(import (chicken io))
(import (chicken format))
(import (chicken string))
(import (chicken condition))
(import srfi-1)

(define (parse-line line)
    (let-values (((command offset) (apply values (string-split line))))
        (list command (string->number offset))))

(define (parse inputs)
    (map parse-line (read-lines)))

(define (part1-direction head tail h d)
    (let-values (((command offset) (apply values head)))
        (cond ((equal? command "forward") 
               (part1 tail (+ h offset) d))
              ((equal? command "down")
               (part1 tail h (+ d offset)))
              ((equal? command "up")
               (part1 tail h (- d offset)))
              (else (abort (format "did not expect command '~A'" command))))))

(define (part1 directions h d)
    (if (not (null? directions))
        (part1-direction (car directions) (cdr directions) h d)
        (* h d)))


(define (part2-direction head tail horiz depth aim)
    (let-values (((command offset) (apply values head))) 
        (cond ((equal? (car command) "forward") 
               (part2 tail (+ horiz offset) (+ depth (* aim offset)) aim))
              ((equal? command "down")
               (part2 tail horiz depth (+ aim offset)))
              ((equal? command "up")
               (part2 tail horiz depth (- aim offset)))
              (else (abort (format "did not expect command '~A'" command))))))

(define (part2 directions horiz depth aim)
    (if (not (null? directions))
        (part2-direction (car directions) (cdr directions) horiz depth aim)
        (* horiz depth)))
    

(let ((directions (parse '())))
    (format #t "part1 = ~A~%" (part1 directions 0 0))
    (format #t "part2 = ~A~%" (part2 directions 0 0 0)))