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

PR Close #25740

packages/router/src/operators/before_preactivation.ts

@@ -0,0 +1,29 @@
+/**
+ * @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 {MonoTypeOperatorFunction} from 'rxjs';
+import {map, mergeMap} from 'rxjs/operators';
+
+import {RouterHook} from '../router';
+import {RouterStateSnapshot} from '../router_state';
+import {UrlTree} from '../url_tree';
+
+export function beforePreactivation(
+    hook: RouterHook, navigationId: number, appliedUrlTree: UrlTree, rawUrlTree: UrlTree,
+    skipLocationChange: boolean, replaceUrl: boolean):
+    MonoTypeOperatorFunction<{appliedUrl: UrlTree, snapshot: RouterStateSnapshot}> {
+  return function(source) {
+    return source.pipe(mergeMap(
+        p => hook(
+                 p.snapshot,
+                 {
+                     navigationId, appliedUrlTree, rawUrlTree, skipLocationChange, replaceUrl,
+                 })
+                 .pipe(map(() => p))));
+  };
+}