Symfony currency exchange demo

Keynotes

• Using a small Symfony installation as possible
• Using SQLite database for simplicity but with price of some caveats
  • There are no real decimal or numeric data type so emulation with harcoded 16,8 precision is used
  • There are no INSERT IGNORE method so unique constraint violation are just skipped
• There is \App\Services\RatesUpdater::makeReverseRate method to make reverse exchange rate. However, separate buy and sell rates should be used in real life.
• There are two tables for rates: rates with provided data and pairs with all currencies combinations ( triangles). Triangulations are implemented in the \App\Services\RatesTriangulator service. It's inspired by http://www.dpxo.net/articles/fx_rate_triangulation_sql.html
• There was some date errors in ECB rates so rates' date are writing to the tables but not using in the finally exchange calculation
• There are simple functional tests with fake data from \App\Providers\FakeRatesProvider provider

There are two commands

• currency:update - Update currencies exchange rates
• currency:exchange - Exchange currency

And two installation & usage ways: local PHP and Docker.

1. Local-way

Requirements

• PHP 8.1
  • ext-bcmath
  • ext-ctype
  • ext-iconv
  • ext-intl
  • ext-pdo_sqlite
  • ext-simplexml
  • ext-sqlite3
• Composer

Installation

git clone https://github.com/vladimirmartsul/symfony-exchange-demo.git
cd symfony-exchange-demo
composer install --no-dev --no-interaction
php bin/console doctrine:database:create
php bin/console doctrine:migrations:migrate --no-interaction

Usage

Update currency rates first

php bin/console currency:update

Use

php bin/console currency:exchange <amount> <from> <to>

For example

php bin/console currency:exchange 2 EUR BTC

should output

[OK] 2 EUR is 0.00005254 BTC

Testing

cd symfony-exchange-demo
echo APP_ENV=test > .env.local
composer install --no-interaction
php bin/console doctrine:database:create
php bin/console doctrine:migrations:migrate --no-interaction
php bin/phpunit

2. Docker-way

Requirements

Docker Desktop (Windows, MacOS) or docker-cli and docker-compose (Linux)

Installation

git clone https://vladimirmartsul@bitbucket.org/vladimirmartsul/symfony-exchange-demo.git
cd symfony-exchange-demo
docker compose up --build

Currency rates will be updated during build.

Usage

docker compose run symfony-exchange-demo currency:exchange <amount> <from> <to>

For example

docker compose run symfony-exchange-demo currency:exchange 2 EUR BTC

should output

[OK] 2 EUR is 0.00005254 BTC

Testing

cd symfony-exchange-demo
echo APP_ENV=test > .env.local
docker compose run symfony-exchange-demo composer install --no-interaction
docker compose run symfony-exchange-demo doctrine:database:create
docker compose run symfony-exchange-demo doctrine:migrations:migrate --no-interaction
docker compose run symfony-exchange-demo bin/phpunit

Extending

There is ability to add new exchange rates providers.

The new provider must implement \App\Contracts\RatesProviderInterface interface with constructor __construct(\Symfony\Contracts\HttpClient\HttpClientInterface $client, string $url, string $base) and __invoke(): App\Dto\Rate[] method.

However, in many cases it is enough to extend abstract \App\Providers\RatesProvider class and implement \App\Providers\RatesProvider::transform(array $data): RateDto[] method.

Additionaly the new provider must be registered in config/services.yaml with its own arguments and app.rates_provider tag. Real params such as URL and base currency must be writen in .env file.