(require :uiop)
(load (sb-ext:posix-getenv "ASDF"))
(asdf:load-system 'str)

(defun read-diagram (lines)
  (let* (
         (dim (length lines))
         (diagram (make-array (list dim dim))))
    (loop for line in lines
          for y from 0
          do (loop for char across line
                   for x from 0
                   do (if (char-equal char #\@)
                          (setf (aref diagram y x) 1))))
    diagram))
(read-diagram (uiop:read-file-lines "04example.txt"))

(defun make-kernel (diagram -x -y)
  (let ( (kernel (make-array '(3 3))))
    (loop for y from -1 to 1
          do (loop for x from -1 to 1
                   do (let ((-x (+ -x x))
                            (-y (+ -y y)))
                        (if (array-in-bounds-p diagram -y -x)
                          (setf (aref kernel (+ y 1) (+ x 1)) (aref diagram -y -x))
                          (setf (aref kernel (+ y 1) (+ x 1)) 0)))))
    kernel))
(make-kernel (read-diagram (uiop:read-file-lines "04example.txt")) 0 2)

(defun sum-kernel (kernel)
  (if (= (aref kernel 1 1) 1)
    (if
      (<
        (-
          (loop for y from 0 to 2
            sum (loop for x from 0 to 2
                      sum (aref kernel y x)))
          1)
        4)
      1
      0)
    0))
(sum-kernel (make-kernel (read-diagram (uiop:read-file-lines "04example.txt")) 2 0))

(defun sum-diagram (lines)
  (let ( (dim (length lines))
        (diagram (read-diagram lines)))
    (loop for y from 0 to dim
          sum (loop for x from 0 to dim
                    sum (sum-kernel (make-kernel diagram x y))))))

(sum-diagram (uiop:read-file-lines "04example.txt"))
(sum-diagram (uiop:read-file-lines "04data.txt"))