Represent prices as BigDecimal

[jon-signal]

The MessageBird API transmits prices as floating point literals rather than arbitrary-precision decimal numbers. This can lead to loss-of-precision issues down the line. For example, consider this (real-world!) API response:

{
  "price": {
    "amount": 0.0018,
    "currency": "USD"
  },
}

If we try to convert the price above into a Joda Money Money instance (again, just as an example), then we run into:

java.lang.ArithmeticException: Scale of amount 0.0017999999690800905 is greater than the scale of the currency USD

While I think it might be wise to transmit the price as a string at the API level, I think there are also things we can do in the client library to help. This pull request, for example, parses the price as a BigDecimal. It preserves the return type of the existing Price#getAmount() method, but introduces a Price#getAmountDecimal() method that returns the BigDecimal representation (ideally without loss of precision).

Although it's beyond the scope of this pull request, if the upstream API response were to change to something like this:

{
  "price": {
    "amount": 0.0018,
    "amountDecimal": "0.0018",
    "currency": "USD"
  },
}

…then this change would be forward-compatible from a Java binary perspective, too.

[denizkilic]

Hi @jon-signal, I agree with using BigDecimal here. The PR looks fine, merging it and the new release will be created.

[jon-signal]

Thanks kindly!

[jon-signal]

@denizkilic Apologies—I've just noticed one problem here. We've changed the structure of this class, and so the serialVersionUID needs to change, too!