cute_pattern_match.ex

# this is a cute pattern match 
# get forms like
# $34.33
# 55
# €123
# €211
# 34 AUD
# 33 EUR
# etc

def convert_amount_str_to_currency_decimal(str) do
    %{
      "possible_currency_symbol" => currency_symbol_optional,
      "expected_positive_decimal_number" => decimal_number_str,
      "possible_currency_code" => currency_code_optional
    } = capture_amount_parts(str)

    %{
      currency:
        process_optional_currency_details(currency_symbol_optional, currency_code_optional),
      decimal: Decimal.new(decimal_number_str),
      raw: decimal_number_str
    }
  end

  defp process_optional_currency_details(symbol, code) do
    case [symbol, code] do
      ["$", ""] ->
        "USD"
      [_, code] ->
        code
      ["£", _] ->
        "GBP"
      ["€", _] ->
        "EUR"
      ["", ""] -> # assume USD
        "USD"
      # let it crash on bad match
    end
  end

  def valid_amount_str?(str) do
    check_valid_amount_str(capture_amount_parts(str))
  end

  defp capture_amount_parts(str) do
    Regex.named_captures(
      ~r/(?<possible_currency_symbol>\D*?)(?<expected_positive_decimal_number>\d{1,}(?:\.?\d{0,})?)(?<possible_currency_code>\D*?)/,
      str
    )
  end

  defp check_valid_amount_str(nil) do
    false
  end

  defp check_valid_amount_str(a) when is_map(a) do
    true
  end