/*
 * Copyright 2018-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
#pragma once

#include <folly/experimental/pushmi/executor.h>
#include <folly/experimental/pushmi/receiver.h>
#include <folly/experimental/pushmi/trampoline.h>

namespace folly {
namespace pushmi {

template <class E, class... VN>
class any_single_sender {
  union data {
    void* pobj_ = nullptr;
    char buffer_[sizeof(std::tuple<VN...>)]; // can hold a V in-situ
  } data_{};
  template <class Wrapped>
  static constexpr bool insitu() {
    return sizeof(Wrapped) <= sizeof(data::buffer_) &&
        std::is_nothrow_move_constructible<Wrapped>::value;
  }
  struct vtable {
    static void s_op(data&, data*) {}
    static any_executor<E> s_executor(data&) {
      return {};
    }
    static void s_submit(data&, any_receiver<E, VN...>) {}
    void (*op_)(data&, data*) = vtable::s_op;
    any_executor<E> (*executor_)(data&) = vtable::s_executor;
    void (*submit_)(data&, any_receiver<E, VN...>) = vtable::s_submit;
  };
  static constexpr vtable const noop_{};
  vtable const* vptr_ = &noop_;
  template <class Wrapped>
  any_single_sender(Wrapped obj, std::false_type) : any_single_sender() {
    struct s {
      static void op(data& src, data* dst) {
        if (dst)
          dst->pobj_ = std::exchange(src.pobj_, nullptr);
        delete static_cast<Wrapped const*>(src.pobj_);
      }
      static any_executor<E> executor(data& src) {
        return any_executor<E>{
            ::folly::pushmi::executor(*static_cast<Wrapped*>(src.pobj_))};
      }
      static void submit(data& src, any_receiver<E, VN...> out) {
        ::folly::pushmi::submit(
            *static_cast<Wrapped*>(src.pobj_), std::move(out));
      }
    };
    static const vtable vtbl{s::op, s::executor, s::submit};
    data_.pobj_ = new Wrapped(std::move(obj));
    vptr_ = &vtbl;
  }
  template <class Wrapped>
  any_single_sender(Wrapped obj, std::true_type) noexcept
      : any_single_sender() {
    struct s {
      static void op(data& src, data* dst) {
        if (dst)
          new (dst->buffer_)
              Wrapped(std::move(*static_cast<Wrapped*>((void*)src.buffer_)));
        static_cast<Wrapped const*>((void*)src.buffer_)->~Wrapped();
      }
      static any_executor<E> executor(data& src) {
        return any_executor<E>{::folly::pushmi::executor(
            *static_cast<Wrapped*>((void*)src.buffer_))};
      }
      static void submit(data& src, any_receiver<E, VN...> out) {
        ::folly::pushmi::submit(
            *static_cast<Wrapped*>((void*)src.buffer_), std::move(out));
      }
    };
    static const vtable vtbl{s::op, s::executor, s::submit};
    new (data_.buffer_) Wrapped(std::move(obj));
    vptr_ = &vtbl;
  }
  template <class T, class U = std::decay_t<T>>
  using wrapped_t =
      std::enable_if_t<!std::is_same<U, any_single_sender>::value, U>;
 public:
  using properties = property_set<is_sender<>, is_single<>>;

  any_single_sender() = default;
  any_single_sender(any_single_sender&& that) noexcept : any_single_sender() {
    that.vptr_->op_(that.data_, &data_);
    std::swap(that.vptr_, vptr_);
  }

  PUSHMI_TEMPLATE(class Wrapped) //
  (requires SenderTo<wrapped_t<Wrapped>, any_receiver<E, VN...>>) //
  explicit any_single_sender(Wrapped obj) noexcept(insitu<Wrapped>())
      : any_single_sender{std::move(obj), bool_<insitu<Wrapped>()>{}} {}
  ~any_single_sender() {
    vptr_->op_(data_, nullptr);
  }
  any_single_sender& operator=(any_single_sender&& that) noexcept {
    this->~any_single_sender();
    new ((void*)this) any_single_sender(std::move(that));
    return *this;
  }
  any_executor<E> executor() {
    return vptr_->executor_(data_);
  }
  void submit(any_receiver<E, VN...> out) {
    vptr_->submit_(data_, std::move(out));
  }
};

// Class static definitions:
template <class E, class... VN>
constexpr typename any_single_sender<E, VN...>::vtable const
    any_single_sender<E, VN...>::noop_;

template <class SF, class EXF>
class single_sender<SF, EXF> {
  SF sf_;
  EXF exf_;

 public:
  using properties = property_set<is_sender<>, is_single<>>;

  constexpr single_sender() = default;
  constexpr explicit single_sender(SF sf) : sf_(std::move(sf)) {}
  constexpr single_sender(SF sf, EXF exf)
      : sf_(std::move(sf)), exf_(std::move(exf)) {}

