#lang racket
(require threading
         memoize)

;; not going to bother importing the data since it's just two lines of text
(define player-1-start 4)
(define player-2-start 6)

(define track (sequence->stream (in-cycle (inclusive-range 1 10))))
(define current-turn (in-cycle (list 'player-1 'player-2)))
(define die-rolls (sequence->stream (in-cycle (inclusive-range 1 100))))

;; part 1
(~> (for/fold ([player-1-score 0]
               [player-1-track (stream-tail track (sub1 player-1-start))]
               [player-2-score 0]
               [player-2-track (stream-tail track (sub1 player-2-start))]
               [dice die-rolls]
               [last-turn 0]
               #:result (list (min player-1-score player-2-score) (* 3 last-turn)))
              ([turn-count (in-naturals 1)]
               [turn-for current-turn]
               #:break (or (player-1-score . >= . 1000) (player-2-score . >= . 1000)))
      (define rolls (apply + (stream->list (stream-take dice 3))))
      (match turn-for
        ['player-1
         (define next-track (stream-tail player-1-track rolls))
         (values (+ player-1-score (stream-first next-track))
                 next-track
                 player-2-score
                 player-2-track
                 (stream-tail dice 3)
                 turn-count)]
        ['player-2
         (define next-track (stream-tail player-2-track rolls))
         (values player-1-score
                 player-1-track
                 (+ player-2-score (stream-first next-track))
                 next-track
                 (stream-tail dice 3)
                 turn-count)]))
    (apply * _))

;; part 2
(define d3 (list 1 2 3))
(define roll-space (~>> (cartesian-product d3 d3 d3) (map (λ~>> (apply +)))))

(define/memo
 (next-turns p1-score p2-score p1-start p2-start)
 (cond
   [(p1-score . >= . 21) '(1 0)]
   [(p2-score . >= . 21) '(0 1)]
   [else
    (for/fold ([wins '(0 0)]) ([roll (in-list roll-space)])
      (define move-to (add1 (modulo (sub1 (+ roll p1-start)) 10)))
      (define possible-wins (next-turns p2-score (+ p1-score move-to) p2-start move-to))
      (list (+ (first wins) (second possible-wins)) (+ (second wins) (first possible-wins))))]))

(~>> (next-turns 0 0 player-1-start player-2-start) (apply max))