest), std::back_inserter(str));
    TR_ASSERT(std::size(str) == TrSha256DigestStrlen);
    return str;
}

std::optional<tr_sha1_digest_t> tr_sha1_from_string(std::string_view hex)
{
    using namespace hex_impl;

    if (std::size(hex) != TrSha1DigestStrlen)
    {
        return {};
    }

    if (!std::all_of(std::begin(hex), std::end(hex), [](unsigned char ch) { return isxdigit(ch); }))
    {
        return {};
    }

    auto digest = tr_sha1_digest_t{};
    tr_hex_to_binary(std::data(hex), std::data(digest), std::size(digest));
    return digest;
}

std::optional<tr_sha256_digest_t> tr_sha256_from_string(std::string_view hex)
{
    using namespace hex_impl;

    if (std::size(hex) != TrSha256DigestStrlen)
    {
        return {};
    }

    if (!std::all_of(std::begin(hex), std::end(hex), [](unsigned char ch) { return isxdigit(ch); }))
    {
        return {};
    }

    auto digest = tr_sha256_digest_t{};
    tr_hex_to_binary(std::data(hex), std::data(digest), std::size(digest));
    return digest;
}

// fallback implementation in case the system crypto library's RNG fails
void tr_rand_buffer_std(void* buffer, size_t length)
{
    static thread_local auto gen = std::mt19937{ std::random_device{}() };
    static thread_local auto dist = std::uniform_int_distribution<unsigned long long>{};

    for (auto *walk = static_cast<uint8_t*>(buffer), *end = walk + length; walk < end;)
    {
        auto const tmp = dist(gen);
        auto const step = std::min(sizeof(tmp), static_cast<size_t>(end - walk));
        walk = std::copy_n(reinterpret_cast<uint8_t const*>(&tmp), step, walk);
    }
}

void tr_rand_buffer(void* buffer, size_t length)
{
    if (!tr_rand_buffer_crypto(buffer, length))
    {
        tr_rand_buffer_std(buffer, length);
    }
}
