Convert numeric to formatted string with cash unit by format

numeric.rb

# frozen_string_literal: true

# Numeric
class Numeric
  # convert numeric (integer or float)
  # to formatted string with cash unit
  #
  # @example
  #   42_000.to_cash '$', ',', '.', '%<unit>s%<amount>.2f' # => $42.000,00
  #   42_000.42.to_cash 'RUB', ',', ' ', '%<amount>.2f %<unit>s' # => 42 000,42 RUB
  #
  # @param [String] unit
  # @param [String] separator
  # @param [String] delimiter
  # @param [String] format
  def to_cash(unit, separator, delimiter, format = '%<amount>.2f %<unit>s')
    value = {
      unit: unit,
      amount: self
    }

    amount_formatted = format % value
    amount_formatted = amount_formatted.gsub '.', separator

    position = amount_formatted.match(separator).begin(0) - 3
    until /[0-9]/.match(amount_formatted[position]).nil?
      amount_formatted.insert position, delimiter
      position -= 3
    end

    amount_formatted
  end
end