#lang htdp/isl

;; Herding Cats, a Start 

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

;; --- DATA DEFINITIONS --------------------------------------------------------
;; [[ from the How to Design Programs/2e: ]]
;; N is one of:
;; -- 0
;; -- (add1 N)
;; INTERPRETATION the natural (counting) numbers
;; Use sub1 as selector and zero? and positive? as predicates. 
;; 
(define MOVEMENTS '(straight turn-left turn-right))
;; A Movement is a member of MOVEMENTS.
;; 
(define DIRECTIONS '(left right up down))
;; A Direction is a member of DIRECTIONS. 
;;
(define-struct cat [dir loc steps])
;; A Cat is a (make-cat Direction Posn [Listof Movement])
;; INTERPRETATION
;; - dir is the direction the cat is facing
;; - loc is the location of the cat
;; - steps is the list of steps the cat will follow

;; EXERCISE 1: Develop data examples using quasiquote and unquote.

;; EXERCISE 2: Develop a template for functions that process N and [Listof Cat]
;; (separately).  

;; --- CONSTANTS ---------------------------------------------------------------
(define WIDTH      500)
(define HEIGHT     500)
(define BACKGROUND (empty-scene WIDTH HEIGHT))
(define CAT-IMG    (circle 20 "solid" "orange")) ;; <-- insert your favorite cat picture here, then delete this comment 
(define CENTER     (make-posn (/ WIDTH 2) (/ HEIGHT 2)))

;; --- MAIN -------------------------------------------------------------------
;; N N -> [Listof Cat]
;; Simulate this many cats,
;; each following a random pattern of the given # of steps
(define (main cats# steps#)
  (big-bang (all-the-cats-in-the-world cats# steps#)
    [to-draw   draw-all-cats]
    [on-tick   all-cats-move]
    [stop-when is-any-cat-out-of-steps?]))

;; EXERCISE 3
;; N -> [Listof Movement]
;; creates a list of n Movements
(define (create-steps n)
  '())

;; EXERCISE 4 
;; [Listof Cat] -> [Listof Cat]
;; Every cat in the list follows the next step in its movement pattern
(define (all-cats-move loc)
  ;; FIX ME I'M A DUMMY HEADER
  loc) 

;; EXERCISE 5 
;; [Listof Cat] -> Boolean
;; Are any of the cats out of steps to take?
(define (is-any-cat-out-of-steps? t)
  #f)

;; --- PROVIDED FUNCTIONS ------------------------------------------------------
;; [Listof X] -> X
;; Picks a random item from lox 
(define (random-choice lox)
  (list-ref lox (random (length lox))))




;; --- COMPLETED FUNCTIONS -----------------------------------------------------

;; *****************************************************************************
;; The functions below use concepts that we will start covering TOMORROW.
;; Do not attempt to follow these examples at home just yet.
;; *****************************************************************************

;; N N -> [Listof Cat]
;; Produces a list of cats# cats, each with steps# steps to follow
(define (all-the-cats-in-the-world cats# steps#)
  (local (;; Any -> Cat
          (define (create-cat _)
            (make-cat (random-choice DIRECTIONS)
                      (make-posn (random WIDTH) (random HEIGHT))
                      (create-steps steps#))))
    (build-list cats# create-cat)))

;; -----------------------------------------------------------------------------
;; [Listof Cat] -> Image
;; Draw all the cats onto the background
(define (draw-all-cats loc)
  (add-cats-to loc BACKGROUND))

;; [Listof Cat] Image -> Image
;; Adds the cats to the given image

(define (add-cats-to loc img)
  (local (;; Cat Image -> Image
          (define (add-one-cat-to cat img)
            (place-cat-at (cat-loc cat) img))
          ;; Posn Image -> Image
          (define (place-cat-at p img)
            (place-image CAT-IMG (posn-x p) (posn-y p) img)))
    (foldr add-one-cat-to img loc)))