riversong code showcase

Source/Riversong/Game/CommonServices/Entities/EntityCache/EntityCache.cs

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+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);
+            }
+        }
+    }
+}