CommandDesignPattern.swift

import UIKit

//MARK: - This example before implementing command pattern
//
class Light {
   func turnOn() {
       print("Light is on")
   }

   func turnOff() {
       print("Light is off")
   }
}

class Switch {
   func press(on: Bool) {
       let light = Light()
       if on {
           light.turnOn()
       } else {
           light.turnOff()
       }
   }
}

let lightSwitch = Switch()
lightSwitch.press(on: true) // Light is on
lightSwitch.press(on: false) // Light is off


//MARK: - This example aftre implementing command pattern
//
protocol Command {
   func execute()
}


class Light {
   func turnOn() {
       print("Light is on")
   }

   func turnOff() {
       print("Light is off")
   }
}

class Switch {
   var command: Command?

   func press() {
       command?.execute()
   }
}

class TurnOnCommand: Command {
   let light: Light

   init(light: Light) {
       self.light = light
   }

   func execute() {
       light.turnOn()
   }
}

class TurnOffCommand: Command {
   let light: Light

   init(light: Light) {
       self.light = light
   }

   func execute() {
       light.turnOff()
   }
}

let light = Light()
let switchButton = Switch()
switchButton.command = TurnOnCommand(light: light)
switchButton.press() // Light is on
switchButton.command = TurnOffCommand(light: light)
switchButton.press() // Light is off



//MARK: - This example aftre implementing command pattern with undo
//
protocol Command {
    func execute()
    func undo()
}

//Receiver
class Light {
    var isOn = false

    func turnOn() {
        isOn = true
        print("Light is on")
    }

    func turnOff() {
        isOn = false
        print("Light is off")
    }
}

//Invoker
class Switch {
    var commandHistory = [Command]()

    func execute(command: Command) {
        command.execute()
        commandHistory.append(command)
    }

    func undo() {
        guard let command = commandHistory.popLast() else { return }
        command.undo()
    }
}

class TurnOnCommand: Command {
    let light: Light

    init(light: Light) {
        self.light = light
    }

    func execute() {
        light.turnOn()
    }

    func undo() {
        light.turnOff()
    }
}

class TurnOffCommand: Command {
    let light: Light

    init(light: Light) {
        self.light = light
    }

    func execute() {
        light.turnOff()
    }

    func undo() {
        light.turnOn()
    }
}

let light = Light()
let switchButton = Switch()

let turnOnCommand = TurnOnCommand(light: light)
switchButton.execute(command: turnOnCommand) // Light is on

let turnOffCommand = TurnOffCommand(light: light)
switchButton.execute(command: turnOffCommand) // Light is off

switchButton.undo() // Light is on