add --preview-app-port option to serve command

Signed-off-by: Morgan Bentell <mbentell@spotify.com>

packages/techdocs-cli/src/commands/index.ts

@@ -255,6 +255,21 @@ export function registerCommands(program: Command) {
       '--preview-app-bundle-path <PATH_TO_BUNDLE>',
       'Preview documentation using another web app',
     )
+    .option(
+      '--preview-app-port <PORT>',
+      'Port for the preview app to be served on',
+      '3000',
+    )
+    .hook('preAction', command => {
+      if (
+        command.opts().previewAppPort &&
+        !command.opts().previewAppBundlePath
+      ) {
+        command.error(
+          '--preview-app-port can only be used together with --preview-app-bundle-path',
+        );
+      }
+    })
     .action(lazy(() => import('./serve/serve').then(m => m.default)));
 }
 

packages/techdocs-cli/src/commands/serve/serve.ts

@@ -56,10 +56,6 @@ export default async function serve(opts: OptionValues) {
     ? true
     : false;
 
-  // TODO: Backstage app port should also be configurable as a CLI option. However, since we bundle
-  // a backstage app, we define app.baseUrl in the app-config.yaml.
-  // Hence, it is complicated to make this configurable.
-  const backstagePort = 3000;
   const backstageBackendPort = 7007;
 
   const mkdocsDockerAddr = `http://0.0.0.0:${opts.mkdocsPort}`;
@@ -119,9 +115,11 @@ export default async function serve(opts: OptionValues) {
     );
   }
 
-  const port = isDevMode ? backstageBackendPort : backstagePort;
+  const port = isDevMode ? backstageBackendPort : opts.previewAppPort;
+  const previewAppPath = getPreviewAppPath(opts);
+  console.log({ previewAppPath });
   const httpServer = new HTTPServer(
-    getPreviewAppPath(opts),
+    previewAppPath,
     port,
     opts.mkdocsPort,
     opts.verbose,