/*
 * Copyright 2017 - 2018 Justas Masiulis
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef JM_XORSTR_HPP
#define JM_XORSTR_HPP

#include <immintrin.h>
#include <cstdint>
#include <cstddef>
#include <utility>

#define JM_XORSTR_DISABLE_AVX_INTRINSICS

#define xorstr_(str)                                             \
    ::jm::make_xorstr(                                           \
        []() { return str; },                                    \
        std::make_index_sequence<sizeof(str) / sizeof(*str)>{},  \
        std::make_index_sequence<::jm::detail::_buffer_size<sizeof(str)>()>{})
#define xorstr(str) xorstr_(str).crypt_get()

#ifdef _MSC_VER
#define XORSTR_FORCEINLINE __forceinline
#else
#define XORSTR_FORCEINLINE __attribute__((always_inline))
#endif

 // you can define this macro to get possibly faster code on gcc/clang
 // at the expense of constants being put into data section.
#if !defined(XORSTR_ALLOW_DATA)
// MSVC - no volatile
// GCC and clang - volatile everywhere
#if defined(__clang__) || defined(__GNUC__)
#define XORSTR_VOLATILE volatile
#endif

#endif
#ifndef XORSTR_VOLATILE
#define XORSTR_VOLATILE
#endif

namespace jm {

    namespace detail {

        template<std::size_t S>
        struct unsigned_;

        template<>
        struct unsigned_<1> {
            using type = std::uint8_t;
        };
        template<>
        struct unsigned_<2> {
            using type = std::uint16_t;
        };
        template<>
        struct unsigned_<4> {
            using type = std::uint32_t;
        };

        template<auto C, auto...>
        struct pack_value_type {
            using type = decltype(C);
        };

        template<std::size_t Size>
        constexpr std::size_t _buffer_size() {
            return ((Size / 16) + (Size % 16 != 0)) * 2;
        }

        template<auto... Cs>
        struct tstring_ {
            using value_type = typename pack_value_type<Cs...>::type;
            constexpr static std::size_t size = sizeof...(Cs);
            constexpr static value_type  str[size] = { Cs... };

            constexpr static std::size_t buffer_size = _buffer_size<sizeof(str)>();
            constexpr static std::size_t buffer_align =
#ifndef JM_XORSTR_DISABLE_AVX_INTRINSICS
            ((sizeof(str) > 16) ? 32 : 16);
#else
                16;
#endif
        };

        template<std::size_t I, std::uint64_t K>
        struct _ki {
            constexpr static std::size_t   idx = I;
            constexpr static std::uint64_t key = K;
        };

        template<std::uint32_t Seed>
        constexpr std::uint32_t key4() noexcept {
            std::uint32_t value = Seed;
            for (char c : __TIME__)
                value = static_cast<std::uint32_t>((value ^ c) * 16777619ull);
            return value;
        }

        template<std::size_t S>
        constexpr std::uint64_t key8() {
            constexpr auto first_part = key4<2166136261 + S>();
            constexpr auto second_part = key4<first_part>();
            return (static_cast<std::uint64_t>(first_part) << 32) | second_part;
        }

        // clang and gcc try really hard to place the constants in data
        // sections. to counter that there was a need to create an intermediate
        // constexpr string and then copy it into a non constexpr container with
        // volatile storage so that the constants would be placed directly into
        // code.
        template<class T, std::uint64_t... Keys>
        struct string_storage {
            std::uint64_t storage[T::buffer_size];

            XORSTR_FORCEINLINE constexpr string_storage() noexcept : storage{ Keys... } {
                using cast_type =
                    typename unsigned_<sizeof(typename T::value_type)>::type;
                constexpr auto value_size = sizeof(typename T::value_type);
                // puts the string into 64 bit integer blocks in a constexpr
                // fashion
                for (std::size_t i = 0; i < T::size; ++i)
                    storage[i / (8 / value_size)] ^=
                    (std::uint64_t{ static_cast<cast_type>(T::str[i]) }
                << ((i % (8 / value_size)) * 8 * value_size));
            }
        };

