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

(defun calc-seat (seat-spec) 
  (loop with len = (1- (length seat-spec))
        for c across seat-spec
        for i downfrom len
        summing (if (or (char= c #\R) (char= c #\B))
                    (ash 1 i) 0)))

(day 05 input
  (let* ((lines (list-from input))
         (seat-ids (-<>> lines 
                     (mapcar #'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
        '(357 567 119 820)
        (mapcar #'calc-seat '("FBFBBFFRLR" "BFFFBBFRRR" 
                              "FFFBBBFRRR" "BBFFBBFRLL")))))

(run! 'day05)