src/app/common/guards/exists-guard.ts

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
import {Observable} from 'rxjs/Observable';
import {of} from 'rxjs/observable/of';
import {Router} from '@angular/router';
import {Inject, Injectable} from '@angular/core';

@Injectable()
export class ExistsGuardService {

  constructor(private router: Router, @Inject('cacheExpiry') private cacheExpiry: number) {}

  isWithinExpiry(observable: Observable<number>): Observable<boolean> {
    return observable
      .map(loadedAtTimestamp => {
        if (!loadedAtTimestamp) {
          return false;
        }
        return loadedAtTimestamp + this.cacheExpiry > Date.now();
      })
      .take(1);
  }

  routeTo404OnError(observable: Observable<any>): Observable<any> {
    return observable.catch(() => {
      this.router.navigate(['/404']);
      return of(false);
    });
  }

}