advent_of_code_2016_d1_p1.ex

defmodule Day1 do
  def main(file_path) do
    file_path |> File.read! |> process |> IO.puts
  end

  def process(input) do
    input
    |> String.split(", ")
    |> Enum.reduce(%{x: 0, y: 0, dir: "N"}, &reducer/2)
    |> extract_answer
  end

  defp reducer(<<"R", steps::binary>>, %{x: x, y: y, dir: "N"}), do: %{x: x + (steps |> clean_steps), y: y, dir: "E"}
  defp reducer(<<"R", steps::binary>>, %{x: x, y: y, dir: "E"}), do: %{x: x, y: y - (steps |> clean_steps), dir: "S"}
  defp reducer(<<"R", steps::binary>>, %{x: x, y: y, dir: "S"}), do: %{x: x - (steps |> clean_steps), y: y, dir: "W"}
  defp reducer(<<"R", steps::binary>>, %{x: x, y: y, dir: "W"}), do: %{x: x, y: y + (steps |> clean_steps), dir: "N"}
  defp reducer(<<"L", steps::binary>>, %{x: x, y: y, dir: "N"}), do: %{x: x - (steps |> clean_steps), y: y, dir: "W"}
  defp reducer(<<"L", steps::binary>>, %{x: x, y: y, dir: "E"}), do: %{x: x, y: y + (steps |> clean_steps), dir: "N"}
  defp reducer(<<"L", steps::binary>>, %{x: x, y: y, dir: "S"}), do: %{x: x + (steps |> clean_steps), y: y, dir: "E"}
  defp reducer(<<"L", steps::binary>>, %{x: x, y: y, dir: "W"}), do: %{x: x, y: y - (steps |> clean_steps), dir: "S"}

  defp clean_steps(steps) do
    steps
    |> String.trim
    |> String.to_integer
  end

  defp extract_answer(%{x: x, y: y, dir: _}) do
    abs(x) + abs(y)
  end
end