CryptoPal

A console application that sources cryptocurrency market data — such as live prices across multiple fiat currencies and historical price, market cap, and trading volume series — from the CoinGecko public API.

Solution

The solution uses the XML-based solution format. Open CryptoPal.slnx in a compatible IDE (Visual Studio 2022 17.10+, JetBrains Rider, or VS Code) or use the .NET CLI from the repository root.

Prerequisites

• .NET SDK 10.0 or later.

Building and testing

# Restore and build every project in the solution.
dotnet build CryptoPal.slnx

# Run the full unit test suite.
dotnet test CryptoPal.slnx

Running the app

The viewer is a console application driven by command-line arguments. Run it through the .NET CLI by passing the arguments after --:

dotnet run --project src/CryptoPal.ViewerApp -- <command> <args...>

It supports two commands:

price — current prices

Fetches the latest price for one or more coins, each quoted in one or more currencies.

price <coins> <currencies>

Argument	Description	Example
<coins>	Comma-separated CoinGecko coin IDs.	bitcoin,ethereum
<currencies>	Comma-separated target currency codes.	eur,usd

dotnet run --project src/CryptoPal.ViewerApp -- price bitcoin,ethereum eur,usd

history — historical market data

Fetches historical price, market cap, and trading volume data for a single coin over a number of days. (The console output currently lists the daily price series.)

history <coin> <currency> <days>

Argument	Description	Example
<coin>	A single CoinGecko coin ID.	bitcoin
<currency>	A single target currency code.	eur
<days>	Number of days of history to retrieve (integer).	7

dotnet run --project src/CryptoPal.ViewerApp -- history bitcoin eur 7

Coin and currency values are trimmed, and any empty entries are ignored. Invoking the app with no arguments, an unknown command, or the wrong number/type of arguments prints a usage message and exits with a non-zero status code.

Projects

The solution is split into a thin presentation host, an application layer that owns the domain workflow, and an isolated API client, plus a unit test project for each layer that contains logic.

Project	Description
CryptoPal.ViewerApp	Console entry point and presentation host. Parses command-line arguments, configures dependency injection and logging, dispatches to the application service, and formats the results for the terminal. Holds no business logic.
CryptoPal.Application	The application layer. Exposes ICryptocurrencyService, which accepts query objects (GetCurrentPriceQuery, GetHistoricalMarketDataQuery), orchestrates calls to the CoinGecko client, and maps the raw API responses into presentation-friendly view models (CurrentPriceView, HistoricalMarketDataView) using domain types such as Price and DatedValue.
CryptoPal.ApiClient.CoinGecko	A focused, reusable client for the CoinGecko REST API. Wraps an HttpClient (configured via IHttpClientFactory), builds the request URLs, deserializes JSON responses, and translates failures into result objects. It is the only project that knows about CoinGecko's wire format and endpoints.
CryptoPal.Application.UnitTests	Unit tests for the application layer, exercising CryptocurrencyService's orchestration, response-to-view mapping, validation, and failure handling with a mocked CoinGecko client.
CryptoPal.ApiClient.CoinGecko.UnitTests	Unit tests for the CoinGecko client, verifying URL construction, JSON deserialization, and error handling against a fake HttpMessageHandler.

Dependencies

CryptoPal.ViewerApp → CryptoPal.Application → CryptoPal.ApiClient.CoinGecko. The dependency flow points inward toward the API client; lower layers never reference the layers above them.