🧾 Billing Service (Currency Conversion Service)

A Spring Boot microservice to calculate the final bill after applying discounts and converting currency based on real-time exchange rates.

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📦 Features

• Calculates percentage and flat discounts based on user type and purchase.
• Converts currency using a third-party API (https://v6.exchangerate-api.com/v6/).
• Basic authentication via Spring Security.
• Caching with @Cacheable for exchange rate calls.
• Unit tests with mocking for all components.
• Maven build with code quality tools and test coverage.
• SonarQube integration-ready.

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🔧 Tech Stack

• Java 21
• Spring Boot
• Spring Security
• Spring Web
• Spring Test
• Maven
• Jacoco (code coverage)
• SonarQube (code quality)
• ExchangeRate-API

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🚀 How to Run

# Clone the repo
git clone https://github.com/danyalafzaal786/bill-service.git
cd bill-service

# Build the project
mvn clean install

# Run the application
mvn spring-boot:run

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🌍 API Endpoint

The service exposes the following API endpoint to calculate the final payable amount based on the provided bill details:

Method	Path	Description
POST	/api/calculate	Returns discounted & converted bill

Sample Request

The request should be sent as a JSON payload with the following structure:

{
  "items": [
    {
      "name": "item1",
      "price": 450,
      "category": "GROCERY"
    },
    {
      "name": "item2",
      "price": 1050,
      "category": "NON_GROCERY"
    }
  ],
  "userType": "EMPLOYEE",
  "customerTenure": 1,
  "originalCurrency": "USD",
  "targetCurrency": "PKR"
}

Sample Response

{
    "totalBill": 1500,
    "totalDiscount": 390.0,
    "conversionRate": 280.8215,
    "totalPayableBillInTargetCurrency": 311711.86500,
    "targetCurrency": "PKR"
}

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✅ Run Tests

Unit Tests

To run the unit tests, execute the following command:

mvn test

Run with Coverage:

To generate test coverage reports using Jacoco, use the following:

mvn clean verify

or

mvn jacoco:report

Generated Jacoco Report:

Once the tests are completed, a report will be generated in target/site/jacoco/. Open the index.html file to view the code coverage summary.

open target/site/jacoco/index.html  # On macOS or Linux
start target/site/jacoco/index.html  # On Windows

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🧼 Code Quality

To run static code analysis and check for code style issues, use the following command:

# Run static analysis (Checkstyle)
mvn checkstyle:check

(Optional) To run a SonarQube scan for code quality, run:

# Run SonarQube scan (make sure SonarQube is running locally)
mvn sonar:sonar \
  -Dsonar.projectKey=billing-service \
  -Dsonar.host.url=http://localhost:9000 \
  -Dsonar.token=sonarqube-token

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🔗 External Integration

• Currency conversion via ExchangeRate-API
• Add your API key to application.properties:

currency.exchange.api.key=your-api-key

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🧠 Assumptions and Future Improvements

This section outlines some design decisions and areas that can be extended in future iterations:

✅ Exception Handling

The current implementation handles basic request flow. Advanced and centralized exception handling (e.g., using @ControllerAdvice or ErrorResponse models) can be added to gracefully manage invalid inputs and system errors.

✅ API Documentation

The project can be extended to integrate OpenAPI/Swagger using Springdoc OpenAPI for auto-generated and interactive API documentation.

✅ Input Validation

Additional validation annotations (e.g., @NotNull, @Min, @Valid) can be added to DTOs to enforce data integrity.

✅ Role-based Authorization

The current basic authentication can be enhanced with role-based access controls for securing different API operations.

✅ Persistent Storage

Currently, the application operates entirely in-memory. A future extension could involve storing user and transaction data in a database (e.g., PostgreSQL, MySQL).

✅ Environment-Specific Config

External configuration (e.g., exchange API keys) can be managed using Spring Profiles or a configuration server for production-readiness.