#lang racket

(require threading
         "../jj-aoc.rkt")

(define data
  (for/vector ([l (in-lines (open-day 9))]
               #:unless (equal? l ""))
    (~>> l
         string->list
         (map (λ~>> ~a string->number))
         list->vector)))

(define max-rows (vector-length data))
(define max-cols (vector-length (vector-ref data 0)))
(define-values (min-rows min-cols) (values 0 0))

(define (vector2d-ref vec coord)
  (match-define `(,r ,c) coord)
  (~> vec
      (vector-ref r)
      (vector-ref c)))

(define (adjacent coords)
  (match-define `(,r ,c) coords)
  `((,(add1 r) ,c)
    (,(sub1 r) ,c)
    (,r ,(add1 c))
    (,r ,(sub1 c))))

(define (valid-coordinate coord)
  (match-define `(,r ,c) coord)
  (and (>= r min-rows)
       (< r max-rows)
       (>= c min-cols)
       (< c max-cols)))

(define (check-adjacent vec coord)
  (define x (vector2d-ref vec coord))
  (for*/and ([neighbor (in-list (adjacent coord))]
             #:when (valid-coordinate neighbor))
    (x . < . (vector2d-ref vec neighbor))))

;; part 1
(for*/sum ([r (in-range min-rows max-rows)]
           [c (in-range min-cols max-cols)]
           [x (in-value (vector2d-ref data `(,r ,c)))]
           #:when (check-adjacent data `(,r ,c)))
  (add1 x))

;; part 2
(define visited (make-hash))
(define (flood-fill vec coord)
  (if (and (< (vector2d-ref vec coord) 9)
           (not (hash-has-key? visited coord)))
      ((hash-set! visited coord 'visited)
       (add1 (for/sum [(neighbor (in-list (adjacent coord)))
                       #:when (valid-coordinate neighbor)]
               (flood-fill vec neighbor))))
      0))