Worker demo

demo.swift

import Foundation

class AccountInfoWorker {
    struct AccountInfo { /* properties */ }
    typealias ApiResult = Result<AccountInfo, Error>
    typealias ApiCompletion = (ApiResult) -> Void

    func fetchAccountInfo(id: String, completion: @escaping ApiCompletion) { /* IMP */ }
}

class LoginInfoWorker {
    struct LoginInfo {
        let id: String
    }

    typealias ApiResult = Result<LoginInfo, Error>
    typealias ApiCompletion = (ApiResult) -> Void

    func fetchLoginInfo(completion: @escaping ApiCompletion) { /* IMP */ }
}

class LoginAccountInfoWorker {
    private let accountInfoWorker = AccountInfoWorker()
    private let loginInfoWorker = LoginInfoWorker()

    func fetchLoginAccountInfo(id: String, completion: @escaping AccountInfoWorker.ApiCompletion) {
        loginInfoWorker.fetchLoginInfo { [weak self] result in
            self?.handle(loginInfo: result, completion: completion)
        }
    }

    private func handle(loginInfo result: LoginInfoWorker.ApiResult, completion: @escaping AccountInfoWorker.ApiCompletion) {
        switch result {
        case let .success(loginInfo):
            accountInfoWorker.fetchAccountInfo(id: loginInfo.id) { result in
                switch result {
                case let .success(accountInfo):
                    completion(.success(accountInfo))
                case let .failure(error):
                    completion(.failure(error))
                }
            }
        case let .failure(error):
            completion(.failure(error))
        }
    }
}