compute_state.hpp

/*
 * live_cells_cpp
 * Copyright (C) 2024  Alexander Gutev <alex.gutev@gmail.com>
 *
 * 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 LIVE_CELLS_COMPUTE_STATE_HPP
#define LIVE_CELLS_COMPUTE_STATE_HPP
 
#include <memory>
#include <utility>
#include <concepts>
#include <cassert>
 
#include "observable.hpp"
#include "cell_state.hpp"
#include "exceptions.hpp"
#include "observer_cell_state.hpp"
 
namespace live_cells {
 
    template <typename T>
    concept Computable = std::invocable<T,observer::ref>;
 
    template <Computable C>
    class compute_cell_state : public cell_state, public observer, public observer_cell_state {
    public:
        typedef std::invoke_result_t<C,observer::ref> value_type;
 
        template <typename... Args>
        requires std::constructible_from<C,Args...>
        compute_cell_state(key_ref k, Args&&... args) :
            cell_state(k),
            compute(std::forward<Args>(args)...) {}
 
        value_type value() {
            if (stale) {
                try {
                    value_ = compute(observer_ptr());
                }
                catch (const stop_compute_exception &) {
                    // Prevent value from being updated
                }
 
                stale = !is_active();
            }
 
            return value_;
        }
 
    protected:
        C compute;
 
        std::shared_ptr<observer> observer_ptr() {
            return std::dynamic_pointer_cast<observer>(this->shared_from_this());
        }
 
        void will_update(const key_ref &k) override {
            handle_will_update([this] {
                notify_will_update();
            });
        }
 
        void update(const key_ref &k, bool changed) override {
            handle_update(changed, [this] (bool changed) {
                notify_update(changed);
            });
        }
 
        void init() override {
            cell_state::init();
            init_observer_state();
        }
 
        void pause() override {
            cell_state::pause();
            pause_observer_state();
        }
 
    private:
        value_type value_;
    };
 
}  // live_cells
 
#endif /* LIVE_CELLS_COMPUTE_STATE_HPP */