This is a simple test app written in kotlin to provide payment services. The payment process itself is not implemented, since the intent with this service is to offer a structure to be expanded with possible providers for those services.

This code was developed based on some principles of DDD and hexagonal architecture, so we have basically 3 main structural divisions:

• Application -> is a layer that offers a way for external applications and services to interact with this app. May provide some decoration on the results presented, since some information from domain may not be exposed.
• Domain -> where the business intelligence of this application is concentrated. This domain is exposed through the Payments class, that can express in a easy way what actions are available in this domain.
• Infrastructure -> where infrastructure code is present (like string utilities or logic really specific to infrastructure intelligence, like queries for a specific database or ways to interact with the file system).

To avoid http request threads being blocked during internal processes, a deferred result is returned during controller calls. This is done using an internal function called defer.

The internal processes are executed by just two internal threads. It was done this way thinking about using really small machines on a cloud environment, and this solution already showed efficiency on environments like that (but it is just a starting point. No load tests were done on this app, and maybe other approaches can bring better results).

• Java 8 or higher
• Kotlin 1.2.71
• Maven 3
• Spring-boot (MVC, Actuator, JDBC)
• Undertow (embedded)
• H2 Database (embedded)

We have basically 3 endpoints:

• POST -> /payments to generate a payment request
• GET -> /payments/{ticket} to check the status of a payment request
• POST -> /validation/card as an aux endpoint for card validation

The full documentation can be obtained at http://localhost:8080/swagger-ui.html

Just execute mvn spring-boot:run -> this app runs by default on port 8080. It will use the database file present on project_path/db/database

In case you want to package and distribute this app, just run mvn package -Pprod to build a jar file, and then use the good and old java -jar builded.jar command replacing builded.jar with the generated jar file. To build this project for production, you will need to provide the env variable H2_DB_LOCATION containing the full path for a valid h2 database (the sql script to create it is at payment-api/src/main/resources/database/sql).

Running the default profile (dev profile), the h2 console is enabled. So it is possible to check the database schema and data accessing http://localhost:8080/h2-console

As the payment process is mocked, it will return ACCEPTED for even payment amounts and REJECTED for odd payment amounts.