  // TODO(T36778706): Workaround issues with `auto` as a method return type in
  // modular builds in older versions of clang.
  invoke_result_t<EXF&> executor() {
    return exf_();
  }
  PUSHMI_TEMPLATE(class Out)
  (requires PUSHMI_EXP(
      lazy::Receiver<Out> PUSHMI_AND lazy::Invocable<SF&, Out>)) //
      void submit(Out out) {
    sf_(std::move(out));
  }
};

template <
    PUSHMI_TYPE_CONSTRAINT(Sender<is_single<>>) Data,
    class DSF,
    class DEXF>
class single_sender<Data, DSF, DEXF> {
  Data data_;
  DSF sf_;
  DEXF exf_;

 public:
  using properties = property_set_insert_t<
      properties_t<Data>,
      property_set<is_sender<>, is_single<>>>;

  constexpr single_sender() = default;
  constexpr explicit single_sender(Data data) : data_(std::move(data)) {}
  constexpr single_sender(Data data, DSF sf)
      : data_(std::move(data)), sf_(std::move(sf)) {}
  constexpr single_sender(Data data, DSF sf, DEXF exf)
      : data_(std::move(data)), sf_(std::move(sf)), exf_(std::move(exf)) {}

  auto executor() {
    return exf_(data_);
  }
  PUSHMI_TEMPLATE(class Out)
  (requires PUSHMI_EXP(
      lazy::Receiver<Out> PUSHMI_AND lazy::Invocable<DSF&, Data&, Out>)) //
      void submit(Out out) {
    sf_(data_, std::move(out));
  }
};

template <>
class single_sender<> : public single_sender<ignoreSF, trampolineEXF> {
 public:
  single_sender() = default;
};

////////////////////////////////////////////////////////////////////////////////
// make_single_sender
PUSHMI_INLINE_VAR constexpr struct make_single_sender_fn {
  inline auto operator()() const {
    return single_sender<ignoreSF, trampolineEXF>{};
  }
  PUSHMI_TEMPLATE(class SF)
  (requires True<> PUSHMI_BROKEN_SUBSUMPTION(&&not Sender<SF>)) //
      auto
      operator()(SF sf) const {
    return single_sender<SF, trampolineEXF>{std::move(sf)};
  }
  PUSHMI_TEMPLATE(class SF, class EXF)
  (requires True<>&& Invocable<EXF&> PUSHMI_BROKEN_SUBSUMPTION(
      &&not Sender<SF>)) //
      auto
      operator()(SF sf, EXF exf) const {
    return single_sender<SF, EXF>{std::move(sf), std::move(exf)};
  }
  PUSHMI_TEMPLATE(class Data)
  (requires True<>&& Sender<Data, is_single<>>) //
      auto
      operator()(Data d) const {
    return single_sender<Data, passDSF, passDEXF>{std::move(d)};
  }
  PUSHMI_TEMPLATE(class Data, class DSF)
  (requires Sender<Data, is_single<>>) //
      auto
      operator()(Data d, DSF sf) const {
    return single_sender<Data, DSF, passDEXF>{std::move(d), std::move(sf)};
  }
  PUSHMI_TEMPLATE(class Data, class DSF, class DEXF)
  (requires Sender<Data, is_single<>>&& Invocable<DEXF&, Data&>) //
      auto
      operator()(Data d, DSF sf, DEXF exf) const {
    return single_sender<Data, DSF, DEXF>{
        std::move(d), std::move(sf), std::move(exf)};
  }
} const make_single_sender{};

////////////////////////////////////////////////////////////////////////////////
// deduction guides
#if __cpp_deduction_guides >= 201703
single_sender()->single_sender<ignoreSF, trampolineEXF>;

PUSHMI_TEMPLATE(class SF)
(requires True<> PUSHMI_BROKEN_SUBSUMPTION(&&not Sender<SF>)) //
    single_sender(SF)
        ->single_sender<SF, trampolineEXF>;

PUSHMI_TEMPLATE(class SF, class EXF)
(requires True<>&& Invocable<EXF&> PUSHMI_BROKEN_SUBSUMPTION(
    &&not Sender<SF>)) //
    single_sender(SF, EXF)
        ->single_sender<SF, EXF>;

PUSHMI_TEMPLATE(class Data)
(requires True<>&& Sender<Data, is_single<>>) //
    single_sender(Data)
        ->single_sender<Data, passDSF, passDEXF>;

PUSHMI_TEMPLATE(class Data, class DSF)
(requires Sender<Data, is_single<>>) //
    single_sender(Data, DSF)
        ->single_sender<Data, DSF, passDEXF>;

PUSHMI_TEMPLATE(class Data, class DSF, class DEXF)
(requires Sender<Data, is_single<>>&& Invocable<DEXF&, Data&>) //
    single_sender(Data, DSF, DEXF)
        ->single_sender<Data, DSF, DEXF>;
#endif

template <>
struct construct_deduced<single_sender> : make_single_sender_fn {};

} // namespace pushmi
} // namespace folly
