index.ts

interface Handler {
  setNext(handler: Handler): Handler

  handle(request: string): string
}

abstract class AbstractHandler implements Handler {
  private nextHandler: Handler

  public setNext(handler: Handler): Handler {
    this.nextHandler = handler
    return handler
  }

  public handle(request: string): string {
    return this.nextHandler ? this.nextHandler.handle(request) : null
  }
}

class MonkeyHandler extends AbstractHandler {
  public handle(request: string): string {
    if (request === 'Banana') {
      return `Monkey: I'll eat the ${request}`
    }
    return super.handle(request)
  }
}

class SquirrelHandler extends AbstractHandler {
  public handle(request: string): string {
    if (request === 'Nut') {
      return `Squirrel: I'll eat the ${request}.`;
    }
    return super.handle(request);
  }
}

class DogHandler extends AbstractHandler {
  public handle(request: string): string {
    if (request === 'MeatBall') {
      return `Dog: I'll eat the ${request}.`;
    }
    return super.handle(request);
  }
}


function clientCodeContext(handle: Handler) {
  const foods = ['Nut', 'Banana', 'Cup of coffee'];

  for (const food of foods) {
    console.log(`Client: Who wants a ${food}?`);

    const result = handle.handle(food);
    if (result) {
      console.log(`  ${result}`);
    } else {
      console.log(`  ${food} was left untouched.`);
    }
  }
}

export function chainOfResponsability() {

  const monkey = new MonkeyHandler();
  const squirrel = new SquirrelHandler();
  const dog = new DogHandler();
  monkey.setNext(squirrel).setNext(dog);

  console.log('Chain: Monkey > Squirrel > Dog\n');
  clientCodeContext(monkey);
  console.log('');

  console.log('Subchain: Squirrel > Dog\n');
  clientCodeContext(squirrel);
}