Add getFirstSelectedAnnotationId to store

This moves the firstKey function from the sidebar-content into
the selection store module.

src/sidebar/components/sidebar-content.js

@@ -7,24 +7,13 @@ const memoize = require('../util/memoize');
 const tabs = require('../tabs');
 const uiConstants = require('../ui-constants');
 
-function firstKey(object) {
-  for (const k in object) {
-    if (!object.hasOwnProperty(k)) {
-      continue;
-    }
-    return k;
-  }
-  return null;
-}
-
 /**
  * Returns the group ID of the first annotation in `results` whose
- * ID is a key in `selection`.
+ * ID is `annId`.
  */
-function groupIDFromSelection(selection, results) {
-  const id = firstKey(selection);
+function getGroupID(annId, results) {
   const annot = results.find(function(annot) {
-    return annot.id === id;
+    return annot.id === annId;
   });
   if (!annot) {
     return null;
@@ -123,10 +112,7 @@ function SidebarContentController(
       if (store.hasSelectedAnnotations()) {
         // Focus the group containing the selected annotation and filter
         // annotations to those from this group
-        let groupID = groupIDFromSelection(
-          store.getState().selectedAnnotationMap,
-          results
-        );
+        let groupID = getGroupID(store.getFirstSelectedAnnotationId(), results);
         if (!groupID) {
           // If the selected annotation is not available, fall back to
           // loading annotations for the currently focused group
@@ -316,7 +302,7 @@ function SidebarContentController(
   };
 
   this.selectedAnnotationUnavailable = function() {
-    const selectedID = firstKey(store.getState().selectedAnnotationMap);
+    const selectedID = store.getFirstSelectedAnnotationId();
     return (
       !this.isLoading() && !!selectedID && !store.annotationExists(selectedID)
     );
@@ -343,7 +329,7 @@ function SidebarContentController(
     // The user is logged out and has landed on a direct linked
     // annotation. If there is an annotation selection and that
     // selection is available to the user, show the CTA.
-    const selectedID = firstKey(store.getState().selectedAnnotationMap);
+    const selectedID = store.getFirstSelectedAnnotationId();
     return (
       !this.isLoading() && !!selectedID && store.annotationExists(selectedID)
     );

src/sidebar/store/modules/selection.js

@@ -10,6 +10,7 @@
 
 'use strict';
 
+const { createSelector } = require('reselect');
 const immutable = require('seamless-immutable');
 
 const toSet = require('../../util/array-util').toSet;
@@ -314,6 +315,16 @@ function clearSelectedAnnotations() {
   return { type: actions.CLEAR_SELECTION };
 }
 
+/**
+ * Returns the annotation ID of the first annotation in `selectedAnnotationMap`.
+ *
+ * @return {string|null}
+ */
+const getFirstSelectedAnnotationId = createSelector(
+  state => state.selectedAnnotationMap,
+  selected => (selected ? Object.keys(selected)[0] : null)
+);
+
 module.exports = {
   init: init,
   update: update,
@@ -335,5 +346,6 @@ module.exports = {
   selectors: {
     hasSelectedAnnotations,
     isAnnotationSelected,
+    getFirstSelectedAnnotationId,
   },
 };

src/sidebar/store/test/index-test.js

@@ -340,6 +340,23 @@ describe('store', function() {
     });
   });
 
+  describe('#getFirstSelectedAnnotationId', function() {
+    it('returns the first selected annotation id it finds', function() {
+      store.selectAnnotations([1, 2]);
+      assert.equal(store.getFirstSelectedAnnotationId(), 1);
+    });
+
+    it('returns null if no selected annotation ids are found', function() {
+      store.selectAnnotations([]);
+      assert.isNull(store.getFirstSelectedAnnotationId());
+    });
+
+    it('returns null if no annotation ids are ', function() {
+      store.selectAnnotations([]);
+      assert.isNull(store.getFirstSelectedAnnotationId());
+    });
+  });
+
   describe('#isAnnotationSelected', function() {
     it('returns true if the id provided is selected', function() {
       store.selectAnnotations([1]);