Use FileMonitor to synchronize Mailer bot (#1108)

Move SessionFileMonitor into a generic FileMonitor class
Use FileMonintor for both SessionCache and the Mailer bot
Allows multiple MCC instances to share the same database files

MinecraftClient/FileMonitor.cs

@@ -0,0 +1,83 @@
+using System;
+using System.IO;
+using System.Threading;
+
+namespace MinecraftClient.Protocol.Session
+{
+    /// <summary>
+    /// Monitor session file changes on disk
+    /// </summary>
+    class SessionFileMonitor
+    {
+        private FileSystemWatcher monitor;
+        private Thread polling;
+
+        /// <summary>
+        /// Create a new SessionFileMonitor and start monitoring
+        /// </summary>
+        /// <param name="folder">Folder to monitor</param>
+        /// <param name="filename">Filename inside folder</param>
+        /// <param name="handler">Callback for file changes</param>
+        public SessionFileMonitor(string folder, string filename, FileSystemEventHandler handler)
+        {
+            if (Settings.DebugMessages)
+                ConsoleIO.WriteLineFormatted("§8Initializing disk session cache using FileSystemWatcher");
+
+            try
+            {
+                monitor = new FileSystemWatcher();
+                monitor.Path = folder;
+                monitor.IncludeSubdirectories = false;
+                monitor.Filter = filename;
+                monitor.NotifyFilter = NotifyFilters.LastWrite;
+                monitor.Changed += handler;
+                monitor.EnableRaisingEvents = true;
+            }
+            catch
+            {
+                if (Settings.DebugMessages)
+                    ConsoleIO.WriteLineFormatted("§8Failed to initialize FileSystemWatcher, retrying using Polling");
+
+                polling = new Thread(() => PollingThread(folder, filename, handler));
+                polling.Start();
+            }
+        }
+
+        /// <summary>
+        /// Fallback polling thread for use when operating system does not support FileSystemWatcher
+        /// </summary>
+        /// <param name="folder">Folder to monitor</param>
+        /// <param name="filename">File name to monitor</param>
+        /// <param name="handler">Callback when file changes</param>
+        private void PollingThread(string folder, string filename, FileSystemEventHandler handler)
+        {
+            string filePath = String.Concat(folder, Path.DirectorySeparatorChar, filename);
+            DateTime lastWrite = GetLastWrite(filePath);
+            while (true)
+            {
+                Thread.Sleep(5000);
+                DateTime lastWriteNew = GetLastWrite(filePath);
+                if (lastWriteNew != lastWrite)
+                {
+                    lastWrite = lastWriteNew;
+                    handler(this, new FileSystemEventArgs(WatcherChangeTypes.Changed, folder, filename));
+                }
+            }
+        }
+
+        /// <summary>
+        /// Get last write for a given file
+        /// </summary>
+        /// <param name="path">File path to get last write from</param>
+        /// <returns>Last write time, or DateTime.MinValue if the file does not exist</returns>
+        private DateTime GetLastWrite(string path)
+        {
+            FileInfo fileInfo = new FileInfo(path);
+            if (fileInfo.Exists)
+            {
+                return fileInfo.LastWriteTime;
+            }
+            else return DateTime.MinValue;
+        }
+    }
+}