Welcome to our coding challenges designed to test your Ruby on Rails expertise. Each challenge focuses on a specific aspect of Rails development, from implementing new features to refactoring existing code. Please select and complete any of the tasks below as instructed.

Objective: Implement a custom scope on the User model to filter users who have logged in within the last week.

Objective: Add a new RESTful API endpoint to create a Comment for a Post.

Instructions: 3. Ensure the controller handles both success and failure cases appropriately.

Objective: Add a validation to the Post model to ensure the title is unique among posts published in the current year.

Instructions:

1. Add a custom validation method in post.rb that checks the uniqueness of the title for the current year.
2. Use this validation only when a new Post is created or its title is updated.

Objective: Create a service object to send an email notification when a new user signs up.

Objective: Refactor the provided code in the PostsController.

Instructions: Ensure the functionality remains intact.