;; Copyright 2004 Mike Burns
;; For research use only. Do not distribute with intent to use.

;; Mike Burns 2004-10-03 mike@mike-burns,com
;; Re-write of rss->xexpr using a hypothetical RDF library.

;; Based on this, the API for RDF will look like:
;; Data:
;;  URI : String
;;  Object : (union String Node (listof Object))
;;  Namespace : String
;;  Node : completely internal, no idea yet
;;  RDF : completely internal, no idea yet
;; Functions:
;;  rdf-namespace : String -> Namespace
;;  rdf-base-node : URI Object ... -> RDF
;;  rdf-node : (cons Symbol Namespace)
;;             (union (cons Symbol Namespace) String #f) Object ... -> Node
;;  rdf->xexpr : RDF -> Xexpr

;; The result of rss->xexpr, for a RSS with one item, will resemble this idea:
;; {
;; ( (rss-link a-rss), rdf#type, rss#channel ),
;; ( (rss-link a-rss), rss#description, (rss-description a-rss) ),
;; ( (rss-link a-rss), rss#items, jklsadjfl ),
;; ( jklsadjfl, rdf#type, rdf#seq ),
;; ( jklsadjfl, rdf#_1, (item-link a-item) ),
;; ( (item-link a-item), rdf#type, rss#item),
;; ( (item-link a-item), rss#title, (item-title a-item) ),
;; ( (item-link a-item), rss#link, (item-link a-item) ),
;; ( (item-link a-item), dc#date, (item-date a-item) ),
;; ( (item-link a-item), dc#creator, (item-author a-item) ),
;; ( (item-link a-item), content#encoded, (item-text a-item) ),
;; }
;; Note that 'jklsadjfl' was completely made up, and replaces the #f. To think
;; about: need this made-up URI remain consistent across runs? With modified
;; input?
(module write mzscheme
  (require (lib "xml.ss" "xml")
           (planet "create.ss" ("mburns" "rdf.plt" 1 0)))

  (provide rss->xexpr)

  ;; rss->xexpr : RSS -> Xexpr
  ;; Produce the XML representation of the RSS, which is just RDF afterall.
  (define (rss->xexpr a-rss)
    (let ((rdf-ns (rdf-namespace "http://www.w3.org/1999/02/22-rdf-syntax-ns#"))
          (rss-ns (rdf-namespace "http://my.netscape.com/rdf/simple/0.9/")))
      (let ((type (cons 'type rdf-ns)))
        (rdf->xexpr
          (rdf-base-node
            (rss-link a-rss)
            (rdf-node type (cons 'channel rss-ns))
            (rdf-node (cons 'description rss-ns) (rss-description a-rss))
            (rdf-node (cons 'items rss-ns) #f
                      (rdf-node type (cons 'seq rdf-ns))
                      (rss-items->rdfs rdf-ns rss-ns (rss-items a-rss))))))))

  ;; rss-items->rdf : Namespace Namespace (listof Item) -> (listof RDF)
  ;; A list of RDFs, each corresponding to a RSS Item.
  (define (rss-items->rdfs rdf-ns rss-ns items)
    (let ((content-ns (rdf-namespace "http://purl.org/rss/1.0/modules/content/"))
          (dc-ns (rdf-namespace "http://purl.org/dc/elements/1.1/")))
      (map (lambda (a-item n)
             (rdf-node (cons n rdf-ns)
                       (item-link a-item)
                       (rdf-node type (cons 'item rss-ns))
                       (rdf-node (cons 'title dc-ns)
                                 (item-title a-item))
                       (rdf-node (cons 'link rss-ns)
                                 (item-link a-item))
                       (rdf-node (cons 'date dc-ns)
                                 (item-date a-item))
                       (rdf-node (cons 'creator dc-ns)
                                 (item-author a-item))
                       (rdf-node (cons 'encoded content-ns)
                                 (item-text a-item))))
           items
           (sequence-numbers (length items)))))

  ;; sequence-numbers : Number -> (listof Symbol)
  ;; Produce the Seq names for all the numbers specified.
  (define (sequence-numbers n)
    (build-list
      n
      (lambda (n)
        (string->symbol (string-append "_" (number->string (add1 n)))))))


  )