Added Prior indicator to viewport overlay based on oldest study date

Packages/viewerbase/components/viewer/viewportOverlay/viewportOverlay.html

@@ -3,7 +3,7 @@
         <div class="topleft dicomTag">
             <div>{{formatPN patientName}}</div>
             <div>{{patientId}}</div>
-            <div></div>
+            <div class='priorIndicator'>{{prior}}</div>
         </div>
         <div class="topright dicomTag">
             <div>{{studyDescription}}</div>

Packages/viewerbase/components/viewer/viewportOverlay/viewportOverlay.js

@@ -151,5 +151,29 @@ Template.viewportOverlay.helpers({
     },
     numImages : function() {
         return getSeries.call(this, 'numImages');
+    },
+    prior : function() {
+        // This helper is updated whenever a new image is displayed in the viewport
+        Session.get('CornerstoneNewImage' + this.viewportIndex);
+        if (!this.imageId) {
+            return;
+        }
+
+        // Make sure there are more than two studies loaded in the viewer
+        //
+        // Here we sort the collection in ascending order by study date, so
+        // that we can obtain the oldest study as the first element of the array
+        //
+        // TODO= Find out if we should encode studyDate as a Date in the ViewerStudies Collection
+        var viewportStudies = ViewerStudies.find({}, {sort: {studyDate: 1}});
+        if (viewportStudies.count() < 2) {
+            return;
+        }
+
+        // Get study data
+        var study = cornerstoneTools.metaData.get('study', this.imageId);
+        if (study.instanceUid === viewportStudies.fetch()[0].studyInstanceUid) {
+            return 'Prior';
+        }
     }
 });

Packages/viewerbase/components/viewer/viewportOverlay/viewportOverlay.styl

@@ -24,4 +24,8 @@
   .bottomright
     bottom: 3px
     right: 3px
-    text-align: right
+    text-align: right
+
+  .priorIndicator
+    font-weight: bold
+    color: yellow