/******************************************************************************
 *                       ____    _    _____                                   *
 *                      / ___|  / \  |  ___|    C++                           *
 *                     | |     / _ \ | |_       Actor                         *
 *                     | |___ / ___ \|  _|      Framework                     *
 *                      \____/_/   \_|_|                                      *
 *                                                                            *
 * Copyright 2011-2018 Dominik Charousset                                     *
 *                                                                            *
 * Distributed under the terms and conditions of the BSD 3-Clause License or  *
 * (at your option) under the terms and conditions of the Boost Software      *
 * License 1.0. See accompanying files LICENSE and LICENSE_ALTERNATIVE.       *
 *                                                                            *
 * If you did not receive a copy of the license files, see                    *
 * http://opensource.org/licenses/BSD-3-Clause and                            *
 * http://www.boost.org/LICENSE_1_0.txt.                                      *
 ******************************************************************************/

#ifndef CAF_COMPOSED_TYPE_HPP
#define CAF_COMPOSED_TYPE_HPP

#include "caf/fwd.hpp"
#include "caf/replies_to.hpp"

#include "caf/detail/type_list.hpp"

namespace caf {

/// Computes the type for f*g (actor composition).
///
/// ~~~
/// let output_type x = case x of Stream y -> y ; Single y -> y
///
/// let propagate_stream from to = case from of
///                                  Stream _ -> Stream (output_type to)
///                                  Single _ -> to
/// let composed_type f g =
///   [(fst x, propagate_stream (snd x) (snd y)) | x <- g, y <- f,
///                                                output_type (snd x) == fst y]
/// ~~~
///
/// This class implements the list comprehension above in a
/// single shot with worst case n*m template instantiations using an
/// inner and outer loop, where n is the size
/// of Xs and m the size of Ys. Zs is a helper that models the
/// "inner loop variable" for generating the cross product of Xs and Ys.
/// The helper function propagate_stream is integrated into the loop with
/// four cases for the matching case. Rs collects the results.

template <class Xs, class Ys, class Zs, class Rs>
struct composed_type;

// end of outer loop over Xs
template <class Ys, class Zs, class... Rs>
struct composed_type<detail::type_list<>, Ys, Zs, detail::type_list<Rs...>> {
  using type = typed_actor<Rs...>;
};

// end of inner loop Ys (Zs)
template <class X, class... Xs, class Ys, class Rs>
struct composed_type<detail::type_list<X, Xs...>, Ys, detail::type_list<>, Rs>
    : composed_type<detail::type_list<Xs...>, Ys, Ys, Rs> {};

// case #1
template <class... In, class... Out, class... Xs, class Ys,
          class... MapsTo, class... Zs, class... Rs>
struct composed_type<detail::type_list<typed_mpi<detail::type_list<In...>,
                                            output_tuple<Out...>>, Xs...>,
                     Ys,
                     detail::type_list<typed_mpi<detail::type_list<Out...>,
                                            output_tuple<MapsTo...>>, Zs...>,
                     detail::type_list<Rs...>>
    : composed_type<detail::type_list<Xs...>, Ys, Ys,
                    detail::type_list<Rs..., typed_mpi<detail::type_list<In...>,
                                                  output_tuple<MapsTo...>>>> {};

// case #2
template <class... In, class... Out, class... Xs, class Ys,
          class... MapsTo, class... Zs, class... Rs>
struct composed_type<detail::type_list<typed_mpi<detail::type_list<In...>,
                                                 output_tuple<Out...>>, Xs...>,
                     Ys,
                     detail::type_list<typed_mpi<detail::type_list<Out...>,
                                                 output_stream<MapsTo...>>,
                                       Zs...>,
                     detail::type_list<Rs...>>
    : composed_type<detail::type_list<Xs...>, Ys, Ys,
                    detail::type_list<Rs...,
                                      typed_mpi<detail::type_list<In...>,
                                                output_stream<MapsTo...>>>> {};

// case #3
template <class... In, class... Out, class... Xs, class Ys,
          class... MapsTo, class... Zs, class... Rs>
struct composed_type<detail::type_list<typed_mpi<detail::type_list<In...>,
                                            output_stream<Out...>>, Xs...>,
                     Ys,
                     detail::type_list<typed_mpi<detail::type_list<Out...>,
                                            output_tuple<MapsTo...>>, Zs...>,
                     detail::type_list<Rs...>>
    : composed_type<detail::type_list<Xs...>, Ys, Ys,
                    detail::type_list<Rs...,
                                      typed_mpi<detail::type_list<In...>,
                                                output_stream<MapsTo...>>>> {};

// case #4
template <class... In, class... Out, class... Xs, class Ys,
          class... MapsTo, class... Zs, class... Rs>
struct composed_type<detail::type_list<typed_mpi<detail::type_list<In...>,
                                            output_stream<Out...>>, Xs...>,
                     Ys,
                     detail::type_list<typed_mpi<detail::type_list<Out...>,
                                            output_stream<MapsTo...>>, Zs...>,
                     detail::type_list<Rs...>>
    : composed_type<detail::type_list<Xs...>, Ys, Ys,
                    detail::type_list<Rs...,
                                      typed_mpi<detail::type_list<In...>,
                                                output_stream<MapsTo...>>>> {};

// default case (recurse over Zs)
template <class In, class Out, class... Xs, class Ys,
          class Unrelated, class MapsTo, class... Zs, class Rs>
struct composed_type<detail::type_list<typed_mpi<In, Out>, Xs...>,
                     Ys,
                     detail::type_list<typed_mpi<Unrelated, MapsTo>, Zs...>,
                     Rs>
    : composed_type<detail::type_list<typed_mpi<In, Out>, Xs...>,
                    Ys, detail::type_list<Zs...>, Rs> {};

/// Convenience type alias.
/// @relates composed_type
template <class F, class G>
using composed_type_t =
  typename composed_type<G, F, F, detail::type_list<>>::type;

} // namespace caf

#endif // CAF_COMPOSED_TYPE_HPP
