#pragma once

#include "../mem/allocconfig.h"
#include "../mem/freelist.h"
#include "../mem/metaslab.h"
#include "../mem/sizeclasstable.h"

#include <array>
#include <atomic>

namespace snmalloc
{
  // Remotes need to be aligned enough that all the
  // small size classes can fit in the bottom bits.
  static constexpr size_t REMOTE_MIN_ALIGN = bits::min<size_t>(
    CACHELINE_SIZE, bits::next_pow2_const(NUM_SIZECLASSES + 1));

  /**
   * Global key for all remote lists.
   */
  inline static FreeListKey key_global(0xdeadbeef);

  struct alignas(REMOTE_MIN_ALIGN) RemoteAllocator
  {
    using alloc_id_t = address_t;

    // Store the message queue on a separate cacheline. It is mutable data that
    // is read by other threads.
    alignas(CACHELINE_SIZE) AtomicCapPtr<FreeObject, CBAlloc> back{nullptr};
    // Store the two ends on different cache lines as access by different
    // threads.
    alignas(CACHELINE_SIZE) CapPtr<FreeObject, CBAlloc> front{nullptr};

    constexpr RemoteAllocator() = default;

    void invariant()
    {
      SNMALLOC_ASSERT(back != nullptr);
      SNMALLOC_ASSERT(front != nullptr);
    }

    void init(CapPtr<FreeObject, CBAlloc> stub)
    {
      stub->atomic_store_null();
      front = stub;
      back.store(stub, std::memory_order_relaxed);
      invariant();
    }

    CapPtr<FreeObject, CBAlloc> destroy()
    {
      CapPtr<FreeObject, CBAlloc> fnt = front;
      back.store(nullptr, std::memory_order_relaxed);
      front = nullptr;
      return fnt;
    }

    inline bool is_empty()
    {
      CapPtr<FreeObject, CBAlloc> bk = back.load(std::memory_order_relaxed);

      return bk == front;
    }

    void enqueue(
      CapPtr<FreeObject, CBAlloc> first,
      CapPtr<FreeObject, CBAlloc> last,
      FreeListKey& key)
    {
      // Pushes a list of messages to the queue. Each message from first to
      // last should be linked together through their next pointers.
      invariant();
      last->atomic_store_null();

      // exchange needs to be a release, so nullptr in next is visible.
      CapPtr<FreeObject, CBAlloc> prev =
        back.exchange(last, std::memory_order_release);

      prev->atomic_store_next(first, key);
    }

    CapPtr<FreeObject, CBAlloc> peek()
    {
      return front;
    }

    std::pair<CapPtr<FreeObject, CBAlloc>, bool> dequeue(FreeListKey& key)
    {
      // Returns the front message, or null if not possible to return a message.
      invariant();
      CapPtr<FreeObject, CBAlloc> first = front;
      CapPtr<FreeObject, CBAlloc> next = first->atomic_read_next(key);

      if (next != nullptr)
      {
        front = next;
        invariant();
        return {first, true};
      }

      return {nullptr, false};
    }

    alloc_id_t trunc_id()
    {
      return address_cast(this);
    }
  };
} // namespace snmalloc