coordinator-purchase.swift

// 1
protocol ProductListViewControllerDelegate: class {
    func productListViewController(_ vc: ProductListViewController, didSelectProduct product: Product)
}

class ProductListViewController: UIViewController {
    weak var delegate: ProductListViewControllerDelegate?
}

protocol ProductDetailViewControllerDelegate: class {
    func productDetailViewController(_ vc: ProductDetailViewController, didAddProduct product: Product)
}

class ProductDetailViewController: UIViewController {
    weak var delegate: ProductDetailViewControllerDelegate?
}

protocol OrderSummaryViewControllerDelegate: class {
    func orderSummaryViewControllerDidCheckout(_ vc: OrderSummaryViewController)
}

class OrderSummaryViewController: UIViewController {
    var items: [Cart.Item]!
    weak var delegate: OrderSummaryViewControllerDelegate?
}

// 2
struct Product {
    let id: String
    let name: String
    let price: Decimal
}

class Cart {
    struct Item {
        let product: Product
        var quantity: Int
    }
    
    var items = [Item]()
    
    func addProduct(_ product: Product) {}
    
    func removeProduct(_ product: Product) {}
}

// 3
class PurchaseCoordinator: ProductListViewControllerDelegate, ProductDetailViewControllerDelegate, OrderSummaryViewControllerDelegate {
    
    
    var cart = Cart()
    
    var paymentMethod: PaymentMethod?
    
    // Removed this in new implementation
    var deliveryAddress: String?
    var shippingOption: ShippingOption?
    
    var rootViewController: UINavigationController
    
    init() {
        let vc = ProductListViewController()
        rootViewController = UINavigationController(rootViewController: vc)
        
        vc.delegate = self
    }
    
    // MARK: - Product list
    // MARK: - Go to product detail
    func productListViewController(_ vc: ProductListViewController, didSelectProduct product: Product) {
        let vc = ProductDetailViewController()
        vc.delegate = self
        vc.navigationItem.rightBarButtonItem = checkoutButton
        
        rootViewController.pushViewController(vc, animated: true)
    }
    
    private var checkoutButton: UIBarButtonItem {
        return UIBarButtonItem(title: "Cart (\(cart.items.count))", style: .plain, target: self, action: #selector(didTapCheckout(_:)))
    }
    
    // MARK: - Go to order summary
    @objc func didTapCheckout(_ sender: UIBarButtonItem) {
        let vc = OrderSummaryViewController()
        vc.items = cart.items
        vc.delegate = self
        vc.navigationItem.leftBarButtonItem = closeButton
        
        rootViewController.present(UINavigationController(rootViewController: vc), animated: true, completion: nil)
    }
    
    // MARK: - Product detail
    // MARK: - Add product
    func productDetailViewController(_ vc: ProductDetailViewController, didAddProduct product: Product) {
        cart.addProduct(product)
    }
    
    // MARK: - Order Summary
    func orderSummaryViewControllerDidCheckout(_ vc: OrderSummaryViewController) {
        // Go to delivery or shipping options
    }
    
    
    // MARK: - Helpers
    private var closeButton: UIBarButtonItem {
        return UIBarButtonItem(barButtonSystemItem: .cancel, target: self, action: #selector(didTapClose(_:)))
    }
    
    @objc func didTapClose(_ sender: UIBarButtonItem) {
        rootViewController.dismiss(animated: true, completion: nil)
    }
}