JIRA-003 Designed Book recommendation system

[AnjaBasara]

What?

Designed Book recommendation system. For more background, see ticket #JIRA-003.

Why?

This feature enhances the user book management experience, as the users are suggested similar books to the ones they like.

How?

This includes a migration for book ratings, rating controller, observer and new services for recommendation algorithms. Every time a user rates a book, RatingObserver dispatches a ProcessCreateRating job that calls the appropriate recommendation service to record that data. For those services, Strategy Pattern is used depending on which strategy/recommendation service should be used. ContentBasedFilteringService calls a third-party API, and CollaborativeFilteringService uses built-in algorithms. To refresh book recommendations, a custom command is made that uses the Recommender facade that builds the model, gets predictions, stores them etc.

Anything else?

ProcessCreateRating is chosen to be a Job since those ratings should be done asynchronously and not stop the user from using the application.