using System;
using System.Collections.Generic;

namespace DanieleMarotta.RiversongCodeShowcase
{
    public class EntityCache : IEntityCache
    {
        private Dictionary<int, Cache> _caches = new();

        public void CreateCache<T>(int key, Predicate<T> filter) where T : Entity
        {
            if (!_caches.TryGetValue(key, out var cache))
            {
                cache = new Cache<T>();
                _caches.Add(key, cache);
            }
            ((Cache<T>)cache).Filter = filter;
        }

        public List<T> Get<T>(int key) where T : Entity
        {
            if (!_caches.TryGetValue(key, out var cache))
            {
                cache = new Cache<T>();
                _caches.Add(key, cache);
            }
            return ((Cache<T>)cache).Entities;
        }

        public void OnAdded(Entity entity)
        {
            foreach (var cache in _caches.Values) cache.TryAdd(entity);
        }

        public void OnRemoved(Entity entity)
        {
            foreach (var cache in _caches.Values) cache.TryRemove(entity);
        }

        private abstract class Cache
        {
            public void TryAdd(Entity entity)
            {
                if (FilterEntity(entity)) Add(entity);
            }

            public void TryRemove(Entity entity)
            {
                if (FilterEntity(entity)) Remove(entity);
            }

            protected abstract bool FilterEntity(Entity entity);

            protected abstract void Add(Entity entity);

            protected abstract void Remove(Entity entity);
        }

        private class Cache<T> : Cache where T : Entity
        {
            public Predicate<T> Filter { get; set; }

            public List<T> Entities { get; } = new();

            protected override bool FilterEntity(Entity entity)
            {
                return entity is T typedEntity && Filter.Invoke(typedEntity);
            }

            protected override void Add(Entity entity)
            {
                Entities.Add((T)entity);
            }

            protected override void Remove(Entity entity)
            {
                Entities.Remove((T)entity);
            }
        }
    }
}