Add implementation code to handle status collapse/expand in timeline

Code has not been added elsewhere to simplify testing.
Once the code will be considered stable it will be also included in other
status action listener implementers.

app/src/main/java/com/keylesspalace/tusky/fragment/TimelineFragment.java

@@ -561,9 +561,46 @@ public class TimelineFragment extends SFragment implements
         }
     }
 
+    /**
+     * Called when the status {@link android.widget.ToggleButton} responsible for collapsing long
+     * status content is interacted with.
+     *
+     * @param isCollapsed Whether the status content is shown in a collapsed state or fully.
+     * @param position    The position of the status in the list.
+     */
     @Override
     public void onContentCollapsedChange(boolean isCollapsed, int position) {
-        // TODO: Implement this method.
+        if(position < 0 || position >= statuses.size()) {
+            Log.e(TAG, String.format("Tried to access out of bounds status position: %d of %d", position, statuses.size() - 1));
+            return;
+        }
+
+        StatusViewData status = statuses.getPairedItem(position);
+        if(!(status instanceof StatusViewData.Concrete)) {
+            // Statuses PairedList contains a base type of StatusViewData.Concrete and also doesn't
+            // check for null values when adding values to it.
+
+            // TODO: Implement @NonNull/@Nullable in PairedList insert methods
+
+            if(status == null) {
+                Log.e(TAG, String.format("Tried to access status but got null at position: %d of %d", position, statuses.size() - 1));
+            } else {
+                Log.e(TAG, String.format(
+                        "Expected StatusViewData.Concrete, got %s instead at position: %d of %d",
+                        status.getClass().getSimpleName(),
+                        position,
+                        statuses.size() -1
+                ));
+            }
+
+            return;
+        }
+
+        StatusViewData updatedStatus = new StatusViewData.Builder((StatusViewData.Concrete) status)
+                .setCollapsed(isCollapsed)
+                .createStatusViewData();
+        statuses.setPairedItem(position, updatedStatus);
+        updateAdapter();
     }
 
     @Override