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

namespace Encompass
{
    public class Entity
    {
        public readonly static List<Component> Empty = new List<Component>();

        public readonly int id;

        private readonly Dictionary<Type, List<Component>> componentBag = new Dictionary<Type, List<Component>>();
        private readonly Dictionary<Type, List<Component>> activeComponents = new Dictionary<Type, List<Component>>();

        public Entity(int id) {
            this.id = id;
        }

        public TComponent AddComponent<TComponent>() where TComponent : Component, new() {
            TComponent component = new TComponent();

            if (!componentBag.ContainsKey(typeof(TComponent))) {
                var componentList = new List<Component>();
                var activeComponentList = new List<Component>();
                componentBag.Add(typeof(TComponent), componentList);
                activeComponents.Add(typeof(TComponent), activeComponentList);
                componentList.Add(component);
                activeComponentList.Add(component);
            } else {
                componentBag[typeof(TComponent)].Add(component);
                activeComponents[typeof(TComponent)].Add(component);
            }

            return component;
        }

        public IEnumerable<TComponent> GetComponents<TComponent>() where TComponent : Component {
            if (activeComponents.ContainsKey(typeof(TComponent))) {
                return activeComponents[typeof(TComponent)].Cast<TComponent>();
            } else {
                return Enumerable.Empty<TComponent>();
            }
        }

        public TComponent GetComponent<TComponent>() where TComponent : Component {
            return GetComponents<TComponent>().First();
        }

        public bool HasComponent<TComponent>() where TComponent : Component {
            return activeComponents.ContainsKey(typeof(TComponent)) &&
                activeComponents[typeof(TComponent)].Count != 0;
        }
    }
}