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

namespace Encompass
{
    internal class ComponentManager
    {
        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>> activeComponents = new Dictionary<Type, List<Guid>>();
        private Dictionary<Type, List<Guid>> inactiveComponents = new Dictionary<Type, List<Guid>>();

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

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

            IDToComponent[componentID] = component;

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

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

            if (!activeComponents.ContainsKey(typeof(TComponent)))
            {
                activeComponents.Add(typeof(TComponent), new List<Guid>());
                inactiveComponents.Add(typeof(TComponent), new List<Guid>());
            }

            MarkForActivation(componentID);

            return componentID;
        }

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

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

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

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

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

            foreach (var componentID in componentIDs)
            {
                var component = IDToComponent[componentID];
                activeComponents[component.GetType()].Remove(componentID);
                inactiveComponents[component.GetType()].Remove(componentID);
            }

            entityIDToComponentIDs.Remove(entityID);
        }

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

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

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

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

            componentsToActivate.Clear();
        }

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

            componentsToDeactivate.Clear();
        }

        internal void RemoveComponents()
        {
            foreach (var componentID in componentsToRemove)
            {
                var component = IDToComponent[componentID];
                activeComponents[component.GetType()].Remove(componentID);
                inactiveComponents[component.GetType()].Remove(componentID);
            }

            componentsToRemove.Clear();
        }
    }
}