Add schema compare generate script operation (#787)

* add generate script operation

src/Microsoft.SqlTools.ServiceLayer/SchemaCompare/SchemaCompareGenerateScriptOperation.cs

@@ -0,0 +1,82 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+using Microsoft.SqlServer.Dac;
+using Microsoft.SqlServer.Dac.Compare;
+using Microsoft.SqlTools.ServiceLayer.Connection;
+using Microsoft.SqlTools.ServiceLayer.SchemaCompare.Contracts;
+using Microsoft.SqlTools.ServiceLayer.TaskServices;
+using Microsoft.SqlTools.Utility;
+using System;
+using System.Diagnostics;
+using System.IO;
+using System.Threading;
+
+namespace Microsoft.SqlTools.ServiceLayer.SchemaCompare
+{
+    /// <summary>
+    /// Class to represent an in-progress schema compare generate script operation
+    /// </summary>
+    class SchemaCompareGenerateScriptOperation : ITaskOperation
+    {
+        private CancellationTokenSource cancellation = new CancellationTokenSource();
+        private bool disposed = false;
+
+        /// <summary>
+        /// Gets the unique id associated with this instance.
+        /// </summary>
+        public string OperationId { get; private set; }
+
+        public SchemaCompareGenerateScriptParams Parameters { get; }
+
+        protected CancellationToken CancellationToken { get { return this.cancellation.Token; } }
+
+        public string ErrorMessage { get; set; }
+
+        public SqlTask SqlTask { get; set; }
+
+        public SchemaComparisonResult ComparisonResult { get; set; }
+
+        public SchemaCompareGenerateScriptOperation(SchemaCompareGenerateScriptParams parameters, SchemaComparisonResult comparisonResult)
+        {
+            Validate.IsNotNull("parameters", parameters);
+            Validate.IsNotNull("scriptFilePath", parameters.ScriptFilePath);
+            this.Parameters = parameters;
+            Validate.IsNotNull("comparisonResult", comparisonResult);
+            this.ComparisonResult = comparisonResult;
+        }
+
+        public void Execute(TaskExecutionMode mode)
+        {
+            if (this.CancellationToken.IsCancellationRequested)
+            {
+                throw new OperationCanceledException(this.CancellationToken);
+            }
+
+            try
+            {
+                SchemaCompareScriptGenerationResult result = this.ComparisonResult.GenerateScript(this.Parameters.TargetDatabaseName);
+                File.WriteAllText(this.Parameters.ScriptFilePath, result.Script);
+
+                if (!string.IsNullOrEmpty(result.MasterScript))
+                {
+                    // master script is only used if the target is Azure SQL db and the script contains all operations that must be done against the master database
+                    string masterScriptPath = Path.Combine(Path.GetDirectoryName(this.Parameters.ScriptFilePath), string.Concat("master_", Path.GetFileName(this.Parameters.ScriptFilePath)));
+                    File.WriteAllText(masterScriptPath, result.MasterScript);
+                }
+            }
+            catch (Exception e)
+            {
+                ErrorMessage = e.Message;
+                Logger.Write(TraceEventType.Error, string.Format("Schema compare generate script operation {0} failed with exception {1}", this.OperationId, e.Message));
+                throw;
+            }
+        }
+
+        // The schema compare public api doesn't currently take a cancellation token so the operation can't be cancelled
+        public void Cancel()
+        {
+        }
+    }
+}