require_relative 'util'

# --- Day 1: Not Quite Lisp ---

# Santa was hoping for a white Christmas, but his weather machine's
# "snow" function is powered by stars, and he's fresh out! To save
# Christmas, he needs you to collect fifty stars by December 25th.

# Collect stars by helping Santa solve puzzles. Two puzzles will be
# made available on each day in the advent calendar; the second puzzle
# is unlocked when you complete the first. Each puzzle grants one
# star. Good luck!

# Here's an easy puzzle to warm you up.

# Santa is trying to deliver presents in a large apartment building,
# but he can't find the right floor - the directions he got are a
# little confusing. He starts on the ground floor (floor 0) and then
# follows the instructions one character at a time.

# An opening parenthesis, `(`, means he should go up one floor, and a
# closing parenthesis, `)`, means he should go down one floor.

# The apartment building is very tall, and the basement is very deep;
# he will never find the top or bottom floors.

# For example:

# - `(())` and `()()` both result in floor 0.
# - `(((` and `(()(()(` both result in floor 3.
# - `))(((((` also results in floor 3.
# - `())` and `))(` both result in floor -1 (the first basement level).
# - `)))` and `)())())` both result in floor -3.

# To what floor do the instructions take Santa?

input = File.open('01.txt') { |f| f.read.chomp }

def easy(string)
  depth = 0
  string.each_char { |c| depth += (c == '(' ? 1 : -1) }
  depth
end

assert(easy('(())') == 0)
assert(easy('()()') == 0)
assert(easy('(((') == 3)
assert(easy('(()(()(') == 3)
assert(easy('))(((((') == 3)
assert(easy('())') == -1)
assert(easy('))(') == -1)
assert(easy(')))') == -3)
assert(easy(')())())') == -3)
puts "easy(input): #{easy(input)}"

# --- Part Two ---

# Now, given the same instructions, find the position of the first
# character that causes him to enter the basement (floor -1). The
# first character in the instructions has position 1, the second
# character has position 2, and so on.

# For example:

# - `)` causes him to enter the basement at character position 1.
# - `()())` causes him to enter the basement at character position 5.

# What is the position of the character that causes Santa to first
# enter the basement?

def hard(string)
  depth = 0
  position = 1
  string.each_char do |c|
    depth += (c == '(' ? 1 : -1)
    return position if depth == -1
    position += 1
  end
  raise "didn't find basement"
end

assert(hard(')') == 1)
assert(hard('()())') == 5)
puts "hard(input): #{hard(input)}"