#!/usr/bin/env elixir
defmodule Day21 do
  @numpad %{
    "7" => {0, 0},
    "8" => {1, 0},
    "9" => {2, 0},
    "4" => {0, 1},
    "5" => {1, 1},
    "6" => {2, 1},
    "1" => {0, 2},
    "2" => {1, 2},
    "3" => {2, 2},
    "0" => {1, 3},
    "A" => {2, 3}
  }

  @keypad %{
    "^" => {1, 0},
    "A" => {2, 0},
    "<" => {0, 1},
    "v" => {1, 1},
    ">" => {2, 1}
  }

  def part1(input) do
    Enum.map(input, &complexity/1)
  end

  def complexity(code) do
    length =
      code
      |> derive_keys(@numpad)
      # asdfsadfsdafdfs for the robot, some derived combinations are shorter, why?
      # Maybe going left non-sequentially is expensive because of round trips to the A buttom
      # so sequentially is cheaper?
      # Need to figure out what the situation that causes a longer sequence is
      |> derive_keys(@keypad)
      |> derive_keys(@keypad)
      |> byte_size()
      |> dbg()

    {numeric, "A"} = Integer.parse(code)
    dbg(numeric)

    numeric * length
  end

  def derive_keys(seq, pad) do
    String.graphemes("A" <> seq)
    |> Enum.chunk_every(2, 1, :discard)
    |> Enum.map_join("", fn [a, b] -> keys(a, b, pad) <> "A" end)
  end

  def numpad, do: @numpad

  def keys(a, b, pad) do
    {x1, y1} = Map.fetch!(pad, a)
    {x2, y2} = Map.fetch!(pad, b)
    dx = x2 - x1
    dy = y2 - y1

    keys_x = keys_x(dx)
    keys_y = keys_y(dy)

    # avoid the gap
    if dx < 0 do
      keys_y <> keys_x
    else
      keys_x <> keys_y
    end
  end

  def keys_x(-2), do: "<<"
  def keys_x(-1), do: "<"
  def keys_x(0), do: ""
  def keys_x(1), do: ">"
  def keys_x(2), do: ">>"

  def keys_y(-3), do: "^^^"
  def keys_y(-2), do: "^^"
  def keys_y(-1), do: "^"
  def keys_y(0), do: ""
  def keys_y(1), do: "v"
  def keys_y(2), do: "vv"
  def keys_y(3), do: "vvv"

  def keypad, do: @keypad

  def part2(_input) do
    :ok
  end

  def input do
    with [input_filename] <- System.argv(),
         {:ok, input} <- File.read(input_filename) do
      String.split(input, "\n", trim: true)
    else
      _ -> :error
    end
  end

  #######################
  # HERE BE BOILERPLATE #
  #######################

  def run do
    case input() do
      :error -> print_usage()
      input -> run_parts_with_timer(input)
    end
  end

  defp run_parts_with_timer(input) do
    run_with_timer(1, fn -> part1(input) end)
    run_with_timer(2, fn -> part2(input) end)
  end

  defp run_with_timer(part, fun) do
    {time, result} = :timer.tc(fun)
    IO.puts("Part #{part} (completed in #{format_time(time)}):\n")
    IO.puts("#{inspect(result)}\n")
  end

  defp format_time(μsec) when μsec < 1_000, do: "#{μsec}μs"
  defp format_time(μsec) when μsec < 1_000_000, do: "#{μsec / 1000}ms"
  defp format_time(μsec), do: "#{μsec / 1_000_000}s"

  defp print_usage do
    IO.puts("Usage: elixir day21.exs input_filename")
  end
end

# Day21.run()