MonoGame.Extended/Source/MonoGame.Extended.Entities/ComponentManager.cs

using System;
using System.Collections.Generic;
using System.Collections.Specialized;
using Microsoft.Xna.Framework;
using MonoGame.Extended.Collections;
using MonoGame.Extended.Entities.Systems;

namespace MonoGame.Extended.Entities
{
    public interface IComponentMapperService
    {
        ComponentMapper<T> GetMapper<T>() where T : class;
    }

    public class ComponentManager : UpdateSystem, IComponentMapperService
    {
        public ComponentManager()
        {
            _componentMappers = new Bag<ComponentMapper>();
            _componentTypes = new Dictionary<Type, int>();
        }

        private readonly Bag<ComponentMapper> _componentMappers;
        private readonly Dictionary<Type, int> _componentTypes;

        public Action<int> ComponentsChanged;

        private ComponentMapper<T> CreateMapperForType<T>(int componentTypeId)
            where T : class
        {
            // TODO: We can probably do better than this without a huge performance penalty by creating our own bit vector that grows after the first 32 bits.
            if (componentTypeId >= 32)
                throw new InvalidOperationException("Component type limit exceeded. We currently only allow 32 component types for performance reasons.");

            var mapper = new ComponentMapper<T>(componentTypeId, ComponentsChanged);
            _componentMappers[componentTypeId] = mapper;
            return mapper;
        }

        public ComponentMapper GetMapper(int componentTypeId)
        {
            return _componentMappers[componentTypeId];
        }

        public ComponentMapper<T> GetMapper<T>() 
            where T : class
        {
            var componentTypeId = GetComponentTypeId(typeof(T));

            if (_componentMappers[componentTypeId] != null)
                return _componentMappers[componentTypeId] as ComponentMapper<T>;

            return CreateMapperForType<T>(componentTypeId);
        }

        public int GetComponentTypeId(Type type)
        {
            if (_componentTypes.TryGetValue(type, out var id))
                return id;

            id = _componentTypes.Count;
            _componentTypes.Add(type, id);
            return id;
        }

        public BitVector32 CreateComponentBits(int entityId)
        {
            var componentBits = new BitVector32();
            var mask = BitVector32.CreateMask();

            for (var componentId = 0; componentId < _componentMappers.Count; componentId++)
            {
                componentBits[mask] = _componentMappers[componentId]?.Has(entityId) ?? false;
                mask = BitVector32.CreateMask(mask);
            }

            return componentBits;
        }

        public void Destroy(int entityId)
        {
            foreach (var componentMapper in _componentMappers)
                componentMapper.Delete(entityId);
        }

        public override void Update(GameTime gameTime)
        {
        }
    }
}