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#lang racket
(require advent-of-code
threading)
(struct coord (x y) #:transparent)
(define input (~> (fetch-aoc-input (find-session) 2023 18 #:cache #true)))
(define (go-to-next-coord c dir dist)
(match-define (coord x y) c)
(match dir
["R" (coord (+ x dist) y)]
["L" (coord (- x dist) y)]
["U" (coord x (+ y dist))]
["D" (coord x (- y dist))]))
(define/match (triangle-area _coord1 _coord2)
[((coord x1 y1) (coord x2 y2)) (/ (- (* x1 y2) (* x2 y1)) 2)])
(define (find-area-using parser)
(for/fold ([area 0]
[perimeter 0]
[current-coord (coord 0 0)]
#:result (+ 1 (abs area) (/ perimeter 2)))
([dig (in-list (string-split input "\n"))])
(define-values (dir dist) (parser dig))
(define next-coord (go-to-next-coord current-coord dir dist))
(values (+ area (triangle-area current-coord next-coord)) (+ perimeter dist) next-coord)))
;; part 1
(define (parse-front dig)
(match-define (regexp #rx"(.) (.*) \\((.*)\\)" (list _ dir (app string->number dist) _hex)) dig)
(values dir dist))
(find-area-using parse-front)
;; part 2
(define (parse-hex dig)
(match-define (regexp #rx".*\\(#(.....)(.)\\)"
(list _ (app (curryr string->number 16) dist) (app num->dir dir)))
dig)
(values dir dist))
(define/match (num->dir _n)
[("0") "R"]
[("1") "D"]
[("2") "L"]
[("3") "U"])
(find-area-using parse-hex)
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