#lang racket
(require advent-of-code
         threading
         algorithms)

(define motion-data
  (~> (open-aoc-input (find-session) 2021 2 #:cache (string->path "./cache"))
      (port->list read _)
      (chunks-of _ 2)))

;; part 1
(for/fold ([depth 0] [position 0] #:result (* depth position)) ([motion (in-list motion-data)])
  (match motion
    [(list 'forward x) (values depth (+ position x))]
    [(list 'up x) (values (- depth x) position)]
    [(list 'down x) (values (+ depth x) position)]))

;; part 2
(for/fold ([aim 0] [depth 0] [position 0] #:result (* depth position))
          ([motion (in-list motion-data)])
  (match motion
    [(list 'forward x) (values aim (+ depth (* aim x)) (+ position x))]
    [(list 'up x) (values (- aim x) depth position)]
    [(list 'down x) (values (+ aim x) depth position)]))