Currency Converter - Multiplatform App

A modern currency converter application built with Kotlin Multiplatform and Jetpack Compose, following Clean Architecture principles and MVI (Model-View-Intent) pattern. The app provides real-time currency conversion and historical rates for the last three days.

🌟 Features

• Real-time currency conversion with latest exchange rates
• Historical exchange rates for the last three days
• Support for multiple currencies
• Offline support with cached exchange rates
• Clean and intuitive UI built with Compose Multiplatform
• Dark/Light theme support
• Cross-platform support (Android, iOS, Desktop)

🏗️ Architecture

The project follows Clean Architecture principles with MVI pattern:

├── app/
│   ├── core/
│   ├── currency/
│   │   ├── presentation/
│   │   ├── domain/
│   │   └── data/
│   ├── android/
│   ├── ios/
│   └── desktop/

Technical Stack

• Multiplatform: Kotlin Multiplatform
• UI Framework: Jetpack Compose Multiplatform
• Architecture Pattern: MVI (Model-View-Intent)
• Dependency Injection: Koin
• Networking: Ktor
• Local Storage: SQLDelight
• Async Operations: Kotlin Coroutines & Flow
• Testing: KotlinTest, JUnit5
• CI/CD: GitHub Actions

🏛️ Clean Architecture Layers

Presentation Layer

• Implements MVI pattern
• ViewModels handle business logic
• UI States represent screen data
• Events handle user interactions
• Side effects manage one-time actions

Domain Layer

• Contains business logic and rules
• Use cases orchestrate data flow
• Repository interfaces define data contracts
• Models represent business objects

Data Layer

• Implements repository interfaces
• Manages data sources (API/Local)
• Handles data caching
• Maps DTOs to domain models

💉 Dependency Injection

Using Koin for dependency injection across all platforms:

val appModule = module {
    single { CurrencyRepository(get(), get()) }
    single { CurrencyDatabase(get()) }
    viewModel { CurrencyViewModel(get(), get()) }
}

🔄 MVI Implementation

State

data class CurrencyState(
    val currencies: List<Currency> = emptyList(),
    val fromCurrency: Currency? = null,
    val toCurrency: Currency? = null,
    val amount: String = "",
    val convertedAmount: String = "",
    val historicalRates: List<HistoricalRate> = emptyList(),
    val isLoading: Boolean = false,
    val error: String? = null
)

Events

sealed class CurrencyEvent {
    data class SelectFromCurrency(val currency: Currency) : CurrencyEvent()
    data class SelectToCurrency(val currency: Currency) : CurrencyEvent()
    data class AmountChanged(val amount: String) : CurrencyEvent()
    object SwapCurrencies : CurrencyEvent()
    object RefreshRates : CurrencyEvent()
}

Effects

sealed class CurrencyEffect {
    data class ShowError(val message: String) : CurrencyEffect()
    object NavigateToSettings : CurrencyEffect()
}

📱 Screenshots


🚀 Getting Started

Prerequisites

• Android Studio Arctic Fox or later
• Xcode 13 or later (for iOS)
• JDK 11 or later
• Kotlin Multiplatform Mobile plugin

Setup

1. Clone the repository:

git clone https://github.com/yourusername/currency-converter.git

2. Open the project in Android Studio

3. Add your API key in local.properties:

CURRENCY_API_KEY=your_api_key_here

4. Build and run the project

🧪 Testing

The project includes:

• Unit tests for business logic
• Integration tests for repositories
• UI tests for components
• End-to-end tests for critical flows

Run tests:

./gradlew test

🤝 Contributing

1. Fork the repository
2. Create your feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

📄 License

This project is licensed under the MIT License - see the LICENSE file for details

🙏 Acknowledgments

• Exchange Rate API for currency data
• Compose Multiplatform for UI framework
• Kotlin Multiplatform for cross-platform development