(asdf:load-system :adventofcode2020)
(in-package #:adventofcode2020)

(defun calc-seat (seat-spec) 
  (let ((row (string-right-trim "RL" seat-spec))
         (col (string-left-trim "FB" seat-spec))
         (convert-to-int 
           (lambda (str one)
             (loop with len = (1- (length str))
                   for c across str
                   for i downfrom len
                   summing (if (char= c one)
                               (ash 1 i) 0)))))
     (mapcar convert-to-int (list row col) '(#\B #\R))))

(defun calc-seat-id (row-col)
  (destructuring-bind (row col) row-col
    (+ (* row 8) col)))

(day 05 input
  (let* ((lines (list-from input))
         (seat-ids (-<>> lines 
                     (mapcar (compose #'calc-seat-id #'calc-seat)) 
                     (sort <> #'>))))
    (part1 (first seat-ids))
    (part2 (loop for big in seat-ids
                 for small in (cdr seat-ids)
                 when (= small (- big 2))
                 return (1+ small)))))

(def-suite day05)
(in-suite day05)

(test calc-seats
  (is (equal
        '((44 5) (70 7) (14 7) (102 4))
        (mapcar #'calc-seat '("FBFBBFFRLR" "BFFFBBFRRR" 
                              "FFFBBBFRRR" "BBFFBBFRLL")))))

(run! 'day05)