Day 16

Mix.install([
  {:kino, "~> 0.6.2"}
])

Input

input = Kino.Input.textarea("In put here:")

data =
  input
  |> Kino.Input.read()
  |> Base.decode16!()

defmodule Bits do
  def apply_operation(op, data) do
    IO.puts("Performing op #{op} on #{inspect(data)}")

    case op do
      0 -> Enum.sum(data)
      1 -> Enum.product(data)
      2 -> Enum.min(data)
      3 -> Enum.max(data)
      5 -> if(Enum.at(data, 0) > Enum.at(data, 1), do: 1, else: 0)
      6 -> if(Enum.at(data, 0) < Enum.at(data, 1), do: 1, else: 0)
      7 -> if(Enum.at(data, 0) == Enum.at(data, 1), do: 1, else: 0)
      _ -> :error
    end
  end

  def parse(<>) when id == 4 do
    IO.puts("Parsing literal ver #{version}")

    with {data, rest} <- parse_payload(payload) do
      size = bit_size(data)
      <> = data
      IO.puts("Value: #{inspect(val)} ")
      {[val], version, rest}
    end
  end

  def parse(<>) do
    IO.puts("Ver #{version},  id #{id}, length #{num} packes ")

    {data, ver, rem} =
      for _i <- 1..num,
          reduce: {[], version, rest} do
        {data, vsum, rest} ->
          # IO.puts("#{i} / #{num}, rest: #{inspect(rest)}")
          {c, ver, rem} = parse(rest)
          {data ++ c, ver + vsum, rem}
      end

    {[apply_operation(id, data)], ver, rem}
  end

  def parse(<>) do
    IO.puts("Ver #{version},  id #{id}, length #{length} bits ")

    <> = rest

    {data, ver, <<>>} = parse_sequence(<>)

    {[apply_operation(id, data)], version + ver, unparsed}
  end

  def parse_sequence(data) do
    {data, ver, remaining} = parse(data)

    case remaining do
      <<>> ->
        {data, ver, <<>>}

      _ ->
        {rest_data, rest_ver, rest_rem} = parse_sequence(remaining)
        {data ++ rest_data, ver + rest_ver, rest_rem}
    end
  end

  def parse_payload(<<1::1, bits::4, rest::bits>>) do
    with {rest_parsed, rest_unparsed} = parse_payload(rest) do
      # |> IO.inspect(label: "literal")
      {<>, rest_unparsed}
    end
  end

  def parse_payload(<<0::1, bits::4, rest::bits>>), do: {<>, rest}
end

Part 1

Bits.parse(data)