using System;
using System.Collections.Generic;

namespace Encompass
{
    internal class ComponentUpdateManager
    {
        private readonly ComponentStore existingAndPendingComponentStore = new ComponentStore();
        private readonly ComponentStore existingComponentStore = new ComponentStore();
        private readonly ComponentStore pendingComponentStore = new ComponentStore();
        private readonly Dictionary<Type, Dictionary<Entity, int>> typeToEntityToPendingComponentPriority = new Dictionary<Type, Dictionary<Entity, int>>(128);

        public ComponentStore UpToDateComponentStore { get; private set; } = new ComponentStore();

        public void RegisterComponentType<TComponent>() where TComponent : struct, IComponent
        {
            existingAndPendingComponentStore.RegisterComponentType<TComponent>();
            existingComponentStore.RegisterComponentType<TComponent>();
            pendingComponentStore.RegisterComponentType<TComponent>();
            UpToDateComponentStore.RegisterComponentType<TComponent>();
        }

        internal void Clear()
        {
            existingAndPendingComponentStore.ClearAll();
            existingComponentStore.ClearAll();
            pendingComponentStore.ClearAll();
            UpToDateComponentStore.ClearAll();

            foreach (var dictionary in typeToEntityToPendingComponentPriority.Values)
            {
                dictionary.Clear();
            }
        }

        internal void SetStartingComponentStore(ComponentStore componentStore)
        {
            UpToDateComponentStore = componentStore;
        }

        internal void AddExistingComponent<TComponent>(Entity entity, TComponent component) where TComponent : struct, IComponent
        {
            RegisterExistingOrPendingComponentMessage(entity, component);

            existingComponentStore.Set(entity, component);
        }

        internal bool AddPendingComponent<TComponent>(Entity entity, TComponent component, int priority) where TComponent : struct, IComponent
        {
            if (pendingComponentStore.Set(entity, component, priority))
            {
                RegisterExistingOrPendingComponentMessage(entity, component);
                return true;
            }

            return false;
        }

        private void RegisterExistingOrPendingComponentMessage<TComponent>(Entity entity, TComponent component) where TComponent : struct, IComponent
        {
            existingAndPendingComponentStore.Set(entity, component);
            UpToDateComponentStore.Set(entity, component);
        }

        public bool UpdateComponent<TComponent>(Entity entity, TComponent component, int priority) where TComponent : struct, IComponent
        {
            return UpToDateComponentStore.Set<TComponent>(entity, component, priority);
        }

        // general component reads by type

        internal IEnumerable<(TComponent, Entity)> ReadExistingAndPendingComponentsByType<TComponent>() where TComponent : struct, IComponent
        {
            return existingAndPendingComponentStore.All<TComponent>();
        }

        internal IEnumerable<(TComponent, Entity)> ReadExistingComponentsByType<TComponent>() where TComponent : struct, IComponent
        {
            return existingComponentStore.All<TComponent>();
        }

        internal IEnumerable<(TComponent, Entity)> ReadPendingComponentsByType<TComponent>() where TComponent : struct, IComponent
        {
            return pendingComponentStore.All<TComponent>();
        }

        // singular component reads by type

        internal (TComponent, Entity) ReadFirstExistingOrPendingComponentByType<TComponent>() where TComponent : struct, IComponent
        {
            if (!SomeExistingOrPendingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
            var enumerator = ReadExistingAndPendingComponentsByType<TComponent>().GetEnumerator();
            enumerator.MoveNext();
            return enumerator.Current;
        }

        internal (TComponent, Entity) ReadFirstExistingComponentByType<TComponent>() where TComponent : struct, IComponent
        {
            if (!SomeExistingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
            var enumerator = ReadExistingComponentsByType<TComponent>().GetEnumerator();
            enumerator.MoveNext();
            return enumerator.Current;
        }

        internal (TComponent, Entity) ReadFirstPendingComponentByType<TComponent>() where TComponent : struct, IComponent
        {
            if (!SomePendingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
            var enumerator = ReadPendingComponentsByType<TComponent>().GetEnumerator();
            enumerator.MoveNext();
            return enumerator.Current;
        }

        // check if some component of type exists in the world

        internal bool SomeExistingOrPendingComponent<TComponent>() where TComponent : struct, IComponent
        {
            return existingAndPendingComponentStore.Any<TComponent>();
        }

        internal bool SomeExistingComponent<TComponent>() where TComponent : struct, IComponent
        {
            return existingComponentStore.Any<TComponent>();
        }

        internal bool SomePendingComponent<TComponent>() where TComponent : struct, IComponent
        {
            return pendingComponentStore.Any<TComponent>();
        }

        // read components by entity and type

        internal TComponent ReadExistingComponentByEntityAndType<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            return existingComponentStore.Get<TComponent>(entity);
        }

        internal TComponent ReadPendingComponentByEntityAndType<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            return pendingComponentStore.Get<TComponent>(entity);
        }

        // check if entity has component of type

        internal bool HasExistingOrPendingComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            return existingAndPendingComponentStore.Has<TComponent>(entity);
        }

        internal bool HasExistingOrPendingComponent(Entity entity, Type type)
        {
            return existingAndPendingComponentStore.Has(type, entity);
        }

        internal bool HasExistingComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            return existingComponentStore.Has<TComponent>(entity);
        }

        internal bool HasExistingComponent(Entity entity, Type type)
        {
            return existingComponentStore.Has(type, entity);
        }

        internal bool HasPendingComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            return pendingComponentStore.Has<TComponent>(entity);
        }

        internal bool HasPendingComponent(Entity entity, Type type)
        {
            return pendingComponentStore.Has(type, entity);
        }

        internal void Remove<TComponent>(Entity entity) where TComponent : struct, IComponent
        {
            UpToDateComponentStore.Remove<TComponent>(entity);
        }
    }
}