start = String.trim(File.read!("inputs/day11.txt"))

startCharlist = String.to_charlist(start)
startNums = Enum.reverse(startCharlist)

defmodule A do
  def incrementPassword([head | tail]) do
    if decreasingStraight?(tail) do
      simpleIncrementPassword([head | tail])
    else
      [second | _] = tail

      if head < second && second < ?z && !(second >= ?h && second <= ?n) do
        [second + 1 | tail]
      else
        [?a | simpleIncrementPassword(tail)]
      end
    end
  end

  def simpleIncrementPassword([?z | tail]) do
    [?a | simpleIncrementPassword(tail)]
  end

  def simpleIncrementPassword([?h | tail]) do
    [?j | tail]
  end

  def simpleIncrementPassword([?n | tail]) do
    [?p | tail]
  end

  def simpleIncrementPassword([?k | tail]) do
    [?m | tail]
  end

  def simpleIncrementPassword([head | tail]) do
    [head + 1 | tail]
  end

  def decreasingStraight?([]) do
    false
  end

  def decreasingStraight?([_]) do
    false
  end

  def decreasingStraight?([_, _]) do
    false
  end

  def decreasingStraight?([a, b, c | _]) when b === a - 1 and c === a - 2 do
    true
  end

  def decreasingStraight?([_ | tail]) do
    decreasingStraight?(tail)
  end

  def twoDifferentPairs?(list) do
    differentPairs =
      Enum.zip(list, Enum.drop(list, 1))
      |> Enum.flat_map(fn
        {a, a} -> [a]
        {_, _} -> []
      end)
      |> Enum.dedup()
      |> Enum.count()

    differentPairs >= 2
  end
end

validPasswords =
  Stream.iterate(startNums, &A.incrementPassword(&1))
  |> Stream.filter(fn password ->
    A.decreasingStraight?(password) &&
      A.twoDifferentPairs?(password)
  end)

nextPasswords =
  Enum.take(validPasswords, 2)
  |> Enum.map(&Enum.reverse(&1))
  |> Enum.join("\n")

IO.puts("New passwords:\n#{nextPasswords}")