From 2f31a6cd06afdfa7619523a67e44d12c7f87a8e4 Mon Sep 17 00:00:00 2001
From: Harald Wolff-Thobaben <harald@l--n.de>
Date: Sat, 17 Jul 2021 20:42:01 +0200
Subject: [PATCH] Added ExtendedCache

---
 ln.collections/ExtendedCache.cs | 149 ++++++++++++++++++++++++++++++++
 1 file changed, 149 insertions(+)
 create mode 100644 ln.collections/ExtendedCache.cs

diff --git a/ln.collections/ExtendedCache.cs b/ln.collections/ExtendedCache.cs
new file mode 100644
index 0000000..e14ecee
--- /dev/null
+++ b/ln.collections/ExtendedCache.cs
@@ -0,0 +1,149 @@
+using System;
+using System.Collections.Generic;
+
+namespace ln.collections
+{
+    public delegate bool CacheMayForget<K,V>(ExtendedCache<K,V> cache,V item);
+    
+    public class ExtendedCache<K,V>
+    {
+        public event CacheMayForget<K, V> OnCacheMayForget;
+
+        private MappingBTree<K, ExtendedCacheItem<K, V>> cacheItems =
+            new MappingBTree<K, ExtendedCacheItem<K, V>>((i) => i.Key);
+
+        private BTreeValueSet<DateTime, ExtendedCacheItem<K, V>> cacheAges =
+            new BTreeValueSet<DateTime, ExtendedCacheItem<K, V>>();
+
+        private int _targetSize = 4096;
+        public int TargetSize
+        {
+            get => _targetSize;
+            set
+            {
+                _targetSize = value;
+                if (Count > _targetSize) Invalidate();
+            }
+        }
+
+        public int Count => cacheItems.Count;
+
+
+        public ExtendedCache()
+        {
+        }
+
+        public ExtendedCache(int targetSize) : this()
+        {
+            TargetSize = targetSize;
+        }
+        
+        public void Clear()
+        {
+            cacheItems.Clear();
+            cacheAges.Clear();
+        }
+
+        public void Invalidate()
+        {
+            if (Count <= _targetSize)
+                return;
+
+            foreach (ExtendedCache<K,V>.ExtendedCacheItem<K,V> eci in cacheAges.Values)
+            {
+                if (MayForget(eci.Value))
+                    Invalidate(eci);
+                
+                if (Count <= _targetSize)
+                    break;
+            }
+        }
+
+        private bool MayForget(V item)
+        {
+            foreach (CacheMayForget<K,V> mayForget in OnCacheMayForget.GetInvocationList() ?? new CacheMayForget<K, V>[0])
+            {
+                if (!mayForget(this, item))
+                    return false;
+            }
+            return true;
+        }
+        
+        public V this[K key]
+        {
+            get
+            {
+                if (TryGet(key, out V value))
+                    return value;
+                throw new KeyNotFoundException();
+            }
+        }
+
+        public bool TryGet(K key, out V value)
+        {
+            if (cacheItems.TryGet(key, out ExtendedCacheItem<K, V> eci))
+            {
+                value = eci.Value;
+                return true;
+            }
+
+            value = default(V);
+            return false;
+        }
+
+        private void UpdateCacheItem(ExtendedCacheItem<K, V> eci)
+        {
+            cacheAges.Remove(eci.Timestamp, eci);
+            eci.Timestamp = DateTime.Now;
+            cacheAges.Add(eci.Timestamp, eci);
+        }
+        
+        public bool Ensure(K key, V value)
+        {
+            if (cacheItems.TryGet(key, out ExtendedCacheItem<K, V> eci))
+            {
+                if (!Object.ReferenceEquals(eci.Value, value))
+                    return false;
+                UpdateCacheItem(eci);
+                return true;
+            }
+            else
+            {
+                eci = new ExtendedCacheItem<K, V>(key, value);
+                cacheItems.Add(eci);
+                cacheAges.Add(eci.Timestamp, eci);
+                return true;
+            }
+        }
+
+        public bool Invalidate(K key)
+        {
+            if (cacheItems.TryGet(key, out ExtendedCacheItem<K, V> eci))
+            {
+                Invalidate(eci);
+                return true;
+            }
+            return false;
+        }
+
+        public void Invalidate(ExtendedCacheItem<K, V> eci)
+        {
+            cacheAges.Remove(eci.Timestamp, eci);
+            cacheItems.RemoveKey(eci.Key);
+        }
+        
+        public class ExtendedCacheItem<TK, TV>
+        {
+            public DateTime Timestamp;
+            public TK Key;
+            public TV Value;
+
+            public ExtendedCacheItem(TK key, TV value)
+            {
+                Key = key;
+                Value = value;
+                Timestamp = DateTime.Now;
+            }
+        }
+    }
+}
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