rollex

defmodule Rollex.Lexer do
  def tokenize(_input, []) do
    {:error,  "No valid list of tokens provided!"}
  end
  def tokenize({:ok, input}, valid_tokens) when is_list(valid_tokens) and length(valid_tokens) > 0 do
    input
    |> String.replace(~r/\s/, "") # Remove whitespace
    |> _do_tokenize(valid_tokens, [])
  end

  defp _do_tokenize("", _valid_tokens, current_result) do
    {:ok, Enum.reverse([%Rollex.Tokens.End{} | current_result])}
  end
  defp _do_tokenize(roll_expr, valid_tokens, result) do
    case _first_match(roll_expr, valid_tokens) do
      nil ->
        {:error, "Unrecognized input!"}
      {token, length} ->
        _do_tokenize(String.slice(roll_expr, length..-1), valid_tokens, [token | result])
    end
  end

  defp _first_match(_roll_expr, []) do
    nil
  end
  defp _first_match(roll_expr, [ candidate | tail ] = tokens) when is_list(tokens) and length(tokens) > 0 do
    case String.match?(roll_expr, candidate.regex) do
      true ->
        case Rollex.Token.create(candidate, roll_expr) do
          {:error, _msg} = result ->
            result
          result ->
            result
        end
      false ->
        _first_match(roll_expr, tail)
    end
  end
end