/*
 * Copyright (C) 2013-2014 Max Kellermann <max@duempel.org>
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 * notice, this list of conditions and the following disclaimer.
 *
 * - Redistributions in binary form must reproduce the above copyright
 * notice, this list of conditions and the following disclaimer in the
 * documentation and/or other materials provided with the
 * distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef WRITABLE_BUFFER_HPP
#define WRITABLE_BUFFER_HPP

#include "Compiler.h"

#include <cstddef>

#ifndef NDEBUG
#include <assert.h>
#endif

template<typename T>
struct WritableBuffer;

template<>
struct WritableBuffer<void> {
  typedef size_t size_type;
  typedef void *pointer_type;
  typedef const void *const_pointer_type;
  typedef pointer_type iterator;
  typedef const_pointer_type const_iterator;

  pointer_type data;
  size_type size;

  WritableBuffer() = default;

  constexpr WritableBuffer(std::nullptr_t):data(nullptr), size(0) {}

  constexpr WritableBuffer(pointer_type _data, size_type _size)
    :data(_data), size(_size) {}

  constexpr static WritableBuffer Null() {
    return { nullptr, 0 };
  }

  constexpr bool IsNull() const {
    return data == nullptr;
  }

  constexpr bool IsEmpty() const {
    return size == 0;
  }
};

/**
 * A reference to a memory area that is writable.
 *
 * @see ConstBuffer
 */
template<typename T>
struct WritableBuffer {
  typedef size_t size_type;
  typedef T &reference_type;
  typedef const T &const_reference_type;
  typedef T *pointer_type;
  typedef const T *const_pointer_type;
  typedef pointer_type iterator;
  typedef const_pointer_type const_iterator;

  pointer_type data;
  size_type size;

  WritableBuffer() = default;

  constexpr WritableBuffer(std::nullptr_t):data(nullptr), size(0) {}

  constexpr WritableBuffer(pointer_type _data, size_type _size)
    :data(_data), size(_size) {}

  constexpr static WritableBuffer Null() {
    return { nullptr, 0 };
  }

  /**
   * Cast a WritableBuffer<void> to a WritableBuffer<T>.  A "void"
   * buffer records its size in bytes, and when casting to "T",
   * the assertion below ensures that the size is a multiple of
   * sizeof(T).
   */
#ifdef NDEBUG
  constexpr
#endif
  static WritableBuffer<T> FromVoid(WritableBuffer<void> other) {
    static_assert(sizeof(T) > 0, "Empty base type");
#ifndef NDEBUG
    assert(other.size % sizeof(T) == 0);
#endif
    return WritableBuffer<T>(pointer_type(other.data),
                             other.size / sizeof(T));
  }

  constexpr WritableBuffer<void> ToVoid() const {
    static_assert(sizeof(T) > 0, "Empty base type");
    return WritableBuffer<void>(data, size * sizeof(T));
  }

  constexpr bool IsNull() const {
    return data == nullptr;
  }

  constexpr bool IsEmpty() const {
    return size == 0;
  }

  constexpr iterator begin() const {
    return data;
  }

  constexpr iterator end() const {
    return data + size;
  }

  constexpr const_iterator cbegin() const {
    return data;
  }

  constexpr const_iterator cend() const {
    return data + size;
  }

#ifdef NDEBUG
  constexpr
#endif
  reference_type operator[](size_type i) const {
#ifndef NDEBUG
    assert(i < size);
#endif

    return data[i];
  }

  /**
   * Returns a reference to the first element.  Buffer must not
   * be empty.
   */
#ifdef NDEBUG
  constexpr
#endif
  reference_type front() const {
#ifndef NDEBUG
    assert(!IsEmpty());
#endif
    return data[0];
  }

  /**
   * Returns a reference to the last element.  Buffer must not
   * be empty.
   */
#ifdef NDEBUG
  constexpr
#endif
  reference_type back() const {
#ifndef NDEBUG
    assert(!IsEmpty());
#endif
    return data[size - 1];
  }

  /**
   * Remove the first element (by moving the head pointer, does
   * not actually modify the buffer).  Buffer must not be empty.
   */
  void pop_front() {
    assert(!IsEmpty());

    ++data;
    --size;
  }

  /**
   * Remove the last element (by moving the tail pointer, does
   * not actually modify the buffer).  Buffer must not be empty.
   */
  void pop_back() {
    assert(!IsEmpty());

    --size;
  }

  /**
   * Remove the first element and return a reference to it.
   * Buffer must not be empty.
   */
  reference_type shift() {
    reference_type result = front();
    pop_front();
    return result;
  }
};

#endif
