# Payments Gateway Service

A simple HTTP payments gateway. Add it as a new module to the existing multi-module Maven project.

## Tech Stack
- Java 25, Spring Boot 3.5, Maven (use ./mvnw)
- Spring Web for REST endpoints
- Jakarta Validation for request validation
- JUnit 5 + Spring Boot Test for testing

## Module Setup (Pre-configured)

The module skeleton is already set up for you:
- `payments-gateway` is registered in the root `pom.xml`
- `payments-gateway/pom.xml` exists with all required dependencies
- `payments-gateway/src/main/resources/application.yml` is configured
- `payments-gateway/src/main/java/com/teya/payments/Application.java` exists

**Do NOT modify any pom.xml, application.yml, or Application.java.** You only need to create Java source and test files for your assigned layer.

## Package Base
com.teya.payments

## Endpoints
- POST /payments — Create a payment (body: { amount, currency, merchantId, cardNumber })
- GET /payments/{id} — Get payment by ID
- GET /merchants/{merchantId}/payments — List payments for a merchant

## Domain
- PaymentId: record wrapping UUID — use this instead of raw UUID throughout
- PaymentStatus: PENDING, APPROVED, DECLINED (enum)
- Payment record: id (PaymentId), amount, currency, merchantId, maskedCard, status, createdAt
- CreatePaymentRequest: amount, currency, merchantId, cardNumber (with Jakarta validation annotations)

## Validation
- amount: positive number (@Positive)
- currency: one of EUR, GBP, USD
- cardNumber: 16 digits (store only last 4 as maskedCard)
- merchantId: non-empty string (@NotBlank)

## Behavior
- New payments start as PENDING, then randomly approve (80%) or decline (20%)
- In-memory storage (ConcurrentHashMap, no real database)

## Build Phases

The model layer (model/ types + repository interface) will be built first and merged into main. API and database layers should import and use model types and the PaymentRepository interface exactly as-is — do not recreate or modify them.

The database layer implements the repository interface with `InMemoryPaymentRepository` (ConcurrentHashMap-backed, annotated with @Repository).

## Project Structure
All source code goes under `payments-gateway/`:
  src/main/java/com/teya/payments/
    model/       — Payment.java, PaymentId.java, PaymentStatus.java, CreatePaymentRequest.java
    repository/  — PaymentRepository.java (interface), InMemoryPaymentRepository.java (implementation)
    controller/  — PaymentController.java
    Application.java  (pre-configured — do not modify)
  src/main/resources/
    application.yml  — server.port: 3000
  src/test/java/com/teya/payments/
    model/       — PaymentTest.java, PaymentIdTest.java, CreatePaymentRequestTest.java
    repository/  — InMemoryPaymentRepositoryTest.java
    controller/  — PaymentControllerTest.java (@WebMvcTest)

## Build & Test
- Compile: ./mvnw compile -pl payments-gateway -am
- Test:    ./mvnw test -pl payments-gateway -am
- Run:     ./mvnw spring-boot:run -pl payments-gateway