Add timed cache to user count queries

server/boot/about.js

@@ -2,40 +2,43 @@ import { Observable } from 'rx';
 import dedent from 'dedent';
 import moment from 'moment';
 
-import { observeMethod } from '../utils/rx';
+import { timeCache, observeMethod } from '../utils/rx';
 
 function numberWithCommas(x) {
   return x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ',');
 }
 
+// userCount(where: Object) => Observable[Number]
+// getCertCount(userCount: userCount, cert: String) => Observable[Number]
+function getCertCount(userCount, cert) {
+  return userCount({ [cert]: true })
+    // using This-Bind operator
+    ::timeCache(2, 'hours');
+}
+
 export default function about(app) {
   const router = app.loopback.Router();
   const User = app.models.User;
-  const userCount$ = observeMethod(User, 'count');
+  const userCount = observeMethod(User, 'count');
+  const frontEndCount$ = getCertCount(userCount, 'isFrontEndCert');
+  const dataVisCount$ = getCertCount(userCount, 'isDataVisCert');
+  const backEndCount$ = getCertCount(userCount, 'isBackEndCert');
 
   function showAbout(req, res, next) {
     const daysRunning = moment().diff(new Date('10/15/2014'), 'days');
 
     Observable.combineLatest(
-      userCount$(),
-      userCount$({ isFrontEndCert: true }),
-      userCount$({ isDataVisCert: true }),
-      userCount$({ isBackEndCert: true }),
-      (
-        userCount,
-        frontEndCount = 0,
-        dataVisCount = 0,
-        backEndCount = 0
-      ) => ({
-        userCount: numberWithCommas(userCount),
+      frontEndCount$,
+      dataVisCount$,
+      backEndCount$,
+      (frontEndCount = 0, dataVisCount = 0, backEndCount = 0) => ({
         frontEndCount,
         dataVisCount,
         backEndCount
       })
     )
-      .doOnNext(({ userCount, frontEndCount, dataVisCount, backEndCount }) => {
+      .doOnNext(({ frontEndCount, dataVisCount, backEndCount }) => {
         res.render('resources/about', {
-          userCount,
           frontEndCount,
           dataVisCount,
           backEndCount,

server/utils/rx.js

@@ -1,4 +1,5 @@
-import Rx from 'rx';
+import Rx, { AsyncSubject, Observable } from 'rx';
+import moment from 'moment';
 import debugFactory from 'debug';
 
 const debug = debugFactory('fcc:rxUtils');
@@ -31,3 +32,22 @@ export function observeQuery(Model, method, query) {
 export function observeMethod(context, methodName) {
   return Rx.Observable.fromNodeCallback(context[methodName], context);
 }
+
+// timeChache(amount: Number, unit: String) => Observable
+export function timeCache(time, unit) {
+  const source = this;
+  let cache;
+  let expireCacheAt;
+  return Observable.create(observable => {
+    // if there is no expire time set
+    // or if expireCacheAt is smaller than now,
+    // set new expire time in MS and create new subscription to source
+    if (!expireCacheAt || expireCacheAt < Date.now()) {
+      // set expire in ms;
+      expireCacheAt = moment().add(time, unit).valueOf();
+      cache = new AsyncSubject();
+      source.subscribe(cache);
+    }
+    return cache.subscribe(observable);
+  });
+}

server/views/resources/about.jade

@@ -9,14 +9,6 @@ block content
                     span.tag Established:	
                     span.text-primary #{daysRunning}
                     | days ago
-                li
-                    span.tag Population:	
-                    span.text-primary #{userCount}
-                    | campers
-                li
-                    span.tag Completed:	
-                    span.text-primary #{globalCompletedCount}
-                    | challenges
                 li.nowrap
                     span.tag Donated:	
                     span.text-primary $850,000