Facade Pattern: Simplify Complex Subsystem Interaction

Client code must coordinate multiple subsystem classes in a specific sequence to accomplish a common task. This spreads orchestration logic across call sites and ties clients to implementation details.

Create a facade class that exposes a simple, high-level interface and hides the orchestration of subsystem calls.

// Complex subsystems
class VideoDecoder { decode(file: string) { return `decoded:${file}`; } }
class AudioMixer { mix(audio: string) { return `mixed:${audio}`; } }
class VideoEncoder { encode(video: string, audio: string) { return `final.mp4`; } }
class FileWriter { save(data: string, path: string) { console.log(`saved ${data} to ${path}`); } }

// Facade
class VideoConversionFacade {
  private decoder = new VideoDecoder();
  private mixer = new AudioMixer();
  private encoder = new VideoEncoder();
  private writer = new FileWriter();

  convert(inputFile: string, outputPath: string): void {
    const video = this.decoder.decode(inputFile);
    const audio = this.mixer.mix(inputFile);
    const result = this.encoder.encode(video, audio);
    this.writer.save(result, outputPath);
  }
}

// Client only needs the facade
const converter = new VideoConversionFacade();
converter.convert('input.avi', '/output/result.mp4');

Facades reduce coupling between clients and complex subsystems. The subsystem can evolve internally without affecting clients as long as the facade contract is preserved.