Write a WebAPI with only 1 method called “ProcessPayment” that receives a request like this

• CreditCardNumber (mandatory, string, it should be a valid CCN)
• CardHolder: (mandatory, string)
• ExpirationDate (mandatory, DateTime, it cannot be in the past)
• SecurityCode (optional, string, 3 digits)
• Amount (mandatoy decimal, positive amount) Write a Payment domain/entity with the same properties as the request and a second entity to store the payment state (pending, processed, failed). Use Entity framework code first approach, write entity configurations and generate the migrations. The response of this method should be 1 of the followings based on
• Payment is processed: 200 OK
• The request is invalid: 400 bad request
• Any error: 500 internal server error
• The request should be validated before processed. The payment could be processed using different payment providers (external services) called:
• IExpensivePaymentGateway or
• ICheapPaymentGateway. The payment gateway that should be used to process each payment follows the next set of business rules: a) If the amount to be paid is less than £20, use ICheapPaymentGateway. b) If the amount to be paid is £21-500, use IExpensivePaymentGateway if available. Otherwise, retry only once with ICheapPaymentGateway. c) If the amount is > £500, try only PremiumPaymentService and retry up to 3 times in case payment does not get processed d) Store/update the payment and payment state entities created previously once the processing is completed. Bonus:
• Use repository/unit of work patterns
• Use eager loading for all entities Recommendations :
• The classes should be written in such a way that they are easy to test.
• Write enough unit tests to cover the developed code (at least 1).
• Use SOLID principles.
• Use any IOC you think is best.
• Use Entity Framework. Optional:
• Use AutoMapper or other mapping tools of your choice
• Use .Net Core to develop the WebAPI and Entity Framework Core.