cpp-lazy-stream/include/stream/common_view.h

//
//  common_view.h
//  stream
//
//  Created by Sam Jaffe on 3/30/23.
//

#pragma once

#include <iterator/proxy.h>
#include <stream/detail/traits.h>
#include <stream/forward.h>

#include <iterator/detail/macro.h>

#define FWD(x) std::forward<decltype(x)>(x)

namespace stream::ranges {

template <typename It, typename S>
class common_iterator : public proxy<It, common_iterator<It, S>> {
public:
  static_assert(!std::is_same_v<It, S>, "cannot operator on common types");
  using super_t = proxy<It, common_iterator<It, S>>;
  using sentinel_type = common_iterator;

public:
  using super_t::super_t;
  common_iterator(S) : super_t() {}

  bool equal_to(common_iterator const & other) const {
    return (at_end() && other.at_end()) || super_t::impl() == other.impl();
  }
  bool at_end() const { return super_t::impl() == S(); }
};

template <typename S> class common_view {
private:
  using iterator = common_iterator<detail::begin_t<S>, detail::end_t<S>>;

private:
  S stream_;

public:
  common_view(S && stream) : stream_(FWD(stream)) {}

  auto begin() const { return iterator(stream_.begin()); }
  auto end() const { return iterator(stream_.end()); }

  SFINAE(detail::has_empty_v<S>, bool) empty() const { return stream_.empty(); }

  SFINAE(detail::has_size_v<S>, bool) size() const { return stream_.size(); }
};

template <typename S> common_view(S &&) -> common_view<S>;
}

namespace stream::ranges::views {
struct common {
  template <typename Stream> friend auto operator|(Stream && stream, common) {
    if constexpr (detail::is_sentinal_v<Stream>) {
      return common_view(FWD(stream));
    } else {
      return FWD(stream);
    }
  }
};
}

MAKE_ITERATOR_FACADE_TYPEDEFS_T(stream::ranges::common_iterator);

#undef FWD
#include <iterator/detail/undef.h>