sunshine-sdk/src/round_robin.h

/**
 * @file src/round_robin.h
 * @brief Declarations for a round-robin iterator.
 */
#pragma once

// standard includes
#include <iterator>

/**
 * @brief A round-robin iterator utility.
 * @tparam V The value type.
 * @tparam T The iterator type.
 */
namespace round_robin_util {
  template<class V, class T>
  class it_wrap_t {
  public:
    using iterator_category = std::random_access_iterator_tag;
    using value_type = V;
    using difference_type = V;
    using pointer = V *;
    using const_pointer = V const *;
    using reference = V &;
    using const_reference = V const &;

    typedef T iterator;
    typedef std::ptrdiff_t diff_t;

    iterator operator+=(diff_t step) {
      while (step-- > 0) {
        ++_this();
      }

      return _this();
    }

    iterator operator-=(diff_t step) {
      while (step-- > 0) {
        --_this();
      }

      return _this();
    }

    iterator operator+(diff_t step) {
      iterator new_ = _this();

      return new_ += step;
    }

    iterator operator-(diff_t step) {
      iterator new_ = _this();

      return new_ -= step;
    }

    diff_t operator-(iterator first) {
      diff_t step = 0;
      while (first != _this()) {
        ++step;
        ++first;
      }

      return step;
    }

    iterator operator++() {
      _this().inc();
      return _this();
    }

    iterator operator--() {
      _this().dec();
      return _this();
    }

    iterator operator++(int) {
      iterator new_ = _this();

      ++_this();

      return new_;
    }

    iterator operator--(int) {
      iterator new_ = _this();

      --_this();

      return new_;
    }

    reference operator*() {
      return *_this().get();
    }

    const_reference operator*() const {
      return *_this().get();
    }

    pointer operator->() {
      return &*_this();
    }

    const_pointer operator->() const {
      return &*_this();
    }

    bool operator!=(const iterator &other) const {
      return !(_this() == other);
    }

    bool operator<(const iterator &other) const {
      return !(_this() >= other);
    }

    bool operator>=(const iterator &other) const {
      return _this() == other || _this() > other;
    }

    bool operator<=(const iterator &other) const {
      return _this() == other || _this() < other;
    }

    bool operator==(const iterator &other) const {
      return _this().eq(other);
    };

    bool operator>(const iterator &other) const {
      return _this().gt(other);
    }

  private:
    iterator &_this() {
      return *static_cast<iterator *>(this);
    }

    const iterator &_this() const {
      return *static_cast<const iterator *>(this);
    }
  };

  template<class V, class It>
  class round_robin_t: public it_wrap_t<V, round_robin_t<V, It>> {
  public:
    using iterator = It;
    using pointer = V *;

    round_robin_t(iterator begin, iterator end):
        _begin(begin),
        _end(end),
        _pos(begin) {
    }

    void inc() {
      ++_pos;

      if (_pos == _end) {
        _pos = _begin;
      }
    }

    void dec() {
      if (_pos == _begin) {
        _pos = _end;
      }

      --_pos;
    }

    bool eq(const round_robin_t &other) const {
      return *_pos == *other._pos;
    }

    pointer get() const {
      return &*_pos;
    }

  private:
    It _begin;
    It _end;

    It _pos;
  };

  template<class V, class It>
  round_robin_t<V, It> make_round_robin(It begin, It end) {
    return round_robin_t<V, It>(begin, end);
  }
}  // namespace round_robin_util