Name: Ionescu Matei-Ștefan
Group: 323CAb

OOP Homework #3 - POO TV V2

Summary:

POO TV implements the core backend mechanics of platforms like HBO GO and Netflix using OOP concepts. The application receives a list of actions from a file in json format and generates a new json file with the required output for each action.

This project builds upon the Homework #2 - POO TV and represents an improved version with more features. In this README I will be taking about the new features and their implementation. For more information about the project check the README from the first version of the application available at https://github.com/Matei77/OOP-POO-TV.

Implementation:

Design Patterns Used

1. Singleton Design Pattern

The core of the application is still represented by the PlatformEngine class. This class has been designed using the Singleton Design Pattern to allow only one instantiation of the class and acts as a database to hold information about the movies and users on the platform, as well as the current user, the movies the current user can see and the current page the user is located in.

2. Factory Design Pattern

Each page has specific actions that can only happen on that page. In my implementation each page represents a class that implements the Page interface and is created using the Factory Design Pattern. The PageFactory is instantiated using the Singleton Design Pattern to save memory by allowing only one instance of the PageFactory. Each page class overrides the required methods from the Page interface. The default output for each method in the interface is the error message.

3. Observer Design Pattern

When a new admin action is executed, all observers are notified. Admin actions are adding and deleting movies to and from the database. The AdminActions represents the observable class, and the User class is the observer. The AdminActions class will store the list of observers and will notify them when an action is executed. The notifyObserver method from the User class will then decide if the user should receive the notification given by the admin.

4. Command Design Pattern

A new feature has been implemented, the back button, and it is using the Command Design Pattern. Changing the page is now executed using the ChangePageInvoker which hold a history of successful change page commands and implements the execute and undo methods that goes to the next page, respectively goes back to the previous page.

Data structure

User

For each user the platform holds information about his credentials, his purchased, watched, liked and rated movies, the type of his account, the number of free premium movies he has available, his tokens and his balance. In this version of the application the notification system was introduced and users now receive notifications from the platform. The Notification class was implemented for this reason.

Movie

For each movie the platform holds information about the name, the year, the duration, the genres, the actors, the countries banned in, the number of likes and the ratings. Movies now have an improved rating system that allows changing the user's rating. This is implemented using the Rating class.

New Actions

When the runEngine method is called movies and users databases will be updated with the information contained in the input json file and the actions received will be executed. The output will be shown in a new json file called results.out.

User Actions

The following new user actions were introduced:

1. subscribe

   This action allows a user to subscribe to a genre.

   When the subscribe command is given, the subscribe() method will be called, and it will check if the movie currently seeing has the selected genre and if the user was not already subscribed to it. If this is the case, the user will now receive notifications when movies from that genre are added.

2. back

   This action allows a user to go to the previous page.

   When the back command is given, the ChangePageInvoker.undo() method will be called, and it will go to the previous page if possible. Otherwise, it will output an error.

Admin Actions

The following admin actions were introduced:

1. add

   This action allows admins to add a movie to the database at any time.

   When the add command is given, the AdminActions.addMovieToDatabase() method will be called, and it will add the movie given in input to the database. Users that subscribed to any of the genres of the movie will be notified about the new movie.

2. delete

   This action allows admins to delete a movie from the database at any time.

   When the delete command is given, the AdminActions.deleteMovieFromDatabase() method will be called, and it will delete the movie given in input from the database. Users that have purchased the movie will be notified about the deleted movie and reimbursed.

The AdminActions class is implemented using the Observer Design Pattern. Admin actions are observable by the observers (the users).

Recommendation System

At the end of the execution of all actions, if there is a premium user logged-in they will be notified about a movie they should watch. The movie recommendation system is implemented in the giveRecommendation() method from the User class. And find a movie the user would probably enjoy by analyzing the user's liked genres and the most popular movies on the platform. The most popular movie that the user hasn't watched yet is recommended. The LikedGenre class was implemented to allow this new feature of the platform.