--- Day 4: Ceres Search ---

"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!

As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: XMAS.

This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of XMAS - you need to find all of them. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:

..X...
.SAMX.
.A..A.
XMAS.S
.X....
The actual word search will be full of letters instead. For example:

MMMSXXMASM
MSAMXMSMSA
AMXSXMAAMM
MSAMASMSMX
XMASAMXAMM
XXAMMXXAMA
SMSMSASXSS
SAXAMASAAA
MAMMMXMMMM
MXMXAXMASX
In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:

....XXMAS.
.SAMXMS...
...S..A...
..A.A.MS.X
XMASAMX.MM
X.....XA.A
S.S.S.S.SS
.A.A.A.A.A
..M.M.M.MM
.X.X.XMASX
Take a look at the little Elf's word search. How many times does XMAS appear?

Your puzzle answer was 2434.

--- Part Two ---

The Elf looks quizzically at you. Did you misunderstand the assignment?

Looking for the instructions, you flip over the word search to find that this isn't actually an XMAS puzzle; it's an X-MAS puzzle in which you're supposed to find two MAS in the shape of an X. One way to achieve that is like this:

M.S
.A.
M.S
Irrelevant characters have again been replaced with . in the above diagram. Within the X, each MAS can be written forwards or backwards.

Here's the same example from before, but this time all of the X-MASes have been kept instead:

.M.S......
..A..MSMS.
.M.S.MAA..
..A.ASMSM.
.M.S.M....
..........
S.S.S.S.S.
.A.A.A.A..
M.M.M.M.M.
..........
In this example, an X-MAS appears 9 times.

Flip the word search from the instructions back over to the word search side and try again. How many times does an X-MAS appear?
cont = File.readlines("day4input.txt").map { |i| i.strip.chars }

def get_neighbors(matrix, x, y)
  rows = matrix.length
  cols = matrix[0].length
  neighbors = []

  directions = [
    [-1, -1], [-1, 0], [-1, 1],
    [0, -1], [0, 0], [0, 1],
    [1, -1], [1, 0], [1, 1]
  ]

  directions.each do |dx, dy|
    nx, ny = x + dx, y + dy
    if nx >= 0 && nx < rows && ny >= 0 && ny < cols
      neighbors << matrix[nx][ny]
    end
  end

  neighbors
end

def check(matrix)
  mas = ["MAS", "SAM"]
  d = [matrix[0][0], matrix[1][1], matrix[2][2]].join
  a = [matrix[0][2], matrix[1][1], matrix[2][0]].join
  mas.include?(d) && mas.include?(a) ? 1 : 0
end

t = 0

(0...cont.length).each do |x|
  (0...cont[x].length).each do |y|
    next if [0, 139].include?(x) || [0, 139].include?(y)

    if cont[x][y] == "A"
      neighbors = get_neighbors(cont, x, y)
      matrix = [neighbors[0..2], neighbors[3..5], neighbors[6..8]]

      t += check(matrix)
    end
  end
end

puts t