Add Schema Compare (#777)

* successfully sends list of differences to ADS

* bumping dacfx nuget package version

* add second schema compare try for case when first db to db comparison fails but works on second try

* move schemacompare out of dacfx folders

* capitalizing

* more capitalizing

* addressing comments

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

@@ -0,0 +1,104 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+using Microsoft.SqlTools.Hosting.Protocol;
+using Microsoft.SqlTools.ServiceLayer.Connection;
+using Microsoft.SqlTools.ServiceLayer.SchemaCompare.Contracts;
+using Microsoft.SqlTools.ServiceLayer.Hosting;
+using Microsoft.SqlTools.ServiceLayer.TaskServices;
+using System;
+using System.Collections.Concurrent;
+using System.Data.SqlClient;
+using System.Threading.Tasks;
+using Microsoft.SqlTools.ServiceLayer.SchemaCompare;
+
+namespace Microsoft.SqlTools.ServiceLayer.SchemaCopmare
+{
+    /// <summary>
+    /// Main class for SchemaCompare service
+    /// </summary>
+    class SchemaCompareService
+    {
+        private static ConnectionService connectionService = null;
+        private static readonly Lazy<SchemaCompareService> instance = new Lazy<SchemaCompareService>(() => new SchemaCompareService());
+
+        /// <summary>
+        /// Gets the singleton instance object
+        /// </summary>
+        public static SchemaCompareService Instance
+        {
+            get { return instance.Value; }
+        }
+
+        /// <summary>
+        /// Initializes the service instance
+        /// </summary>
+        /// <param name="serviceHost"></param>
+        public void InitializeService(ServiceHost serviceHost)
+        {
+            serviceHost.SetRequestHandler(SchemaCompareRequest.Type, this.HandleSchemaCompareRequest);
+        }
+
+        /// <summary>
+        /// Handles schema compare request
+        /// </summary>
+        /// <returns></returns>
+        public async Task HandleSchemaCompareRequest(SchemaCompareParams parameters, RequestContext<SchemaCompareResult> requestContext)
+        {
+            try
+            {
+                ConnectionInfo sourceConnInfo;
+                ConnectionInfo targetConnInfo;
+                ConnectionServiceInstance.TryFindConnection(
+                        parameters.SourceEndpointInfo.OwnerUri,
+                        out sourceConnInfo);
+                ConnectionServiceInstance.TryFindConnection(
+                    parameters.TargetEndpointInfo.OwnerUri,
+                    out targetConnInfo);
+
+                Task schemaCompareTask = Task.Run(async () =>
+                {
+                    try
+                    {
+                        SchemaCompareOperation operation = new SchemaCompareOperation(parameters, sourceConnInfo, targetConnInfo);
+                        operation.Execute(parameters.TaskExecutionMode);
+
+                        await requestContext.SendResult(new SchemaCompareResult()
+                        {
+                            OperationId = operation.OperationId,
+                            Success = true,
+                            ErrorMessage = operation.ErrorMessage,
+                            AreEqual = operation.ComparisonResult.IsEqual,
+                            Differences = operation.Differences
+                        });
+                    }
+                    catch(Exception e)
+                    {
+                        await requestContext.SendError(e);
+                    }
+                });
+            }
+            catch (Exception e)
+            {
+                await requestContext.SendError(e);
+            }
+        }
+
+        internal static ConnectionService ConnectionServiceInstance
+        {
+            get
+            {
+                if (connectionService == null)
+                {
+                    connectionService = ConnectionService.Instance;
+                }
+                return connectionService;
+            }
+            set
+            {
+                connectionService = value;
+            }
+        }
+    }
+}