#lang racket
(require "02-sharing-data.rkt")          ;; for the send function
(provide make-account make-account make-interest-bearing-account)

;; ------------------------------------------------------------------------
;; using a closure to implement a class

(define make-account                  ;; class
  (let ((count 0))                    ;; class variable
    (lambda (transaction)
      (case transaction
        ('new                         ;; constructor call = message
          (lambda (balance)           ;; constructor method + inst var
            (set! count (+ count 1))
            ; ------------------------------------------------------------
            (lambda (transaction)     ;; this is the object being returned
              (case transaction
                ('withdraw            ;; instance message
                  (lambda (amount)    ;; instance method
                    (if (>= balance amount)
                        (begin (set! balance (- balance amount))
                               balance)
                        (error "Insufficient funds" balance))))
                ('deposit
                  (lambda (amount)
                    (set! balance (+ balance amount))
                    balance))
                ('balance
                  (lambda ()
                    balance))
                (else (error "Unknown request -- ACCOUNT" transaction))))   ))
            ; ------------------------------------------------------------
        ('count                       ;; class message
          (lambda ()                  ;; class method
            count))
        (else (error "Unknown request to BANK ACCOUNT class" transaction))))))

;; (define eugene ((bank-account 'new) 100))
;; ((eugene 'balance))
;; ((eugene 'deposit) 100)
;; ((eugene 'balance))
;; ((bank-account 'count))
;; (define mary ((bank-account 'new) 100))
;; ((bank-account 'count))

;; ------------------------------------------------------------------------
;; using copy-and-paste to implement a new kind of account
;; ------------------------------------------------------------------------

(define make-interest-bearing-account-v0              ;; COPY AND PASTE
  (lambda (balance             ;; Creates a closure over balance
           interest-rate)      ;; ** NEW ** and interest-rate.
    (lambda (transaction)
      (case transaction
        ('withdraw
           (lambda (amount)
             (if (>= balance amount)
                 (begin (set! balance (- balance amount))
                        balance)
                 (error "Insufficient funds" balance))))
        ('deposit
           (lambda (amount)
             (set! balance (+ balance amount))
             balance))
        ('balance
           (lambda ()
             balance))
        ('accrue-interest                                         ;; NEW
           (lambda ()                                             ;; NEW
             (set! balance (* balance (+ 1.0 interest-rate)))     ;; NEW
             balance))                                            ;; NEW
        (else (error "Unknown request -- ACCOUNT" transaction))))))

;; ------------------------------------------------------------------------
;; using delegation to simulate inheritance
;; ------------------------------------------------------------------------

(define make-interest-bearing-account
  (lambda (balance interest-rate)
    (let ((my-account (make-account balance))) ;; make a bank account to use
      (lambda (transaction)
        (case transaction
          ('accrue-interest
             (lambda ()
               ((my-account 'deposit)
                   (* ((my-account 'balance)) interest-rate)) ))
          (else
             (my-account transaction)))))))    ;; delegate messages to it

;; ----------------------------------------------------------------------------