;; 9:39 start
;; 10:17 part 1
;;
(ql:quickload '(fiveam))

(defun roll (direction row col)
  (ecase direction
    (north (list (1- row) col))
    (south (list (1+ row) col))
    (west (list row (1- col)))
    (east (list row (1+ col)))))

(defun in-bounds (field row col)
  (destructuring-bind (maxrow maxcol) (array-dimensions field)
    (and (< -1 row maxrow)
         (< -1 col maxcol))))

(defun roll-rocks (field direction)
  (loop for i below (array-dimension field 0) do
    (loop for j below (array-dimension field 1) do
      (loop
        for (row col) = (list i j) then (list new-row new-col)
        for (new-row new-col) = (roll direction row col)
        while (and
               (in-bounds field new-row new-col)
               (eq #\O (aref field row col))
               (eq #\. (aref field new-row new-col)))
        do (setf (aref field new-row new-col) #\O
                 (aref field row col) #\.)))))

(defun array-slice (arr row)
  (make-array (array-dimension arr 1)
              :displaced-to arr
              :displaced-index-offset (* row (array-dimension arr 1))))

(defun north-load (field)
  (loop
    with rows = (array-dimension field 0)
    for row below rows
    sum (* (- rows row) (count #\O (array-slice field row)))))

(defun solve1 (input)
  (let* ((rows (length input))
         (field
           (make-array (list rows (length (car input))) :initial-contents input)))
    (roll-rocks field 'north)
    (north-load field)))

(defun draw-field (field &optional (out *standard-output*))
  (destructuring-bind (maxrow maxcol) (array-dimensions field)
    (loop for i below maxrow do
      (loop for j below maxcol do
        (write-char (aref field i j) out))
      (terpri out))
    (terpri out)))

(defun solve2 (input iters)
  (let* ((rows (length input))
         (field
           (make-array (list rows (length (car input))) :initial-contents input)))
    (loop
      do (dolist (dir '(north west south east))
           (roll-rocks-full field dir))
      repeat iters
      collect
      (north-load field))))

;; (solve2 (uiop:read-file-lines "eg-in") 1000000000)
;; (solve2 (uiop:read-file-lines "eg-in") 100)
;; (solve2 (uiop:read-file-lines "input") 100)
(fiveam:test solutions
  (fiveam:is (= 136 (solve1 (uiop:read-file-lines "eg-in"))))
  (fiveam:is (= 108935 (solve1 (uiop:read-file-lines "input"))))
  )

(fiveam:run!)