/*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * Licensed under the Apache License Version 2.0 with LLVM Exceptions
 * (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
 *
 *   https://llvm.org/LICENSE.txt
 *
 * 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 <unifex/tag_invoke.hpp>
#include <unifex/type_traits.hpp>

#include <unifex/detail/prologue.hpp>

namespace unifex {

enum class blocking_kind {
  // No guarantees about the timing and context on which the receiver will
  // be called.
  maybe,

  // Always completes asynchronously.
  // Guarantees that the receiver will not be called on the current thread
  // before .start() returns. The receiver may be called on another thread
  // before .start() returns, however, or may be called on the current thread
  // some time after .start() returns.
  never,

  // Guarantees that the receiver will be called strongly-happens-before
  // .start() returns. Does not guarantee the call to the receiver happens
  // on the same thread that called .start(), however.
  always,

  // Caller guarantees that the receiver will be called inline on the
  // current thread that called .start() before .start() returns.
  always_inline
};

namespace _blocking {
inline const struct _fn {
  template(typename Sender)
    (requires tag_invocable<_fn, const Sender&>)
  constexpr auto operator()(const Sender& s) const
      noexcept(is_nothrow_tag_invocable_v<_fn, const Sender&>)
      -> tag_invoke_result_t<_fn, const Sender&> {
    return tag_invoke(_fn{}, s);
  }
  template(typename Sender)
    (requires (!tag_invocable<_fn, const Sender&>))
  constexpr blocking_kind operator()(const Sender&) const noexcept {
    return blocking_kind::maybe;
  }
} blocking{};
} // namespace _blocking
using _blocking::blocking;

} // namespace unifex

#include <unifex/detail/epilogue.hpp>