cpp-useful-iterators/include/iterator/cascade_iterator.h

#pragma once

#include <cstddef>

#include <iterator/concepts.h>
#include <iterator/detail/projection_tuple.h>
#include <iterator/detail/recursive_expander.h>
#include <iterator/end_aware_iterator.h>
#include <iterator/forwards.h>
#include <iterator/recursive_iterator.h>

namespace iterator {
template <typename It, typename Projs, typename MaxDepth>
class cascade_iterator;

template <typename It, typename... Projs, typename MaxDepth>
class cascade_iterator<It, detail::Projections<Projs...>, MaxDepth>
    : public recursive_iterator_helper<It, MaxDepth,
                                       detail::Projections<Projs...>>::type,
      public facade<
          cascade_iterator<It, detail::Projections<Projs...>, MaxDepth>> {
public:
  using sentinel_type = sentinel_t;

public:
  cascade_iterator() = default;

  explicit cascade_iterator(Range auto & range, Projs... projs)
      : cascade_iterator(end_aware_iterator(range), projs...) {}

  explicit cascade_iterator(Range auto & range, MaxDepth, Projs... projs)
      : cascade_iterator(end_aware_iterator(range), projs...) {}

  explicit cascade_iterator(end_aware_iterator<It> iter, MaxDepth,
                            Projs... projs)
      : cascade_iterator::recursive_iterator_base(iter, projs...) {}

  explicit cascade_iterator(end_aware_iterator<It> iter, Projs... projs)
      : cascade_iterator::recursive_iterator_base(iter, projs...) {}

  template <typename Ot>
  explicit cascade_iterator(end_aware_iterator<Ot> other, Projs... projs)
      : cascade_iterator(end_aware_iterator<It>(other), projs...) {}

  template <typename Ot>
  explicit cascade_iterator(end_aware_iterator<Ot> other, MaxDepth,
                            Projs... projs)
      : cascade_iterator(end_aware_iterator<It>(other), projs...) {}
};

template <Range R, typename... Projs>
cascade_iterator(R, Projs...)
    -> cascade_iterator<iterator_t<R>, detail::Projections<Projs...>,
                        bounded<sizeof...(Projs) + 1>>;

template <typename It, typename... Projs>
cascade_iterator(end_aware_iterator<It>, Projs...)
    -> cascade_iterator<It, detail::Projections<Projs...>,
                        bounded<sizeof...(Projs) + 1>>;

template <Range R, typename... Projs, size_t N>
  requires(N > sizeof...(Projs))
cascade_iterator(R, bounded<N>, Projs...)
    -> cascade_iterator<iterator_t<R>, detail::Projections<Projs...>,
                        bounded<N>>;

template <typename It, typename... Projs, size_t N>
  requires(N > sizeof...(Projs))
cascade_iterator(end_aware_iterator<It>, bounded<N>, Projs...)
    -> cascade_iterator<It, detail::Projections<Projs...>, bounded<N>>;

template <Range R, typename... Projs>
cascade_iterator(R, unbounded, Projs...)
    -> cascade_iterator<iterator_t<R>, detail::Projections<Projs...>,
                        unbounded>;

template <typename It, typename... Projs>
cascade_iterator(end_aware_iterator<It>, unbounded, Projs...)
    -> cascade_iterator<It, detail::Projections<Projs...>, unbounded>;
}