🐛 Fixed meta twitter_image output when using data: post.{slug} for …

…routes

refs #10082

```
routes:
  /news/:
    data: post.news
```

The twitter_image was not available, because the context is [news, post] and the data is in `data.post`.
The context helper was incorrect. I think it is still not fully correct, but only focused on this use case.
The meta layer needs a full refactoring.

core/server/data/meta/context_object.js

@@ -5,16 +5,29 @@ function getContextObject(data, context) {
     /**
      * If the data object does not contain the requested context, we return the fallback object.
      */
-    var blog = {
-            cover_image: settingsCache.get('cover_image'),
-            twitter: settingsCache.get('twitter'),
-            facebook: settingsCache.get('facebook')
-        },
-        contextObject;
+    const blog = {
+        cover_image: settingsCache.get('cover_image'),
+        twitter: settingsCache.get('twitter'),
+        facebook: settingsCache.get('facebook')
+    };
 
-    context = _.includes(context, 'page') || _.includes(context, 'amp') ? 'post' : context;
-    contextObject = data[context] || blog;
-    return contextObject;
+    let chosenContext;
+
+    // @TODO: meta layer is very broken, it's really hard to understand what it's doing
+    // The problem is that handlebars root object is structured differently. Sometimes the object is flat on data
+    // and sometimes the object is part of a key e.g. data.post. This needs to be prepared at the very first stage and not in each helper.
+    if (_.includes(context, 'page') || _.includes(context, 'amp') && data.post) {
+        chosenContext = data.post;
+    } else if (_.includes(context, 'post') && data.post) {
+        chosenContext = data.post;
+    } else if (data[context]) {
+        // @NOTE: This is confusing as hell. It tries to get data[['author']], which works, but coincidence?
+        chosenContext = data[context];
+    } else {
+        chosenContext = blog;
+    }
+
+    return chosenContext;
 }
 
 module.exports = getContextObject;

core/test/unit/data/meta/twitter_image_spec.js

@@ -38,6 +38,18 @@ describe('getTwitterImage', function () {
         twitterImageUrl.should.match(/\/content\/images\/my-special-twitter-image\.jpg$/);
     });
 
+    it('should return absolute url for Twitter image in post context', function () {
+        var twitterImageUrl = getTwitterImage({
+            context: ['news', 'post'],
+            post: {
+                feature_image: '/content/images/my-test-image.jpg',
+                twitter_image: '/content/images/my-special-twitter-image.jpg'
+            }
+        });
+        twitterImageUrl.should.not.equal('/content/images/my-special-twitter-image.jpg');
+        twitterImageUrl.should.match(/\/content\/images\/my-special-twitter-image\.jpg$/);
+    });
+
     it('should return absolute url for feature image in post context', function () {
         var twitterImageUrl = getTwitterImage({
             context: ['post'],