class Part<T> {
  constructor(
    public type: string,
    public value: T
  ) {}
}

class Director<T> {
  constructor(public builder: Builder<T>) {}

  construct(structure: Array<Part<T>>) {
    for (const part of structure) {
      switch (part.type) {
        case "a": {
          this.builder.buildPartA(part);
          break;
        }

        case "b": {
          this.builder.buildPartB(part);
          break;
        }

        default: {
          this.builder.buildPartA(part);
        }
      }
    }
  }
}

class Product<U> {
  constructor(public result: U[] = []) {}

  append(object: U) {
    this.result.push(object);
  }

  get() {
    return this.result;
  }
}

class Builder<T> {
  buildPartA(_part: Part<T>) {
    // Unimplemented
  }

  buildPartB(_part: Part<T>) {
    // Unimplemented
  }
}

class ConcreteBuilder1<T, U> extends Builder<T> {
  product = new Product<U>();

  buildPartA(part: Part<T>) {
    // Example building a part
    const value: U = String(part.value).toLowerCase() as unknown as U;
    this.product.append(value);
  }

  buildPartB(part: Part<T>) {
    // Example building a part
    const value: U = String(part.value).toUpperCase() as unknown as U;
    this.product.append(value);
  }

  getResult() {
    return this.product;
  }
}

// Other builders:
// class ConcreteBuilder2<T, U> extends Builder<T> {
// class ConcreteBuilder3<T, U> extends Builder<T> {

const client = {
  run() {
    const concreteBuilder = new ConcreteBuilder1<string, string>();
    const director = new Director(concreteBuilder);
    director.construct([new Part("a", "Hello"), new Part("b", "World")]);
    const result = concreteBuilder.getResult();
    console.log(result.get());
  }
};

client.run();