powerset.hpp

#ifndef ITER_POWERSET_HPP_
#define ITER_POWERSET_HPP_

#include "internal/iterbase.hpp"
#include "combinations.hpp"

#include <cassert>
#include <memory>
#include <utility>
#include <iterator>
#include <type_traits>

namespace iter {
  namespace impl {
    template <typename Container>
    class Powersetter;
  }
  template <typename Container>
  impl::Powersetter<Container> powerset(Container&&);

}

template <typename Container>
class iter::impl::Powersetter {
 private:
  Container container;
  using CombinatorType = decltype(combinations(std::declval<Container&>(), 0));

  friend Powersetter iter::powerset<Container>(Container&&);

  Powersetter(Container&& in_container)
      : container(std::forward<Container>(in_container)) {}

 public:
  Powersetter(Powersetter&&) = default;

  class Iterator
      : public std::iterator<std::input_iterator_tag, CombinatorType> {
   private:
    std::remove_reference_t<Container>* container_p;
    std::size_t set_size;
    std::shared_ptr<CombinatorType> comb;
    iterator_type<CombinatorType> comb_iter;
    iterator_type<CombinatorType> comb_end;

   public:
    Iterator(Container& in_container, std::size_t sz)
        : container_p{&in_container},
          set_size{sz},
          comb{
              std::make_shared<CombinatorType>(combinations(in_container, sz))},
          comb_iter{std::begin(*comb)},
          comb_end{std::end(*comb)} {}

    Iterator& operator++() {
      ++this->comb_iter;
      if (this->comb_iter == this->comb_end) {
        ++this->set_size;
        this->comb = std::make_shared<CombinatorType>(
            combinations(*this->container_p, this->set_size));

        this->comb_iter = std::begin(*this->comb);
        this->comb_end = std::end(*this->comb);
      }
      return *this;
    }

    Iterator operator++(int) {
      auto ret = *this;
      ++*this;
      return ret;
    }

    iterator_deref<CombinatorType> operator*() {
      return *this->comb_iter;
    }

    iterator_arrow<CombinatorType> operator->() {
      apply_arrow(this->comb_iter);
    }

    bool operator!=(const Iterator& other) const {
      return !(*this == other);
    }

    bool operator==(const Iterator& other) const {
      return this->set_size == other.set_size
             && this->comb_iter == other.comb_iter;
    }
  };

  Iterator begin() {
    return {this->container, 0};
  }

  Iterator end() {
    return {this->container, dumb_size(this->container) + 1};
  }
};

template <typename Container>
iter::impl::Powersetter<Container> iter::powerset(Container&& container) {
  return {std::forward<Container>(container)};
}

#endif