In your language of choice among Python, PHP or Java, write a working program to demonstrate typical interactions between various objects that represent the foundations of an e-commerce engine (Online shopping cart).

It will work this way - A User will have a Cart in which he/she can add many Products. So a cart will have many Products. To make a purchase, User will "checkout" and an Order will be created from the items in the Cart.
(Hint: If you are familiar with OOP, you can define classes for users, products, carts and orders.)

Finally write a "main" or "runner" script that can be run in the terminal as follows -

1. First, prompt the user for name, email.
2. Show a list of products (id, name, model, price) which can be stored in a database or simply hardcoded in the code itself.
3. Prompt user to enter 1 or more products along with quantities which will be added to the Cart.
4. Calculate total price and show the amount on screen. Ask the user to enter the correct amount again. If it's entered correctly, consider payment is complete and create an Order!
5. Print the order details (invoice) on screen and exit

Add documentation about how to get the program running eg. list of dependencies, installation instructions if required, the available command(s) etc.

Some important points:

• No need to create a web application or use a web framework for this, just something that works in the terminal.
• You must handle errors and edge cases appropriately.
• Bonus points for writing unit tests.
• No need to use a database although there are extra points for using one and providing an additional command for adding products to it.
• Use minimum required data attributes to keep it simple for eg. only name, email for User; only id, name, model, price for Product.
• You may use any "helper" libraries if applicable.
• You may refer to any resource/books/videos etc.

Once you have done this, please send us the code or link to the code and we will get back to you.