0004-Invalid-State.md

Invalid State

app.swift

func app() {
    let idToken = ...
    let baseUrl = ...
    let configuration = Configuration(idToken: idToken, baseUrl: baseUrl)

    do {
        try Client.shared.preloadMedia()
        let controller = Client.shared.start()
        present(controller, animated: true)
    } catch {
        print(":boom: Unexpected error: \(error)") // Uh oh, you forgot to call `configure(with:)`
    }
}

app2.swift

func app() {
    let idToken = ...
    let baseUrl = ...
    let configuration = Configuration(idToken: idToken, baseUrl: baseUrl)
    let scope = Client.shared.configure(with: configuration) // _must_ be called
    scope.preloadMedia()

    let controller = scope.start()
    present(controller, animated: true)
}

Authentication.swift

struct Authentication {
    var accessToken: String
    var refreshToken: String
    var tokenType: String
    var expiry: UInt
}

Client.swift

public class Client {

    public static let shared: Client = .init()
    private init() { }

    // MARK: - Configuration

    private var configuration: Configuration!

    public func configure(with configuration: Configuration) throws {
        self.configuration = configuration
        try self.authenticate()
    }

    // MARK: - Authentication

    private var authentication: Authentication!

    private func authenticate() throws {
        guard configuration != nil else { throw ConfigurationError.mustBeConfigured }
        self.authentication = /* using configuration.idToken and configuration.baseUrl */
    }

    // MARK: - UI
    public func start() throws -> UIViewController {
        guard configuration != nil else { throw ConfigurationError.mustBeConfigured }
        guard authentication != nil else { throw AuthenticationError.mustBeAuthenticated }

        let controller = ...
        return controller
    }

    public func preloadMedia() throws {
        guard configuration != nil else { throw ConfigurationError.mustBeConfigured }
        guard authentication != nil else { throw AuthenticationError.mustBeAuthenticated }

        // fetch media and cache it
        ...
    }
}

Client2.swift

public class Client {

    public static let shared: Client = .init()
    private init() { }

    public func configure(with configuration: Configuration) -> AuthenticatedScope {
        let authentication = authenticate(
            with: configuration.idToken,
            at: configuration.serviceBaseUrl
        )
        return AuthenticatedScope(authentication: authentication)
    }

    private func authenticate(with idToken: String, at baseUrl: URL) -> Authentication {
        // Authenticate user
        return Authentication(/* with obtained values */)
    }
}

Client3.swift

extension Client {
    public class AuthenticatedScope {

        private let authentication: Authentication

        init(authentication: Authentication) {
            self. authentication = authentication
        }

        // MARK: - UI
        public func start() -> UIViewController {
            let controller = ...
            return controller
        }

        public func preloadMedia() {
            // fetch media and cache it
            ...
        }
    }
}

Configuration.swift

struct Configuration {
    var idToken: String
    var baseUrl: URL
}

defensivelyThrowing.swift

guard configuration != nil else { throw ConfigurationError.mustBeConfigured }
guard authentication != nil else { throw AuthenticationError.mustBeAuthenticated }

optionality.swift

private var configuration: Configuration!
private var authentication: Authentication!