;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname union-of-structs-before) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
;;; Data Definiton:
; A book is:
(define-struct book (title author num-pages is-copyrighted?))
; make-book : string string natnum boolean  ->  book


;;; Examples of the data
(define b0 (make-book "Soul and Wit" "Barland" 0 #false))
(define b1 (make-book "The Cat in the Hat" "Seuss" 37 #true))


;;; Template:

; func-for-book : book -> ...
;
(define (func-for-book a-book)
  (... (book-title a-book)
   ... (book-author a-book)
   ... (book-num-pages a-book)
   ... (book-is-copyrighted? a-book)))



; reading-time : book -> non-negative real
; The amount of time it takes the average reader to read a book (in minutes)
;
(define (reading-time a-book)
  (* (book-num-pages a-book) 2))


(check-expect (reading-time (make-book "The Cat in the Hat" "Seuss" 37 #true))
              74)
(check-expect (reading-time b0) 0)



; book->string : book -> string
; Return a string-representation of a book struct, user-friendly.
(define (book->string a-book)
  (string-append (book-title a-book)
                 ", by "
                 (book-author a-book)
                 " ("
                 (number->string (book-num-pages a-book))
                 "pp)"
                 (if (book-is-copyrighted? a-book) ", ©" "")))

  
(check-expect (book->string (make-book "The Cat in the Hat" "Seuss" 37 #true))
              "The Cat in the Hat, by Seuss (37pp), ©")
(check-expect (book->string b0)
              "Soul and Wit, by Barland (0pp)")




; Create a brand new book, based on an original.
; The result's author will be the original author & the new-author,
; and the result has pages added to the original.
;
(define (derive-from original co-author num-new-pages)
  (make-book (string-append "Son of " (book-title original))
             (string-append (book-author original) " & " co-author)
             (+ (book-num-pages original) num-new-pages)
             #false))


(check-expect (derive-from b1 "Sauced" 3)
              (make-book "Son of The Cat in the Hat" "Seuss & Sauced" 40 #false))
(check-expect (derive-from b0 "Freund" 0)
              (make-book "Son of Soul and Wit" "Barland & Freund" 0 #false))





;;; Data Def'n:

(define-struct dvd (title year length rating))
; make-dvd : string natnum real? symbol?  ->  dvd
; The length is in minutes.

;;; Examples of the data:
(make-dvd "The Fellowship of the Ring" 2001 178 'PG-13)
(make-dvd "Logan Lucky" 2017 118 'PG-13)


;;; Template
; func-for-dvd : dvd -> ...
;
(define (func-for-dvd a-dvd)
  (... (dvd-title a-dvd)
   ... (dvd-year a-dvd)
   ... (dvd-length a-dvd)
   ... (dvd-rating a-dvd)))













; Datatype def'n:
; A lib-item is:
;  - a book, OR
;  - a dvd, OR
;  - 'other

; Examples of the data:
(make-book "Cat in Hat" ....)
(make-dvd "The Fellowship of the Ring" 2001 178 'PG-13)
'other


; template: code for ANY function which processes a lib-item.
(define (func-for-lib-item a-li)
  (cond [(book? a-li) (... (book-author a-li) (book-title a-li)]
        [(dvd? a-li) (... (dvd-title a-dvd)  (dvd-year a-dvd)  (dvd-length a-dvd)  (dvd-rating a-dvd))]
        [(symbol? a-li) ...]
        ))





;; N.B. we are NOT worrying about inheritance, and the fact that both books and dvds
;; have a field like "title" in common.  It is a correct impulse/desire is to use
;; your O.O. design and have a superclass that both `book` and `dvd` might inherit from.
;; However, to keep things straight (and, to understand that we want to be able to
;; process union-types where branches might have *nothing* in common), we won't do
;; any inheritance.  (You can look at full-rackets `define-struct` though, to see that
;; it actually can inherit fields, in real-life racket.)




; func-for-lib-item : lib-item -> ...?
;
#;(define (func-for-lib-item an-item)
  (cond [(book? an-item) ...]
        [(dvd? an-item)  ...]
        [(symbol=? an-item 'other) ...]))










; func-for-lib-item : lib-item -> ...?
;
#;(define (func-for-lib-item an-item)
  (cond [(book? an-item) (... (book-title an-item)
                          ... (book-author an-item)
                          ... (book-num-pages an-item)
                          ... (book-copyrighted? an-item))]
        [(dvd? an-item)  (... (dvd-title an-item)
                          ... (dvd-length an-item)
                          ... (dvd-rating an-item))]
        [(symbol=? an-item 'other) ...]))





; time-to-waste : lib-item -> non-negative real
; Return how much time I can waste from this library item.
(define (time-to-waste an-item)
  ; time-to-waste: a dvd's run time plus 5min to get it going,
  ;  or (for a book) its reading time plus 1min to read back cover.
  (cond [(book? an-item) (+ 1 (reading-time an-item))]
        [(dvd? an-item)  (+ 5 (dvd-length an-item))]
        [(symbol=? an-item 'other) ...])





;;;; one more notion: struct-of-structs
;; A collectors-edition contains a DVD *and* a book (the deluxe artwork hardback version, perhaps).


; TEMPLATE: same as ever: pull out the two fields. BUT STOP THERE; you'll call helpers
; rather than extract all its fields.




(define-struct collectors-edition (disc bk extra-art-pages))
; collectors-edition : (-> dvd book natnum  collectors-edition)

; ripoff: derive-from the book by having Barland add 50% more pages, and replace the DVD with the emoji movie (86min)





; verify-title : collectors-edition -> boolean


;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; TODO:  a struct-of-unions.
; [Template: Call a helper;
; don't have a cond inside the struct-processing program.]