/*
 * libfud
 * Copyright 2025 Dominick Allen
 *
 * 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 FUD_HASH_HPP
#define FUD_HASH_HPP

#include "fud_string.hpp"
#include "fud_string_view.hpp"
#include "fud_utf8.hpp"

#include <type_traits>

/*
namespace fud {
template <typename Key>
concept Hashable = requires(Key key) {
    { sink.drain(source) } -> std::same_as<DrainResult>;
};
} // namespace fud
*/

namespace fud::detail {

constexpr uint64_t roundToNearest2(uint64_t inputValue) noexcept
{
    if (inputValue == 0) {
        return 1;
    }
    uint64_t outputValue = inputValue - 1;
    constexpr uint8_t max2PowerShift = 32;
    for (uint8_t shift = 1; shift <= max2PowerShift; shift *= 2) {
        outputValue |= outputValue >> shift;
    }
    outputValue++;
    return outputValue;
}

/** \brief The djb2 algorithm by Dan Bernstein. See http://www.cse.yorku.ca/~oz/hash.html
 *
 * If passed a null pointer for data, returns the initial hash value.
 */
size_t djb2(const utf8* data, size_t length);

template <typename T>
struct DefaultHash {
    static_assert(std::is_integral_v<T> || std::is_enum_v<T>);
    size_t operator()(const T& value, size_t seed) const
    {
        static_cast<void>(seed);
        return djb2(std::bit_cast<const utf8*>(&value), sizeof(value));
    }
};

template <>
struct DefaultHash<String> {
    size_t operator()(const String& value, size_t seed) const;
};

template <>
struct DefaultHash<StringView> {
    size_t operator()(const StringView& value, size_t seed) const;
};

} // namespace fud::detail

#endif