#| -*-Scheme-*-

Copyright (C) 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994,
    1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005,
    2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016,
    2017, 2018, 2019, 2020 Massachusetts Institute of Technology

This file is part of MIT/GNU Scheme.

MIT/GNU Scheme 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 2 of the License, or (at
your option) any later version.

MIT/GNU Scheme 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 MIT/GNU Scheme; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301,
USA.

|#

;;;; Codec for RDF N-triples syntax

(declare (usual-integrations))

;;;; Decoder

(define (read-rdf/nt-file pathname)
  (call-with-input-file pathname
    (lambda (port)
      (let loop ((triples '()))
	(let ((triple (read-rdf/nt port)))
	  (if (eof-object? triple)
	      triples
	      (loop (cons triple triples))))))))

(define (rdf/nt-file->source pathname)
  (let ((port (open-input-file pathname)))
    (lambda ()
      (let ((triple (read-rdf/nt port)))
	(if (eof-object? triple)
	    #f
	    triple)))))

(define (read-rdf/nt port)
  (let loop ()
    (let ((line (read-line port)))
      (if (eof-object? line)
	  line
	  (let ((v
		 (or (with-rdf-input-port port
		       (lambda ()
			 (parse-one-line (string->parser-buffer line))))
		     (error "Failed to parse RDF/NT line:" line))))
	    (if (fix:= (vector-length v) 0)
		(loop)
		(vector-ref v 0)))))))

(define parse-one-line
  (*parser
   (complete
    (seq (noise match-ws*)
	 (? (alt parse-triple parse-comment))))))

(define parse-triple
  (*parser
   (encapsulate (lambda (v)
		  (make-rdf-triple (vector-ref v 0)
				   (vector-ref v 1)
				   (vector-ref v 2)))
     (seq (alt parse-uri-ref parse-node-id)
	  (noise match-ws+)
	  parse-uri-ref
	  (noise match-ws+)
	  (alt parse-uri-ref parse-node-id parse-literal)
	  (noise match-ws*)
	  "."
	  (noise match-ws*)))))

(define parse-comment
  (*parser (noise (seq "#" (* (char-set char-set:character))))))

(define parse-uri-ref
  (*parser (seq #\< parse-absolute-uri #\>)))

(define parse-node-id
  (*parser
   (encapsulate (lambda (v) (make-rdf-bnode (vector-ref v 0)))
     (seq "_:"
	  (match match-bnode-name)))))

(define match-bnode-name
  (let* ((name-head
	  (char-set-union (ucs-range->char-set #x41 #x5B)
			  (ucs-range->char-set #x61 #x7B)))
	 (name-tail
	  (char-set-union name-head
			  (ucs-range->char-set #x30 #x3A))))
    (*matcher
     (seq (char-set name-head)
	  (* (char-set name-tail))))))

(define parse-literal
  (*parser
   (encapsulate (lambda (v)
		  (make-rdf-literal (vector-ref v 0) (vector-ref v 1)))
     (seq #\"
	  parse-string
	  #\"
	  (alt (seq #\@ parse-language)
	       (seq "^^" parse-uri-ref)
	       (values #f))))))

(define parse-language
  (*parser (map intern (match match-language))))

(define (parse-string b)
  (let ((port (open-output-string)))

    (define (loop)
      (let ((p (get-parser-buffer-pointer b)))
	(if (match-parser-buffer-char-in-set b char-set:unescaped)
	    (begin
	      (let loop ()
		(if (match-parser-buffer-char-in-set b char-set:unescaped)
		    (loop)))
	      (call-with-parser-buffer-tail b p
		(lambda (string start end)
		  (write-string string port start end))))))
      (let ((char
	     (let ((p (get-parser-buffer-pointer b)))
	       (and (match-parser-buffer-char b #\\)
		    (cond ((match-parser-buffer-char b #\t) #\tab)
			  ((match-parser-buffer-char b #\n) #\newline)
			  ((match-parser-buffer-char b #\r) #\return)
			  ((match-parser-buffer-char b #\") #\")
			  ((match-parser-buffer-char b #\\) #\\)
			  ((or (and (match-parser-buffer-char b #\u)
				    (match-hex 4))
			       (and (match-parser-buffer-char b #\U)
				    (match-hex 8)))
			   (integer->char
			    (call-with-parser-buffer-tail b p
			      (lambda (string start end)
				(string->number string 16 #t (+ start 2)
						end)))))
			  (else #f))))))
	(if char
	    (begin
	      (write-char char port)
	      (loop))
	    (vector (get-output-string port)))))

