You are creating an application allowing a library to manage books count. Your current task is to finish implementation of missing service methods. Data store is accessed by repository layer to which interfaces are provided in repository package.

Implement borrowBook method in the BookService class which should:

• Save information that user borrowed particular book from library
• Decrement available book copies count at library by 1
• Throw BookNotFoundException if the book is not available in data store
• Throw BookNotAvailableException if the book count is already equal to 0
• Throw BookAlreadyBorrowedException if the book is already borrowed by the user

Implement returnBook method in the BookService class which should:

• Save information that user returned particular book to library
• Increment available book copies count at library by 1
• Throw BookBorrowingNotFoundException if the user does not have such book borrowed in data store

Implement addBookCopy method in the BookService class which should:

• Save a book copies count of 1 if the book is not present in data store
• Increment copies count by 1 if the book is already present in data store

Implement removeBookCopy method in the BookService class which should:

• Decrement copies count by 1 if the book is present in data store
• Throw BookNotFoundException if the book is not present in data store
• Throw BookNotAvailableException if the book count is already equal to 0

Implement getAvailableBookCopies method in the BookService class which should:

• Return book count if the book is present in data store
• Throw BookNotFoundException if the book is not present in data store

• Repository interfaces contain Javadocs describing their methods behaviour
• You are not allowed to add/delete/modify methods available in repository interface
• You are not allowed to modify existing tests, but you are free to add new ones
• Remember to keep high code quality