radio-with-a-view/SOLID_PRINCIPLES.md

SOLID Principles Implementation

This project has been refactored to follow the SOLID principles of Object-Oriented Programming.

Overview

The codebase is organized into:

• Interfaces (src/interfaces/) - Define contracts following Interface Segregation Principle
• Classes (src/classes/) - Implementations following Single Responsibility Principle
• Main (src/main.ts) - Entry point that uses Dependency Inversion Principle

SOLID Principles Applied

1. Single Responsibility Principle (SRP)

Each class has one reason to change:

• VideoSource: Only responsible for managing video source elements
• VideoSeekController: Only responsible for seeking operations
• AudioController: Only responsible for audio control (mute/unmute)
• VideoPlayer: Only responsible for orchestrating the components

2. Open/Closed Principle (OCP)

The system is open for extension but closed for modification:

• New video source types can be added by implementing IVideoSource
• New seeking strategies can be added by implementing IVideoSeekController
• New audio control mechanisms can be added by implementing IAudioController
• The VideoPlayer class doesn't need modification when adding new implementations

3. Liskov Substitution Principle (LSP)

Any implementation of an interface can be substituted without breaking functionality:

• Any class implementing IVideoSource can replace VideoSource
• Any class implementing IVideoSeekController can replace VideoSeekController
• Any class implementing IAudioController can replace AudioController

4. Interface Segregation Principle (ISP)

Interfaces are small and focused on specific behaviors:

• IVideoSource: Only methods related to video source management
• IVideoSeekController: Only methods related to seeking
• IAudioController: Only methods related to audio control
• IVideoPlayer: High-level interface for the complete player

5. Dependency Inversion Principle (DIP)

High-level modules depend on abstractions, not concrete implementations:

• VideoPlayer depends on interfaces (IVideoSource, IVideoSeekController, IAudioController)
• Concrete implementations are injected via constructor
• This allows easy testing and swapping of implementations

Architecture Benefits

1. Testability: Each component can be tested in isolation
2. Maintainability: Changes to one component don't affect others
3. Extensibility: New features can be added without modifying existing code
4. Flexibility: Implementations can be swapped easily (e.g., for testing or different behaviors)

Example: Adding a New Feature

To add a new video source type (e.g., DASH streaming):

1. Create a new class DashVideoSource implementing IVideoSource
2. Use it in VideoPlayer constructor: this.videoSource = new DashVideoSource()
3. No other code needs to change!

File Structure

src/
├── interfaces/
│   ├── IVideoSource.ts          # Video source contract
│   ├── IVideoSeekController.ts  # Seeking contract
│   ├── IAudioController.ts      # Audio control contract
│   └── IVideoPlayer.ts          # Main player contract
├── classes/
│   ├── VideoSource.ts           # Video source implementation
│   ├── VideoSeekController.ts   # Seeking implementation
│   ├── AudioController.ts       # Audio control implementation
│   └── VideoPlayer.ts           # Main player orchestrator
└── main.ts                      # Application entry point