;; 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 struct-intro-book-before) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
;; a book has info:
;; title, author, # of pages, is copyrighted?

;;;    structs in racket, a "product type"
;;;    i.e. aggregate data: take several pieces of data,
;;;     and wrap them up together and consider it *one* thing
;;;     (understanding it is comprised of several internal fields).
;;;    "encapsulation" -- we put a capsule around the fields.



; Datatype Definiton:
(define-struct book (title author num-pages is-copyrighted?))
; A book is:
;(make-book [string] [string] [natnum] [boolean])


; Examples of the data
(define cih (make-book "The Cat in the Hat"     "Dr. Seuss" (+ 2 35) #true))
(define b0 (make-book "The Soul of Wit"  "Barland"  0  #false))



; `define-struct` actually introduces additional functions:
; a constructor
; and four getters ("selectors").
; In this case, the constructor is named
;   make-book : string, string, natural, boolean -> book
; and the getters are named
;   book-title : book -> string
;   book-author
;   book-num-pages : book -> natnum
;   book-is-copyrighted?

(book-title (make-book "The Cat in the Hat" "Seuss" 37 #true))

(define (foo a-book)
  (if (string=? "Cat" (book-title 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))

; class Book{      int readingTime( /* Book this*/  ) { return 2*this.num-pages; }

(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)
              "The Soul of Wit, by Barland (0pp)")


(check-expect (enbiggen b0)
              b0)
(check-expect (enbiggen (make-book "The Bat in the Mat" "Streuss" 1 #true))
              (make-book "The Bat in the Mat" "Streuss" 2 #true))
(check-expect (enbiggen (make-book "The Cat in the Hat" "Seuss" 37 #true))
              (make-book "The Cat in the Hat" "Seuss" 74 #true))


; enbiggen : book -> book
; Return a book just like `a-book`, but with bigger text (hence, more pages).
;
(define (enbiggen a-book)
  (make-book (book-title a-book)
             (book-author a-book)
             (* 2 (book-num-pages a-book))
             (book-is-copyrighted? a-book)))



; derive-from
; 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 `#new-pages` pages added to the original.
;



;;; template (we'll come back)
; 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)))