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

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

        private EntityManager entityManager;
        private ComponentManager componentManager;
        private MessageManager messageManager;

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

            var emitsAttribute = this.GetType().GetCustomAttribute<Emits>(false);
            if (emitsAttribute != null)
            {
                emitMessageTypes = emitsAttribute.emitMessageTypes;
            }

            var readsAttribute = this.GetType().GetCustomAttribute<Reads>(false);
            if (readsAttribute != null)
            {
                readMessageTypes = readsAttribute.readMessageTypes;
            }
        }

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

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

        internal void AssignMessageManager(MessageManager messageManager)
        {
            this.messageManager = messageManager;
        }

        public abstract void Update(float dt);

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

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

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

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

        protected void UpdateComponent<TComponent>(Guid componentID, TComponent newComponentValue) where TComponent : struct, IComponent
        {
            this.UpdateComponentInWorld(componentID, newComponentValue);
        }

        protected void EmitMessage<TMessage>(TMessage message) where TMessage : struct, IMessage
        {
            if (emitMessageTypes.Contains(typeof(TMessage)))
            {
                this.messageManager.AddMessage(message);
            }
            else
            {
                throw new IllegalMessageEmitException("Engine {0} tried to emit undeclared Message {1}", this.GetType().Name, typeof(TMessage).Name);
            }
        }

        protected IEnumerable<TMessage> ReadMessages<TMessage>() where TMessage : struct, IMessage
        {
            if (readMessageTypes.Contains(typeof(TMessage)))
            {
                return this.messageManager.GetMessagesByType<TMessage>();
            }
            else
            {
                throw new IllegalMessageReadException("Engine {0} tried to read undeclared Message {1}", this.GetType().Name, typeof(TMessage).Name);
            }
        }

        protected bool Some<TMessage>() where TMessage : struct, IMessage
        {
            if (readMessageTypes.Contains(typeof(TMessage)))
            {
                return messageManager.GetMessagesByType<TMessage>().Count() > 0;
            }
            else
            {
                throw new IllegalMessageReadException("Engine {0} tried to read undeclared Message {1}", this.GetType().Name, typeof(TMessage).Name);
            }
        }
    }
}