LRUCache

src/Squidex.Infrastructure/Caching/LRUCache.cs

@@ -0,0 +1,108 @@
+// ==========================================================================
+//  LRUCache.cs
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex Group
+//  All rights reserved.
+// ==========================================================================
+
+using System.Collections.Generic;
+
+namespace Squidex.Infrastructure.Caching
+{
+    public sealed class LRUCache
+    {
+        private readonly Dictionary<object, LinkedListNode<LRUCacheItem>> cacheMap = new Dictionary<object, LinkedListNode<LRUCacheItem>>();
+        private readonly LinkedList<LRUCacheItem> cacheHistory = new LinkedList<LRUCacheItem>();
+        private readonly int capacity;
+
+        public LRUCache(int capacity)
+        {
+            Guard.GreaterThan(capacity, 0, nameof(capacity));
+
+            this.capacity = capacity;
+        }
+
+        public bool Set(object key, object value)
+        {
+            Guard.NotNull(key, nameof(key));
+
+            if (cacheMap.TryGetValue(key, out var node))
+            {
+                node.Value.Value = value;
+
+                cacheHistory.Remove(node);
+                cacheHistory.AddLast(node);
+
+                cacheMap[key] = node;
+
+                return true;
+            }
+            else
+            {
+                if (cacheMap.Count >= capacity)
+                {
+                    RemoveFirst();
+                }
+
+                var cacheItem = new LRUCacheItem { Key = key, Value = value };
+
+                node = new LinkedListNode<LRUCacheItem>(cacheItem);
+
+                cacheMap.Add(key, node);
+                cacheHistory.AddLast(node);
+
+                return false;
+            }
+        }
+
+        public bool Remove(object key)
+        {
+            Guard.NotNull(key, nameof(key));
+
+            if (cacheMap.TryGetValue(key, out var node))
+            {
+                cacheMap.Remove(key);
+                cacheHistory.Remove(node);
+
+                return true;
+            }
+
+            return false;
+        }
+
+        public bool TryGetValue(object key, out object value)
+        {
+            Guard.NotNull(key, nameof(key));
+
+            value = null;
+
+            if (cacheMap.TryGetValue(key, out var node))
+            {
+                value = node.Value.Value;
+
+                cacheHistory.Remove(node);
+                cacheHistory.AddLast(node);
+
+                return true;
+            }
+
+            return false;
+        }
+
+        public bool Contains(object key)
+        {
+            Guard.NotNull(key, nameof(key));
+
+            return cacheMap.ContainsKey(key);
+        }
+
+        private void RemoveFirst()
+        {
+            var node = cacheHistory.First;
+
+            cacheMap.Remove(node.Value.Key);
+            cacheHistory.RemoveFirst();
+        }
+    }
+}

src/Squidex.Infrastructure/Caching/LRUCacheItem.cs

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+// ==========================================================================
+//  LRUCacheItem.cs
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex Group
+//  All rights reserved.
+// ==========================================================================
+
+#pragma warning disable SA1401 // Fields must be private
+
+namespace Squidex.Infrastructure.Caching
+{
+    internal class LRUCacheItem
+    {
+        public object Key;
+        public object Value;
+    }
+}

tests/Squidex.Infrastructure.Tests/Caching/LRUCacheTests.cs

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+// ==========================================================================
+//  LRUCacheTests.cs
+//  Squidex Headless CMS
+// ==========================================================================
+//  Copyright (c) Squidex Group
+//  All rights reserved.
+// ==========================================================================
+
+using Xunit;
+
+namespace Squidex.Infrastructure.Caching
+{
+    public class LRUCacheTests
+    {
+        private readonly LRUCache sut = new LRUCache(10);
+        private readonly string key = "Key";
+
+        [Fact]
+        public void Should_always_override_when_setting_value()
+        {
+            sut.Set(key, 1);
+            sut.Set(key, 2);
+
+            Assert.True(sut.TryGetValue(key, out var value));
+            Assert.True(sut.Contains(key));
+
+            Assert.Equal(2, value);
+        }
+
+        [Fact]
+        public void Should_remove_old_items_when_capacity_reached()
+        {
+            for (int i = 0; i < 15; i++)
+            {
+                sut.Set(i.ToString(), i);
+            }
+
+            for (int i = 0; i < 5; i++)
+            {
+                Assert.False(sut.TryGetValue(i.ToString(), out var value));
+                Assert.Null(value);
+            }
+
+            for (int i = 5; i < 15; i++)
+            {
+                Assert.True(sut.TryGetValue(i.ToString(), out var value));
+                Assert.NotNull(value);
+            }
+        }
+
+        [Fact]
+        public void Should_return_false_when_item_to_remove_does_not_exist()
+        {
+            Assert.False(sut.Remove(key));
+        }
+
+        [Fact]
+        public void Should_remove_inserted_item()
+        {
+            sut.Set(key, 2);
+
+            Assert.True(sut.Remove(key));
+            Assert.False(sut.Contains(key));
+            Assert.False(sut.TryGetValue(key, out var value));
+            Assert.Null(value);
+        }
+    }
+}