#pragma once

#include <xrpl/beast/hash/xxhasher.h>

#include <cstdint>
#include <mutex>
#include <random>
#include <utility>

namespace xrpl {

namespace detail {

using seed_pair = std::pair<std::uint64_t, std::uint64_t>;

template <bool = true>
seed_pair
makeSeedPair() noexcept
{
    struct StateT
    {
        std::mutex mutex;
        std::random_device rng;
        std::mt19937_64 gen;
        std::uniform_int_distribution<std::uint64_t> dist;

        StateT() : gen(rng())
        {
        }
        // state_t(state_t const&) = delete;
        // state_t& operator=(state_t const&) = delete;
    };
    static StateT kState;
    std::scoped_lock const lock(kState.mutex);
    return {kState.dist(kState.gen), kState.dist(kState.gen)};
}

}  // namespace detail

/**
 * Seed functor once per construction
 *
 * A std compatible hash adapter that resists adversarial inputs.
 * For this to work, T must implement in its own namespace:
 *
 * @code
 *
 * template <class Hasher>
 * void
 * hash_append (Hasher& h, T const& t) noexcept
 * {
 *     // hash_append each base and member that should
 *     //  participate in forming the hash
 *     using beast::hash_append;
 *     hash_append (h, static_cast<T::base1 const&>(t));
 *     hash_append (h, static_cast<T::base2 const&>(t));
 *     // ...
 *     hash_append (h, t.member1);
 *     hash_append (h, t.member2);
 *     // ...
 * }
 *
 * @endcode
 *
 * Do not use any version of Murmur or CityHash for the Hasher
 * template parameter (the hashing algorithm).  For details
 * see https://131002.net/siphash/#at
 */

template <class HashAlgorithm = beast::Xxhasher>
class HardenedHash
{
private:
    detail::seed_pair seeds_{detail::makeSeedPair<>()};

public:
    using result_type = HashAlgorithm::result_type;

    HardenedHash() = default;

    template <class T>
    result_type
    operator()(T const& t) const noexcept
    {
        HashAlgorithm h(seeds_.first, seeds_.second);
        hash_append(h, t);
        return static_cast<result_type>(h);
    }
};

}  // namespace xrpl