(define-struct times (h m))
(define-struct client (id entry exit))

;; parking-time: client -> number
;; calculates the parking time of the vehicle
(define (parking-time x)
  (- (+ (* (times-h (client-exit x)) 60) (times-m (client-exit x)))
     (+ (* (times-h (client-entry x)) 60) (times-m (client-entry x)))))
(check-expect (parking-time (make-client 1233 (make-times 10 30) (make-times 15 30))) (* 5 60))
(check-expect (parking-time (make-client 1234 (make-times 12 30) (make-times 13 00))) 30)

;; parking-fee (listof client) -> number
;; berechnet die parkgebuehren nach einer tabelle
(define (parking-fee lst)
  (foldr (lambda (x y) (+ y (cond [(<= (parking-time x) 30) 0.50]
                                  [(<= (parking-time x) 60) 1.20]
                                  [(<= (parking-time x) 360) 
                                   (* (- (times-h (client-exit x)) 
                                         (times-h (client-entry x))) 
                                      1.50)]
                                  [else 10])))
         0
         lst))
(check-expect (parking-fee (list (make-client 1233 (make-times 10 30) (make-times 15 30)))) (* 5 1.50)) 
(check-expect (parking-fee (list (make-client 1233 (make-times 10 30) (make-times 11 00)))) 0.50)
(check-expect (parking-fee (list (make-client 1233 (make-times 10 30) (make-times 18 00)))) 10)


(define-struct file (name mb))

(define f1 (make-file "A" 10.8))
(define f2 (make-file "B" 11.1))
(define f3 (make-file "C" 0.15))

(define files (list f1 f2 f3))

;; fill-medium: number (listof file) -> (listof string)
;; fuellt das speicher medium mit dateien
(define (fill-medium cap lst)
  (cond [(empty? lst) empty]
        [(< (file-mb (first lst)) cap) (cons (file-name (first lst)) (fill-medium (- cap (file-mb (first lst))) (rest lst)))]
        [else (fill-medium cap (rest lst))]))
(fill-medium 11 files)