sumup

defmodule Sumup.Money do
  @moduledoc """
  SumUp represents money in two different, incompatible shapes depending on
  which API generation you're calling:

    * `Sumup.Money.Float` — legacy major-unit float + currency, used by
      Checkouts, Customers, Transactions and Payouts.
    * `Sumup.Money.MinorUnit` — integer minor units + explicit exponent +
      currency, used by Readers.

  This module intentionally does **not** unify them into one struct: doing
  so would either lose precision (coercing minor units to float) or require
  guessing a currency's exponent (coercing float to minor units). Instead,
  each resource module returns whichever shape the underlying endpoint
  actually returns, and this module offers currency metadata shared by
  both.
  """

  @zero_decimal_currencies ~w(BIF CLP DJF GNF ISK JPY KMF KRW PYG RWF UGX
                               UYI VND VUV XAF XOF XPF HUF)

  @doc """
  Returns the ISO 4217 decimal exponent for a currency code, defaulting to
  `2` for anything not explicitly known.

  Useful for converting `Sumup.Money.Float` amounts to minor units, since
  legacy endpoints don't send the exponent explicitly.

      iex> Sumup.Money.exponent_for("JPY")
      0
      iex> Sumup.Money.exponent_for("EUR")
      2
  """
  @spec exponent_for(String.t()) :: non_neg_integer()
  def exponent_for(currency) when is_binary(currency) do
    if String.upcase(currency) in @zero_decimal_currencies, do: 0, else: 2
  end

  @doc "Returns true if `currency` has no minor unit (e.g. JPY, KRW)."
  @spec zero_decimal?(String.t()) :: boolean()
  def zero_decimal?(currency), do: exponent_for(currency) == 0
end