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+;;; Copyright © 2018 swedebugia <swedebugia@riseup.net>
+;;;
+;;; This file is part of guile-wikidata.
+;;;
+;;; guile-wikidata is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; guile-wikidata is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with guile-wikidata.  If not, see <http://www.gnu.org/licenses/>.
+
+;; See the example-sparql.scm for how to use this library.
+
+(define-module (wikidata sparql)
+  #:use-module (ice-9 format)
+  #:use-module (ice-9 rdelim)
+  #:use-module (ice-9 receive)
+  #:use-module (guix http-client)
+;;  #:use-module (guix import utils) ; useful stuff there
+;;  #:use-module (sparql driver) ; does not support blazegraph
+;;  #:use-module (sparql lang) ; did not work ??
+  #:use-module (sparql util)
+  #:use-module (srfi srfi-1)
+  #:use-module (srfi srfi-34)
+  #:use-module (web uri)
+  #:export (show-sparql))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Low-level proc.
+;; URI-decorators and fetching
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+;; TODO flesh out http-code from giux into a new guile-http library to
+;; avoid pulling in all of guix in this library.
+(define* (xml-fetch url
+                     ;; Note: many websites returns 403 if we omit a
+                     ;; 'User-Agent' header.
+                     #:key (headers `((user-agent . "GNU Guile")
+                                      (Accept . "application/json"))))
+  "Return a representation of the JSON resource URL (a list or hash table), or
+#f if URL returns 403 or 404.  HEADERS is a list of HTTP headers to pass in
+the query. Returns RESULT from port."
+  (guard (c ((and (http-get-error? c)
+                  (let ((error (http-get-error-code c)))
+                    (or (= 403 error)
+                        (= 404 error))))
+             #f))
+    (let* ((port   (http-fetch url #:headers headers))
+	   ;; Return result without any modification.
+           (result port))
+;;      (close-port port)
+      result)))
+
+(define (wdquery-xml uri)
+  "Fetch the data, return PORT"
+  (xml-fetch uri))
+
+
+;; Inspired by http://r.duckduckgo.com/l/?kh=-1&uddg=http%3A%2F%2Fstackoverflow.com%2Fquestions%2F29886388%2Fddg%2335118127
+;;;
+;;; Wikidata-specific SPARQL-QUERY using a GET request (it also accept POST)
+;;; ---------------------------------------------------------------------------
+(define* (wdsparql-uri query
+		       #:key
+                       (uri #f)
+                       (type "json"))
+    "Build URI for the Wikidata HTTP GET SPARQL API."
+  (let* ((get-uri "http://query.wikidata.org/sparql")
+         (get-url (if uri
+                      uri
+                      get-uri)))
+    (string->uri
+     (string-append get-url "?" (uri-encode query))
+     )
+    ))
+
+
+;;;
+;;; Medium-level proc.
+;;; ---------------------------------------------------------------------------
+
+;; TODO add rationale for why this is copied from (sparql util)
+(define (display-query-results port)
+  "Format the output from the port and close it"
+  (begin
+    (let ((line (read-line port)))
+     (if (eof-object? line)
+         #t
+         ;; The default output format is comma-separated values (CSV).
+         (let ((tokens (string-split line #\,)))
+           (format #t "~{~a~/~}~%" tokens)
+           (display-query-results port))))
+    (close-port port)))
+
+;;;
+;;; High-level proc.
+;;; ---------------------------------------------------------------------------
+
+;; See example-sparql.scm for how to enter the query
+(define (show-sparql query)
+  "Run the query on the Wikidata Blazegraph server. Show the result on current-output-port."
+  (display-query-results 
+   (xml-fetch
+    (wdsparql-uri
+     query))))