Implementing a Resolver in Angular for Data Fetching

Resolvers in Angular are a powerful mechanism for fetching data before a route is activated. This ensures that the component has the necessary data when it's rendered, preventing loading spinners and improving the user experience. This challenge asks you to implement a resolver that fetches data from a mock API and makes it available to a component.

Problem Description

You need to create an Angular resolver that fetches user data based on a user ID provided in the route parameters. The resolver should call a mock API endpoint (/users/{id}) to retrieve the user's information. If the user is found, the resolver should return the user data. If the user is not found (status code 404), the resolver should return null. The component using this resolver should display the user's information if found, and an error message if the user is not found.

Key Requirements:

• Data Fetching: The resolver must successfully fetch data from the mock API.
• Error Handling: The resolver must handle the case where the user is not found (404 status code) and return null.
• Type Safety: Use TypeScript to ensure type safety throughout the resolver and component.
• Route Integration: The resolver must be correctly integrated with an Angular route.
• Component Display: The component should display the fetched user data or an appropriate error message.

Expected Behavior:

1. When a user navigates to a route with a user ID (e.g., /users/123), the resolver should be triggered.
2. The resolver should fetch user data from the mock API for the specified ID.
3. If the user is found, the resolver should return the user data.
4. The component should receive the user data and display it.
5. If the user is not found (404), the resolver should return null.
6. The component should receive null and display an error message.

Edge Cases to Consider:

• Invalid User ID: What happens if the user ID is not a valid number? (Consider this in your component's error handling, not necessarily the resolver itself).
• API Errors: While the mock API is reliable, consider how you might handle general API errors (e.g., network issues) in a real-world scenario. (Hint: Observables and error handling operators).
• Loading State: While not explicitly required, consider how you might indicate a loading state while the data is being fetched.

Examples

Example 1:

Input: Route navigated to /users/1
Output: Component displays user data for user ID 1 (e.g., { id: 1, name: "John Doe", email: "john.doe@example.com" })
Explanation: The resolver successfully fetches user data from the mock API.

Example 2:

Input: Route navigated to /users/999 (user not found)
Output: Component displays an error message (e.g., "User not found")
Explanation: The resolver returns null because the user with ID 999 is not found in the mock API.

Constraints

• Mock API: Use a simple mock API for demonstration purposes. You can use HttpClientTestingModule and of() or throwError() to simulate API responses. No external API calls are required.
• Angular Version: Assume Angular version 14 or higher.
• Performance: The resolver should execute quickly. Focus on clarity and correctness rather than extreme optimization.
• Data Structure: Assume the user data returned from the API is an object with properties id, name, and email.

Notes

• You'll need to create an Angular module, a component, a route, and the resolver.
• Use the ActivatedRoute service to access the user ID from the route parameters.
• Use the HttpClient service (mocked) to simulate the API call.
• Consider using RxJS operators to handle the Observable returned by the HttpClient.
• Focus on the resolver's logic and the component's display of the data. Styling is not required.
• The mock API should return a JSON object with the user data if the user exists, and a 404 status code if the user does not exist. You can simulate this using throwError.