Day 25

Mix.install([{:kino, "~> 0.5.0"}])

Section

input = Kino.Input.textarea("paste input here:")

input = Kino.Input.read(input)

defmodule SNAFU do
  def to_integer(snafu) do
    snafu
    |> String.to_charlist()
    |> Enum.reverse()
    |> Enum.with_index(fn chr, digit ->
      5 ** digit *
        case chr do
          ?2 -> 2
          ?1 -> 1
          ?0 -> 0
          ?- -> -1
          ?= -> -2
        end
    end)
    |> Enum.sum()
  end

  def to_snafu(n, last_power \\ nil)
  def to_snafu(0, last_power), do: List.duplicate(?0, last_power)

  def to_snafu(n, last_power) do
    {pow, max_subtraction} =
      Stream.iterate({1, 0}, fn {pow, _} ->
        {pow + 1, div(5 ** pow, 2)}
      end)
      |> Stream.take_while(fn {_, prev} -> prev < abs(n) end)
      |> Enum.at(-1)
      |> IO.inspect()

    pow = pow - 1

    digit = div(n + div(n, abs(n)) * max_subtraction, 5 ** pow)

    chr_digit =
      case digit do
        2 -> ?2
        1 -> ?1
        0 -> ?0
        -1 -> ?-
        -2 -> ?=
      end

    IO.inspect([digit])
    IO.inspect(n - digit * 5 ** pow)

    # IO.inspect({last_power, pow})
    if last_power do
      List.duplicate(?0, last_power - pow - 1)
    else
      []
    end ++
      [chr_digit | to_snafu(n - digit * 5 ** pow, pow)]
  end
end

SNAFU.to_integer("2=-1=0")
SNAFU.to_snafu(4890)

input
|> String.split()
|> Enum.map(&SNAFU.to_integer/1)
|> Enum.sum()
|> SNAFU.to_snafu()

SNAFU.to_integer("20-1-0=-2=-2220=0011")