Observer.swift

class ActivityLog {
    func logActivity(activity: String) {
        print("Log: \(activity)")
    }
}

class FileCache {
    func loadFiles(user: String) {
        print("Load files for \(user)")
    }
}

class AttackMonitor {
    var monitorSuspiciousActivity: Bool = false {
        didSet {
            print("Monitoring for attack: \(monitorSuspiciousActivity)")
        }
    }
}

class AuthenticationManager {
    private let log = ActivityLog()
    private let cache = FileCache()
    private let monitor = AttackMonitor()
    
    func authenticate(user: String, pass: String) -> Bool {
        var result = false
        if (user == "bob" && pass == "secret") {
            result = true
            print("User \(user) is authenticated")
            log.logActivity("Authenticated \(user)")
            cache.loadFiles(user)
            monitor.monitorSuspiciousActivity = false
        } else {
            print("Faild authentication attempt")
            log.logActivity("Failed authentication: \(user)")
            monitor.monitorSuspiciousActivity = true
        }
        return result
    }
}

let authM = AuthenticationManager()
authM.authenticate("bob", pass: "secret")
print("--------")
authM.authenticate("joe", pass: "shhh")