;; https://adventofcode.com/2022/day/13

;; (defparameter *day13-file-name* "day13-test.txt")
(defparameter *day13-file-name* "day13-input.txt")
(defparameter *day13-all-list* nil)

;; 5739 is too low & incorrect
;; 6398 too high

(defun nest-2-< (left right)
  (cond
    ((and (numberp left) (numberp right)) (- left right))
    ((numberp left) (nest-2-< (list left) right))
    ((numberp right) (nest-2-< left (list right)))
    ((and (listp left) (listp right))
     (cond
       ((and (not left) (not right)) 0) ; both equal and empty
       ((not left) -1)                     ; only left empty, left is smaller
       ((not right) 1)                  ; only right is empty, left is bigger
       (t (if (equal (first left) (first right))
              (nest-2-< (rest left) (rest right))
              (let ((head-comparison (nest-2-< (first left) (first right))))
                (if (= 0 head-comparison)
                    (nest-2-< (rest left) (rest right))
                    head-comparison))))))
    (t 'default)))

(progn
  (defparameter *day13-all-list* nil)
  (setq *day13-all-list*
      (with-open-file (in *day13-file-name*)
        (read in)))
  (defparameter *day13-lefts* nil)
  (defparameter *day13-rights* nil)

  (loop for i from 0 below (length *day13-all-list*)
        when (= 0 (mod i 2)) do (push (nth i *day13-all-list*) *day13-lefts*)
          when (= 1 (mod i 2)) do (push (nth i *day13-all-list*) *day13-rights*))
  (setq *day13-lefts* (reverse *day13-lefts*))
  (setq *day13-rights* (reverse *day13-rights*))

  (defparameter *day13-indices* nil)
  (setq *day13-indices* (loop
                          for i from 0 below (length *day13-lefts*)
                          when (< (nest-2-< (nth i *day13-lefts*) (nth i *day13-rights*)) 0)
                              collect (1+ i)))
  (apply #'+ *day13-indices*))

;;; PART 2
(let ((sorted (sort  (copy-list *day13-all-list*) (lambda (left right)
                                                    (< (nest-2-< left right) 0)))))
  (* (1+ (position '((2)) sorted :test #'equal))
     (1+ (position '((6)) sorted :test #'equal))))
;; 24477 yay