;; 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-intermediate-lambda-reader.ss" "lang")((modname textbox-demo-ti-before) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
(require 2htdp/image)
(require 2htdp/universe)
(require "student-extras.rkt")




; Datatype def'n:
;
(define-struct/contract tb ([contents string?]  [cursor natural?]))
;
; Interpretation: a textbox, with the text `contents`,
;     with `cursor` characters preceding the insertion-point(caret/cursor).
;     Thus:  (<= 0  cursor  (string-length contents))
;

; racket auto-creates constructer as above, getters, and a predicate:
;    tb-contents : (-> tb? string?)
;    tb-cursor   : (-> tb? natural?)
;    tb? : (-> any/c  boolean?)

; examples of data
(make-tb "hello" 0)  ; cursor before entire word
(make-tb "hello" 1)
(make-tb "hello" 5)
(make-tb "hello" 3)

(make-tb "h" 0)
(make-tb "h" 1)

(define EMPTY-TEXTBOX (make-tb "" 0))


; template:
(define/c (func-for-tb a-tb)
  (-> tb? ...?)
  (...  (tb-contents a-tb)  (tb-cursor a-tb)))

; draw-tb






;========== implement `draw`

(check-expect (draw (make-tb "hello" 3))
              (overlay/align "left" "center"
                             (beside (text "hel" 20 'blue)
                                     (rectangle 1 17 'solid 'orange)
                                     (text "lo" 20 'blue))
                             (rectangle 200 20 'outline 'green)))


(check-expect (draw (make-tb "hello" 0))
              (overlay/align "left" "center"
                             (beside (rectangle 1 17 'solid 'orange)
                                     (text "hello" 20 'blue))
                             (rectangle 200 20 'outline 'green)))

(check-expect (draw (make-tb "hello" 5))
              (overlay/align "left" "center"
                             (beside (text "hello" 20 'blue)
                                     (rectangle 1 17 'solid 'orange))
                             (rectangle 200 20 'outline 'green)))


(check-expect (draw (make-tb "" 0))
              (overlay/align "left" "center"
                             (rectangle 1 17 'solid 'orange)
                             (rectangle 200 20 'outline 'green)))


; draw : tb? -> image?
; Create an image corresponding to the tb.
;
(define (draw a-tb)
  (... (tb-contents a-tb) ... (tb-cursor a-tb) ...))




;===========

(check-expect (handle-key (make-tb "hello" 5) "right")
              (make-tb "hello" 5))
(check-expect (handle-key (make-tb "hello" 0) "left")
              (make-tb "hello" 0))
(check-expect (handle-key (make-tb "hello" 0) "\b")
              (make-tb "hello" 0))

(check-expect (handle-key (make-tb "hello" 3) "x")
              (make-tb "helxlo" 4))
(check-expect (handle-key (make-tb "hello" 3) "right")
              (make-tb "hello" 4))
(check-expect (handle-key (make-tb "hello" 3) "left")
              (make-tb "hello" 2))
(check-expect (handle-key (make-tb "hello" 3) "\b")
              (make-tb "helo" 2))



; handle-key : tb?, key-event? -> tb?
; Update `a-tb` to incorporate `key`.
;
(define (handle-key a-tb key)
  (cond [(key=? key "right") (make-tb (tb-contents a-tb)
                                           (min (add1 (tb-cursor a-tb))
                                                (string-length (tb-contents a-tb))))]
        [(key=? key "left") ...]
        [(key=? key "\b") ...]
        [else 
        (make-tb (tb-contents a-tb)
                        (tb-cursor a-tb))]
  ))

                                           





#;(big-bang (make-tb "" 0)
  [on-draw draw]
  [on-key handle-key])