// Copyright 2020 The Dawn Authors
//
// 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 SRC_DAWN_COMMON_TYPEDINTEGER_H_
#define SRC_DAWN_COMMON_TYPEDINTEGER_H_

#include <limits>
#include <type_traits>

#include "dawn/common/Assert.h"
#include "dawn/common/UnderlyingType.h"

// TypedInteger is helper class that provides additional type safety in Debug.
//  - Integers of different (Tag, BaseIntegerType) may not be used interoperably
//  - Allows casts only to the underlying type.
//  - Integers of the same (Tag, BaseIntegerType) may be compared or assigned.
// This class helps ensure that the many types of indices in Dawn aren't mixed up and used
// interchangably.
// In Release builds, when DAWN_ENABLE_ASSERTS is not defined, TypedInteger is a passthrough
// typedef of the underlying type.
//
// Example:
//     using UintA = TypedInteger<struct TypeA, uint32_t>;
//     using UintB = TypedInteger<struct TypeB, uint32_t>;
//
//  in Release:
//     using UintA = uint32_t;
//     using UintB = uint32_t;
//
//  in Debug:
//     using UintA = detail::TypedIntegerImpl<struct TypeA, uint32_t>;
//     using UintB = detail::TypedIntegerImpl<struct TypeB, uint32_t>;
//
//     Assignment, construction, comparison, and arithmetic with TypedIntegerImpl are allowed
//     only for typed integers of exactly the same type. Further, they must be
//     created / cast explicitly; there is no implicit conversion.
//
//     UintA a(2);
//     uint32_t aValue = static_cast<uint32_t>(a);
//
namespace detail {
template <typename Tag, typename T>
class TypedIntegerImpl;
}  // namespace detail

template <typename Tag, typename T, typename = std::enable_if_t<std::is_integral<T>::value>>
#if defined(DAWN_ENABLE_ASSERTS)
using TypedInteger = detail::TypedIntegerImpl<Tag, T>;
#else
using TypedInteger = T;
#endif

namespace detail {
template <typename Tag, typename T>
class alignas(T) TypedIntegerImpl {
    static_assert(std::is_integral<T>::value, "TypedInteger must be integral");
    T mValue;

  public:
    constexpr TypedIntegerImpl() : mValue(0) {
        static_assert(alignof(TypedIntegerImpl) == alignof(T));
        static_assert(sizeof(TypedIntegerImpl) == sizeof(T));
    }

    // Construction from non-narrowing integral types.
    template <typename I,
              typename =
                  std::enable_if_t<std::is_integral<I>::value &&
                                   std::numeric_limits<I>::max() <= std::numeric_limits<T>::max() &&
                                   std::numeric_limits<I>::min() >= std::numeric_limits<T>::min()>>
    explicit constexpr TypedIntegerImpl(I rhs) : mValue(static_cast<T>(rhs)) {}

    // Allow explicit casts only to the underlying type. If you're casting out of an
    // TypedInteger, you should know what what you're doing, and exactly what type you
    // expect.
    explicit constexpr operator T() const { return static_cast<T>(this->mValue); }

// Same-tag TypedInteger comparison operators
#define TYPED_COMPARISON(op) \
    constexpr bool operator op(const TypedIntegerImpl& rhs) const { return mValue op rhs.mValue; }
    TYPED_COMPARISON(<)
    TYPED_COMPARISON(<=)
    TYPED_COMPARISON(>)
    TYPED_COMPARISON(>=)
    TYPED_COMPARISON(==)
    TYPED_COMPARISON(!=)
#undef TYPED_COMPARISON

    // Increment / decrement operators for for-loop iteration
    constexpr TypedIntegerImpl& operator++() {
        ASSERT(this->mValue < std::numeric_limits<T>::max());
        ++this->mValue;
        return *this;
    }

    constexpr TypedIntegerImpl operator++(int) {
        TypedIntegerImpl ret = *this;

        ASSERT(this->mValue < std::numeric_limits<T>::max());
        ++this->mValue;
        return ret;
    }

    constexpr TypedIntegerImpl& operator--() {
        ASSERT(this->mValue > std::numeric_limits<T>::min());
        --this->mValue;
        return *this;
    }

    constexpr TypedIntegerImpl operator--(int) {
        TypedIntegerImpl ret = *this;

        ASSERT(this->mValue > std::numeric_limits<T>::min());
        --this->mValue;
        return ret;
    }

    template <typename T2 = T>
    static constexpr std::enable_if_t<std::is_unsigned<T2>::value, decltype(T(0) + T2(0))> AddImpl(
        TypedIntegerImpl<Tag, T> lhs,
        TypedIntegerImpl<Tag, T2> rhs) {
        static_assert(std::is_same<T, T2>::value);

