cyclic_buffer.h

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/*
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  it under the terms of the GNU General Public License, version 2.0,
  as published by the Free Software Foundation.
 
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  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  GNU General Public License for more details.
 
  You should have received a copy of the GNU General Public License
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*/
 
#ifndef MYSQL_HARNESS_UTILITY_CONTAINER_CYCLE_BUFFER_H_
#define MYSQL_HARNESS_UTILITY_CONTAINER_CYCLE_BUFFER_H_
 
#include <array>
#include <cstdint>
#include <iterator>
 
namespace mysql_harness {
namespace utility {
namespace container {
 
template <uint32_t buffer_size, typename Container>
class CycleBuffer {
  using Cbuffer = CycleBuffer<buffer_size, Container>;
  using Cinterator = typename Container::iterator;
  using Cpointer = typename Container::pointer;
  using Cconst_interator = typename Container::const_iterator;
  using Creference = typename Container::reference;
  using Cconst_reference = typename Container::const_reference;
  using value_type = typename Container::value_type;
 
  class Position {
   public:
    Cinterator it_;
    uint32_t flips_{0};
 
    bool operator==(const Position &other) const {
      return it_ == other.it_ && flips_ == other.flips_;
    }
  };
 
  class Const_position {
   public:
    Const_position() {}
    Const_position(const Const_position &p) : it_{p.it_}, flips_{p.flips_} {}
    Const_position(const Position &p) : it_{p.it_}, flips_{p.flips_} {}
 
    Cconst_interator it_;
    uint32_t flips_{0};
 
    bool operator==(const Const_position &other) const {
      return it_ == other.it_ && flips_ == other.flips_;
    }
  };
 
  void try_resize(std::array<value_type, buffer_size> &) {}
 
  template <typename C>
  void try_resize(C &c) {
    c.resize(buffer_size);
  }
 
 public:
  template <typename Pos = Position, typename Buffer = CycleBuffer,
            typename Reference = Creference>
  class Iterator {
   public:
    using iterator_category = std::bidirectional_iterator_tag;
    using value_type = CycleBuffer::value_type;
    using difference_type = long;
    using pointer = Cpointer;
    using reference = Creference;
 
    explicit Iterator(Pos position, Buffer *buffer)
        : position_(position), buffer_{buffer} {}
 
    Iterator &operator++() {
      ++position_.it_;
      if (position_.it_ == buffer_->container_.end()) {
        position_.it_ = buffer_->container_.begin();
        ++position_.flips_;
      }
      return *this;
    }
 
    Iterator &operator--() {
      if (position_.it_ == buffer_->container_.begin()) {
        position_.it_ = buffer_->container_.end();
        --position_.it_;
        --position_.flips_;
      } else {
        --position_.it_;
      }
      return *this;
    }
 
    Iterator operator++(int) {
      Iterator retval = *this;
      ++(*this);
      return retval;
    }
    Iterator operator--(int) {
      Iterator retval = *this;
      --(*this);
      return retval;
    }
 
    bool operator==(const Iterator &other) const {
      return position_ == other.position_;
    }
 
    bool operator!=(Iterator other) const { return !(*this == other); }
 
    Reference operator*() const { return *position_.it_; }
 
   private:
    Pos position_;
    Buffer *buffer_;
  };
 
  using iterator = Iterator<Position>;
  using const_iterator =
      Iterator<Const_position, const CycleBuffer, Cconst_reference>;
 
 public:
  CycleBuffer() {
    try_resize(container_);
    begin_.it_ = container_.begin();
    end_.it_ = container_.begin();
  }
 
  Container &container() { return container_; }
 
  iterator begin() { return iterator(begin_, this); }
  iterator end() { return iterator(end_, this); }
 
  const_iterator begin() const { return const_iterator(begin_, this); }
  const_iterator end() const { return const_iterator(end_, this); }
 
  template <typename V>
  void push_back(V &&v) {
    Iterator<Position &> e{end_, this};
    *e = std::forward<V>(v);
    ++e;
    if (elements_ != buffer_size) {
      ++elements_;
    } else {
      Iterator<Position &> b{begin_, this};
      ++b;
    }
  }
 
  uint32_t size() const { return elements_; }
 
  bool empty() const { return 0 == elements_; }
 
  value_type &front() { return *begin(); }
 
  value_type &back() { return *--end(); }
 
  void pop_front() {
    if (!elements_) return;
 
    Iterator<Position &> b{begin_, this};
    b++;
    --elements_;
  }
 
  void pop_back() {
    if (!elements_) return;
 
    Iterator<Position &> e{end_, this};
    e--;
    --elements_;
  }
 
 private:
  Container container_;
  uint32_t elements_{0};
  Position begin_{container_.begin(), 0};
  Position end_{container_.begin(), 0};
};
 
template <typename Type, uint32_t buffer_size>
class CycleBufferArray
    : public CycleBuffer<buffer_size, std::array<Type, buffer_size>> {};
 
}  // namespace container
}  // namespace utility
}  // namespace mysql_harness
 
#endif  // MYSQL_HARNESS_UTILITY_CONTAINER_CYCLE_BUFFER_H_