#pragma once

#include <iterator>
#include "../concepts/snplib_concepts.h"

namespace snplib
{

template <snplib_input_char_range_c R>
static constexpr size_t hash_FNV1a(const R& r)
{
    static_assert(sizeof(size_t) == 8 || sizeof(size_t) == 4, "The ONLY 32 or 64-bit std::size_t are supported!!!");

    size_t hash = 0, prime = 0;
    if constexpr (sizeof(size_t) == 8) {  // 64-bit
        prime = 1099511628211UL;
        hash = 14695981039346656037UL;
    } else if constexpr (sizeof(size_t) == 4) {  // 32-bit
        prime = 16777619;
        hash = 2166136261;
    }

    for (const char& ch : r) {
        hash ^= ch;
        hash *= prime;
    }

    return hash;
}

static constexpr size_t hash_FNV1a(std::forward_iterator auto begin, std::sentinel_for<decltype(begin)> auto end)
    requires std::same_as<std::remove_cv_t<std::iter_value_t<decltype(begin)>>, char>
{
    static_assert(sizeof(size_t) == 8 || sizeof(size_t) == 4, "The ONLY 32 or 64-bit std::size_t are supported!!!");

    size_t hash = 0, prime = 0;
    if constexpr (sizeof(size_t) == 8) {  // 64-bit
        prime = 1099511628211UL;
        hash = 14695981039346656037UL;
    } else if constexpr (sizeof(size_t) == 4) {  // 32-bit
        prime = 16777619;
        hash = 2166136261;
    }

    for (auto it = begin; it != end; ++it) {
        hash ^= *it;
        hash *= prime;
    }

    return hash;
}


// Boost implementation of hash combining
template <snplib_hashable_c T, snplib_hashable_c... Ts>
static constexpr void snplib_hash_combine(std::size_t& seed, const T& v, Ts&&... vs)
{
    static constexpr auto digits = std::numeric_limits<std::size_t>::digits;
    static_assert(digits == 64 || digits == 32, "The ONLY 32 or 64-bit std::size_t are supported!!!");

    if constexpr (digits == 64) {
        std::size_t x = seed + 0x9e3779b9 + std::hash<T>()(v);
        const std::size_t m = 0xe9846af9b1a615d;
        x ^= x >> 32;
        x *= m;
        x ^= x >> 32;
        x *= m;
        x ^= x >> 28;
        seed = x;
    } else {  // 32-bits
        std::size_t x = seed + 0x9e3779b9 + std::hash<T>()(v);
        const std::size_t m1 = 0x21f0aaad;
        const std::size_t m2 = 0x735a2d97;
        x ^= x >> 16;
        x *= m1;
        x ^= x >> 15;
        x *= m2;
        x ^= x >> 15;
        seed = x;
    }

    if constexpr (sizeof...(Ts)) {
        snplib_hash_combine(seed, std::forward<Ts>(vs)...);
    }
}

}  // namespace snplib