#!/usr/bin/guile \
-e main -s
!#

(use-modules
 (web client)
 (web response)
 (sxml simple)
 (sxml xpath)
 (sxml transform)
 (ice-9 regex)
 )



(define transformer
  `((rss:item
     . ,(lambda (key . children)
          (define tag (cons key children))
          (call-with-values (lambda () (apply values ((sxpath '(rss:title *text*)) tag)))
            (case-lambda (() tag)
                         ((title . _)
                          (if (string-match "^\\[\\$\\]" title)
                              '() tag))))))))

(define (parse-rss port)
  (xml->sxml port
             #:namespaces
             '((rdf . "http://www.w3.org/1999/02/22-rdf-syntax-ns#")
               (dc . "http://purl.org/dc/elements/1.1/")
               (syn . "http://purl.org/rss/1.0/modules/syndication/")
               (rss . "http://purl.org/rss/1.0/"))) )

(define (filter-tree transformers tree)
  (pre-post-order
   tree
   `(,@transformer
     (*text* . ,(lambda (_ x . xs) x))
     (*default* . ,(lambda (item  . children)
                     (cons item children))))) )

(define (main args)

  (define response
    (http-get "https://lwn.net/headlines/Features"
              #:streaming? #t))

  (unless (= 200 (response-code response))
    (format (current-error-port) "HTTP error ~a"
            (response-code response))
    (exit 1))

  (with-output-to-file "lwn-unlocked-features.xml"
    (lambda ()
      (sxml->xml
       (filter-tree
        transformer
        (parse-rss (response-body-port response)))))))