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#lang racket
(require advent-of-code)
(struct posn (r c) #:transparent)
(define (make-tree-grid data)
(for*/hash ([(row r) (in-indexed data)] [(col c) (in-indexed (in-string row))])
(values (posn r c) (string->number (string col)))))
(define tree-grid (make-tree-grid (in-lines (open-aoc-input (find-session) 2022 8))))
;; part 1
(define (can-see-to-outside? p height dr dc h)
(match-define (posn r c) p)
(not (for/first ([n (in-naturals 1)]
#:do [(define p* (posn (+ r (* n dr)) (+ c (* n dc))))]
#:break (not (hash-has-key? h p*))
#:when (<= height (hash-ref h p*)))
#true)))
(define (visible-in-any-direction? p height h)
(for*/or ([dr (in-list '(-1 0 1))] [dc (in-list '(-1 0 1))] #:when (= 1 (abs (+ dr dc))))
(can-see-to-outside? p height dr dc h)))
(define (count-visible-trees trees)
(for/sum ([(tree-posn height) (in-hash trees)])
(cond
[(visible-in-any-direction? tree-posn height trees) 1]
[else 0])))
(count-visible-trees tree-grid)
;; part 2
(define (scenic-score-in-direction p height dr dc h)
(match-define (posn r c) p)
(define score
(for/last ([n (in-naturals 1)]
#:do [(define p* (posn (+ r (* n dr)) (+ c (* n dc))))]
#:break (not (hash-has-key? h p*))
#:final (<= height (hash-ref h p*)))
n))
(if (not score) 0 score))
(define (scenic-score p height h)
(for*/product ([dr (in-list '(-1 0 1))] [dc (in-list '(-1 0 1))] #:when (= 1 (abs (+ dr dc))))
(scenic-score-in-direction p height dr dc h)))
(define (find-best-scenic-score trees)
(apply max
(for/list ([(tree-posn height) (in-hash trees)])
(scenic-score tree-posn height trees))))
(find-best-scenic-score tree-grid)
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