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

namespace Encompass
{
    internal class ComponentManager
    {
        private DrawLayerManager drawLayerManager;

        private Dictionary<Guid, Type> componentIDToType = new Dictionary<Guid, Type>();
        private Dictionary<Guid, IComponent> IDToComponent = new Dictionary<Guid, IComponent>();
        private Dictionary<Guid, List<Guid>> entityIDToComponentIDs = new Dictionary<Guid, List<Guid>>();
        private Dictionary<Guid, Guid> componentIDToEntityID = new Dictionary<Guid, Guid>();

        private Dictionary<Type, List<Guid>> typeToComponentIDs = new Dictionary<Type, List<Guid>>();
   
        private List<Guid> activeComponents = new List<Guid>();
        private List<Guid> inactiveComponents = new List<Guid>();

        private List<Guid> componentsToActivate = new List<Guid>();
        private List<Guid> componentsToDeactivate = new List<Guid>();
        private List<Guid> componentsToRemove = new List<Guid>();

        //shared references with EntityManager
        private List<Guid> entitiesWithAddedComponents; 
        private List<Guid> entitiesWithRemovedComponents;

        public ComponentManager(
            DrawLayerManager drawLayerManager,
            List<Guid> entitiesWithAddedComponents,
            List<Guid> entitiesWithRemovedComponents
        )
        {
            this.drawLayerManager = drawLayerManager;
            this.entitiesWithAddedComponents = entitiesWithAddedComponents;
            this.entitiesWithRemovedComponents = entitiesWithRemovedComponents;
        }

        internal Guid AddComponent<TComponent>(Guid entityID, TComponent component) where TComponent : struct, IComponent
        {
            var componentID = Guid.NewGuid();

            IDToComponent[componentID] = component;
            componentIDToType[componentID] = typeof(TComponent);
            
            if (!typeToComponentIDs.ContainsKey(typeof(TComponent)))
            {
                typeToComponentIDs.Add(typeof(TComponent), new List<Guid>());
            }

            typeToComponentIDs[typeof(TComponent)].Add(componentID);

            if (!entityIDToComponentIDs.ContainsKey(entityID))
            {
                entityIDToComponentIDs.Add(entityID, new List<Guid>());
            }

            entityIDToComponentIDs[entityID].Add(componentID);
            componentIDToEntityID[componentID] = entityID;

            inactiveComponents.Add(componentID);
            MarkForActivation(componentID);

            entitiesWithAddedComponents.Add(entityID);

            return componentID;
        }

        internal Guid AddDrawComponent<TComponent>(Guid entityID, TComponent component, int layer = 0) where TComponent : struct, IComponent
        {
            var componentID = AddComponent(entityID, component);
            drawLayerManager.RegisterComponentWithLayer(componentID, layer);
            return componentID;
        }

        internal IEnumerable<Guid> GetComponentIDsByEntityID(Guid entityID)
        {
            return entityIDToComponentIDs.ContainsKey(entityID) ?
                entityIDToComponentIDs[entityID] :
                Enumerable.Empty<Guid>();
        }

        internal IEnumerable<KeyValuePair<Guid, IComponent>> GetComponentsByEntity(Guid entityID)
        {
            return GetComponentIDsByEntityID(entityID).Intersect(activeComponents).Select((id) => new KeyValuePair<Guid, IComponent>(id, IDToComponent[id]));
        }

        internal IEnumerable<KeyValuePair<Guid, TComponent>> GetActiveComponentsByType<TComponent>() where TComponent : struct, IComponent
        {
            return typeToComponentIDs.ContainsKey(typeof(TComponent)) ?
                typeToComponentIDs[typeof(TComponent)].Select((id) => new KeyValuePair<Guid, TComponent>(id, (TComponent)IDToComponent[id])) :
                Enumerable.Empty<KeyValuePair<Guid, TComponent>>();
        }

        internal IEnumerable<KeyValuePair<Guid, IComponent>> GetActiveComponentsByType(Type type)
        {
            return typeToComponentIDs.ContainsKey(type) ?
                typeToComponentIDs[type].Select((id) => new KeyValuePair<Guid, IComponent>(id, IDToComponent[id])) :
                Enumerable.Empty<KeyValuePair<Guid, IComponent>>();
        }

        internal KeyValuePair<Guid, TComponent> GetActiveComponentByType<TComponent>() where TComponent : struct, IComponent
        {
            return GetActiveComponentsByType<TComponent>().Single();
        }

