Offline mode: Add REST-based HNService fallback

Author: addyosmani

src/services/HNServiceRest.js

@@ -0,0 +1,62 @@
+/*global fetch*/
+require('isomorphic-fetch')
+/*
+A version of HNService which concumes the Firebase REST
+endpoint (https://www.firebase.com/docs/rest/api/). This
+is used when a user has enabled 'Offline Mode' in the
+Settings panel and ensures responses can be easily fetched
+and cached when paired with Service Worker. This cannot be
+trivially done using just Web Sockets with the default
+Firebase API and provides a sufficient fallback that works.
+ */
+var endPoint = 'https://hacker-news.firebaseio.com/v0'
+var options = {
+  method: 'GET',
+  headers: {
+    'Accept': 'application/json'
+  }
+}
+
+function storiesRef(path) {
+  return fetch(endPoint + '/' + path + '.json', options)
+}
+
+function itemRef(id) {
+  return fetch(endPoint + '/item/' + id + '.json', options)
+}
+
+function userRef(id) {
+  return fetch(endPoint + '/user/' + id + '.json', options)
+}
+
+function updatesRef() {
+  return fetch(endPoint + '/updates/items/' + '.json', options)
+}
+
+function fetchItem(id, cb) {
+  itemRef(id).once('value', function(snapshot) {
+    cb(snapshot.val())
+  })
+}
+
+function fetchItems(ids, cb) {
+  var items = []
+  ids.forEach(function(id) {
+    fetchItem(id, addItem)
+  })
+  function addItem(item) {
+    items.push(item)
+    if (items.length >= ids.length) {
+      cb(items)
+    }
+  }
+}
+
+module.exports = {
+  fetchItem,
+  fetchItems,
+  storiesRef,
+  itemRef,
+  userRef,
+  updatesRef
+}