(require (lib "xml.ss" "xml"))

(define i (open-input-file "forecast.xml"))
(define doc-elem (document-element(read-xml i)))

;****************** xml data definitions 

;Element = (make-element Location Location
;                        Symbol
;                        (listof Attribute)
;                        (listof Content))

;Content = Pcdata
;          |  Element
;          |  Entity
;          |  Misc

;Pcdata = (make-pcdata Location Location String)

;Entity = (make-entity (U Nat Symbol))

;Misc = Comment
;    |  Processing-instruction

;********************


;******************** forecast internal data definition

; A forecast is
; (make-forecast date/string num num '(num num))
(define-struct forecast (target-date low-temp high-temp pair-of-pop))

;******************** templates

;f-of-element : element -> ...
;(define (f-of-element el)
;  ... (f-of-name (element-name el)) 
;  ... (f-of-listof-content (element-content el))
;    )

;f-of-listofcontent : content -> ...
;(define (f-of-listofcontent l)
;  ... (f-of-pcdata (car l))
;  ... (f-of-element (car l))
;  ... (f-of-entity (car l))
;  ... (f-of-listofcontent (cdr l))
;  )

; the two functions below extract and translate xml data

; return listof-X for all elements satisfying COMP
; get-content-from-element : (element->bool) (listof-content->listof-X) element -> listof-X
(define (get-content-from-element COMP F el)
  (cond
    [(COMP el) (F (element-content el))]
    [else (get-content-from-listof-content COMP F (element-content el))])
   )

; get-content-from-listof-content : (element->bool) (content->X) listof-content -> listof-X
(define (get-content-from-listof-content COMP F l)
  (cond
    [(eq? l '()) l]
    
    [(element? (car l)) 
     (append (get-content-from-element COMP F (car l))
             (get-content-from-listof-content COMP F (cdr l)))]

    ; don't care about entity or pcdata ... just process rest of list
    [else (get-content-from-listof-content COMP F (cdr l))]
    )
  )


;**************************** utilities

(define (curry f)
  (lambda (v1)
    (lambda (v2)
      (f v1 v2))))

; strip-string : string -> string
; strip whitespace characters from s
(define (strip-string s)
  (letrec ((strip-c (lambda(c l) 
                      (cond
                        [(char-whitespace? c) l]
                        [else (cons c l)]))))
  (list->string (foldr strip-c '() (string->list s)))))


; name=? symbol element -> bool
(define (name=? name el)
  (eq? name (element-name el)))

;*******************************


; test cases (specific to forecast.xml)

; forecastCreationTime

(define (content->fcd l)
  (list (pcdata-string (car l))))

(get-content-from-element ((curry name=?) '|forecastCreationTime|) content->fcd doc-elem)
"should be " '("Mon Feb  9 23:13:40 2004")


; target date

(define (content->date l)
  (list (pcdata-string (car l))))

(get-content-from-element ((curry name=?) '|validDate|) content->date doc-elem)
"should be" '("Feb 10" "Feb 11" "Feb 12" "Feb 13" "Feb 14" "Feb 15" "Feb 16")

; temperature

(define (content->number l)
  (list (string->number (strip-string (pcdata-string (car l))))))

(get-content-from-element ((curry name=?) '|maxTemp|) content->number doc-elem)
"should be" '(28 30 26 29 35 37 29)

; forecast

(define (content->forecast l)
  (letrec ((g (lambda (name F)
                (get-content-from-listof-content ((curry name=?) name) F l))))
  (list (make-forecast
         (car (g '|validDate| content->date))
         (car (g '|minTemp| content->number))
         (car (g '|maxTemp| content->number))
         (g '|pop| content->number)))))

(get-content-from-element ((curry name=?) '|forecastDay|) content->forecast doc-elem)