fix(oembed): make sure we have a valid embedUrl

Author: MichaelDeBoey

src/lambda/oembed/oembed.js

@@ -52,8 +52,9 @@ function handler(event, context, callback) {
 
   // map /gist urls to /embed
   const url = pathname.startsWith('/gist/')
-    ? params.url.replace('/gist/', '/embed/')
-    : params.url;
+    ? pathname.replace('/gist/', '/embed/')
+    : pathname;
+  const embedUrl = `${host}/${url}?panes=query,preview`;
 
   callback(null, {
     statusCode: 200,
@@ -66,7 +67,7 @@ function handler(event, context, callback) {
         provider_name: 'testing-playground.com',
         provider_url: host,
 
-        html: `<iframe src="${url}" height="${maxheight}" width="${maxwidth}" scrolling="no" frameBorder="0" allowTransparency="true" title="Testing Playground" style="overflow: hidden; display: block; width: 100%"></iframe>`,
+        html: `<iframe src="${embedUrl}" height="${maxheight}" width="${maxwidth}" scrolling="no" frameBorder="0" allowTransparency="true" title="Testing Playground" style="overflow: hidden; display: block; width: 100%"></iframe>`,
         width: maxwidth,
         height: maxheight,