Added way to chain FileLifeCycleHooks together

Author: EamonHetherton

src/Serilog.Sinks.File/Sinks/File/FileLifecycleHooksExtensions.cs

@@ -0,0 +1,71 @@
+// Copyright 2019 Serilog Contributors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+using System;
+using System.IO;
+using System.Text;
+
+namespace Serilog.Sinks.File
+{
+    /// <summary>
+    /// FileLifecycleHooks extension methods
+    /// </summary>
+    public static class FileLifecycleHooksExtensions
+    {
+        /// <summary>
+        /// Creates a chain of <see cref="FileLifecycleHooks"/> that have their methods called sequentially
+        /// Can be used to compose <see cref="FileLifecycleHooks"/> together; e.g. add header information to each log file and
+        /// compress it.
+        /// </summary>
+        /// <example>
+        /// <code>
+        /// var hooks = new GZipHooks().ChainTo(new HeaderWriter("File Header"));
+        /// </code>
+        /// </example>
+        /// <param name="first">The first <see cref="FileLifecycleHooks"/> to have its methods called in the chain</param>
+        /// <param name="second">The second <see cref="FileLifecycleHooks"/> to have its methods called in the chain</param>
+        /// <returns></returns>
+        public static FileLifecycleHooks ChainTo(this FileLifecycleHooks first, FileLifecycleHooks second)
+        {
+            return new FileLifeCycleHookChain(first, second);
+        }
+
+        class FileLifeCycleHookChain : FileLifecycleHooks
+        {
+            private readonly FileLifecycleHooks[] hooks;
+
+            public FileLifeCycleHookChain(params FileLifecycleHooks[] hooks)
+            {
+                this.hooks = hooks ?? throw new ArgumentNullException(nameof(hooks));
+            }
+
+            public override Stream OnFileOpened(Stream underlyingStream, Encoding encoding)
+            {
+                for (int i = 0; i < hooks.Length; i++)
+                {
+                    underlyingStream = hooks[i].OnFileOpened(underlyingStream, encoding);
+                }
+                return underlyingStream;
+            }
+
+            public override void OnFileDeleting(string path)
+            {
+                for (int i = 0; i < hooks.Length; i++)
+                {
+                    hooks[i].OnFileDeleting(path);
+                }
+            }
+        }
+    }
+}