defmodule DayFive do
  def part_one(input) do
    shortened = fully_react_new(input)
    # IO.puts shortened
    (String.length shortened) - 1
  end

  def fully_react(input) do
    replacer = ~r/Aa|Bb|Cc|Dd|Ee|Ff|Gg|Hh|Ii|Jj|Kk|Ll|Mm|Nn|Oo|Pp|Qq|Rr|Ss|Tt|Uu|Ww|Vv|Xx|Yy|Zz|aA|bB|cC|dD|eE|fF|gG|hH|iI|jJ|kK|lL|mM|nN|oO|pP|qQ|rR|sS|tT|uU|wW|vV|xX|yY|zZ/
    replace_forever(input, replacer, "")
  end


  def replace_forever(string, pattern, replacement) do
    if Regex.match?(pattern, string) do
      replace_forever(Regex.replace(pattern, string, replacement), pattern, replacement)
    else
      string
    end
  end

  def react([<< char1 >> , << char2 >> | tail]) when char1 == char2 - 32 or char2 == char1 - 32, do: react(tail)
  def react([char | tail]), do: [char | react(tail)]
  def react(""), do: []
  def react([]), do: []

  def fully_react_new(input) do
    # IO.puts "mark"
    Enum.join( fully_react_new(String.codepoints(input), []) )
  end

  def fully_react_new(input, acc) when input == acc, do: acc
  def fully_react_new(input, _acc) do
    # IO.puts("#{length _acc} #{length input}")
    fully_react_new(react(input), input)
  end

  def part_two(input) do
    chars = Enum.map(?a..?z, &(<< &1 >>))
    [{_char, poly} | _ ] = Enum.map(chars, fn char -> {char, String.replace(input, char, "")} end)
        |> Enum.map(fn {char, poly} -> {char, String.replace(poly, String.upcase(char), "") } end)
        |> Enum.map(fn {char, poly} -> {char, fully_react_new(poly)} end)
        |> Enum.sort_by(fn {_char, poly} -> String.length(poly) end)
    # IO.puts poly
    String.length(poly) - 1
  end
end

{:ok, content} = File.read "input5.txt"

IO.puts "Part 1: #{DayFive.part_one(content)}"
IO.puts "Part 2: #{DayFive.part_two(content)}"