From 37dffcfb6fb82f390fb5809da14228d43b07bf36 Mon Sep 17 00:00:00 2001
From: Sumanth Chinthagunta <xmlking@gmail.com>
Date: Wed, 3 Jul 2019 15:55:15 -0700
Subject: [PATCH] feat(core): adding custom rxjs operator  retryWithBackoff

inspired by https://blog.angularindepth.com/retry-failed-http-requests-in-angular-f5959d486294
---
 libs/core/src/lib/services/profile.service.ts | 14 ++++++---
 libs/utils/src/index.ts                       |  1 +
 libs/utils/src/lib/retry-with-backoff.ts      | 31 +++++++++++++++++++
 package.json                                  |  2 +-
 4 files changed, 43 insertions(+), 5 deletions(-)
 create mode 100644 libs/utils/src/lib/retry-with-backoff.ts

diff --git a/libs/core/src/lib/services/profile.service.ts b/libs/core/src/lib/services/profile.service.ts
index 467bc45fd..20dc23dd8 100644
--- a/libs/core/src/lib/services/profile.service.ts
+++ b/libs/core/src/lib/services/profile.service.ts
@@ -3,7 +3,8 @@ import { Injectable } from '@angular/core';
 import { Profile } from '@ngx-starter-kit/models';
 import { environment } from '@env/environment';
 import { catchError } from 'rxjs/operators';
-import { throwError } from 'rxjs';
+import { EMPTY, throwError } from 'rxjs';
+import { retryWithBackoff } from '@ngx-starter-kit/utils';
 
 @Injectable({
   providedIn: 'root',
@@ -15,9 +16,14 @@ export class ProfileService {
   constructor(private httpClient: HttpClient) {}
 
   getMyProfile() {
-    return this.httpClient
-      .get<Profile>(`${this.baseUrl}/${this.entityPath}/myprofile`)
-      .pipe(catchError(this.handleError));
+    return this.httpClient.get<Profile>(`${this.baseUrl}/${this.entityPath}/myprofile`).pipe(
+      retryWithBackoff(1000, 3),
+      catchError(error => {
+        this.handleError(error);
+        return EMPTY;
+      }),
+      // catchError(this.handleError)
+    );
   }
 
   create(entity: Partial<Profile>) {
diff --git a/libs/utils/src/index.ts b/libs/utils/src/index.ts
index 3b69e22f7..1fea229cf 100644
--- a/libs/utils/src/index.ts
+++ b/libs/utils/src/index.ts
@@ -3,6 +3,7 @@ export { waitUntil } from './lib/wait-until';
 export { DeepPartial } from './lib/deep-partial';
 export { ObjectLiteral } from './lib/object-literal';
 export { delayAtLeast } from './lib/delay-at-least';
+export { retryWithBackoff } from './lib/retry-with-backoff';
 export { toClass } from './lib/to-class';
 export { fromAsyncIterator } from './lib/from-async-iterator';
 export * from './lib/require-multi';
diff --git a/libs/utils/src/lib/retry-with-backoff.ts b/libs/utils/src/lib/retry-with-backoff.ts
new file mode 100644
index 000000000..91f3779d0
--- /dev/null
+++ b/libs/utils/src/lib/retry-with-backoff.ts
@@ -0,0 +1,31 @@
+import { Observable, of, throwError } from 'rxjs';
+import { delay, mergeMap, retryWhen } from 'rxjs/operators';
+
+const getErrorMessage = (maxRetry: number) =>
+  `Tried to load Resource over XHR for ${maxRetry} times without success. Giving up.`;
+
+const DEFAULT_MAX_RETRIES = 5;
+const DEFAULT_BACKOFF = 1000;
+
+export function retryWithBackoff<T>(
+  delayMs: number,
+  maxRetry = DEFAULT_BACKOFF,
+  backoffMs = DEFAULT_BACKOFF,
+): (src$: Observable<T>) => Observable<T> {
+  let retries = maxRetry;
+
+  return (src$: Observable<T>): Observable<T> =>
+    src$.pipe(
+      retryWhen((errors: Observable<T>) =>
+        errors.pipe(
+          mergeMap(error => {
+            if (retries-- > 0) {
+              const backoffTime = delayMs + (maxRetry - retries) * backoffMs;
+              return of(error).pipe(delay(backoffTime));
+            }
+            return throwError(getErrorMessage(maxRetry));
+          }),
+        ),
+      ),
+    );
+}
diff --git a/package.json b/package.json
index 5425df213..2bbf2edb3 100644
--- a/package.json
+++ b/package.json
@@ -77,7 +77,7 @@
   },
   "lint-staged": {
     "{apps,libs}/**/*.{ts,json,md,scss,html}": [
-      "yarn affected:lint  --uncommitted --parallel --fix",
+      "yarn affected:lint  --uncommitted --parallel -- --fix",
       "yarn format:write --uncommitted",
       "git add"
     ]