refactor: move app to monorepo

frontend/app/src/app/util/internet-connection.service.ts

@@ -0,0 +1,106 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {fromEvent, merge, ObservableInput, of, race, RetryConfig, share, Subject, takeUntil} from 'rxjs';
+import {Injectable} from '@angular/core';
+import {filter, map, startWith, take, tap} from 'rxjs/operators';
+import {NGXLogger} from 'ngx-logger';
+import {Router} from '@angular/router';
+
+@Injectable({
+  providedIn: 'root',
+})
+export class InternetConnectionService {
+  private readonly manualRetry$ = new Subject<void>();
+
+  private readonly abortRetry$ = new Subject<void>();
+
+  /**
+   * Emits whenever the browser goes online or offline.
+   */
+  readonly offline$ = window
+    ? merge(
+        fromEvent(window, 'online').pipe(map(() => false)),
+        fromEvent(window, 'offline').pipe(map(() => true)),
+      ).pipe(startWith(!window.navigator.onLine), share())
+    : of(true);
+
+  /**
+   * Emits whenever http requests should be retried
+   *
+   * Also keeps track of when a retry is needed, automatically
+   * registering itself.
+   */
+  readonly retryConfig: RetryConfig = {
+    delay: this.doRetry.bind(this),
+  };
+
+  private doRetry(error: unknown, retryCount: number): ObservableInput<unknown> {
+    return race(
+      this.offline$.pipe(
+        tap(it => console.log(it)),
+        filter(it => !it),
+        take(1),
+      ),
+      this.manualRetry$,
+    ).pipe(
+      tap({
+        subscribe: () => {
+          this.errors.add(error);
+          if (this.errors.size > 0) {
+            this.error$.next(true);
+          }
+        },
+        next: () => {
+          this.logger.error(`${retryCount}x`, error);
+        },
+        unsubscribe: () => {
+          this.errors.delete(error);
+          if (this.errors.size === 0) {
+            this.error$.next(false);
+          }
+        },
+      }),
+      takeUntil(
+        merge(
+          this.abortRetry$.pipe(tap(() => this.logger.warn('HTTP Request retry aborted manually'))),
+          this.router.events.pipe(tap(() => this.logger.warn('HTTP Request retry aborted by routing'))),
+        ),
+      ),
+    );
+  }
+
+  /**
+   * Emits when there are errors
+   */
+  readonly error$ = new Subject<boolean>();
+
+  private readonly errors = new Set<unknown>();
+
+  constructor(private readonly logger: NGXLogger, private readonly router: Router) {}
+
+  /**
+   * Retry all failed http requests
+   */
+  retry() {
+    this.manualRetry$.next();
+  }
+
+  /**
+   * Abandon all failed http requests
+   */
+  dismissError() {
+    this.abortRetry$.next();
+  }
+}