In this lesson, we will integrate design patterns into a practical project: building a smart home system. You'll learn how to create and adapt various smart home devices using the Singleton, Builder, Composite, and Abstract Factory patterns in TypeScript. By the end, you will have a solid understanding of how these design patterns, combined with TypeScript's type system, can make your smart home system more efficient, modular, and easier to maintain.

1. Singleton Pattern:

   • Purpose: Ensures a class has only one instance and provides a global point of access to it.
   • TypeScript Features: Use private constructors, static properties, and type annotations to enforce singleton behavior.

2. Builder Pattern:

   • Purpose: Constructs complex objects step by step, providing a flexible solution for object creation.
   • TypeScript Features: Use classes, interfaces, and method chaining with type annotations for clarity and safety.

3. Composite Pattern:

   • Purpose: Treats individual objects and compositions of objects uniformly.
   • TypeScript Features: Use interfaces or abstract classes to define a common contract for components and leverage type safety for composite structures.

4. Abstract Factory Pattern:

   • Purpose: Provides an interface for creating families of related or dependent objects without specifying their concrete classes.
   • TypeScript Features: Use abstract classes or interfaces to define factories and product types, ensuring type-safe object creation.

To start, we implement the Singleton pattern in TypeScript to ensure that a class has only one instance and provides a global point of access to it. TypeScript's private constructors and static properties help enforce this pattern.

The instance property is now typed as Singleton | undefined, and the check uses undefined, which is more idiomatic in TypeScript.

Next, we use the Builder pattern to construct complex SmartHomeDevice objects step by step. TypeScript interfaces and type annotations make the process clear and type-safe.

The SmartHomeDeviceBuilder class provides methods to set device properties and construct the final SmartHomeDevice, with all types enforced by TypeScript.

Now, we implement the Composite pattern to manage individual and composite objects uniformly. TypeScript interfaces and type annotations help define the structure and ensure type safety.

The CompositeDevice class allows us to treat individual DeviceComponent objects uniformly as part of a composite structure, with all types enforced by TypeScript.

Finally, we implement the Abstract Factory pattern to create families of related objects without specifying their concrete classes. TypeScript's abstract classes and interfaces help define clear contracts for factories and products.

The LightFactory and FanFactory classes implement methods to create specific sensor and actuator objects, with all types and contracts enforced by TypeScript.

Implementing Singleton, Builder, Composite, and Abstract Factory patterns in our smart home system using TypeScript allows us to create, organize, and manage devices in a structured and reusable manner. TypeScript's type safety, interfaces, and abstract classes help prevent errors and make the codebase more robust and maintainable. This approach makes our smart home system more modular, flexible, and easier to extend, while leveraging the full power of TypeScript's static typing.