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>();
        }

        internal void UpdateComponentInWorld<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().Name, typeof(TComponent).Name);
            }
        }

        protected void UpdateComponent<TComponent>(TComponent component, Func<TComponent, TComponent> updateFunction) where TComponent : struct, IComponent
        {
            var updatedComponent = updateFunction(component);
            this.UpdateComponentInWorld(component, updatedComponent);
        }

        protected void UpdateComponents<TComponent>(IEnumerable<TComponent> components, Func<TComponent, TComponent> updateFunction) where TComponent : struct, IComponent
        {
            foreach (var component in components)
            {
                this.UpdateComponent(component, updateFunction);
            }
        }
    }
}