From be6dc557a3b819248b014992eb96c1cb21f8112b Mon Sep 17 00:00:00 2001
From: vnugent <public@vaughnnugent.com>
Date: Sun, 8 Jan 2023 14:44:01 -0500
Subject: Initial commit

---
 Utils/src/Async/AsyncUpdatableResource.cs | 111 ++++++++++++++++++++++++++++++
 1 file changed, 111 insertions(+)
 create mode 100644 Utils/src/Async/AsyncUpdatableResource.cs

(limited to 'Utils/src/Async/AsyncUpdatableResource.cs')

diff --git a/Utils/src/Async/AsyncUpdatableResource.cs b/Utils/src/Async/AsyncUpdatableResource.cs
new file mode 100644
index 0000000..b4ce519
--- /dev/null
+++ b/Utils/src/Async/AsyncUpdatableResource.cs
@@ -0,0 +1,111 @@
+/*
+* Copyright (c) 2022 Vaughn Nugent
+* 
+* Library: VNLib
+* Package: VNLib.Utils
+* File: AsyncUpdatableResource.cs 
+*
+* AsyncUpdatableResource.cs is part of VNLib.Utils which is part of the larger 
+* VNLib collection of libraries and utilities.
+*
+* VNLib.Utils is free software: you can redistribute it and/or modify 
+* it under the terms of the GNU General Public License as published
+* by the Free Software Foundation, either version 2 of the License,
+* or (at your option) any later version.
+*
+* VNLib.Utils is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
+* General Public License for more details.
+*
+* You should have received a copy of the GNU General Public License 
+* along with VNLib.Utils. If not, see http://www.gnu.org/licenses/.
+*/
+
+using System;
+using System.IO;
+using System.Text.Json;
+using System.Threading.Tasks;
+
+using VNLib.Utils.IO;
+using VNLib.Utils.Resources;
+
+namespace VNLib.Utils.Async
+{
+    /// <summary>
+    /// A callback delegate used for updating a <see cref="AsyncUpdatableResource"/>
+    /// </summary>
+    /// <param name="source">The <see cref="AsyncUpdatableResource"/> to be updated</param>
+    /// <param name="data">The serialized data to be stored/updated</param>
+    /// <exception cref="ResourceUpdateFailedException"></exception>
+    public delegate Task AsyncUpdateCallback(object source, Stream data);
+    /// <summary>
+    /// A callback delegate invoked when a <see cref="AsyncUpdatableResource"/> delete is requested
+    /// </summary>
+    /// <param name="source">The <see cref="AsyncUpdatableResource"/> to be deleted</param>
+    /// <exception cref="ResourceDeleteFailedException"></exception>
+    public delegate Task AsyncDeleteCallback(object source);
+
+    /// <summary>
+    /// Implemented by a resource that is backed by an external data store, that when modified or deleted will 
+    /// be reflected to the backing store.
+    /// </summary>
+    public abstract class AsyncUpdatableResource : BackedResourceBase, IAsyncExclusiveResource
+    {
+        protected abstract AsyncUpdateCallback UpdateCb { get; }
+        protected abstract AsyncDeleteCallback DeleteCb { get; }
+
+        /// <summary>
+        /// Releases the resource and flushes pending changes to its backing store.
+        /// </summary>
+        /// <returns>A task that represents the async operation</returns>
+        /// <exception cref="InvalidOperationException"></exception>
+        /// <exception cref="ResourceDeleteFailedException"></exception>
+        /// <exception cref="ResourceUpdateFailedException"></exception>
+        public virtual async ValueTask ReleaseAsync()
+        {
+            //If resource has already been realeased, return
+            if (IsReleased)
+            {
+                return;
+            }
+            //If deleted flag is set, invoke the delete callback
+            if (Deleted)
+            {
+                await DeleteCb(this).ConfigureAwait(true);
+            }
+            //If the state has been modifed, flush changes to the store
+            else if (Modified)
+            {
+                await FlushPendingChangesAsync().ConfigureAwait(true);
+            }
+            //Set the released value
+            IsReleased = true;
+        }
+
+        /// <summary>
+        /// <para>
+        /// Writes the current state of the the resource to the backing store
+        /// immediatly by invoking the specified callback. 
+        /// </para>
+        /// <para>
+        /// Only call this method if your store supports multiple state updates
+        /// </para>
+        /// </summary>
+        protected virtual async Task FlushPendingChangesAsync()
+        {
+            //Get the resource
+            object resource = GetResource();
+            //Open a memory stream to store data in
+            using VnMemoryStream data = new();
+            //Serialize and write to stream
+            VnEncoding.JSONSerializeToBinary(resource, data, resource.GetType(), base.JSO);
+            //Reset stream to begining
+            _ = data.Seek(0, SeekOrigin.Begin);
+            //Invoke update callback
+            await UpdateCb(this, data).ConfigureAwait(true);
+            //Clear modified flag
+            Modified = false;
+        }
+    }
+}
-- 
cgit