        // Overflow would wrap around
        ASSERT(lhs.mValue + rhs.mValue >= lhs.mValue);
        return lhs.mValue + rhs.mValue;
    }

    template <typename T2 = T>
    static constexpr std::enable_if_t<std::is_signed<T2>::value, decltype(T(0) + T2(0))> AddImpl(
        TypedIntegerImpl<Tag, T> lhs,
        TypedIntegerImpl<Tag, T2> rhs) {
        static_assert(std::is_same<T, T2>::value);

        if (lhs.mValue > 0) {
            // rhs is positive: |rhs| is at most the distance between max and |lhs|.
            // rhs is negative: (positive + negative) won't overflow
            ASSERT(rhs.mValue <= std::numeric_limits<T>::max() - lhs.mValue);
        } else {
            // rhs is postive: (negative + positive) won't underflow
            // rhs is negative: |rhs| isn't less than the (negative) distance between min
            // and |lhs|
            ASSERT(rhs.mValue >= std::numeric_limits<T>::min() - lhs.mValue);
        }
        return lhs.mValue + rhs.mValue;
    }

    template <typename T2 = T>
    static constexpr std::enable_if_t<std::is_unsigned<T>::value, decltype(T(0) - T2(0))> SubImpl(
        TypedIntegerImpl<Tag, T> lhs,
        TypedIntegerImpl<Tag, T2> rhs) {
        static_assert(std::is_same<T, T2>::value);

        // Overflow would wrap around
        ASSERT(lhs.mValue - rhs.mValue <= lhs.mValue);
        return lhs.mValue - rhs.mValue;
    }

    template <typename T2 = T>
    static constexpr std::enable_if_t<std::is_signed<T>::value, decltype(T(0) - T2(0))> SubImpl(
        TypedIntegerImpl<Tag, T> lhs,
        TypedIntegerImpl<Tag, T2> rhs) {
        static_assert(std::is_same<T, T2>::value);

        if (lhs.mValue > 0) {
            // rhs is positive: positive minus positive won't overflow
            // rhs is negative: |rhs| isn't less than the (negative) distance between |lhs|
            // and max.
            ASSERT(rhs.mValue >= lhs.mValue - std::numeric_limits<T>::max());
        } else {
            // rhs is positive: |rhs| is at most the distance between min and |lhs|
            // rhs is negative: negative minus negative won't overflow
            ASSERT(rhs.mValue <= lhs.mValue - std::numeric_limits<T>::min());
        }
        return lhs.mValue - rhs.mValue;
    }

    template <typename T2 = T>
    constexpr std::enable_if_t<std::is_signed<T2>::value, TypedIntegerImpl> operator-() const {
        static_assert(std::is_same<T, T2>::value);
        // The negation of the most negative value cannot be represented.
        ASSERT(this->mValue != std::numeric_limits<T>::min());
        return TypedIntegerImpl(-this->mValue);
    }

    constexpr TypedIntegerImpl operator+(TypedIntegerImpl rhs) const {
        auto result = AddImpl(*this, rhs);
        static_assert(std::is_same<T, decltype(result)>::value, "Use ityp::Add instead.");
        return TypedIntegerImpl(result);
    }

    constexpr TypedIntegerImpl operator-(TypedIntegerImpl rhs) const {
        auto result = SubImpl(*this, rhs);
        static_assert(std::is_same<T, decltype(result)>::value, "Use ityp::Sub instead.");
        return TypedIntegerImpl(result);
    }
};

}  // namespace detail

namespace std {

template <typename Tag, typename T>
class numeric_limits<detail::TypedIntegerImpl<Tag, T>> : public numeric_limits<T> {
  public:
    static detail::TypedIntegerImpl<Tag, T> max() noexcept {
        return detail::TypedIntegerImpl<Tag, T>(std::numeric_limits<T>::max());
    }
    static detail::TypedIntegerImpl<Tag, T> min() noexcept {
        return detail::TypedIntegerImpl<Tag, T>(std::numeric_limits<T>::min());
    }
};

}  // namespace std

namespace ityp {

// These helpers below are provided since the default arithmetic operators for small integer
// types like uint8_t and uint16_t return integers, not their same type. To avoid lots of
// casting or conditional code between Release/Debug. Callsites should use ityp::Add(a, b) and
// ityp::Sub(a, b) instead.

template <typename Tag, typename T>
constexpr ::detail::TypedIntegerImpl<Tag, T> Add(::detail::TypedIntegerImpl<Tag, T> lhs,
                                                 ::detail::TypedIntegerImpl<Tag, T> rhs) {
    return ::detail::TypedIntegerImpl<Tag, T>(
        static_cast<T>(::detail::TypedIntegerImpl<Tag, T>::AddImpl(lhs, rhs)));
}

template <typename Tag, typename T>
constexpr ::detail::TypedIntegerImpl<Tag, T> Sub(::detail::TypedIntegerImpl<Tag, T> lhs,
                                                 ::detail::TypedIntegerImpl<Tag, T> rhs) {
    return ::detail::TypedIntegerImpl<Tag, T>(
        static_cast<T>(::detail::TypedIntegerImpl<Tag, T>::SubImpl(lhs, rhs)));
}

template <typename T>
constexpr std::enable_if_t<std::is_integral<T>::value, T> Add(T lhs, T rhs) {
    return static_cast<T>(lhs + rhs);
}

template <typename T>
constexpr std::enable_if_t<std::is_integral<T>::value, T> Sub(T lhs, T rhs) {
    return static_cast<T>(lhs - rhs);
}

}  // namespace ityp

#endif  // SRC_DAWN_COMMON_TYPEDINTEGER_H_