require "./common.cr"
require "big"

lines = File.read("day12_input").split "\n"
lines.pop

initial = lines[0].split(": ")[1].chars
original = initial.join("")
rules = lines[2..-1].map do |it|
  split = it.split " => "
  line = split[0]
  into = split[1][0]
  { line.chars, into }
end

class Array
  def has_plant(i)
    return false if i < 0 || i >= size
    return self[i] == '#'
  end
end

def step(initial, rules)
  array = [] of Char
  (-2..initial.size + 2).each do |i|
    rule = [] of Char
    (i-2..i+2).each do |ind|
      rule << (initial.has_plant(ind) ? '#' : '.')
    end

    new_char = rules.find(&.[0].==(rule)).try(&.[1]) || '.'
    array << new_char
  end
  return array
end

def get_total(initial, offset)
  total = 0
  initial.each_with_index do |char, i|
    total += (char == '#') ? (i + offset) : 0
  end
  return total
end

offset = 0

20.times do |it|
  initial = step(initial, rules)
  offset -= 2
end
puts get_total(initial, offset)

total = BigInt.new("0")
fivebil = BigInt.new("50000000000")
first_index = (fivebil - 11)

total += first_index * 57
total += get_total("###.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#.#".chars, 0)
puts total

# 2850000002508