mutable_compute_cell_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_MUTABLE_DEPENDENT_CELL_HPP
#define LIVE_CELLS_MUTABLE_DEPENDENT_CELL_HPP
 
#include <memory>
#include <functional>
#include <unordered_set>
 
#include "observable.hpp"
#include "mutable_cell.hpp"
#include "exceptions.hpp"
#include "observer_cell_state.hpp"
 
namespace live_cells {
 
    template <typename T>
    class mutable_compute_cell_state :
        public mutable_cell_state<T>,
        public observer,
        public observer_cell_state {
 
        typedef mutable_cell_state<T> parent;
 
    public:
 
        mutable_compute_cell_state(key_ref key, const std::unordered_set<cell> &arguments) :
            parent(key),
            arguments(arguments) {}
 
        T value() {
            if (stale) {
                computed = true;
 
                try {
                    this->silent_set(compute());
                }
                catch (const stop_compute_exception &) {
                    // Prevent value from being updated
                }
 
                stale = !this->is_active();
            }
 
            return parent::value();
        }
 
        void value(T value) {
            reverse = true;
            this->notify_will_update();
 
            updating = false;
            stale = false;
            computed = false;
 
            this->silent_set(value);
 
            try {
                batch([&, this] () {
                    reverse_compute(value);
                });
            }
            catch (...) {
                // Prevent exception from being propagated to caller
            }
 
            if (parent::is_batch_update()) {
                this->add_to_batch();
            }
            else {
                this->notify_update();
            }
 
            reverse = false;
        }
 
        void will_update(const key_ref &k) override {
            if (!reverse) {
                handle_will_update([this] {
                    this->notify_will_update();
                });
            }
        }
 
        void update(const key_ref &k, bool changed) override {
            handle_update(changed, [this] (bool changed) {
                this->notify_update(changed);
            });
        }
 
        void init() override {
            cell_state::init();
            init_observer_state();
 
            try {
                this->silent_set(this->value());
            }
            catch (...) {
                // Prevent exception from being propagated to caller
            }
 
            for (auto arg : arguments) {
                arg.add_observer(observer_ptr());
            }
        }
 
        void pause() override {
            cell_state::pause();
            pause_observer_state();
 
            for (auto arg : arguments) {
                arg.remove_observer(observer_ptr());
            }
        }
 
    protected:
        std::unordered_set<cell> arguments;
 
        bool reverse = false;
 
        bool computed = true;
 
        virtual T compute() = 0;
 
        virtual void reverse_compute(T value) = 0;
 
        std::shared_ptr<observer> observer_ptr() {
            return std::dynamic_pointer_cast<observer>(this->shared_from_this());
        }
    };
 
}  // live_cells
 
#endif /* LIVE_CELLS_MUTABLE_DEPENDENT_CELL_HPP */