    (define (match-hex n)
      (let loop ((i 0))
	(if (fix:< i n)
	    (and (match-parser-buffer-char-in-set b char-set:hex)
		 (loop (fix:+ i 1)))
	    #t)))

    (loop)))

(define match-ws*
  (*matcher (* (char-set char-set:ws))))

(define match-ws+
  (*matcher (+ (char-set char-set:ws))))

(define char-set:ws
  (char-set #\space #\tab))

(define char-set:character
  (ucs-range->char-set #x20 #x7F))

(define char-set:hex
  (char-set-union (ucs-range->char-set #x30 #x3A)
		  (ucs-range->char-set #x41 #x47)))

(define char-set:unescaped
  (char-set-difference char-set:character (char-set #\" #\\)))

;;;; Encoder

(define (write-rdf/nt-file triples pathname)
  (call-with-output-file pathname
    (lambda (port)
      (for-each (lambda (triple)
		  (write-rdf/nt triple port))
		triples))))

(define (write-rdf/nt triple port)
  (let ((s (rdf-triple-subject triple)))
    (cond ((uri? s) (write-rdf/nt-uri s port))
	  ((rdf-bnode? s) (write-rdf/nt-bnode s port))))
  (write-string " " port)
  (write-rdf/nt-uri (rdf-triple-predicate triple) port)
  (write-string " " port)
  (let ((o (rdf-triple-object triple)))
    (cond ((uri? o) (write-rdf/nt-uri o port))
	  ((rdf-bnode? o) (write-rdf/nt-bnode o port))
	  ((rdf-literal? o) (write-rdf/nt-literal o port))))
  (write-string " ." port)
  (newline port))

(define (write-rdf/nt-uri uri port)
  (write-string "<" port)
  (write-uri uri port)
  (write-string ">" port))

(define (write-rdf/nt-bnode bnode port)
  (write-string "_:" port)
  (write-string (rdf-bnode-name bnode) port))

(define (write-rdf/nt-literal literal port)
  (write-rdf/nt-literal-text (rdf-literal-text literal) port)
  (cond ((rdf-literal-type literal)
	 => (lambda (uri)
	      (write-string "^^" port)
	      (write-rdf/nt-uri uri port)))
	((rdf-literal-language literal)
	 => (lambda (lang)
	      (write-string "@" port)
	      (write-string (symbol->string lang) port)))))

(define (write-rdf/nt-literal-text text port)
  (let ((text (open-input-string text)))
    (write-string "\"" port)
    (let loop ()
      (let ((char (read-char text)))
	(if (not (eof-object? char))
	    (begin
	      (write-literal-char char port)
	      (loop)))))
    (write-string "\"" port)))

(define (write-literal-char char port)
  (if (char-in-set? char char-set:unescaped)
      (write-char char port)
      (begin
	(write-char #\\ port)
	(if (or (char=? char #\")
		(char=? char #\\))
	    (write-char char port)
	    (let ((n (char->integer char)))
	      (cond ((fix:= n #x9) (write-char #\t port))
		    ((fix:= n #xA) (write-char #\n port))
		    ((fix:= n #xD) (write-char #\r port))
		    ((fix:< n #x10000)
		     (write-char #\u port)
		     (write-hex n 4 port))
		    (else
		     (write-char #\U port)
		     (write-hex n 8 port))))))))

(define (write-hex n digits port)
  (let loop ((n n) (m (expt 16 digits)))
    (if (> m 1)
	(begin
	  (write-char (string-ref "0123456789ABCDEF" (quotient n m)) port)
	  (loop (remainder n m) (quotient m 16))))))