observer_cell_state.hpp

#ifndef LIVE_CELLS_OBSERVER_CELL_STATE_HPP
#define LIVE_CELLS_OBSERVER_CELL_STATE_HPP
 
#include <cassert>
#include <concepts>
 
namespace live_cells {
 
    class observer_cell_state {
    protected:
        bool stale = true;
 
        bool updating = false;
 
        void init_observer_state() {
            stale = true;
        }
 
        void pause_observer_state() {
            stale = true;
        }
 
        void handle_will_update(const std::invocable auto &notify_will_update) {
            handle_will_update([] {}, notify_will_update);
        }
 
        void handle_will_update(const std::invocable auto &pre_update,
                                const std::invocable auto &notify_will_update) {
            if (!updating) {
                assert(changed_dependencies == 0 && "Number of changed dependencies == 0 at start of update cycle.");
 
                pre_update();
 
                updating = true;
                has_changed = false;
                changed_dependencies = 0;
 
                notify_will_update();
            }
 
            changed_dependencies++;
        }
 
        void handle_update(bool changed, const std::invocable<bool> auto &notify_update) {
            handle_update(changed, [] { return true; }, notify_update, [] { });
        }
 
        void handle_update(bool changed,
                           const std::invocable auto &did_change,
                           const std::invocable<bool> auto &notify_update,
                           const std::invocable auto &post_update) {
            if (updating) {
                assert(changed_dependencies > 0 && "Calls to update() are not more than calls to will_update().");
 
                has_changed = has_changed || changed;
 
                if (--changed_dependencies == 0) {
                    stale = stale || has_changed;
 
                    notify_update(has_changed && did_change());
                    updating = false;
 
                    if (has_changed) {
                        post_update();
                    }
                }
            }
        }
 
    private:
 
        int changed_dependencies = 0;
 
        int has_changed = false;
    };
 
}  // live_cells
 
#endif /* LIVE_CELLS_OBSERVER_CELL_STATE_HPP */