generic way to support scriptable operations (#438)

* implemented a generic way to support scriptable operations

src/Microsoft.SqlTools.ServiceLayer/TaskServices/TaskOperationHelper.cs

@@ -0,0 +1,113 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using System;
+using System.Threading.Tasks;
+
+namespace Microsoft.SqlTools.ServiceLayer.TaskServices
+{
+    /// <summary>
+    /// Helper class for task operations
+    /// </summary>
+    public static class TaskOperationHelper
+    {
+        /// <summary>
+        /// Async method to execute the operation
+        /// </summary>
+        /// <param name="sqlTask">Sql Task</param>
+        /// <returns>Task Result</returns>
+        public static async Task<TaskResult> ExecuteTaskAsync(SqlTask sqlTask)
+        {
+            sqlTask.AddMessage(SR.TaskInProgress, SqlTaskStatus.InProgress, true);
+            ITaskOperation taskOperation = sqlTask.TaskMetadata.TaskOperation as ITaskOperation;
+            TaskResult taskResult = null;
+
+            if (taskOperation != null)
+            {
+                taskOperation.SqlTask = sqlTask;
+                
+                return await Task.Factory.StartNew(() =>
+                {
+                    TaskResult result = new TaskResult();
+                    try
+                    {
+                        if (string.IsNullOrEmpty(taskOperation.ErrorMessage))
+                        {
+                            taskOperation.Execute(sqlTask.TaskMetadata.TaskExecutionMode);
+                            result.TaskStatus = SqlTaskStatus.Succeeded;
+                        }
+                        else
+                        {
+                            result.TaskStatus = SqlTaskStatus.Failed;
+                            result.ErrorMessage = taskOperation.ErrorMessage;
+                        }
+                    }
+                    catch (Exception ex)
+                    {
+                        result.TaskStatus = SqlTaskStatus.Failed;
+                        result.ErrorMessage = ex.Message;
+                        if (ex.InnerException != null)
+                        {
+                            result.ErrorMessage += Environment.NewLine + ex.InnerException.Message;
+                        }
+                        if (taskOperation != null && taskOperation.ErrorMessage != null)
+                        {
+                            result.ErrorMessage += Environment.NewLine + taskOperation.ErrorMessage;
+                        }
+                    }
+                    return result;
+                });
+            }
+            else
+            {
+                taskResult = new TaskResult();
+                taskResult.TaskStatus = SqlTaskStatus.Failed;
+            }
+
+            return taskResult;
+        }
+
+        /// <summary>
+        /// Async method to cancel the operations
+        /// </summary>
+        public static async Task<TaskResult> CancelTaskAsync(SqlTask sqlTask)
+        {
+            ITaskOperation taskOperation = sqlTask.TaskMetadata.TaskOperation as ITaskOperation;
+            TaskResult taskResult = null;
+
+            if (taskOperation != null)
+            {
+              
+                return await Task.Factory.StartNew(() =>
+                {
+                    try
+                    {
+                        taskOperation.Cancel();
+
+                        return new TaskResult
+                        {
+                            TaskStatus = SqlTaskStatus.Canceled
+                        };
+                    }
+                    catch (Exception ex)
+                    {
+                        return new TaskResult
+                        {
+                            TaskStatus = SqlTaskStatus.Failed,
+                            ErrorMessage = ex.Message
+                        };
+                    }
+                });
+            }
+            else
+            {
+                taskResult = new TaskResult();
+                taskResult.TaskStatus = SqlTaskStatus.Failed;
+            }
+
+            return taskResult;
+        }
+    }
+}