iyzico coding challenge

Thank you for applying to work in Iyzico Engineering.

As part of our interview process, we expect you to complete a coding challenge in order for us to better understand your coding skills. The challenge is a Java8 + Spring Boot project which uses HSQLDB as the database.

Question 1: Product Management

Most of iyzico's merchants sell products online. For these merchants the necessary REST services are listed below. We kindly ask you to implement them.

Requirements

• Product adding, removing or updating services.
• Product listing service which returns product name, description, remaining stock count and price.
• Payment service for the end user to buy their selected product.
• A product should not be sold for more than its stock.
• Customers paying for the same product at the same time should not buy the product if the stock is depleted. (i.e. if there are 2 stocks left and 3 customers pay at the same time, first 2 successful should buy the product and the 3rd one should fail with an appropriate message.)
• No front end is necessary.
• Test coverage for the implemented service should be above 80%. We expect both Integration and unit tests.
• Bonus: Iyzico payment integration can be implemented for payment step. Reference: https://dev.iyzipay.com/

Question 2 : Latency Management

Iyzico provides its payment service by calling bank endpoints. The bank responses are persisted to database.In IyzicoPaymentServiceTest.java class we have simulated 100 customers calling the payment service.

    public void pay(BigDecimal price) {
        //pay with bank
        BankPaymentRequest request = new BankPaymentRequest();
        request.setPrice(price);
        BankPaymentResponse response = bankService.pay(request);

        //insert records
        Payment payment = new Payment();
        payment.setBankResponse(response.getResultCode());
        payment.setPrice(price);
        paymentRepository.save(payment);
        logger.info("Payment saved successfully!");
    }

In the simulation for some reason the bank response times take ~5 seconds. Due to this latency, a database connection problem is encountered after some time. (Running the IyzicoPaymentServiceTest.java class displays "Connection is not available, request timed out after 30005ms." error after some time.)

Find a way to persist bank responses to the database in this situation.

Requirements

• DB connection pool should stay the same.
• BankService.java, PaymentServiceClients.java and IyzicoPaymentServiceTest.java classes should not be changed.
• In case of an error, there should not be any dirty data in the database.