#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 22
  (define (score cards)
    (for/sum ([card (in-list cards)] [mult (in-range (length cards) 0 -1)])
      (* card mult)))

  (define (play p1 p2)
    (cond
      [(empty? p1) (score p2)]
      [(empty? p2) (score p1)]
      [else
       (define p1-card (first p1))
       (define p2-card (first p2))
       (cond
        [(> p1-card p2-card) (play (append (rest p1) (list p1-card p2-card)) (rest p2))]
        [else (play (rest p1) (append (rest p2) (list p2-card p1-card)))])]))

(define (part1 input)
  (match-define (list p1 p2) input)

  (play p1 p2))


(define (part2 input)
  (match-define (list p1 p2) input)

  (define memo (make-hash))
  (define (do-memo level p1 p2)
    (hash-update! memo level (lambda (x) (set-add x (list p1 p2))) (set)))

  (define (play/recur p1 p2 [level 0])
    ; (printf "~a ~a\n" p1 p2)
    (cond
      [(set-member? (hash-ref memo level (set)) (list p1 p2)) (cons 'p1 (score p1))]
      [(empty? p1) (cons 'p2 (score p2))]
      [(empty? p2) (cons 'p1 (score p1))]
      [else
       (define p1-card (first p1))
       (define p1-rest (rest p1))
       (define p2-card (first p2))
       (define p2-rest (rest p2))
       (cond
        [(and (>= (length p1-rest) p1-card)
              (>= (length p2-rest) p2-card))
         (match-define (cons winner score)
           (play/recur (take p1-rest p1-card) (take p2-rest p2-card) (add1 level)))
         ; (printf "submatch ~a\n" winner)
         (do-memo level p1 p2)
         (if (symbol=? winner 'p1)
           (play/recur (append p1-rest (list p1-card p2-card)) p2-rest level)
           (play/recur p1-rest (append p2-rest (list p2-card p1-card)) level))]
        [(> p1-card p2-card)
         (do-memo level p1 p2)
         (play/recur (append p1-rest (list p1-card p2-card)) p2-rest level)]
        [else
          (do-memo level p1 p2)
           (play/recur p1-rest (append p2-rest (list p2-card p1-card)) level)])]))

  (cdr (play/recur p1 p2)))

;; parse input file
(define (parse fname)
  (match-define (list p1 p2) (string-split (file->string fname) "\n\n"))
  (list
    (map string->number (rest (string-split p1 "\n")))
    (map string->number (rest (string-split p2 "\n")))))

(module+ test
  (require rackunit)
  ;; tests here
  (displayln "no tests :("))

(module+ main
  (define input (parse "inputs/22"))
  (answer 22 1 (time (part1 input)))
  (answer 22 2 (time (part2 input)))
  (displayln "meow"))