require_relative 'util'
require 'openssl'

# --- Day 4: The Ideal Stocking Stuffer ---

# Santa needs help mining some AdventCoins (very similar to bitcoins)
# to use as gifts for all the economically forward-thinking little
# girls and boys.

# To do this, he needs to find MD5 hashes which, in hexadecimal, start
# with at least five zeroes. The input to the MD5 hash is some secret
# key (your puzzle input, given below) followed by a number in
# decimal. To mine AdventCoins, you must find Santa the lowest
# positive number (no leading zeroes: 1, 2, 3, ...) that produces such
# a hash.

# For example:

# - If your secret key is `abcdef`, the answer is `609043`, because
#   the MD5 hash of `abcdef609043` starts with five zeroes
#   (`000001dbbfa`...), and it is the lowest such number to do so.
# - If your secret key is `pqrstuv`, the lowest number it combines
#   with to make an MD5 hash starting with five zeroes is `1048970`;
#   that is, the MD5 hash of `pqrstuv1048970` looks like
#   `000006136ef`....

input = 'ckczppom'

def md5(input)
  OpenSSL::Digest::MD5.hexdigest(input)
end

def easy(input)
  i = 1
  loop do
    return i if md5("#{input}#{i}").start_with?('00000')
    i += 1
  end
end

assert(easy('abcdef') == 609_043)
assert(easy('pqrstuv') == 1_048_970)
puts "easy(input): #{easy(input)}"

# --- Part Two ---
# Now find one that starts with six zeroes.

def hard(input)
  i = 1
  loop do
    return i if md5("#{input}#{i}").start_with?('000000')
    i += 1
  end
end

puts "hard(input): #{hard(input)}"