        internal IEnumerable<KeyValuePair<Guid, TComponent>> GetComponentsByEntityAndType<TComponent>(Guid entityID) where TComponent : struct, IComponent
        {
            var entity_components = GetComponentsByEntity(entityID).Select((kv) => new KeyValuePair<Guid, TComponent>(kv.Key, (TComponent)kv.Value));
            var active_components_by_type = GetActiveComponentsByType<TComponent>();
            return entity_components.Intersect(active_components_by_type);
        }

        internal IEnumerable<KeyValuePair<Guid, IComponent>> GetComponentsByEntityAndType(Guid entityID, Type type)
        {
            var entityComponents = GetComponentsByEntity(entityID);
            var activeComponentsByType = GetActiveComponentsByType(type);
            return entityComponents.Intersect(activeComponentsByType);
        }

        internal IEnumerable<Type> GetAllComponentTypesOfEntity(Guid entityID)
        {
            return GetComponentIDsByEntityID(entityID).Select((id) => componentIDToType[id]);
        }

        internal bool EntityHasComponentOfType<TComponent>(Guid entityID) where TComponent : struct, IComponent
        {
            return GetComponentsByEntityAndType<TComponent>(entityID).Any();
        }

        internal bool EntityHasComponentOfType(Guid entityID, Type type)
        {
            return GetComponentsByEntityAndType(entityID, type).Any();
        }

        internal IComponent GetComponentByID(Guid componentID)
        {
            return IDToComponent[componentID];
        }

        internal Type GetComponentTypeByID(Guid componentID)
        {
            return componentIDToType[componentID];
        }

        internal Guid GetEntityIDFromComponentID(Guid componentID)
        {
            return componentIDToEntityID[componentID];
        }

        internal void UpdateComponent<TComponent>(Guid componentID, TComponent newComponentValue) where TComponent : struct, IComponent
        {
            var entityID = GetEntityIDFromComponentID(componentID);
            IDToComponent[componentID] = newComponentValue;
        }

        internal void RemoveAllComponentsFromEntity(Guid entityID)
        {
            var componentIDs = entityIDToComponentIDs[entityID];

            foreach (var componentID in componentIDs)
            {
                MarkForRemoval(componentID);
            }
        }

        internal void MarkForActivation(Guid componentID)
        {
            componentsToActivate.Add(componentID);

            var entityID = GetEntityIDFromComponentID(componentID);
            entitiesWithAddedComponents.Add(entityID);
        }

        internal void MarkForDeactivation(Guid componentID)
        {
            componentsToDeactivate.Add(componentID);

            var entityID = GetEntityIDFromComponentID(componentID);
            entitiesWithRemovedComponents.Add(entityID);
        }

        internal void MarkForRemoval(Guid componentID)
        {
            componentsToRemove.Add(componentID);

            var entityID = GetEntityIDFromComponentID(componentID);
            entitiesWithRemovedComponents.Add(entityID);
        }

        internal void ActivateMarkedComponents()
        {
            foreach (var componentID in componentsToActivate)
            {
                var component = IDToComponent[componentID];
                if (inactiveComponents.Remove(componentID))
                {
                    activeComponents.Add(componentID);
                }
            }

            componentsToActivate.Clear();
        }

        internal void DeactivateMarkedComponents()
        {
            foreach (var componentID in componentsToDeactivate)
            {
                var component = IDToComponent[componentID];
                if (activeComponents.Remove(componentID))
                {
                    inactiveComponents.Add(componentID);
                }
            }

            componentsToDeactivate.Clear();
        }

        public void RemoveMarkedComponents()
        {
            foreach (var componentID in componentsToRemove)
            {
                var component = IDToComponent[componentID];
                var type = componentIDToType[componentID];

                activeComponents.Remove(componentID);
                inactiveComponents.Remove(componentID);

                var entityID = componentIDToEntityID[componentID];
                if (entityIDToComponentIDs.ContainsKey(entityID))
                {
                    entityIDToComponentIDs[entityID].Remove(componentID);
                }

                IDToComponent.Remove(componentID);
                componentIDToType.Remove(componentID);
                componentIDToEntityID.Remove(componentID);
                typeToComponentIDs[type].Remove(componentID);

                drawLayerManager.UnRegisterComponentWithLayer(componentID);
            }

            componentsToRemove.Clear();
        }

        public void RegisterDestroyedEntity(Guid entityID)
        {
            entityIDToComponentIDs.Remove(entityID);
        }
    }
}