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

;;; =======================================================
;;;  CMPU-101, Spring 2013
;;;  Lab 8 
;;; =======================================================

(display "\n         CS101 Lab 8, Spring 2013")
(display "\n        Please write your name here\n\n")

;; IMPORTANT!  MAKE SURE YOUR LINES OF CODE DO NOT WRAP WHEN YOUR
;; WINDOW IS ABOUT 80 COLUMNS ACROSS (SEE A COACH OR YOUR PROF IF YOU 
;; ARE UNSURE HOW TO DO THIS). 

(display "\n\n----------------------------\n")
(display "Problem 1(a): Generate posn list")
(display "\n----------------------------\n")
; 
;  A list of posns is either
;  1. empty, or
;  2. it's a (cons p lop), where p is a posn and lop is a list of posns 
;     that is one element shorter than (cons p lop).
; 
;  Write a function gen-posn-list that consumes one positive natural   
;  number n, and produces a list of n posns with x and y fields that 
;  are random numbers generated between 0 and SIDE (that is, the x field 
;  is a random number between 0 and SIDE and the y field is a random 
;  number between 0 and SIDE).  
;  
;  SIDE is a constant that represents the width and height of an empty 
;  scene and you should define this to be 800.
;  
;  Some results of running this function in the interactions window are
;  shown below:
;  
;  > (gen-posn-list 3)
;  (#(struct:posn 474 23) #(struct:posn 496 420) #(struct:posn 660 415))
;  > (gen-posn-list 2)
;  (#(struct:posn 522 189) #(struct:posn 31 617))
;  > (gen-posn-list 0)
;  empty
;  
;  You should use the function you write for this problem to generate
;  lists of posns for the printf statements in problem 1(b).
; 


;;Constant definitions:

;;Contract: 
;;Header:   
;;Purpose: 

;;Pre-function tests: Can be done to test length of list. Contents
;;                    of posns are set at random, so can't be easily
;;                    tested.


;;Function definition:
;(define gen-posn-list


;;Post-function printfs: (uncomment after writing the function)
;(printf "(gen-posn-list 0) => ~a~%" (gen-posn-list 0))
;(printf "(gen-posn-list 13) => ~a~%" (gen-posn-list 13))
;(printf "(gen-posn-list 3) => ~a~%" (gen-posn-list 3))


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(display "\n\n-------------------------------------------------------\n")
(display "    Problem 1(b): Connect the dots ")
(display "\n-------------------------------------------------------\n")     
; 
;  Write a function called connect-the-dots that consumes a list of  
;  posns (the type of list created in problem 1(a) and produces a
;  scene in which each consecutive pair of posns is connected by a line, 
;  including a line between the last posn and the first posn on the list, 
;  to form a path linking all posns in the input list. The result 
;  produced by this function should be a scene containing a polygon 
;  (a plane figure that is bounded by a closed path, composed of a 
;  finite sequence of straight line segments (i.e., by a closed 
;  polygonal chain)).
;  
;  You should use the built-in function scene+line as part of the 
;  connect-the-dots function (instead of using place-image as you 
;  usually have when you create a scene). The scene+line function
;  consumes 6 arguments: an image, the x and y coordinates of one posn
;  (numbers), the x and y coordinates of another posn (numbers), and a 
;  color. The scene+line function draws a line of a specified color 
;  between the first x and y coordinate values and the second x and y
;  coordinate values. The image consumed as the first argument to  
;  scene+line will be the result of a recursive call that eventually 
;  returns the base case, an empty scene.
;  
;  Since function connect-the-dots returns a scene, you should define 
;  a constant for the empty-scene, as well as for the line color. You 
;  can add any other constants you need to avoid writing literal values 
;  in your code. You are free to choose a line color.
;  
;  If the list of posns is < 3 in length, a polygon cannot be formed, 
;  so your function must include checks for lists that are < 3 posns 
;  long and produce a string "Error, not enough points for a polygon."
;  
;  Note that the function you wrote for part (a) is used in the printf
;  statements for this problem, but not in the actual function body.
;  


;;Constant definitions:

;;Contract: 
;;Header:   
;;Purpose: 

;;Pre-function tests: Can test the cases that produce a string, the
;;other cases can be tested by visual inspection.

;;Function definition:
;(define connect-the-dots


;;Post-function printfs: (uncomment after writing the function)
;(printf "(connect-the-dots (gen-posn-list 8)) => ~a~%"
;        (connect-the-dots (gen-posn-list 8)))
;(printf "(connect-the-dots (gen-posn-list 4)) => ~a~%"
;        (connect-the-dots (gen-posn-list 4)))
;(printf "(connect-the-dots (gen-posn-list 0)) => ~a~%"
;        (connect-the-dots (gen-posn-list 0)))

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(display "\n\n--------------------------------------\n")
(display "Problem 2: Creating a list of posn pairs")
(display "\n--------------------------------------\n")
;  
;  This problem is not related to the functions you wrote in problem
;  1, but it will help prepare you for homework assignment 6. 
; 
;  A list of posn pairs is either
;  1. empty, or
;  2. it's a (cons (list p q) lopp), where p and q are posns and lopp is 
;     a list of posn pairs.
;  
;  Write a function called make-endpoints, that consumes 3 numbers, 
;  n, width, and depth, and creates a list of n lists that each contain 
;  2 posns. The posn-x field of each posn should be a random number
;  between 1 and width, and the posn-y field should be a random number
;  between 1 and depth.
;   
;  Each inner list will contain 2 posns. 
;  
;  Suppose n=5, width=800 and depth=200. The following invocations of
;  make-endpoints could produce a list like the one shown below:
;  
;  > (make-endpoints 3 800 200)
;  ((#(struct:posn 474 23) #(struct:posn 496 120)) 
;   (#(struct:posn 660 415)(#(struct:posn 474 23)) 
;   (#(struct:posn 96 40) #(struct:posn 660 115))))
;  


;;Contract: 
;;Header:   
;;Purpose: 

;;Pre-function tests: Can be done to test length of list. Contents
;;                    of posns are set at random, so those can't be 
;;                    easily tested. 

;;Function definition:
;(define make-endpoints



;;Post-function printfs: (uncomment after writing the function)
;(printf "(make-endpoints 9 200 200) => ~a~%" (make-endpoints 9 200 200))
;(printf "(make-endpoints 3 400 200) => ~a~%" (make-endpoints 3 400 200))
;(printf "(make-endpoints 0 200 200) => ~a~%" (make-endpoints 0 200 200))


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