Introduces event queue processor to create a consistent UI (#11780)

extensions/sql-migration/src/models/migrationWizardPage.ts

@@ -4,7 +4,7 @@
  *--------------------------------------------------------------------------------------------*/
 
 import * as azdata from 'azdata';
-import { MigrationStateModel } from './stateMachine';
+import { MigrationStateModel, StateChangeEvent } from './stateMachine';
 export abstract class MigrationWizardPage {
 	constructor(protected readonly wizardPage: azdata.window.WizardPage, protected readonly migrationStateModel: MigrationStateModel) { }
 
@@ -16,5 +16,37 @@ export abstract class MigrationWizardPage {
 
 	public abstract async onPageEnter(): Promise<void>;
 	public abstract async onPageLeave(): Promise<void>;
+
+	private readonly stateChanges: (() => Promise<void>)[] = [];
+	protected async onStateChangeEvent(e: StateChangeEvent) {
+
+		this.stateChanges.push((): Promise<void> => {
+			return this.handleStateChange(e);
+		});
+
+		this.enableQueueProcessor();
+	}
+
+	private queueActive = false;
+	private async enableQueueProcessor(): Promise<void> {
+		if (this.queueActive) {
+			return;
+		}
+		this.queueActive = true;
+		while (true) {
+			const stateChangeFunction = this.stateChanges.shift();
+			if (!stateChangeFunction) {
+				break;
+			}
+			try {
+				await stateChangeFunction();
+			} catch (ex) {
+				console.error(ex);
+			}
+		}
+		this.queueActive = false;
+	}
+
+	protected abstract async handleStateChange(e: StateChangeEvent): Promise<void>;
 }
 

extensions/sql-migration/src/models/stateMachine.ts

@@ -27,6 +27,7 @@ export enum State {
 export interface Model {
 	readonly sourceConnection: azdata.connection.Connection;
 	readonly currentState: State;
+	gatheringInformationError: string | undefined;
 }
 
 export interface StateChangeEvent {
@@ -37,6 +38,7 @@ export interface StateChangeEvent {
 export class MigrationStateModel implements Model, vscode.Disposable {
 	private _stateChangeEventEmitter = new vscode.EventEmitter<StateChangeEvent>();
 	private _currentState: State;
+	private _gatheringInformationError: string | undefined;
 
 	constructor(private readonly _sourceConnection: azdata.connection.Connection) {
 		this._currentState = State.INIT;
@@ -58,6 +60,14 @@ export class MigrationStateModel implements Model, vscode.Disposable {
 		this._stateChangeEventEmitter.fire({ oldState, newState: this.currentState });
 	}
 
+	public get gatheringInformationError(): string | undefined {
+		return this._gatheringInformationError;
+	}
+
+	public set gatheringInformationError(error: string | undefined) {
+		this._gatheringInformationError = error;
+	}
+
 	public get stateChangeEvent(): vscode.Event<StateChangeEvent> {
 		return this._stateChangeEventEmitter.event;
 	}