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

#pragma once

#include <functional>

#include <stream/forward.h>

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

#include <stream/detail/macro.h>

namespace stream::ranges {
template <typename S, typename Proj> class transform_view {
private:
private:
  S stream_;
  Proj projection_;

public:
  transform_view(S && stream, Proj projection)
      : stream_(FWD(stream)), projection_(projection) {}

  auto begin() const { return transform_iterator(stream_.begin(), invoke()); }

  auto end() const {
    if constexpr (detail::is_sentinal_v<S>) {
      return stream_.end();
    } else {
      return transform_iterator(stream_.end(), invoke());
    }
  }

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

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

private:
  auto invoke() const {
    return std::function([this](detail::cref_t<S> t) -> decltype(auto) {
      return std::invoke(projection_, t);
    });
  }
};

template <typename S, typename Proj>
transform_view(S &&, Proj) -> transform_view<S, Proj>;
}

namespace stream::ranges::views {
template <typename Proj> class transform {
public:
  transform(Proj const & projection) : projection_(projection) {}

  template <typename Stream>
  friend auto operator|(Stream && stream, transform map) {
    // TODO: if constexpr transform_view
    return transform_view(FWD(stream), std::move(map.projection_));
  }

private:
  Proj projection_;
};
}

#include <stream/detail/undef.h>