trikitrok

export class MessageRouter {
    public route(message: Message): void {
        //!! ouch... x(
        ExternalRouter.getInstance().sendMessage(message);
    }
}

export class ExternalRouter { // another Singleton! x(
    private static instance: ExternalRouter | null = null;

trikitrok

// After applying Subclass & Override Method

class RegisterSale {
    // more code...

    public addItem(code: Barcode): void {
        const newItem = this.getInventory().getItemForBarCode(code);
        this.items.push(newItem);
    }

trikitrok

class RegisterSale {
    // more code...

    public addItem(code: Barcode): void {
        //!! After Extract Method
        const newItem = this.getInventory().getItemForBarCode(code);
        this.items.push(newItem);
    }

    //!! Extracted method. Now we can apply Subclass & Override Method here!!

trikitrok

class Inventory {
    private static inventory: Inventory | null = null;

    public static getInstance(): Inventory {
        if (this.inventory === null) {
            this.inventory = new Inventory();
        }
        return this.inventory;
    }

trikitrok

class FileTransactionsRepository implements TransactionsRepository {
    public getAll(): Transaction[] {
        let transactions: Transaction[] = [];

        // read the transactions from some file...

        return transactions;
    }
}

trikitrok

class Account {
    private balance: number;
    private readonly logger: AcmeLogger;

    constructor(balance: number) {
        this.balance = balance;
        this.logger = new AcmeLogger();
    }

    public withdraw(value: number): void {

trikitrok

class Account {
    private balance: number;
    private readonly logger: AcmeLogger;

    constructor(balance: number) {
        this.balance = balance;
        this.logger = new AcmeLogger();
    }

    public withdraw(value: number): void {

trikitrok

// New interface comes from applying Extract Interface to the wrapper
interface LibraryData {
    getLibraryName(): string;
}

// Notice how we renamed the wrapper to free the interface name
class AcmeInputReaderLibraryData implements LibraryData {
    private readonly inputReader: AcmeInputReader ;

    constructor(inputReader: AcmeInputReader) {

trikitrok

class Library {
    private display: Display;

    constructor(display: Display) {
        this.display = display;
    }

    printBooks(books: Book[], inputReader: AcmeInputReader): void {
        const libraryData = new LibraryData(inputReader);
        const libraryName = libraryData.getLibraryName(); // <- moved method

trikitrok

// After steps 1 and 2

class Library {
    private readonly display: Display;

    constructor(display: Display) {
        this.display = display;
    }

    printBooks(books: Book[], inputReader: AcmeInputReader): void {