cpp-lazy-stream/include/stream/view/any.h

//
//  any.h
//  stream
//
//  Created by Sam Jaffe on 3/29/23.
//

#pragma once

#include <memory>

#include <stream/forward.h>

#include <stream/detail/traits.h>
#include <stream/iterator/any_iterator.h>

namespace stream::ranges {

template <typename T> class any_view {
private:
  template <typename S>
  using sentinel_iterator =
      common_iterator<detail::begin_t<S>, detail::end_t<S>>;
  template <typename S, typename It>
  using iter_cast_t =
      std::conditional_t<detail::has_sentinal_v<S>, sentinel_iterator<S>, It>;

  using make_iter_t = any_iterator<T> (*)(void *);

private:
  std::shared_ptr<void> impl_{nullptr};
  make_iter_t begin_{nullptr};
  make_iter_t end_{nullptr};

public:
  template <typename S>
  any_view(std::shared_ptr<S> impl)
      : impl_(impl), begin_(begin_function<S>()), end_(end_function<S>()) {}

  template <typename S>
  any_view(S & impl) : any_view(std::shared_ptr<S>(&impl, [](void *) {})) {}

  template <typename S>
  any_view(S const & impl)
      : any_view(std::shared_ptr<S const>(&impl, [](void *) {})) {}

  template <typename S>
  any_view(S && impl) : any_view(std::make_shared<S>(std::forward<S>(impl))) {}

  auto begin() const { return begin_(impl_.get()); }
  auto end() const { return end_(impl_.get()); }

private:
  template <typename S> static make_iter_t begin_function() {
    return [](void * p) -> any_iterator<T> {
      return iter_cast_t<S, detail::begin_t<S>>(static_cast<S *>(p)->begin());
    };
  }

  template <typename S> static make_iter_t end_function() {
    return [](void * p) -> any_iterator<T> {
      return iter_cast_t<S, detail::end_t<S>>(static_cast<S *>(p)->end());
    };
  }
};

template <typename S>
any_view(std::shared_ptr<S>) -> any_view<detail::value_type<S>>;
template <typename S> any_view(S &) -> any_view<detail::value_type<S>>;
template <typename S> any_view(S const &) -> any_view<detail::value_type<S>>;
template <typename S> any_view(S &&) -> any_view<detail::value_type<S>>;

}