From dc7ad57c845cc9b1b502e5e8b12ce96af4183dc4 Mon Sep 17 00:00:00 2001
From: vman <public@vaughnnugent.com>
Date: Fri, 18 Nov 2022 17:15:36 -0500
Subject: Add project files.

---
 VNLib.Data.Caching.Global/GlobalDataCache.cs | 145 +++++++++++++++++++++++++++
 1 file changed, 145 insertions(+)
 create mode 100644 VNLib.Data.Caching.Global/GlobalDataCache.cs

(limited to 'VNLib.Data.Caching.Global/GlobalDataCache.cs')

diff --git a/VNLib.Data.Caching.Global/GlobalDataCache.cs b/VNLib.Data.Caching.Global/GlobalDataCache.cs
new file mode 100644
index 0000000..2c60ae2
--- /dev/null
+++ b/VNLib.Data.Caching.Global/GlobalDataCache.cs
@@ -0,0 +1,145 @@
+using VNLib.Data.Caching.Global.Exceptions;
+
+namespace VNLib.Data.Caching.Global
+{
+    /// <summary>
+    /// A static library for caching data in-process or a remote data 
+    /// cache
+    /// </summary>
+    public static class GlobalDataCache
+    {
+
+        private static IGlobalCacheProvider? CacheProvider;
+        private static CancellationTokenRegistration _reg;
+
+        private static readonly object CacheLock = new();
+        private static readonly Dictionary<string, WeakReference<object>> LocalCache = new();
+
+        /// <summary>
+        /// Gets a value that indicates if global cache is available
+        /// </summary>
+        public static bool IsAvailable => CacheProvider != null && CacheProvider.IsConnected;
+
+        /// <summary>
+        /// Sets the backing cache provider for the process-wide global cache
+        /// </summary>
+        /// <param name="cacheProvider">The cache provider instance</param>
+        /// <param name="statusToken">A token that represents the store's validity</param>
+        public static void SetProvider(IGlobalCacheProvider cacheProvider, CancellationToken statusToken)
+        {
+            CacheProvider = cacheProvider ?? throw new ArgumentNullException(nameof(cacheProvider));
+            //Remove cache provider when cache provider is no longer valid
+            _reg = statusToken.Register(Cleanup);
+        }
+
+        private static void Cleanup()
+        {
+            CacheProvider = null;
+            //Clear local cache
+            lock (CacheLock)
+            {
+                LocalCache.Clear();
+            }
+            _reg.Dispose();
+        }
+
+        /// <summary>
+        /// Asynchronously gets a value from the global cache provider 
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="key">The key identifying the object to recover from cache</param>
+        /// <returns>The value if found, or null if it does not exist in the store</returns>
+        /// <exception cref="GlobalCacheException"></exception>
+        /// <exception cref="CacheNotLoadedException"></exception>
+        public static async Task<T?> GetAsync<T>(string key) where T: class
+        {            
+            //Check local cache first
+            lock (CacheLock)
+            {
+                if (LocalCache.TryGetValue(key, out WeakReference<object>? wr))
+                {
+                    //Value is found
+                    if(wr.TryGetTarget(out object? value))
+                    {
+                        //Value exists and is loaded to local cache
+                        return (T)value;
+                    }
+                    //Value has been collected
+                    else
+                    {
+                        //Remove the key from the table
+                        LocalCache.Remove(key);
+                    }
+                }
+            }
+            //get ref to local cache provider
+            IGlobalCacheProvider? prov = CacheProvider;
+            if(prov == null)
+            {
+                throw new CacheNotLoadedException("Global cache provider was not found");
+            }
+            //get the value from the store
+            T? val = await prov.GetAsync<T>(key);
+            //Only store the value if it was successfully found
+            if (val != null)
+            {
+                //Store in local cache
+                lock (CacheLock)
+                {
+                    LocalCache[key] = new WeakReference<object>(val);
+                }
+            }
+            return val;
+        }
+
+        /// <summary>
+        /// Asynchronously sets (or updates) a cached value in the global cache
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="key">The key identifying the object to recover from cache</param>
+        /// <param name="value">The value to set at the given key</param>
+        /// <returns>A task that completes when the update operation has compelted</returns>
+        /// <exception cref="GlobalCacheException"></exception>
+        /// <exception cref="CacheNotLoadedException"></exception>
+        public static async Task SetAsync<T>(string key, T value) where T : class
+        {
+            //Local record is stale, allow it to be loaded from cache next call to get
+            lock (CacheLock)
+            {
+                LocalCache.Remove(key);
+            }
+            //get ref to local cache provider
+            IGlobalCacheProvider? prov = CacheProvider;
+            if (prov == null)
+            {
+                throw new CacheNotLoadedException("Global cache provider was not found");
+            }
+            //set the value in the store
+            await prov.SetAsync<T>(key, value);
+        }
+
+        /// <summary>
+        /// Asynchronously deletes an item from cache by its key
+        /// </summary>
+        /// <param name="key"></param>
+        /// <returns>A task that completes when the delete operation has compelted</returns>
+        /// <exception cref="GlobalCacheException"></exception>
+        /// <exception cref="CacheNotLoadedException"></exception>
+        public static async Task DeleteAsync(string key)
+        {
+            //Delete from local cache 
+            lock (CacheLock)
+            {
+                LocalCache.Remove(key);
+            }
+            //get ref to local cache provider
+            IGlobalCacheProvider? prov = CacheProvider;
+            if (prov == null)
+            {
+                throw new CacheNotLoadedException("Global cache provider was not found");
+            }
+            //Delete value from store
+            await prov.DeleteAsync(key);
+        }
+    }
+}
\ No newline at end of file
-- 
cgit