refactor(router): create pipeable applyRedirects function (#25740)

PR Close #25740

packages/router/src/operators/apply_redirects.ts

@@ -0,0 +1,31 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {Injector} from '@angular/core';
+import {Observable, OperatorFunction} from 'rxjs';
+import {flatMap} from 'rxjs/operators';
+
+import {applyRedirects as applyRedirectsFn} from '../apply_redirects';
+import {Routes} from '../config';
+import {RouterConfigLoader} from '../router_config_loader';
+import {UrlSerializer, UrlTree} from '../url_tree';
+
+
+/**
+ * Returns the `UrlTree` with the redirection applied.
+ *
+ * Lazy modules are loaded along the way.
+ */
+export function applyRedirects(
+    moduleInjector: Injector, configLoader: RouterConfigLoader, urlSerializer: UrlSerializer,
+    config: Routes): OperatorFunction<UrlTree, UrlTree> {
+  return function(source: Observable<UrlTree>) {
+    return source.pipe(flatMap(
+        urlTree => applyRedirectsFn(moduleInjector, configLoader, urlSerializer, urlTree, config)));
+  };
+}