require_relative 'util'
require 'set'

# --- Day 11: Corporate Policy ---

# Santa's previous password expired, and he needs help choosing a new
# one.

# To help him remember his new password after the old one expires,
# Santa has devised a method of coming up with a password based on the
# previous one. Corporate policy dictates that passwords must be
# exactly eight lowercase letters (for security reasons), so he finds
# his new password by incrementing his old password string repeatedly
# until it is valid.

# Incrementing is just like counting with numbers: `xx`, `xy`, `xz`,
# `ya`, `yb`, and so on. Increase the rightmost letter one step; if it
# was `z`, it wraps around to `a`, and repeat with the next letter to
# the left until one doesn't wrap around.

# Unfortunately for Santa, a new Security-Elf recently started, and he
# has imposed some additional password requirements:

# - Passwords must include one increasing straight of at least three
#   letters, like `abc`, `bcd`, `cde`, and so on, up to `xyz`. They
#   cannot skip letters; `abd` doesn't count.
# - Passwords may not contain the letters `i`, `o`, or `l`, as these
#   letters can be mistaken for other characters and are therefore
#   confusing.
# - Passwords must contain at least two different, non-overlapping
#   pairs of letters, like `aa`, `bb`, or `zz`.

# For example:

# - `hijklmmn` meets the first requirement (because it contains the
#   straight `hij`) but fails the second requirement requirement
#   (because it contains `i` and `l`).
# - `abbceffg` meets the third requirement (because it repeats `bb`
#   and `ff`) but fails the first requirement.
# - `abbcegjk` fails the third requirement, because it only has one
#   double letter (`bb`).
# - The next password after `abcdefgh` is `abcdffaa`.
# - The next password after `ghijklmn` is `ghjaabcc`, because you
#   eventually skip all the passwords that start with `ghi`..., since
#   `i` is not allowed.

# Given Santa's current password (your puzzle input), what should his
# next password be?

input = 'vzbxkghb'

STRAIGHTS = 'abcdefghijklmnopqrstuvwxyz'.each_char.each_cons(3).map(&:join)

def first_requirement?(pw)
  STRAIGHTS.any? { |s| pw.include?(s) }
end

def second_requirement?(pw)
  !pw[/[iol]/]
end

def third_requirement?(pw)
  Set.new(pw.scan(/(.)\1/)).length >= 2
end

def valid_password?(pw)
  first_requirement?(pw) && second_requirement?(pw) && third_requirement?(pw)
end

def easy(input)
  loop do
    input = input.next
    return input if valid_password?(input)
  end
end

assert(first_requirement?('hijklmmn'))
assert(!second_requirement?('hijklmmn'))
assert(!first_requirement?('abbceffg'))
assert(third_requirement?('abbceffg'))
assert(!third_requirement?('abbcegjk'))
assert(easy('abcdefgh') == 'abcdffaa')
assert(easy('ghijklmn') == 'ghjaabcc')
pw = easy(input)
puts "easy(input): #{pw}"

# --- Part Two ---

# Santa's password expired again. What's the next one?

puts "easy(input(input)): #{easy(pw)}"