Added option --enable-logging to enable diagnostic logging (#106)

* Added option --enable-logging to enable diagnostic logging

* Addressing feedback

* Addressing feedback, round 2

src/Microsoft.SqlTools.ServiceLayer/Utility/CommandOptions.cs

@@ -0,0 +1,91 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+
+namespace Microsoft.SqlTools.ServiceLayer.Utility
+{
+    /// <summary>
+    /// The command-line options helper class.
+    /// </summary>
+    internal class CommandOptions
+    {
+        /// <summary>
+        /// Construct and parse command line options from the arguments array
+        /// </summary>
+        public CommandOptions(string[] args)
+        {
+            ErrorMessage = string.Empty;
+
+            try
+            {
+                for (int i = 0; i < args.Length; ++i)
+                {
+                    string arg = args[i];
+                    if (arg.StartsWith("--") || arg.StartsWith("-"))
+                    {
+                        arg = arg.Substring(1).ToLowerInvariant();
+                        switch (arg)
+                        {
+                            case "-enable-logging":
+                                EnableLogging = true;
+                                break;
+                            case "h":
+                            case "-help":
+                                ShouldExit = true;
+                                return;
+                            default:
+                                ErrorMessage += String.Format("Unknown argument \"{0}\"" + Environment.NewLine, arg);
+                                break;
+                        }
+                    }
+                }
+            }
+            catch (Exception ex)
+            {
+                ErrorMessage += ex.ToString();
+                return;
+            }
+            finally
+            {
+                if (!string.IsNullOrEmpty(ErrorMessage) || ShouldExit)
+                {
+                    Console.WriteLine(Usage);
+                    ShouldExit = true;
+                }
+            }
+        }
+
+        internal string ErrorMessage { get; private set; }
+
+
+        /// <summary>
+        /// Whether diagnostic logging is enabled
+        /// </summary>
+        public bool EnableLogging { get; private set; }
+
+        /// <summary>
+        /// Whether the program should exit immediately. Set to true when the usage is printed.
+        /// </summary>
+        public bool ShouldExit { get; private set; }
+
+        /// <summary>
+        /// Get the usage string describing command-line arguments for the program
+        /// </summary>
+        public string Usage
+        {
+            get
+            {
+                var str = string.Format("{0}" + Environment.NewLine +
+                    "Microsoft.SqlTools.ServiceLayer.exe " + Environment.NewLine +
+                    "   Options:" + Environment.NewLine +
+                    "        [--enable-logging]" + Environment.NewLine +
+                    "        [--help]" + Environment.NewLine,
+                    ErrorMessage);
+                return str;
+            }
+        }
+    }
+}