Implementing the createBook method

Next up is the createBook method. This is the most complicated one.

First of all, implement all the required validations:

createBook(collectionIdentifier: string): void {
    if (!collectionIdentifier) {
        throw new Error("The collection identifier is required to 
        create a new book!");
    }

    console.log("Retrieving the details about the new book to 
    create...");

    const bookDetailsResult = 
    this._view.getNewBookDetails(collectionIdentifier);

    if (bookDetailsResult.error) {
        console.error("Failed to retrieve the book details: ", 
        bookDetailsResult.error);
        return;
    }

    if (!this._bookCollections.has(collectionIdentifier) || 
    !this._bookCollections.get(collectionIdentifier)) {
        console.error("Tried to add a book to an unknown collection. 
        Identifier: ", collectionIdentifier);
        this._view.displayErrorMessage("Failed to create the new 
        book!");
        return;
    }

    const existingCollection = 
    this._bookCollections.get(collectionIdentifier);
    if (!existingCollection || !bookDetailsResult.book) {
        throw new Error("The collection couldn't be retrieved or we 
        could not get the book details from the view!");
    }

    // add the rest of the code here
}

Then add the following:

const newBook: Readonly<Book> = bookDetailsResult.book;
existingCollection.addMedia(newBook);
this._bookService.saveMediaCollection(existingCollection)
    .then(() => {
        console.log(`Book collection called 
        "${existingCollection.name}" updated successfully.`);
        this._view.clearNewBookForm(collectionIdentifier);
        this._view.renderBook(existingCollection.identifier, newBook); // here we are sure that the book property is set
    })
    .catch(error => {
        console.error("Error while updating an existing book 
        collection: ", error);
        this._view.displayErrorMessage(`Failed to update the existing 
        book collection called ${existingCollection.name}`);
    });

In this second part of the method, we have added our new book to the existing collection and then asked the service to persist the updated collection.

Again, in the event of an error, the view is asked to display an error message.