Revenue Management System

A robust REST API application designed to manage the complex process of Revenue Recognition for a corporate software provider.

Purpose

In enterprise environments, receiving payment and recognizing revenue are two different concepts. A simple transaction (like buying coffee) is recognized immediately, but long-term software licenses and contracts require strict business rules.

This system was built to solve this problem by clearly separating current revenue (actual money received and recognized from fully paid contracts) from predicted revenue (contracts waiting for payment). It provides a full suite of endpoints to manage clients, software products, discounts, contracts, and payments, ensuring that financial data remains consistent and compliant with internal business logic.

Features

• Client Management: Supports both Individual Clients (using PESEL) and Company Clients (using KRS). Includes role-based access control where only Administrators can edit or softly delete clients.
• Software & Contracts: Allows creating time-bound software contracts (3 to 30 days) with optional years of extended support.
• Smart Discount Engine: Automatically applies the highest available promotional discount for a specific timeframe and adds an extra 5% discount for returning customers.
• Payment Processing: Handles partial and full payments. Automatically cancels contracts if payment is not completed before the deadline.
• Revenue Calculation: Calculates both actual and predicted revenue on a company-wide or per-product basis.
• Live Currency Conversion: Integrates with the National Bank of Poland (NBP) public API to instantly convert revenue from PLN to other currencies (e.g., USD, EUR).
• JWT Security: Fully secured API using JSON Web Tokens with role-based authorization.

Tech Stack

• Language: C#
• Framework: .NET 10 / ASP.NET Core Web API
• Database / ORM: Entity Framework Core (Code-First approach)
• Testing: xUnit, EF Core In-Memory Database
• Security: JWT (JSON Web Tokens) Authentication
• Documentation: Swagger / OpenAPI

Architecture & Solutions Used

• Clean Architecture / N-Tier: The project is logically divided into API, Application, Domain, and Infrastructure layers, ensuring the separation of concerns and maintainability.
• Dependency Injection (DI): Heavily utilized for loosely coupled code and easier unit testing.
• Global Exception Handling: Uses modern .AddProblemDetails() and custom middleware to catch domain exceptions (e.g., NotFoundException, ConflictException) and return standardized, clean HTTP error responses (404, 409, 400).
• Soft Delete Pattern: Individual clients are never physically removed from the database to preserve historical contract data. Instead, their personal data is anonymized and marked with an IsDeleted flag.
• External API Integration: Uses HttpClient factory to communicate with external public web services (NBP API) for real-time exchange rates.
• Unit Testing: Business logic (like complex discount calculations in ContractService) is covered by automated unit tests using xUnit and an In-Memory database to simulate real-world scenarios without touching a real SQL server.

How to run locally

1. Clone the repository.
2. Open the solution in JetBrains Rider or Visual Studio.
3. Build the project to restore NuGet packages.
4. Run the API project. The database will be seeded automatically on startup (including a default Admin account).
5. Use the provided .http files or the Swagger UI to interact with the endpoints.