fn_parens.ex

use Dogma.RuleBuilder

defrule Dogma.Rule.FnParens, [] do
  @moduledoc """
  A rule that enforces using parens in a fn that takes parens
  """
  @fn_pattern ~r/fn(\s*)(\(|->)?/

  def test(rule, script) do
    script.processed_lines
    |> Enum.filter(fn(line) -> check_line(rule, line) end)
    |> Enum.map(fn(line) ->  error(rule, line) end)
  end

  defp check_line(rule, {pos, line}) do
    @fn_pattern
    |> Regex.scan(line)
    |> Enum.map(&(check_matches(rule, pos, &1)))
    |> Enum.reject(fn(r) -> r === :ok end)
  end

  defp check_matches(rule, pos, [_full, spaces]) do
    error(pos, "Parens required for fn with params")
  end
  defp check_matches(rule, pos, [_full, " ", "->"]), do: :ok
  defp check_matches(rule, pos, [_full, other_spacing, "->"]) do
    error(pos, "1 space required between fn and ->")
  end
  defp check_matches(rule, pos, [_full, "", "("]), do: :ok
  defp check_matches(rule, pos, [_full, other_spacing, "("]) do
     error(pos, "No space allowed between fn and (")
  end
  defp check_matches(_, pos, _) do
    error(pos, "Bad pattern check, halp")
  end

  defp error(pos, error_msg) do
    %Error{
      rule:     __MODULE__,
      message:  error_msg,
      line:     Dogma.Script.line(15), # pos),
    }
  end
end