feat(updates): Store updates if the server is not responding

packages/learn/src/redux/app/failed-updates-epic.js

@@ -0,0 +1,74 @@
+import { merge } from 'rxjs/observable/merge';
+import { empty } from 'rxjs/observable/empty';
+import {
+  tap,
+  filter,
+  map,
+  ignoreElements,
+  switchMap,
+  catchError
+} from 'rxjs/operators';
+import { ofType } from 'redux-observable';
+import store from 'store';
+import uuid from 'uuid/v4';
+
+import { types, onlineStatusChange, isOnlineSelector } from './';
+import postUpdate$ from '../../templates/Challenges/utils/postUpdate$';
+
+const key = 'fcc-failed-updates';
+
+function delay(time = 0, fn) {
+  return setTimeout(fn, time);
+}
+
+function failedUpdateEpic(action$, { getState }) {
+  const storeUpdates = action$.pipe(
+    ofType(types.updateFailed),
+    tap(({ payload }) => {
+      const failures = store.get(key) || [];
+      payload.id = uuid();
+      store.set(key, [...failures, payload]);
+    }),
+    map(() => onlineStatusChange(false))
+  );
+
+  const flushUpdates = action$.pipe(
+    ofType(types.fetchUserComplete, types.updateComplete),
+    filter(() => store.get(key)),
+    filter(() => isOnlineSelector(getState())),
+    tap(() => {
+      const failures = store.get(key) || [];
+      let delayTime = 0;
+      const batch = failures.map(update => {
+        delayTime += 300;
+        // we stagger the updates here so we don't hammer the server
+        return delay(delayTime, () =>
+          postUpdate$(update)
+            .pipe(
+              switchMap(response => {
+                if (response && response.message) {
+                  // the request completed successfully
+                  const failures = store.get(key) || [];
+                  const newFailures = failures.filter(x => x.id !== update.id);
+                  store.set(key, newFailures);
+                }
+                return empty();
+              }),
+              catchError(() => empty())
+            )
+            .toPromise()
+        );
+      });
+      Promise.all(batch)
+        .then(() => console.info('progress updates processed where possible'))
+        .catch(err =>
+          console.warn('unable to process progress updates', err.message)
+        );
+    }),
+    ignoreElements()
+  );
+
+  return merge(storeUpdates, flushUpdates);
+}
+
+export default failedUpdateEpic;