add support for showing filter descriptions in narrativised mode

src/common/utilities.js

@@ -198,3 +198,16 @@ export function binarySearch (ar, el, compareFn) {
   }
   return -m - 1
 }
+
+export const isFilterLeaf = node => (Object.keys(node.children).length === 0)
+export const isFilterDuplicate = (node, set) => { return (set.has(node.key)) }
+
+export function findDescriptionInFilterTree (key, node) {
+  if (node.key === key) return node.description
+  if (isFilterLeaf(node)) return false
+  const descs = Object.keys(node.children)
+    .map(c => findDescriptionInFilterTree(key, node.children[c]))
+    .filter(v => !!v)
+  if (descs.length !== 1) return false
+  return descs[0]
+}