Building a Flexible Smart Home System with Command and Decorator Patterns in Scala

Welcome to the third lesson of our "Applying Design Patterns for Real World Problems using Scala" course! In this lesson, we'll delve into two powerful design patterns: the Command pattern and the Decorator pattern. These patterns will empower you to design a robust and flexible smart home automation and lighting control system in Scala 3. Let's embark on this journey to create a system that’s as adaptable as it is efficient! 🚀

Here's a brief overview of what we'll be doing in this lesson:

1. Basic Setup:

   • Abstract Device: Define a trait Device and create specific device classes (Light, Fan) that extend from it.
   • Factory Method: Leverage companion objects to serve as factories for generating instances of these devices.

2. Command Pattern:

   • Purpose: Encapsulates a request as an object, facilitating parameterization, queuing, logging, and support for undoable operations.
   • Components:
     • Define a Command trait and concrete command classes (LightOnCommand, LightOffCommand).
     • Implement a RemoteControl class for command executions.

3. Decorator Pattern:

   • Purpose: Dynamically adds functionalities to existing objects without altering their structure.
   • Components:
     • Use a decorator class (ColoredLight) to add color capabilities to a Light device.

Let’s dive into the Scala code and bring these patterns to life! 🎉

Let's start by defining the devices we'll be working with. We'll create a trait Device and extend it with concrete device classes Light and Fan.

// Abstract Device
trait Device:
  def on(): Unit
  def off(): Unit

// Concrete Device: Light
class Light extends Device:
  def on(): Unit = println("Light is on.")
  def off(): Unit = println("Light is off.")

// Concrete Device: Fan
class Fan extends Device:
  private var speed: Int = 0
  def on(): Unit = println("Fan is on.")
  def off(): Unit = println("Fan is off.")
  def setSpeed(speed: Int): Unit =
    this.speed = speed
    println(s"Fan speed set to $speed.")

This code defines the foundational elements of our smart home system:

• The Device trait establishes a common interface with on() and off() methods.
• The Light class extends Device with basic functionality to turn the light on and off.
• The Fan class extends Device and adds the ability to set the fan's speed through the setSpeed() method.