2_chain_with_dynamic_messages.swift

protocol Logger {
  func takeAction(flag: Bool) -> Void
  func passDownChain(flag: Bool) -> Void
}

class LoggerA: Logger {

  private var child: Logger?

  public init(child: Logger?) {
    self.child = child
  }

  func takeAction(flag: Bool) {
    print("LoggerA will always print the same message")
    passDownChain(flag: flag)
  }

  func passDownChain(flag: Bool) {
    child?.takeAction(flag: flag)
  }

}

class LoggerB: Logger {

  private var child: Logger?

  public init(child: Logger?) {
    self.child = child
  }

  func takeAction(flag: Bool) {
    if flag {
      print("LoggerB prints this message if the flag is true.")
    } else {
      print("LoggerB prints this message if the flag is false.")
    }
    passDownChain(flag: flag)
  }

  func passDownChain(flag: Bool) {
    child?.takeAction(flag: flag)
  }

}

class FakeServer {

  var logger = LoggerA(child: LoggerB(child: nil))

  func run() {
    someImportantAction()
    logger.takeAction(flag: true)
    anotherImportantAction()
    logger.takeAction(flag: false)
  }

  private func someImportantAction() -> Void {
    print("This is some important action!")
  }

  private func anotherImportantAction() -> Void {
    print("This is another important action!")
  }

}

var server = FakeServer()
server.run();