;; lab 05 


;; mul : List-of-Numbers -> Number
;; multiply the numbers in the list with each other

(define (mul loi)
  (cond 
    [(empty? loi) 1]
    [(cons? loi) (* (first 
                  loi)
                  (mul (rest loi)))]))


;; how-many: Number List-of-Numbers -> Number
;; returns back the number of times Number is found in List-of-Numbers

(define (how-many n lon)
  (cond 
    [(empty? lon) 0 ]
    [(cons? lon)  (cond 
                    [(= n (first lon)) (add1 (how-many n 
                                        (rest lon)))]
                    [else (how-many n (rest 
                     lon))])]))

;; list-of-occurrences : List-of-Numbers List-of-Numbers -> List-of-Numbers
;; return a list with the number of times numbers in the first list appear 
;; in the second. 

(define (list-of-occurrences nums lon)
  (cond 
    [(empty? nums) empty]
    [(cons? nums) (cons (how-many (first nums) lon) (
                         list-of-occurrences (rest nums) 
                   lon))])) 

;; list-of-occurrences-percent : List-of-Numbers List-of-Numbers -> List-of-Numbers
;; return a list with the frequency percentage of numbers in the first list appear 
;; in the second. 

(define (list-of-occurrences-percent nums lon)
  (cond 
    [(empty? nums) empty]
    [(cons? nums) (cons (calc-percentage (first nums) 
                   lon)
                        (list-of-occurrences-percent (rest nums) 
                   lon))])) 

(define (calc-percentage n lon)
  (cond 
    [(empty? lon) 0]
    [else (* 100 (/ 
            (how-many n lon)
            (length lon)))]))



(define-struct date (month day year))
;; A Date is (make-date Month Day Year) 

;; Year is a 4-digit Number e.g. 2006
;; Day is a 2-digit number between 1 - 31 
;; Month is a 2-digit Number between 1 - 12

;;interpretation: (make-date x y z) creates a date x/y/z


(define-struct file (name size owner created))
;; A File is a (make-file String Number String Date)
;; Date is defined at the top of this page. 

;; interpretation: (make-file s n u (make-date x y z)) creates the file s with
;; size n and owner u , created on date x/y/z


;; du : List-of-Files -> Number
;; add file sizes and return the total 

(define (du lof)
  (cond 
    [(empty? lof) 0]
    [(cons? lof) (+ (file-size (first lof)) (du 
     (rest lof)))]))

;; upto-size : List-of-Files size -> List-of-Files
;; return a list of files whose size is <= to size 
;; size is a Number

(define (upto-size lof n)
  (cond
    [(empty? lof) empty]
    [(cons? lof) (cond 
    [(filesize<=? (first lof) n) (cons (first lof) (upto-size (rest lof) n))]
    [else (upto-size (rest lof) n)])]))


;; filesize<=? : File Number -> Boolean 
;; is the file size <= to Number ?
(define (filesize<=? file n)
  (cond 
    [(<= (file-size file) 
     n) true]
    [else false]))

;; to-backup : List-of-Files Date -> List-of-Files
;; if file was modified since Date, then add to list of files to backup

(define (to-backup lof d) 
  (cond 
    [(empty? lof) empty]
    [(cons? lof) (cond 
    [(filedate>? (first lof) d) 
                         (cons (first lof) 
                 (to-backup (rest lof) d))]
    [else (to-backup (rest lof) d)])]))

;;filedate>? : File Date -> Boolean 
;; file date is after Date ? 
(define (filedate>? file date)
  (cond 
    [(date>? (file-created file) date) true]
    [else false]))

;;date>? : Date Date -> Boolean 
;; is the first date1 greater (earlier in the past) than second date

(define (date>? d1 d2)
  (cond 
    [(< (date-year d1) (date-year d2)) false]
    [(= (date-year d1) (date-year d2)) 
     (cond [(< (date-month d1) (date-month d2)) 
            false]
           [(= (date-month d1) (date-month d2)) (cond
    [(< (date-day d1) (date-day d2)) false]
    [(= (date-day d1) (date-day d2)) false]
    [else true])]
       [else true])]
    [else true]))


(define date1 (make-date 10 10 2005))
(define date2 (make-date 11 10 2005))
(define date3 (make-date 20 10 2005))

(define file1 (make-file "test.ss" 124 "skotthe" date1)) 
(define file2 (make-file "address-book" 256 "skotthe" date2))
(define file3 (make-file "index.html" 1024 "skotthe" date3))