From procedural code to decorator pattern

code1.swift

// CODE 1
class HTTPClient {
    func load(url: URL, completion: @escaping (Response) -> Void) {
        // call server
        // complete with result
    }
}
// Responsibilities:
/// - Send request and return response

code10.swift

// CODE 10

/// Initialization of controller with dependency injection
let vc = ClientViewController(httpClient: HTTPClientFactory.makeHTTPClient())

class ClientViewController: UIViewController {
    let httpClient: HTTPClientProtocol

    init(httpClient: HTTPClientProtocol) {
        self.httpClient = httpClient
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        let someURL = URL(string: "http://some-url.com")!
        httpClient.load(url: someURL, completion: { response in
            // handle result
        })
    }
}

code2.swift

// CODE 2
class HTTPClient {
    let storage = CredentialsStorage()

    func load(url: URL, completion: @escaping (Response) -> Void) {
        if storage.isTokenExpired {
            refreshToken(token: storage.token, completion: { _ in
                // call server
                // complete with response
            })
        } else {
            // call server
            // complete with response
        }
    }

    private func refreshToken(token: String, completion: @escaping (Response) -> Void) {
        // refresh token
        // complete with new tokens or error
    }
}

// Responsibilities:
/// - Send request and return response
/// - Managing auth token lifetime, credentials storage
/// - Refreshing credentials

code3.swift

// CODE 3
class HTTPClient {
    let storage = CredentialsStorage()
    let permanentBlockList = PermanentBlockList()

    func load(url: URL, completion: @escaping (Response) -> Void) {
        guard !permanentBlockList.isBlocked else {
            completion(.failure(NSError(domain: "PERMANENTLY__BLOCKED", code: 418)))
            return
        }

        if storage.isTokenExpired {
            refreshToken(token: storage.token, completion: { _ in
                // call server
                // if statusC0de = 418 blockList.blockCurrentAccout()
                // complete with response
            })
        } else {
            // call server
            // if statusC0de = 418 blockList.blockCurrentAccout()
            // complete with response
        }
    }

    private func refreshToken(token: String, completion: @escaping (Response) -> Void) {
        // refresh token
        // completion with result
    }
}

// Responsibilities:
/// - Send request and return response
/// - Managing auth token lifetime, credentials storage
/// - Refreshing credentials
/// - Managing blocked users list, blocked users storage
/// - Saving current user to list, and block it from any interactions with our production server

code4.swift

// CODE 4
protocol HTTPClientProtocol {
    func load(url: URL, completion: @escaping (Response) -> Void)
}

code5.swift

// CODE 5
class HTTPClient: HTTPClientProtocol {
    func load(url: URL, completion: @escaping (Response) -> Void) {
        // refresh token
        // completion with result
    }
}

// Responsibilities:
/// - Send request and return response

code6.swift

// CODE 6
class RefreshCredentialsHTTPClientDecorator: HTTPClientProtocol {
    private let storage = CredentialsStorage()
    private let decoratee: HTTPClientProtocol

    init(decoratee: HTTPClientProtocol) {
        self.decoratee = decoratee
    }

    func load(url: URL, completion: @escaping (Response) -> Void) {
        if storage.isTokenExpired {
            refreshToken(token: storage.token, completion: { [weak self] _ in
                // refresh token
                self?.decoratee.load(url: url, completion: completion)
            })
        } else {
            // refresh token
            decoratee.load(url: url, completion: completion)
        }
    }

    private func refreshToken(token: String, completion: @escaping (Response) -> Void) {
        // refresh token
        // completion with result
    }
}

// Responsibilities:
/// - Managing auth token lifetime, credentials storage
/// - Refreshing credentials

code7.swift

// CODE 7
class PermanentBlockHTTPClientDecorator: HTTPClientProtocol {
    private let permanentBlockList = PermanentBlockList()
    private let decoratee: HTTPClientProtocol

    init(decoratee: HTTPClientProtocol) {
        self.decoratee = decoratee
    }

    func load(url: URL, completion: @escaping (Response) -> Void) {
        guard !permanentBlockList.isBlocked else {
            completion(.failure(NSError(domain: "PERMANENTLY__BLOCKED", code: 418)))
            return
        }

        decoratee.load(url: url, completion: { result in
            // if statusC0de = 418 blockList.blockCurrentAccout() complete with block error

            // else complete with decoratee's result
            completion(result)
        })
    }
}

// Responsibilities:
/// - Managing blocked users list, blocked users storage
/// - Saving current user to list, and block it from any interactions with our production server

code8.swift

// CODE 8
class HTTPClientLoggerDecorator: HTTPClientProtocol {
    private let decoratee: HTTPClientProtocol

    init(decoratee: HTTPClientProtocol) {
        self.decoratee = decoratee
    }

    func load(url: URL, completion: @escaping (Response) -> Void) {
        // start measure
        decoratee.load(url: url) { result in
            // end measure and save to some storage the results
            // completion with result
        }
    }
}

// Responsibilities:
/// - Measure real network requests to the server

code9.swift

// CODE 9
//// MARK: - Objects graph:
/// PermanentBlockHTTPClientDecorator
/// -> RefreshCredentialsHTTPClientDecorator
/// -> HTTPClientLoggerDecorator
/// -> HTTPClient
class HTTPClientFactory {
    private init() {}
    static func makeHTTPClient() -> HTTPClientProtocol {
        let httpClient = HTTPClient()
        let httpClientLoggerDecorator = HTTPClientLoggerDecorator(decoratee: httpClient)
        let refreshCredentialsHTTPClientDecorator = RefreshCredentialsHTTPClientDecorator(decoratee: httpClientLoggerDecorator)
        let permanentBlockHTTPClientDecorator = PermanentBlockHTTPClientDecorator(decoratee: refreshCredentialsHTTPClientDecorator)
        return permanentBlockHTTPClientDecorator
    }
}