propagate.hpp

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// Copyright 2024 Ekumen, 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.
 
#ifndef BELUGA_ACTIONS_PROPAGATE_HPP
#define BELUGA_ACTIONS_PROPAGATE_HPP
 
#include <algorithm>
#include <execution>
#include <type_traits>
 
#include <beluga/type_traits/particle_traits.hpp>
#include <beluga/views/particles.hpp>
 
#include <range/v3/action/action.hpp>
#include <range/v3/utility/random.hpp>
#include <range/v3/view/common.hpp>
 
namespace beluga::actions {
 
namespace detail {
 
struct propagate_base_fn {
 
  template <
      class ExecutionPolicy,
      class Range,
      class StateSamplingFunction,
      std::enable_if_t<std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>, int> = 0,
      std::enable_if_t<ranges::range<Range>, int> = 0>
  constexpr auto operator()(ExecutionPolicy&& policy, Range& range, StateSamplingFunction fn) const -> Range& {
    static_assert(beluga::is_particle_range_v<Range>);
    auto states = range | beluga::views::states | ranges::views::common;
 
    auto unary_fn = [&]() {
      using States = decltype(states);
      using State = ranges::range_value_t<States>;
      using Generator = decltype(ranges::detail::get_random_engine());
      if constexpr (std::is_invocable_v<StateSamplingFunction, State, Generator>) {
        return [fn = std::move(fn)](const State& state) { return fn(state, ranges::detail::get_random_engine()); };
      } else {
        return std::move(fn);
      }
    }();
 
    std::transform(
        policy,              // rvalue policies are not supported in some STL implementations
        std::begin(states),  //
        std::end(states),    //
        std::begin(states),  //
        std::move(unary_fn));
    return range;
  }
 
  template <
      class Range,
      class StateSamplingFunction,
      class ExecutionPolicy,
      std::enable_if_t<ranges::range<Range>, int> = 0,
      std::enable_if_t<std::is_execution_policy_v<ExecutionPolicy>, int> = 0>
  constexpr auto operator()(Range&& range, StateSamplingFunction fn, ExecutionPolicy policy) const -> Range& {
    return (*this)(std::move(policy), std::forward<Range>(range), std::move(fn));
  }
 
  template <
      class ExecutionPolicy,        //
      class StateSamplingFunction,  //
      std::enable_if_t<std::is_execution_policy_v<ExecutionPolicy>, int> = 0>
  constexpr auto operator()(ExecutionPolicy policy, StateSamplingFunction fn) const {
    return ranges::make_action_closure(ranges::bind_back(propagate_base_fn{}, std::move(fn), std::move(policy)));
  }
};
 
struct propagate_fn : public propagate_base_fn {
  using propagate_base_fn::operator();
 
  template <
      class Range,                  //
      class StateSamplingFunction,  //
      std::enable_if_t<ranges::range<Range>, int> = 0>
  constexpr auto operator()(Range&& range, StateSamplingFunction fn) const -> Range& {
    return (*this)(std::execution::seq, std::forward<Range>(range), std::move(fn));
  }
 
  template <class StateSamplingFunction>
  constexpr auto operator()(StateSamplingFunction fn) const {
    return ranges::make_action_closure(ranges::bind_back(propagate_fn{}, std::move(fn)));
  }
};
 
}  // namespace detail
 
 
inline constexpr detail::propagate_fn propagate;
 
}  // namespace beluga::actions
 
#endif