crypto-wallet

Given a CSV file of crypto assets in a wallet, this program fetches the current price of those assets and generate a report with total updated value, and best/worst performing assets with their percent of variation.

Sample input:

symbol,quantity,price
BTC,0.12345,37870.5058
ETH,4.89532,2004.9774
DOGE,32344.2222,0.3000
ADA,2000.99999,2.5000
USDT,4.999,0.59234
XRP,333.222,0.40999

Sample output:

total=21694.72,best_asset=XRP,best_performance=2.37,worst_asset=DOGE,worst_performance=0.20

This project is part of a take-home assessment for a selection process. The requirements are described in this PDF document.

Design decisions

• the package layout and classes structure is following the Hexagonal Architecture pattern. The I/O logics and pumbling are separate from domain logic and data models, and the domain classes are not coupled with external integrations. This facilitates maintaining automated tests, should facilitate understanding of each component, and expanding the software capabilities without breaking unrelated code. I have decided to use this pattern despite the problem being simple, to demonstrate an extensible design. It is possible to solve the assessment with less classes/code.
• I decided to create a NumberFormatter that would handle all money and number formatting/parsing to make sure that it would run the same on every environment. Depending on Locale or a program-wide configuration was avoided with the intention of increasing stability.
• as part of the requirements, I've added parallelism on fetching the prices with a concurrency of 3 threads. This is done using a custom thread pool that is used by parallelStream() on CoincapAPI.
• error handling is done in a broad sense. I've tried to separate file reading, parsing and fetching errors to facilitate debugging. Other than that, every failure is fatal and exits the program with an error message.
• the price request uses history API of Coincap with a fixated datetime. This is to follow a requirement set of the challenge to facilitate validating the solution correctness.
• The CSV and JSON parsing were built having simplicity in mind and using the lightest of libraries, if any. In a more complex scenario or long term solution, I would probably use commons-csv and gson, as they are more robust and deal with unexpected cases that would still be valid (like ';' as the CSV separator).

Dependencies

This program was built with Java 17, and uses the following libraries and plugins:

• json org lib: used to parse the responses of Coincap API
• junit: to build automated unit and integration tests
• mockito, hamcrest: to test classes that depend on other components by mocking them and checking behavior.
• build-helper and surefire maven plugins: to separate integration and unit tests.
• maven-assembly plugin: to build a JAR file with embedded dependencies.

Build

The project uses Maven to manage building, running tests and other processes.

To build the project run mvn package or execute build.sh.

After that, you can execute the program with java -jar target/crypto-wallet-1.0-jar-with-dependencies.jar or executing run.sh.

Tests

Run all tests with mvn integration-test or executing integration-tests.sh at the project base directory. You can selectively run only unit tests with mvn test or executing unit-tests.sh.