hybrid engine example.swift

protocol Engine {
   func start()
   func started() -> Bool
   func stop()
}

class GasEngine: Engine {
   private var running: Bool

   init() {
       self.running = false
   }

   func start() {
       if self.started() {
           return
       }
     
       print("Gas engine starting...")
       self.running = true
   }

   func started() -> Bool {
       return self.running
   }

   func stop() {
       self.running = false
   }
}


class ElectricEngine: Engine {
   private var running: Bool

   init() {
       self.running = false
   }

   func start() {
       if self.started() {
           return
       }
     
       print("Electric engine starting...")
       self.running = true
   }


   func started() -> Bool {
       return self.running
   }

   func stop() {
       self.running = false
   }
}

class HybridEngine: Engine {
   var primaryEngine: Engine
   var secondaryEngine: Engine
   var activeEngine: Engine

   init(pEngine: Engine, sEngine: Engine) {
       self.primaryEngine = pEngine
       self.secondaryEngine = sEngine
       self.activeEngine = self.primaryEngine
   }

   // this method is for private use to switch engine by internal logic
   private func switchEngine() {
       if activeEngine === primaryEngine {
           activeEngine = secondaryEngine
       } else {
           activeEngine = primaryEngine
       }
       print("Switched engine.")
   }
   
   // internal logic of working engine
   private func loop() {
       // based on some logic can switch engine
       self.switchEngine()
   }

   func start() {
       activeEngine.start()
   }

   func started() -> Bool {
       return activeEngine.started()
   }

   func stop() {
       activeEngine.stop()
   }
}


class Car {
    private engine: Engine
   
    func init(engine: Engine) {
        self.engine = engine 
    }

    func startCar() {
        self.engine.start()  
    }
}

let hybridEngine = HybridEngine(
    GasEngine(), 
    ElectricEngine()
)
let hybridCar = Car(hybridEngine)
hybridCar.startCar()