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_CELL_STATE_HPP
#define LIVE_CELLS_CELL_STATE_HPP
 
#include <unordered_map>
#include <memory>
 
#include "keys.hpp"
#include "observable.hpp"
 
namespace live_cells {
    class cell_state : public std::enable_shared_from_this<cell_state> {
    public:
        typedef std::shared_ptr<cell_state> ref;
 
        cell_state(key_ref k) : key_(k) {}
 
        virtual ~cell_state() noexcept;
 
        cell_state& operator=(const cell_state &other) = delete;
 
        virtual void init() {}
 
        virtual void pause() {}
 
        virtual void add_observer(observer::ref o);
 
        virtual void remove_observer(observer::ref o);
 
        virtual void notify_will_update();
 
        virtual void notify_update(bool did_change = true);
 
    protected:
        key_ref key_;
 
        std::unordered_map<observer::ref, std::size_t> observers;
 
        bool is_active() const {
            return !observers.empty();
        }
 
    private:
 
#ifndef NDEBUG
        int notify_count = 0;
#endif
    };
 
    class state_manager {
    public:
        static state_manager &global() {
            return instance_;
        }
 
        template <typename S, typename... Args>
        std::shared_ptr<S> get(key_ref k, Args... args) {
            if (k->is_unique()) {
                return std::make_shared<S>(k, args...);
            }
 
            // TODO: Ensure that dynamic_pointer_cast succeeds.
 
            auto it = states.find(k);
 
            if (it != states.end()) {
                if (auto state = it->second.lock()) {
                    return std::dynamic_pointer_cast<S>(state);
                }
                else {
                    states.erase(it);
                }
            }
 
            auto state = states.emplace(k, std::weak_ptr<S>(std::make_shared<S>(k, args...))).first->second.lock();
            return std::dynamic_pointer_cast<S>(state);
        }
 
        void remove(key_ref k) {
            if (!k->is_unique()) {
                states.erase(k);
            }
        }
 
    private:
        static state_manager instance_;
 
        std::unordered_map<key_ref, std::weak_ptr<cell_state>> states;
 
        state_manager() = default;
        state_manager(const state_manager &) = delete;
 
        state_manager &operator=(const state_manager &) = delete;
    };
 
}  // live_cells
 
#endif /* LIVE_CELLS_CELL_STATE_HPP */