defmodule Aoc2024.Day07 do
  def parse(input) do
    input 
      |> String.split("\n", trim: true)
      |> Enum.map(fn x -> x |> String.split(": ") |> Enum.into([]) end)
      |> Enum.map(fn [x, y] -> {String.to_integer(x), y |> String.split(" ") |> Enum.map(&String.to_integer/1)} end)
      |> Enum.into([])
  end

  def part1(input) do
    input
      |> Enum.map(fn {target, numbers} -> Task.async(fn -> compute(target, numbers) end) end)
      |> Enum.map(&Task.await/1)
      |> Enum.filter(&Kernel.is_integer/1)
      |> Enum.sum()
  end

  defp compute(target, numbers), do: compute(target, Enum.reverse(numbers), target)
  defp compute(_, _, current) when current < 0, do: nil
  defp compute(target, [], 0), do: target
  defp compute(_, _, 0), do: nil 
  defp compute(_, [], _), do: nil 
  defp compute(target, [x | numbers], current) do
    if rem(current, x) == 0 do
      if compute(target, numbers, div(current, x)) == target do
        target
      else 
        compute(target, numbers, current - x)
      end
    else 
      compute(target, numbers, current - x)
    end
  end

    

  def part2(input) do
    input
      |> Enum.map(fn {target, numbers} -> Task.async(fn -> compute2(target, numbers) end) end)
      |> Enum.map(&Task.await/1)
      |> Enum.filter(&Kernel.is_integer/1)
      |> Enum.sum()
  end

  defp compute2(target, numbers), do: compute2(target, Enum.reverse(numbers), target)
  defp compute2(_, _, current) when current < 0, do: nil
  defp compute2(target, [], 0), do: target
  defp compute2(_, _, 0), do: nil 
  defp compute2(_, [], _), do: nil 
  defp compute2(target, [x | numbers], current) do
    s_c = current |> Integer.to_string()
    s_x = x |> Integer.to_string()
    nc = s_c |> String.replace_suffix(s_x, "") 
    cond do
      s_c |> String.ends_with?(s_x)
        and nc != ""
        and compute2(target, numbers, nc |> String.to_integer()) == target ->
        target
      rem(current, x) == 0 and compute2(target, numbers, div(current, x)) == target -> 
        target
      true -> 
        compute2(target, numbers, current - x)
    end
  end
end