good_liskov_substitution_principle.ts

type Order = {
  id: number;
  value: number;
  customer: string;
};

class Payment {
  private order: Order;

  constructor(order: Order) {
    this.order = order;
  }

  public getOrder(): Order {
    return this.order;
  }

  public getFinalValue(): number {
    const finalValue = this.order.value;

    return finalValue;
  }
}

class CreditPayment extends Payment {
  private feeValue: number;
  
  constructor(order: Order) {
    super(order);
    this.feeValue = 5;
  }

  public getFinalValue(): number {
    const order = this.getOrder();
    const finalValue = order.value + this.getFee(order.value);

    return finalValue;
  }

  private getFee(value: number): number {
    return (value * this.feeValue) / 100;
  }
}

class PixPayment extends Payment {
  private discountValue: number;
  
  constructor(order: Order) {
    super(order);
    this.discountValue = 10;
  }

  public getFinalValue(): number {
    const order = this.getOrder();
    const finalValue = order.value - this.getDiscount(order.value);

    return finalValue;
  }

  private getDiscount(value: number): number {
    return (value * this.discountValue) / 100;
  }
}