defmodule Submarine1 do
  import AoC.Util.Tuple

  @sub_key :sub
  @default {0,0}

  def reset(), do: Process.delete(@sub_key)
  defp update(key, f, default), do: Process.put(key, f.(Process.get(key, default)))
  def forward(n), do: update(@sub_key, &pairwise_sum(&1, {n, 0}), @default)
  def down(n), do: update(@sub_key, &pairwise_sum(&1, {0, n}), @default)
  def up(n), do: update(@sub_key, &pairwise_sum(&1, {0, -n}), @default)
  
  def checksum() do
    {x, y} = Process.get(@sub_key, @default)
    x * y
  end
end

defmodule Submarine2 do
  import AoC.Util.Tuple

  @sub_key :sub
  @default {0, 0, 0}

  def reset(), do: Process.delete(@sub_key)
  defp update(key, f, default), do: Process.put(key, f.(Process.get(key, default)))
  def forward(n), do: update(@sub_key, fn {_,_,a} = p -> pairwise_sum(p, {n, a*n, 0}) end, @default)
  def down(n), do: update(@sub_key, &pairwise_sum(&1, {0, 0, n}), @default)
  def up(n), do: update(@sub_key, &pairwise_sum(&1, {0, 0, -n}), @default)
  
  def checksum() do
    {x, y, _} = Process.get(@sub_key, @default)
    x * y
  end
end

gen_code = fn instructions, part ->
  instructions = Code.string_to_quoted(instructions)

  quote do
    unquote(
      case part do
        :part1 -> quote do: import Submarine1
        :part2 -> quote do: import Submarine2
      end
    )

    reset()

    unquote(instructions)

    checksum()
  end
end

solve = fn instructions, part ->
  {soln, _} = Code.eval_quoted(gen_code.(instructions, part))

  soln
end

test_input = """
forward 5
down 5
forward 8
up 3
down 8
forward 2
"""

if solve.(test_input, :part1) != 150 or solve.(test_input, :part2) != 900 do
  raise "unable to solve example input"
end

input = File.read!("./lib/Y2021/day2.txt")

solve.(input, :part2)
|> IO.puts()