// =====================================================================================================================
//  fennec, a free and open source game engine
//  Copyright © 2025 - 2026  Medusa Slockbower
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <https://www.gnu.org/licenses/>.
// =====================================================================================================================

#ifndef FENNEC_LANG_HASHING_H
#define FENNEC_LANG_HASHING_H

#include <fennec/lang/types.h>
#include <fennec/lang/type_traits.h>
#include <fennec/lang/bits.h>

namespace fennec
{

///
/// \brief Struct for hashing types, there is no default hashing function
/// \tparam Key The type to hash
template<typename Key> struct hash;

/// \brief Murmur3 Hash for 64-bit ints
template<>
struct hash<uint64_t> {
	using type_t = uint64_t; //!< the type of the hash
	/// \brief hash operator
	/// \param x the value to hash
	/// \returns an integer hash for the value
	constexpr size_t operator()(uint64_t x) const {
		// Murmur3
		x ^= x >> 33U;
		x *= 0xff51afd7ed558ccd;
		x ^= x >> 33U;
		x *= 0xc4ceb9fe1a85ec53;
		x ^= x >> 33U;
		return x;
	}
};

/// \brief Hashing for integer types
/// \tparam IntT the integer type
template<typename IntT>
	requires is_integral_v<IntT>
struct hash<IntT> : hash<uint64_t> {
	using type_t = IntT; //!< the type of the hash
};

/// \brief Hashing for pointer types
/// \tparam PtrT The base type
template<typename PtrT>
struct hash<PtrT*> : hash<uintptr_t> {
	using type_t = PtrT*; //!< the type of the hash
	/// \brief hash operator
	/// \param ptr the pointer to hash
	/// \returns an integer hash for the value
	constexpr size_t operator()(PtrT* ptr) const {
		return hash<uintptr_t>::operator()(fennec::bit_cast<uintptr_t>(ptr));
	}
};

/// \brief Hashing for `float`
template<>
struct hash<float> : hash<uint32_t> {
	using type_t = float; //!< the type of the hash
	/// \brief hash operator
	/// \param x the value to hash
	/// \returns an integer hash for the value
	constexpr size_t operator()(float x) const {
		return hash<uint32_t>::operator()(bit_cast<uint32_t>(x));
	}
};

/// \brief Hashing for `double`
template<>
struct hash<double> : hash<uint64_t> {
	using type_t = double; //!< the type of the hash
	/// \brief hash operator
	/// \param x the value to hash
	/// \returns an integer hash for the value
	constexpr size_t operator()(double x) const {
		return hash<uint64_t>::operator()(bit_cast<uint64_t>(x));
	}
};


///
/// \brief Pairs two hashes
/// \param x first hash
/// \param y second hash
/// \returns a pairing of the two hashes
constexpr size_t pair_hash(size_t x, size_t y) {
	// Szudzik Pairing
	return (x >= y ? (x * x) + x + y : (y * y) + x);
}

}

#endif // FENNEC_LANG_HASHING_H
