/*
 * 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 CONST_BUFFER_HPP
#define CONST_BUFFER_HPP

#include "Compiler.h"

#include <cstddef>

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

template<typename T>
struct ConstBuffer;

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

  pointer_type data;
  size_type size;

  ConstBuffer() = default;

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

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

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

  constexpr static ConstBuffer<void> FromVoid(ConstBuffer<void> other) {
    return other;
  }

  constexpr ConstBuffer<void> ToVoid() const {
    return *this;
  }

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

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

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

  pointer_type data;
  size_type size;

  ConstBuffer() = default;

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

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

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

  /**
   * Cast a ConstBuffer<void> to a ConstBuffer<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 ConstBuffer<T> FromVoid(ConstBuffer<void> other) {
    static_assert(sizeof(T) > 0, "Empty base type");
#ifndef NDEBUG
    assert(other.size % sizeof(T) == 0);
#endif
    return ConstBuffer<T>(pointer_type(other.data),
                          other.size / sizeof(T));
  }

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

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

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

  template<typename U>
  gcc_pure
  bool Contains(U &&u) const {
    for (const auto &i : *this)
      if (u == i)
        return true;

    return false;
  }

  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() {
#ifndef NDEBUG
    assert(!IsEmpty());
#endif

    ++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() {
#ifndef NDEBUG
    assert(!IsEmpty());
#endif

    --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;
  }

  void skip_front(size_type n) {
#ifndef NDEBUG
    assert(size >= n);
#endif

    data += n;
    size -= n;
  }
};

#endif
