(define-struct account (name num balance))
;; An Account is a (make-account String Number Number)

;; make-account : String Number Number -> Account
;; account?     : Any -> Boolean
;; account-name : Account -> String
;; account-num  : Account -> Number
;; account-balance : Account -> Number

(define acct-pnk    (make-account "Felix Klock"     101 20000.00))
(define acct-nin    (make-account "Trent Reznor"    102 100000000.00))
(define acct-gobias (make-account "Tobias Fumke"    103 10.00))

;; meets-balance-requirement? : Account Number -> Boolean
;; Does acct meet the balance requirement req ?
(define (meets-balance-requirement? acct req)
  (>= (account-balance acct) req))

(equal? (meets-balance-requirement? (make-account (string-append "Mr." "T") 10 (+ 10.00 15.00)) 20.00) true) 
(equal? (meets-balance-requirement? acct-gobias 50.00) false) (equal? (meets-balance-requirement? acct-pnk 50.00) true)
(equal? (meets-balance-requirement? acct-nin 1000000) true) 
(equal? (meets-balance-requirement? acct-pnk 1000000) false)

;; bigger-balance? : Account Account -> Boolean
;; Does acct-1 have a bigger balance than acct-2 ?
(define (bigger-balance? acct-1 acct-2) (> (account-balance acct-1) 
     (account-balance acct-2)))

(equal? (bigger-balance? acct-gobias acct-pnk) false)
(equal? (bigger-balance? acct-nin    acct-pnk) true) (equal? (bigger-balance? acct-pnk acct-pnk) false)

;; bear-interest : Account -> Account
;; Produces a new account that has earned 1% interest
(define (bear-interest acct)
  (make-account (account-name acct) (account-num acct) (* 1.01 (account-balance acct))))

(equal? (bear-interest acct-gobias) (make-account "Tobias Fumke" 103 10.10))    (equal? (bear-interest acct-pnk)    (make-account "Felix Klock"  101 20200.00)) 
(equal? (bear-interest acct-nin)    (make-account "Trent Reznor" 102 101000000.00))

;;;;;;;;;;;;;;;;;;;;;;;;;;

(define-struct artist (first last))
;; An Artist is a (make-artist String String)

(define-struct cd (title artist num-discs))
(define-struct tape (title artist))
;; A Recording is either a 
;; - (make-cd String Artist Number)
;; - (make-tape String Artist)

(define venus-and-back (make-cd "To Venus and Back Again" (make-artist "Tori" "Amos") 2))
(define the-fragile (make-cd "The Fragile" (make-artist "Trent" "Reznor") 2))
(define harvest (make-tape "Harvest" (make-artist "Neil" "Young")))
(define pallelujah (make-cd "Paullelujah" (make-artist "Paul" "Barman") 1))

;; TEMPLATE FOR PROCESSING RECORDINGS:
#|
;; func : Recording -> ???
;; ??????
(define (func rec)
  (cond [(cd? rec) ... (cd-title rec) ... ... (cd-artist rec)  ... ... (cd-num-discs rec) ...] [(tape? rec) ... (tape-title rec) ...  ... (tape-artist rec) ...]))
|#

;; recording-price : Recording -> Number
;; Returns price for rec
(define (recording-price rec)
  (cond [(cd? rec) (* 11 (cd-num-discs rec))]
[(tape? rec) 9]))

(equal? (recording-price harvest) 9)         (equal? (recording-price the-fragile) 22)
(equal? (recording-price venus-and-back) 22) (equal? (recording-price pallelujah) 11)

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

(define-struct empty-inventory ())
(define-struct bigger-inventory (album rest))
;; An Inventory is either:
;; - (make-empty-inventory), or
;; - (make-bigger-inventory Recording Inventory)
;; Nothing else is an Inventory.

;;; Examples of Inventorys.
(define in1 (make-empty-inventory))
(define in2 (make-bigger-inventory harvest (make-empty-inventory)))
(define in3 (make-bigger-inventory pallelujah (make-empty-inventory)))
(define in4 (make-bigger-inventory venus-and-back (make-bigger-inventory the-fragile (make-empty-inventory))))