; BEWARE -- in this text-version,
;    there are dots (.) below where the penguin images should be!

; CS 131 - Week 3, Lecture 1
; in-class examples

(require 2htdp/image)
(require 2htdp/universe)

; SO -- conditional expression lets us
;    specify branching situations...

; SYNTAX:
; (cond 
;    [boolean-expr1 expresion1]
;    [boolean-expr2 expression2]
;    ...
;    [else expression-n]
; )
;
; SEMANTICS:
; *   boolean-expr1 is evaluated; if it is true, the cond
;     expression's value is expression1
; *   OTHERWISE, boolean-expr2 is evaluated; if it is true,
;     the cond expression's value is expression2
; *   OTHERWISE... (continuing for each boolean expression
;     ...)
; *   ...and if you reach an else, the cond expression's
;     value is expression-n

; MAKE SURE THIS IS CLEAR -- as SOON as a true boolean expression
;    is found, its expression becomes the value of the whole
;    cond expression, and that's it -- none of the other
;    cond expressions is evaluated.

;-------------------------------------------------
; let's develop a function that can produce
;    a greeting appropriate to the time of day

; signature: greet: string number -> string
; purpose: expects a person's name and the hour
;    of the day expressed in 24-hour time,
;    and it produces a greeting to that person
;    appropriate to the time of day
;    (morning is [0, 11],
;     afternoon is (11, 17],
;     evening is (17, 23])
; NOTE: this is an overly-trusting function,
;    it greets one in the evening for any out-of-bounds
;    time

(define (greet name time)
  
  ; remember: greet's body was only filled in AFTER the 
  ;    check-expects (yes, all 5 of them, in this case) were 
  ;    written;
  
  (cond
    [(and (>= time 0)(<= time 11)) 
        (string-append "Good morning, " name)]
    [(and (>= time 0) (<= time 17))
        (string-append "Good afternoon, " name)]
    [else (string-append "Good evening, " name)]
  )
)

(check-expect (greet "Ann" 8)
              "Good morning, Ann")
(check-expect (greet "Lonyx" 15)
              "Good afternoon, Lonyx")
(check-expect (greet "Carol" 21)
              "Good evening, Carol")
(check-expect (greet "David" 11)
              "Good morning, David")
(check-expect (greet "Katherine" 17)
              "Good afternoon, Katherine")
(greet "Ann" 8)

; the design recipe template step -- after the check-expects
;    were written, before the function body was completed:
;
; for a 3-case situation, a template for the function
;    body would be:

;  (cond
;    [... ...]
;    [... ...]
;    [else ...]
;  )

; now for a floating penguin that lands...

; images are from
;http://wallofgame.com/free-online-games/arcade/231/Parachute_Penguin_Shootout.html
(define FLOATING-PENGUIN.)
(save-image FLOATING-PENGUIN "floating-penguin.png")
(define LANDED-PENGUIN.)
(save-image LANDED-PENGUIN "landed-penguin.png")

(define WIDTH 200)
(define HEIGHT 250)
(define BACKDROP (empty-scene WIDTH HEIGHT))

;-------------
; signature: get-1-bigger: number -> number
; purpose: expects a number, and produces the number
;     that is 1 bigger

(define (get-1-bigger a-number)
  (+ a-number 1)
)

; note -- this check-expect was written BEFORE get-1-bigger's
;    body was filled in!

(check-expect (get-1-bigger 15) 16)
(get-1-bigger 45)

;-------------------
; signature: draw-penguin: number -> scene
; purpose: expects a number, and if that number
;    is in the range 
;    [0, (- HEIGHT (* .5 (image-height LANDED-PENGUIN))) ),
;    produces a scene with a floating penguin
;    whose y-coordinate is that number;
;    otherwise, produces a scene with a
;    standing penguin at a y-coordinate of 
;    (- HEIGHT (* .5 (image-height LANDED-PENGUIN)))

(define (draw-penguin a-number)
  
  ; again, remember -- this function body was completed
  ;    AFTER developing the check-expects
  ; (and after inserting a 2-case cond expression template)
  
  (cond
    [(< a-number 
        (- HEIGHT (* .5 (image-height LANDED-PENGUIN))))
       (place-image FLOATING-PENGUIN
                    (/ WIDTH 2)
                    a-number
                    BACKDROP)]
    [else 
       (place-image LANDED-PENGUIN
                    (/ WIDTH 2)
                    (- HEIGHT (* .5 
                                 (image-height LANDED-PENGUIN)))
                    BACKDROP)]
  )
)

(check-expect (draw-penguin 5)
              (place-image FLOATING-PENGUIN
                           (/ WIDTH 2)
                           5
                           BACKDROP))
(check-expect (draw-penguin (+ HEIGHT 1000))
              (place-image LANDED-PENGUIN
                           (/ WIDTH 2)
                           (- HEIGHT (* .5 
                              (image-height LANDED-PENGUIN)))
                           BACKDROP))
(check-expect (draw-penguin 
                  (- HEIGHT (* .5 
                              (image-height LANDED-PENGUIN)))
              )
              (place-image LANDED-PENGUIN
                           (/ WIDTH 2)
                           (- HEIGHT (* .5 
                              (image-height LANDED-PENGUIN)))
                           BACKDROP))
              
; remember -- STOP this animation when you are done with it,
;    even though it "looks" stopped, it is actually keeping on
;    redrawing that standing penguin with each clock tick of
;    the running universe...!

(big-bang 0
          (on-tick get-1-bigger)
          (on-draw draw-penguin))