From 4a4ce10c04e0660b213edd61bb6d247caf62833b Mon Sep 17 00:00:00 2001
From: Sergey Gut <kruzefag@gmail.com>
Date: Tue, 3 Mar 2020 11:36:00 +0400
Subject: [PATCH] Initial work on cache

---
 Core/Cache/ICacheStorage.cs | 10 ++++
 Core/Cache/MemoryCache.cs   | 93 +++++++++++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)
 create mode 100644 Core/Cache/ICacheStorage.cs
 create mode 100644 Core/Cache/MemoryCache.cs

diff --git a/Core/Cache/ICacheStorage.cs b/Core/Cache/ICacheStorage.cs
new file mode 100644
index 0000000..016f554
--- /dev/null
+++ b/Core/Cache/ICacheStorage.cs
@@ -0,0 +1,10 @@
+using System;
+
+namespace Kruzya.TelegramBot.Core.Cache
+{
+    public interface ICacheStorage<TKey, TValue>
+    {
+        public bool TryGetValue(TKey key, ref TValue value);
+        public void SetValue(TKey key, TValue value, int timeToLive);
+    }
+}
\ No newline at end of file
diff --git a/Core/Cache/MemoryCache.cs b/Core/Cache/MemoryCache.cs
new file mode 100644
index 0000000..b4afc69
--- /dev/null
+++ b/Core/Cache/MemoryCache.cs
@@ -0,0 +1,93 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+
+namespace Kruzya.TelegramBot.Core.Cache
+{
+    public class MemoryCache<TKey, TValue> : ICacheStorage<TKey, TValue>
+    {
+        /// <summary>
+        /// Represents a cache entry in internal dictionary.
+        /// </summary>
+        /// <typeparam name="TVal"></typeparam>
+        internal struct CacheEntry<TVal>
+        {
+            public TVal Value;
+            public DateTime Created;
+            public int ExpiresAt;
+
+            public bool IsExpired()
+            {
+                if (ExpiresAt == Timeout.Infinite)
+                {
+                    return false;
+                }
+
+                return (Created.AddSeconds(ExpiresAt)) < DateTime.Now;
+            }
+        }
+        
+        /// <summary>
+        /// 
+        /// </summary>
+        private Dictionary<TKey, CacheEntry<TValue>> dict = new Dictionary<TKey, CacheEntry<TValue>>();
+        
+        /// <summary>
+        /// The TTL for all entries if not set.
+        /// </summary>
+        private int _defaultTtl;
+
+        public MemoryCache() : this(Timeout.Infinite)
+        {
+        }
+
+        public MemoryCache(int defaultTtl)
+        {
+            _defaultTtl = defaultTtl;
+        }
+        
+        public bool TryGetValue(TKey key, ref TValue value)
+        {
+            if (dict.ContainsKey(key))
+            {
+                return false;
+            }
+
+            CacheEntry<TValue> temp;
+            if (!dict.TryGetValue(key, out temp))
+            {
+                return false;
+            }
+
+            if (temp.IsExpired())
+            {
+                dict.Remove(key);
+                return false;
+            }
+
+            value = temp.Value;
+            return true;
+        }
+
+        public void SetValue(TKey key, TValue value)
+        {
+            SetValue(key, value, _defaultTtl);
+        }
+        
+        public void SetValue(TKey key, TValue value, int timeToLive)
+        {
+            if (dict.ContainsKey(key))
+            {
+                dict.Remove(key);
+            }
+
+            dict.Add(key, new CacheEntry<TValue>()
+            {
+                Created = DateTime.Now,
+                ExpiresAt = timeToLive,
+                Value = value
+            });
+        }
+    }
+}
\ No newline at end of file