#pragma once

#include <cstdint>
#include <cstring>
#include <type_traits>

namespace Slang
{
    //
    // Types
    //

    struct StableHashCode64
    {
        uint64_t hash;
        explicit operator uint64_t() const { return hash; }
        bool operator==(StableHashCode64 other) const { return other.hash == hash; };
        bool operator!=(StableHashCode64 other) const { return other.hash != hash; };
    };

    struct StableHashCode32
    {
        uint32_t hash;
        explicit operator uint32_t() const { return hash; }
        bool operator==(StableHashCode32 other) const { return other.hash == hash; };
        bool operator!=(StableHashCode32 other) const { return other.hash != hash; };
    };

    /* The 'Stable' hash code functions produce hashes that must be

    * The same result for the same inputs on all targets
    * Rarely change - as their values can change the output of the Slang API/Serialization

    Hash value used from the 'Stable' functions can also be used as part of serialization -
    so it is in effect part of the API.

    In effect this means changing a 'Stable' algorithm will typically require doing a new release.
    */
    inline StableHashCode64 getStableHashCode64(const char* buffer, size_t numChars)
    {
        uint64_t hash = 0;
        for (size_t i = 0; i < numChars; ++i)
        {
            hash = uint64_t(buffer[i]) + (hash << 6) + (hash << 16) - hash;
        }
        return StableHashCode64{hash};
    }

    template<typename T>
    inline StableHashCode64 getStableHashCode64(const T& t)
    {
        static_assert(std::has_unique_object_representations_v<T>);
        return getStableHashCode64(reinterpret_cast<const char*>(&t), sizeof(T));
    }

    inline StableHashCode32 getStableHashCode32(const char* buffer, size_t numChars)
    {
        uint32_t hash = 0;
        for (size_t i = 0; i < numChars; ++i)
        {
            hash = uint32_t(buffer[i]) + (hash << 6) + (hash << 16) - hash;
        }
        return StableHashCode32{hash};
    }

    template<typename T>
    inline StableHashCode32 getStableHashCode32(const T& t)
    {
        static_assert(std::has_unique_object_representations_v<T>);
        return getStableHashCode32(reinterpret_cast<const char*>(&t), sizeof(T));
    }

    inline StableHashCode64 combineStableHash(StableHashCode64 h)
    {
        return h;
    }

    inline StableHashCode32 combineStableHash(StableHashCode32 h)
    {
        return h;
    }

    // A left fold with a mixing operation
    template<typename H, typename... Hs>
    H combineStableHash(H n, H m, Hs... args)
    {
        return combineStableHash(H{(n.hash * 16777619) ^ m.hash}, args...);
    }
}

// > Please draw a small horse in ASCII art:
//
//           ,~~.
//          (  9 )-_,
//  (\___ )=='-' )
//   \ .   ) )  /
//    \ `-' /  /
// ~'`~'`~'`~'`~
//