ApplicationServices.swift

class ApplicationServices {
    
    // ApplicationServices is a singleton, because it makes it easier to be accessed from anywhere to access its functions/services
    static let shared = ApplicationServices()
    let appRouter = ApplicationRouter()
    
    func pay(amount: Double,
             username: String,
             password: String,
             completion: @escaping (() -> Void)) {
        
        // Get payment token from `LoginModule` with `username` and `password`
        guard let moduleUrl = URL(schema: "tandem",
                                  host: "login",
                                  path: "/payment-token",
                                  parameters: ["username": username,
                                               "password": password]) else {
                return
        }
        appRouter.open(url: moduleUrl) { [weak self] (response, responseData, urlResponse, error) in
            
            // Use `token` in response to make an actual payment through `PaymentsModule`
            guard let response = response,
                    let token = response["paymentToken"] as? String,
                    let moduleUrl = URL(schema: "tandem",
                                        host: "payments",
                                        path: "/pay",
                                        parameters: ["token": token,
                                                     "amount": String(amount)]) else {
                    return
            }
            self?.appRouter.open(url: moduleUrl) { (response, responseData, urlResponse, error) in
                
                // Final callback, basically just to synchronize our example here with the NonCompliantModule
                completion()
            }
        }
    }
}