#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)