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Section

[unparsed_crates, unparsed_moves] = File.read!("./input.txt") |> String.split("\n\n")
IO.puts(unparsed_crates)

crates =
  unparsed_crates
  |> String.split("\n")
  |> Enum.drop(-1)
  |> Enum.flat_map(fn x ->
    Enum.chunk_every(to_charlist(x), 4)
    |> Enum.map(&to_string/1)
    |> Enum.map(&String.at(&1, 1))
    |> Enum.zip(1..9)
  end)
  |> Enum.filter(fn {l, _} -> l != " " end)
  |> Enum.reverse()
  |> Enum.reduce(%{}, fn {crate, stack_index}, acc ->
    Map.update(acc, stack_index, [crate], fn stack -> [crate | stack] end)
  end)

IO.puts(unparsed_moves)

moves =
  unparsed_moves
  |> String.split("\n")
  |> Enum.drop(-1)
  |> Enum.map(&String.split/1)
  |> Enum.map(fn [_, n, _, from, _, to] -> [n, from, to] |> Enum.map(&String.to_integer/1) end)
  |> Enum.map(fn [n, from, to] -> {n, from, to} end)

moves
|> Enum.reduce(crates, fn {n, from, to}, c ->
  {taken, c} = Map.get_and_update!(c, from, &Enum.split(&1, n))
  Map.update!(c, to, fn stack -> Enum.reverse(taken) ++ stack end)
end)
|> IO.inspect()
|> Map.values()
|> Enum.map(&hd/1)
|> Enum.join()

moves
|> Enum.reduce(crates, fn {n, from, to}, c ->
  {taken, c} = Map.get_and_update!(c, from, &Enum.split(&1, n))
  Map.update!(c, to, fn stack -> taken ++ stack end)
end)
|> IO.inspect()
|> Map.values()
|> Enum.map(&hd/1)
|> Enum.join()