/*
  Copyright (c) 2014-2015 DataStax

  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 __CASS_FIXED_ALLOCATOR_HPP_INCLUDED__
#define __CASS_FIXED_ALLOCATOR_HPP_INCLUDED__

#include "aligned_storage.hpp"
#include "macros.hpp"

#include <limits>
#include <memory>
#include <vector>

namespace cass {

// This is an allocator that starts using a fixed size buffer that only
// uses the heap when exceeded. The allocator can be
// copied so the vector itself needs to hold on to the fixed buffer.

template <class T, size_t N>
class FixedAllocator {
public:
  typedef size_t size_type;
  typedef ptrdiff_t difference_type;
  typedef T value_type;
  typedef T* pointer;
  typedef const T* const_pointer;
  typedef T& reference;
  typedef const T& const_reference;

  template <class U> struct rebind { typedef FixedAllocator<U, N> other; };

  struct Fixed {
    Fixed()
      : is_used(false) {}

    // See aligned_storage.hpp for why this is required
    typedef AlignedStorage<N * sizeof(T), ALIGN_OF(T)> Storage;

    bool is_used;
    Storage data;
  };

  FixedAllocator()
    : fixed_(NULL) {}

  FixedAllocator(Fixed* fixed)
    : fixed_(fixed) {}

  FixedAllocator(const FixedAllocator<T, N>& allocator)
    : fixed_(allocator.fixed_) {}

  template<class U, size_t M>
  FixedAllocator(const FixedAllocator<U, M>& allocator)
    : fixed_(NULL) {}

  FixedAllocator(const std::allocator<T>& allocator)
    : fixed_(NULL) {}

  pointer address(reference x) const {
    return &x;
  }

  const_pointer address(const_reference x) const {
    return &x;
  }

  pointer allocate(size_type n, const_pointer hint = NULL) {
    if (fixed_ != NULL && !fixed_->is_used && n <= N) {
      fixed_->is_used = true; // Don't reuse the buffer
      return static_cast<T*>(fixed_->data.address());
    } else {
      return static_cast<T*>(::operator new(sizeof(T) * n));
    }
  }

  void deallocate(pointer p, size_type n) {
    if (fixed_ != NULL && fixed_->data.address() == p) {
      fixed_->is_used = false; // It's safe to reuse the buffer
    } else {
      ::operator delete(p);
    }
  }

  void construct(pointer p, const_reference x) {
    new (p) value_type(x);
  }

  void destroy(pointer p) {
    p->~value_type();
  }

  size_type max_size() const throw() {
    return std::numeric_limits<size_type>::max();
  }

private:
  Fixed* fixed_;
};

// This vector uses the fixed buffer as long as it doesn't exceed N items.
// This can help to avoid heap allocation in the common cases while also
// handling the cases that do exceed the fixed buffer.

template<class T, size_t N>
class FixedVector : public std::vector<T, FixedAllocator<T, N> > {
public:
  FixedVector()
    : std::vector<T, FixedAllocator<T, N> >(FixedAllocator<T, N>(&fixed_)) {
    this->reserve(N);
  }

  FixedVector(size_t inital_size)
    : std::vector<T, FixedAllocator<T, N> >(FixedAllocator<T, N>(&fixed_)) {
    this->resize(inital_size);
  }

  const typename FixedAllocator<T, N>::Fixed& fixed() const { return fixed_; }

private:
  typename FixedAllocator<T, N>::Fixed fixed_;

private:
  DISALLOW_COPY_AND_ASSIGN(FixedVector);
};

} // namespace cass

#endif // FIXED_ALLOCATOR_HPP