using System;
using System.Reflection;
using System.Collections.Generic;

namespace Encompass {
    public abstract class Engine {
        public readonly List<Type> mutateComponentTypes = new List<Type>();

        private EntityManager entityManager;
        private ComponentManager componentManager;

        public Engine() {
            var mutatesAttribute = this.GetType().GetCustomAttribute<Mutates>(false);
            if (mutatesAttribute != null) {
                mutateComponentTypes = mutatesAttribute.mutateComponentTypes;
            }
        }

        internal void AssignEntityManager(EntityManager entityManager) {
            this.entityManager = entityManager;
        }

        internal void AssignComponentManager(ComponentManager componentManager) {
            this.componentManager = componentManager;
        }

        public abstract void Update(float dt);

        protected Entity CreateEntity() {
            return this.entityManager.CreateEntity();
        }

        protected IEnumerable<TComponent> ReadComponents<TComponent>() where TComponent : struct, IComponent {
            return this.componentManager.GetActiveComponentsByType<TComponent>();
        }

        protected TComponent ReadComponent<TComponent>() where TComponent : struct, IComponent {
            return this.componentManager.GetActiveComponentByType<TComponent>();
        }

        protected void UpdateComponent<TComponent>(TComponent originalComponent, TComponent newComponent) where TComponent : struct, IComponent {
            if (mutateComponentTypes.Contains(typeof(TComponent))) {
                this.componentManager.UpdateComponent(originalComponent, newComponent);
            } else {
                throw new IllegalComponentMutationException("Engine {0} tried to mutate undeclared Component {1}", this.GetType().ToString(), typeof(TComponent).ToString());
            }
        }
    }
}