#!/usr/bin/env ruby

problem = 4
input = File.readlines("#{problem}.input").map { _1.chomp.chars }.reject { _1.empty? }
#input = DATA.read.split("\n").map(&:chars)

mas = [["M", "M", "S", "S"], ["M", "S", "M", "S"],
       ["S", "M", "S", "M"], ["S", "S", "M", "M"]]

x_mas = 0
matches = []
(1...input.size-1).each do |y|
  (1...input.first.size-1).each do |x|
    next unless input[y][x] == "A"

    corners = [
      input.dig(y-1, x-1),
      input.dig(y-1, x+1),
      input.dig(y+1, x-1),
      input.dig(y+1, x+1)
    ]

    if match = mas.find { corners == _1 }
      matches << [y,x]

      x_mas += 1
    end
  end
end

relevant = matches.map do |match|
  [
    match,
    [match[0] - 1, match[1] - 1],
    [match[0] - 1, match[1] + 1],
    [match[0] + 1, match[1] - 1],
    [match[0] + 1, match[1] + 1]
  ]
end.flatten(1)

# input.each_with_index do |_, y|
#   input[y].each_with_index do |v, x|
#     if relevant.include?([y,x])
#       print v
#     else
#       print "."
#     end
#   end
#   puts
# end

p x_mas
# wrong
# - 1968

__END__
MMMSXXMASM
MSAMXMSMSA
AMXSXMAAMM
MSAMASMSMX
XMASAMXAMM
XXAMMXXAMA
SMSMSASXSS
SAXAMASAAA
MAMMMXMMMM
MXMXAXMASX