core/modules/Components.cppm

export module Core.Components;

export import Core.Utility;
export import Core.New;

import Core.HashMap;
import Core.List;
import Core.Meta;

export namespace Core {
    using Entity = size_t;

    template<Moveable T>
    class Components final {
        HashMap<Entity, size_t> entityToIndex{};
        List<Entity> indexToEntity{};
        List<T> components{};

    public:
        template<typename R>
        struct Node final {
            Entity entity;
            R& component;
        };

        template<typename C>
        class Iterator final {
            using EntityIterator = decltype(C().indexToEntity.begin());
            using ComponentIterator = decltype(C().components.begin());
            using Component = decltype(*ComponentIterator());

            EntityIterator entityIterator{};
            ComponentIterator componentIterator{};

        public:
            Iterator(EntityIterator e, ComponentIterator c) noexcept :
                entityIterator(e), componentIterator(c) {
            }

            Iterator& operator++() noexcept {
                ++entityIterator;
                ++componentIterator;
                return *this;
            }

            bool operator!=(const Iterator& other) const noexcept {
                return entityIterator != other.entityIterator;
            }

            Node<Component> operator*() const noexcept {
                return {*entityIterator, *componentIterator};
            }
        };

        template<typename C>
        struct IteratorAdapter final {
            C& c;

            Iterator<C> begin() noexcept {
                return Iterator<C>(
                    c.indexToEntity.begin(), c.components.begin());
            }

            Iterator<C> end() noexcept {
                return Iterator<C>(c.indexToEntity.end(), c.components.end());
            }
        };

        template<typename... Args>
        bool put(T*& t, Entity e, Args&&... args) noexcept {
            size_t index = components.getLength();
            size_t* indexP = nullptr;
            if(!entityToIndex.tryEmplace(indexP, e, index)) {
                return false;
            }
            indexToEntity.add(e);
            t = &components.put(Core::forward<Args>(args)...);
            return true;
        }

        template<typename... Args>
        bool add(Entity e, Args&&... args) noexcept {
            T* t = nullptr;
            return put(t, e, Core::forward<Args>(args)...);
        }

        bool remove(Entity e) noexcept {
            size_t* indexP = entityToIndex.search(e);
            if(indexP == nullptr) {
                return false;
            }
            size_t lastIndex = components.getLength() - 1;
            size_t index = *indexP;
            entityToIndex.remove(e);
            components.removeBySwap(index);
            if(index == lastIndex) {
                indexToEntity.removeBySwap(index);
                return true;
            }
            Entity other = indexToEntity[lastIndex];
            indexToEntity.removeBySwap(index);
            entityToIndex.add(other, index);
            return true;
        }

        T* search(Entity e) noexcept {
            return const_cast<T*>(
                static_cast<const Components*>(this)->search(e));
        }

        const T* search(Entity e) const noexcept {
            const size_t* index = entityToIndex.search(e);
            if(index == nullptr) {
                return nullptr;
            }
            return &(components[*index]);
        }

        auto begin() noexcept {
            return components.begin();
        }

        auto begin() const noexcept {
            return components.begin();
        }

        auto end() noexcept {
            return components.end();
        }

        auto end() const noexcept {
            return components.end();
        }

        IteratorAdapter<Components> entities() noexcept {
            return {*this};
        }

        IteratorAdapter<const Components> entities() const noexcept {
            return {*this};
        }
    };
}