here is the playgorund on heroku https://railsbuycoinapi.herokuapp.com/graphiql

You're going to create a GraphQL API with one query. The query calculatePrice will accept three required arguments:

• type: This can either be buy or sell, nothing else.
• margin: This is a percentage that will be used in a calculation. Not a fraction, a percentage. For example, if 0.2 is passed into this argument, then the calculation should be done with 0.2%.
• exchangeRate: This is a custom USD/NGN exchange rate that will be used in the calculation detailed below.

• When calculatePrice is called, your API must make a request to Coindesk's API to retrieve the current price of Bitcoin in USD.
• If the type is sell, then your API should subtract the computed value of the margin percentage from the current Bitcoin price it just retrieved.
• If the type is buy, then your API should add the computed value of the margin percentage to the current Bitcoin price it just retrieved.
• Finally, the number calculatePrice responds will be in NGN and not USD. This should be calculated using the exchangeRate argument.

• Your API must mount a GraphiQL interface at /graphiql.
• Cleanliness, readability of code and good separation of concerns are very important with this challenge.
• Writing [good] tests is recommended and will attract extra points!
• Host the API wherever you want. Heroku is a good place to host something like this for free.