currency-rate

Converter for fiat and crypto currencies

Installation

gem install currency-rate

or in Gemfile

gem "currency-rate"

Usage

Basically, all you'll need is to use the top level class to fetch any rates you want. For example:

CurrencyRate.convert('Bitstamp', amount: 5, from: 'BTC', to: 'USD')
CurrencyRate.convert('Bitstamp', amount: 2750, from: 'USD', to: 'BTC')
CurrencyRate.convert('Bitstamp', amount: 1000, from: 'USD', to: 'EUR')

In the third case, because Bitstamp doesn't really support direct conversion from USD to EUR, the 1000 will first be converted to BTC, then the BTC amount will be converted to EUR.

This introduced the concept of anchor currency. For all Btc adapters in this lib, it's set to BTC by default. For all Fiat adapters it's set to USD by default. To specify anchor currency manually, simply pass it as another argument, for example:

CurrencyRate.convert('Bitstamp', amount: 1000, from: 'USD', to: 'EUR', anchor_currency: 'BTC')

You can also use #get method to get just the rate. It basically works as #convert, but only returns the rate and the method signature (attributes passed) is different - attributes are not named:

CurrencyRate.get('Bitstamp', 'BTC', 'USD') # => 750
CurrencyRate.get('Bitstamp', 'USD', 'BTC') # => 0.001818182

In the second case, we are trying to get the exchange rate for USD/BTC pair, which literally means "how much in BTC would 1 USD be?". If the source (Bitstamp, in this case) doesn't provide the inverted rate, the Adapter inverts the rate itself using the exchange rate for BTC/USD.

You can also use anchor_currency argument with #get:

CurrencyRate.get('Bitstamp', 'USD', 'EUR', anchor_currency: 'BTC')

For a list of available adapters, please see lib/btc_adapters and lib/fiat_adapters. To specify an adapter for #convert or #get, remove the last Adapter part from its name.

Caching and Storage

By default, a simple in-memory caching mechanism with a timeout of 1800 seconds is set. To change the default timeout and also implement your very own caching mechanism you can try reloading CurrencyRate::Storage methods and writing your own functionality, storing data in Redis, for example.

While I agree it'd be nicer to have the timeout set somewhere in CurrencyRate class, for simplicity reasons I've avoided that. It also makes sense that the Storage class is responsible for how and when to store/fetch data, not other classes.

Credits

This gem was extracted from straight gem, thanks to all the people who added various exchange rate adapters and contributed code.

TODO

  1. Remove code duplication in Adapters, specifically for #rate_for, #invert_rate and #currency_pair_rate methods.

  2. Allow both lower case and upper case currency codes.

  3. Clean up tests, I have a feeling there some completely useless ones.

  4. Adapters should have a default "to" currency. For example, everyone knows Bitfinex trades BTC for USD mostly.