fix: only allow a single instance of the app (#109)

Author: mscharley

src/main/Entrypoint.ts

@@ -22,23 +22,32 @@ export class Entrypoint {
   }
 
   public readonly start = (): void => {
+    // Check we're the first instance of this application.
+    if (!this.application.requestSingleInstanceLock()) {
+      this.application.quit();
+    }
+
     const privSchemes = this.customProtocols.map((p) => p.privilegedSchemes).flat();
     log.verbose(
       'Registering schemes as privileged:',
       privSchemes.map((s) => s.scheme),
     );
     protocol.registerSchemesAsPrivileged(privSchemes);
 
+    this.application.on('second-instance', this.onSecondInstance);
     this.application.on('window-all-closed', this.onWindowAllClosed);
 
-    // Signal to Electron that we're ready to go when it is.
+    // The ready handler should be the last registered as it may be fired immediately.
     this.application.on('ready', this.onReady);
   };
 
-  private readonly onWindowAllClosed = (): void => {
-    if (process.platform !== 'darwin') {
-      this.application.quit();
-    }
+  private readonly onSecondInstance = (
+    _event: Electron.Event,
+    _argv: string[],
+    _workingDirectory: string,
+    _additionalData: unknown,
+  ): void => {
+    this.mainWindow.bringWindowToTop();
   };
 
   private readonly onReady = (): void => {
@@ -49,6 +58,10 @@ export class Entrypoint {
       .catch(this.onFatalError);
   };
 
+  private readonly onWindowAllClosed = (): void => {
+    this.application.quit();
+  };
+
   private readonly onFatalError = (error: unknown): never => {
     log.error(error);
     // eslint-disable-next-line no-process-exit

src/main/MainWindow.ts

@@ -76,6 +76,15 @@ export class MainWindow implements OnReadyHandler {
     );
   };
 
+  public readonly bringWindowToTop = (): void => {
+    if (this.window != null) {
+      if (this.window.isMinimized()) {
+        this.window.restore();
+      }
+      this.window.focus();
+    }
+  };
+
   private readonly isAllowedInternalNavigationUrl = (url: string): boolean => {
     const parsed = new URL(url);