;; ticketnum:  Natural
;; remembers the last ticket number that was handed out
(define ticketnum 4)

;; get-ticket:  -> Natural
;; produces the next ticket number
(define (get-ticket)
  (begin
    (if (= ticketnum 4)
        (set! ticketnum 1)
        (set! ticketnum (+ 1 ticketnum)))
    ticketnum))



(define-struct account (acctnum balance))
;; an Account is a (make-account Natural Number)
;; where acctnum is the account number
;; balance is the balance in the account (in dollars)

;; a ListOfAccount is one of
;; empty
;; (cons Account ListOfAccount)


;; Citibank:  ListOfAccount
;; remembers the information about each account in the list
(define Citibank (list (make-account 1 500)
                       (make-account 2 1000)
                       (make-account 3 10)))

;; add-account:  Natural Number -> void
;; makes a new account and adds it to Citibank
;; EFFECT: changes the contents of Citibank
(define (add-account acctnum amt)
  (set! Citibank
        (cons (make-account acctnum amt) Citibank)))

;; remove-account:  Natural -> void
;; removes the account with the given account number from Citibank
;; EFFECT:  removes an account from Citibank
(define (remove-account acctnum)
  (set! Citibank (remove-acct-list acctnum Citibank)))

;; remove-acct-list:  Natural ListOfAccount -> ListOfAccount
;; removes the account with the given account number from the list
(define (remove-acct-list acctnum aloa)
  (cond [(empty? aloa) (error "No such account")]
        [(cons? aloa) (if (= (account-acctnum (first aloa)) acctnum)
                          (rest aloa)
                          (cons (first aloa) (remove-acct-list acctnum (rest aloa))))]))

"show Citibank (it contains an account with account number 2)"
Citibank
"run remove-account on Citibank, removing account 2"
(remove-account 2)
"show that Citibank no longer contains account 2, but all other accounts are still there"
Citibank

;;---------- Vending machine example --------------------

;; Here's the code we've developed so far.  Make one more modification to the
;; vending machine that will tell you how much change you'll get back.  For example,
;; if you insert 60 cents into the machine, then choose a soda, choose-item should
;; return a string that says "dispense soda and 10 cents change"

(define soda-cost 50)
(define candy-cost 65)

;; amt:  Natural
;; remembers the amount of money in the vending machine
(define amt 0)

;; insert-coin:  Natural -> void
;; inserts the given amount of cents into the machine
;; EFFECT:  changes amt
(define (insert-coin cents)
  (set! amt (+ amt cents)))

;; choose-item:  String -> String
;; consumes the item the user wants and produces a status message
;; EFFECT:  can change the amt in the vending machine
(define (choose-item item)
  
  (cond [(string=? item "soda")
         (if (>= amt soda-cost)
             (begin
               (set! amt (- amt soda-cost))
               "dispense soda")
             (format "need ~a more cents" (- soda-cost amt)))]
        
        [(string=? item "candy")
         (if (>= amt candy-cost)             
             "dispense candy"
             "need more money")]))