    } // namespace detail

    template<class T, class... Keys>
    class xor_string {
        alignas(T::buffer_align) std::uint64_t _storage[T::buffer_size];

        // _single functions needed because MSVC crashes without them
        XORSTR_FORCEINLINE void _crypt_256_single(const std::uint64_t *keys,
            std::uint64_t *storage) noexcept

        {
            _mm256_store_si256(
                reinterpret_cast<__m256i *>(storage),
                _mm256_xor_si256(
                    _mm256_load_si256(reinterpret_cast<const __m256i *>(storage)),
                    _mm256_load_si256(reinterpret_cast<const __m256i *>(keys))));
        }

        template<std::size_t... Idxs>
        XORSTR_FORCEINLINE void _crypt_256(const std::uint64_t *keys,
            std::index_sequence<Idxs...>) noexcept {
            (_crypt_256_single(keys + Idxs * 4, _storage + Idxs * 4), ...);
        }

        XORSTR_FORCEINLINE void _crypt_128_single(const std::uint64_t *keys,
            std::uint64_t *storage) noexcept {
            _mm_store_si128(
                reinterpret_cast<__m128i *>(storage),
                _mm_xor_si128(_mm_load_si128(reinterpret_cast<const __m128i *>(storage)),
                    _mm_load_si128(reinterpret_cast<const __m128i *>(keys))));
        }

        template<std::size_t... Idxs>
        XORSTR_FORCEINLINE void _crypt_128(const std::uint64_t *keys,
            std::index_sequence<Idxs...>) noexcept {
            (_crypt_128_single(keys + Idxs * 2, _storage + Idxs * 2), ...);
        }

        // loop generates vectorized code which places constants in data dir
        XORSTR_FORCEINLINE constexpr void _copy() noexcept {
            constexpr detail::string_storage<T, Keys::key...> storage;
            static_cast<void>(std::initializer_list<std::uint64_t>{
                (const_cast<XORSTR_VOLATILE std::uint64_t *>(_storage))[Keys::idx] =
                    storage.storage[Keys::idx]... });
        }

    public:
        using value_type = typename T::value_type;
        using size_type = std::size_t;
        using pointer = value_type *;
        using const_pointer = const pointer;

        XORSTR_FORCEINLINE xor_string() noexcept { _copy(); }

        XORSTR_FORCEINLINE constexpr size_type size() const noexcept {
            return T::size - 1;
        }

        XORSTR_FORCEINLINE void crypt() noexcept {
            alignas(T::buffer_align) std::uint64_t keys[T::buffer_size];
            static_cast<void>(std::initializer_list<std::uint64_t>{
                (const_cast<XORSTR_VOLATILE std::uint64_t *>(keys))[Keys::idx] =
                    Keys::key... });

            _copy();

#ifndef JM_XORSTR_DISABLE_AVX_INTRINSICS
            _crypt_256(keys, std::make_index_sequence<T::buffer_size / 4>{});
            if constexpr (T::buffer_size % 4 != 0)
                _crypt_128(keys, std::index_sequence<T::buffer_size / 2 - 1>{});
#else
            _crypt_128(keys, std::make_index_sequence<T::buffer_size / 2>{});
#endif
        }

        XORSTR_FORCEINLINE const_pointer get() const noexcept {
            return reinterpret_cast<const_pointer>(_storage);
        }

        XORSTR_FORCEINLINE const_pointer crypt_get() noexcept {
            crypt();
            return reinterpret_cast<const_pointer>(_storage);
        }
    };

    template<class Tstr, std::size_t... StringIndices, std::size_t... KeyIndices>
    XORSTR_FORCEINLINE constexpr auto
        make_xorstr(Tstr str_lambda,
            std::index_sequence<StringIndices...>,
            std::index_sequence<KeyIndices...>) noexcept {
        return xor_string<detail::tstring_<str_lambda()[StringIndices]...>,
            detail::_ki<KeyIndices, detail::key8<KeyIndices>()>...>{};
    }

} // namespace jm

#endif // include guard