#ifndef SHORT_ALLOC_H
#define SHORT_ALLOC_H

// The MIT License (MIT)
//
// Copyright (c) 2015 Howard Hinnant
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
// SOFTWARE.

#include <cassert>
#include <cstddef>
#include <cstdint>
#include <vector>

template<std::size_t N, std::size_t alignment = alignof(std::max_align_t)>
class arena {
    alignas(alignment) char buf_[N];
    char* ptr_;

public:
    ~arena() { ptr_ = nullptr; }
    arena() noexcept : ptr_(buf_) {}
    arena(const arena&) = delete;
    arena& operator=(const arena&) = delete;

    template<std::size_t ReqAlign>
    char* allocate(std::size_t n);
    void deallocate(char* p, std::size_t n) noexcept;

    static constexpr std::size_t size() noexcept { return N; }
    std::size_t used() const noexcept
    {
        return static_cast<std::size_t>(ptr_ - buf_);
    }
    void reset() noexcept { ptr_ = buf_; }

private:
    static std::size_t align_up(std::size_t n) noexcept
    {
        return (n + (alignment - 1)) & ~(alignment - 1);
    }

    bool pointer_in_buffer(char* p) noexcept
    {
        return std::uintptr_t(buf_) <= std::uintptr_t(p)
            && std::uintptr_t(p) <= std::uintptr_t(buf_) + N;
    }
};

template<std::size_t N, std::size_t alignment>
template<std::size_t ReqAlign>
char*
arena<N, alignment>::allocate(std::size_t n)
{
    static_assert(ReqAlign <= alignment,
                  "alignment is too small for this arena");
    assert(pointer_in_buffer(ptr_) && "short_alloc has outlived arena");
    auto const aligned_n = align_up(n);
    if (static_cast<decltype(aligned_n)>(buf_ + N - ptr_) >= aligned_n) {
        char* r = ptr_;
        ptr_ += aligned_n;
        return r;
    }

    static_assert(
        alignment <= alignof(std::max_align_t),
        "you've chosen an "
        "alignment that is larger than alignof(std::max_align_t), and "
        "cannot be guaranteed by normal operator new");
    return static_cast<char*>(::operator new(n));
}

template<std::size_t N, std::size_t alignment>
void
arena<N, alignment>::deallocate(char* p, std::size_t n) noexcept
{
    assert(pointer_in_buffer(ptr_) && "short_alloc has outlived arena");
    if (pointer_in_buffer(p)) {
        n = align_up(n);
        if (p + n == ptr_)
            ptr_ = p;
    } else
        ::operator delete(p);
}

template<class T, std::size_t N, std::size_t Align = alignof(std::max_align_t)>
class short_alloc {
public:
    using value_type = T;
    static auto constexpr alignment = Align;
    static auto constexpr size = N;
    using arena_type = arena<size, alignment>;

private:
    arena_type& a_;

public:
    short_alloc(const short_alloc&) = default;
    short_alloc& operator=(const short_alloc&) = delete;

    short_alloc(arena_type& a) noexcept : a_(a)
    {
        static_assert(size % alignment == 0,
                      "size N needs to be a multiple of alignment Align");
    }
    template<class U>
    short_alloc(const short_alloc<U, N, alignment>& a) noexcept : a_(a.a_)
    {
    }

    template<class _Up>
    struct rebind {
        using other = short_alloc<_Up, N, alignment>;
    };

    T* allocate(std::size_t n)
    {
        return reinterpret_cast<T*>(
            a_.template allocate<alignof(T)>(n * sizeof(T)));
    }
    void deallocate(T* p, std::size_t n) noexcept
    {
        a_.deallocate(reinterpret_cast<char*>(p), n * sizeof(T));
    }

    template<class T1,
             std::size_t N1,
             std::size_t A1,
             class U,
             std::size_t M,
             std::size_t A2>
    friend bool operator==(const short_alloc<T1, N1, A1>& x,
                           const short_alloc<U, M, A2>& y) noexcept;

    template<class U, std::size_t M, std::size_t A>
    friend class short_alloc;
};

template<class T,
         std::size_t N,
         std::size_t A1,
         class U,
         std::size_t M,
         std::size_t A2>
inline bool
operator==(const short_alloc<T, N, A1>& x,
           const short_alloc<U, M, A2>& y) noexcept
{
    return N == M && A1 == A2 && &x.a_ == &y.a_;
}

template<class T,
         std::size_t N,
         std::size_t A1,
         class U,
         std::size_t M,
         std::size_t A2>
inline bool
operator!=(const short_alloc<T, N, A1>& x,
           const short_alloc<U, M, A2>& y) noexcept
{
    return !(x == y);
}

template<typename T, std::size_t BufSize = 256>
using stack_vector = std::vector<T, short_alloc<T, BufSize, alignof(T)>>;

struct stack_buf {
    static constexpr auto SIZE = 256;
    char sb_backing[SIZE];
    char* sb_value{nullptr};

    stack_buf() = default;

    stack_buf(const stack_buf&) = delete;
    stack_buf(stack_buf&&) = delete;

    stack_buf& operator=(const stack_buf&) = delete;
    stack_buf& operator=(stack_buf&&) = delete;

    ~stack_buf()
    {
        if (this->sb_value != nullptr) {
            delete[] this->sb_value;
        }
    }

    char* allocate(std::size_t amount)
    {
        if (amount < SIZE) {
            return this->sb_backing;
        }
        this->sb_value = new char[amount];
        return this->sb_value;
    }
};

#endif  // SHORT_ALLOC_H
