Currency Exchange Office Application

A comprehensive currency exchange platform built with .NET technologies, featuring a WCF service backend, console client, and cross-platform MAUI mobile application.

Project Overview

This application allows users to:

• View current and historical currency exchange rates from NBP API (National Bank of Poland)
• Check gold prices
• Register and authenticate users
• Manage currency balances
• Buy and sell currencies
• Track transaction history

Architecture

The solution consists of four main projects:

CurrencyService

• CoreWCF-based SOAP service
• Integrates with NBP API for real-time currency data
• Connects to MongoDB for data persistence
• Provides comprehensive API for currency operations, user management, and trading

CurrencyData

• Contains shared data models and MongoDB repositories
• Implements data access logic for user accounts, balances, and transactions
• Defines DTOs (Data Transfer Objects) for service communication

CurrencyClient

• Console application client for the WCF service
• Allows testing of all service operations
• Provides command-line interface for currency operations

CurrencyMobile

• .NET MAUI cross-platform mobile application
• Targets Android and iOS platforms
• Features MVVM architecture
• Includes:
  • User authentication (login and registration)
  • Currency rates display
  • Trading interface
  • Account balance overview
  • Transaction history

Getting Started

Prerequisites

• .NET 8.0 SDK
• MongoDB (local or remote instance)
• Visual Studio 2022 or Visual Studio Code
• Android SDK or iOS development tools (for mobile app)

Configuration

1. Update the connection string in CurrencyService/appsettings.json to point to your MongoDB instance

2. Configure service endpoints:

   • For development: Uses http://0.0.0.0:5001 and https://0.0.0.0:7074
   • For Android emulator connection: Special IP 10.0.2.2 is used in the mobile app

Running the Application

Running the Service

cd CurrencyService
dotnet run

Running the Console Client

cd CurrencyClient
dotnet run

Running the Mobile App

For Android:

cd CurrencyMobile
dotnet build -t:Run -f net8.0-android

For iOS:

cd CurrencyMobile
dotnet build -t:Run -f net8.0-ios

Features

Currency Data

• Current exchange rates for multiple currencies
• Historical exchange rates with date range selection
• Buy/Sell rates (bid/ask prices)
• Current and historical gold prices

User Management

• User registration with email and password
• Secure authentication with SHA-256 password hashing
• Account balance management

Trading Operations

• Currency purchase (exchange PLN for foreign currency)
• Currency selling (exchange foreign currency for PLN)
• PLN deposits for initial balance
• Error checking for insufficient funds

Mobile Application

• Responsive UI that works across device sizes
• Secure credential storage
• Offline capability for viewing previous transaction history
• Real-time currency rate updates

Database Schema

Users Collection

Stores user authentication data:

• Email (unique identifier)
• Username
• Password hash (SHA-256)
• Creation timestamp

UserBalances Collection

Stores currency balances for each user:

{
  "_id": ObjectId("..."),
  "UserId": ObjectId("..."),
  "Currencies": {
    "PLN": 612.833,
    "USD": 49.764,
    "EUR": 46.852
  }
}

Transactions Collection

Records trading history:

{
  "_id": ObjectId("..."),
  "UserId": ObjectId("..."),
  "Type": "buy|sell",
  "CurrencyCode": "USD",
  "Amount": 79.764,
  "Timestamp": ISODate("2025-04-27T11:03:03.392Z")
}

NBP API Integration

The application integrates with the National Bank of Poland's API:

• Base URL: https://api.nbp.pl/api/
• Endpoints used:
  • Current rate: /exchangerates/rates/a/{code}/
  • Historical rates: /exchangerates/rates/a/{code}/{startDate}/{endDate}/
  • Buy/Sell rates: /exchangerates/rates/c/{code}/
  • Current gold price: /cenyzlota/
  • Historical gold prices: /cenyzlota/{startDate}/{endDate}/

Technical Details

WCF Service Implementation

• Uses CoreWCF for modern .NET implementation
• Configured with BasicHttpBinding for broad client compatibility
• Exposes comprehensive API for all currency operations

Mobile App Implementation

• Built with .NET MAUI for cross-platform compatibility
• Uses MVVM pattern with data binding
• Custom converters for UI presentation
• AppShell-based navigation

Android-macOS Connectivity

• Special configuration for Android emulator to connect to macOS host
• Network security configuration to allow cleartext traffic in development
• Uses 10.0.2.2 special IP from Android emulator to connect to host machine

Future Enhancements

• Password reset functionality
• User profile management
• HTTPS for production environment
• Comprehensive logging and telemetry
• Performance optimizations for larger datasets
• Additional currencies and trading pairs