(module lex mzscheme

  ;; Provides the syntax used to create lexers and the functions needed to
  ;; create and use the buffer that the lexer reads from.  See doc.txt.
	
  (require-for-syntax "private-lex/generate-code.ss"
                      "private-lex/structs.ss")

  (require (lib "list.ss")
           (lib "readerr.ss" "syntax")
           "private-lex/token.ss")

  (provide lexer lexer-src-pos define-lex-abbrev define-lex-abbrevs
	   make-lex-buf
	   get-position position-offset position-line position-col position?
           define-tokens define-empty-tokens)
  
  
  (define-syntaxes (lexer lexer-src-pos)
    (values
     (build-lexer #'here '(lambda (x) x))
     (build-lexer #'here '(lambda (x) (list x first-pos end-pos)))))

  
  (define-syntax (define-lex-abbrev stx)
    (syntax-case stx ()
      ((_ name re)
       (syntax
        (define-syntax name
          (make-lex-abbrev (quote-syntax re)))))
      (_ 
       (raise-syntax-error
        #f
        "Form should be (define-lex-abbrev name re)"
        stx))))

  (define-syntax (define-lex-abbrevs stx)
    (syntax-case stx ()
      ((_ x ...)
       (let* ((abbrev (syntax->list (syntax (x ...))))
              (r (map (lambda (a)
                        (syntax-case a ()
                          ((name re)
                           (identifier? (syntax name))
                           (syntax (define-lex-abbrev name re)))
                          (_ (raise-syntax-error
                              'Lexer-abbreviation 
                              "Form should be (identifier value)"
                              a))))
                      abbrev)))
         (datum->syntax-object
          #'here
          (cons 'begin r)
          stx)))
      (_
       (raise-syntax-error
        #f
        "Form should be (define-lex-abbrevs (name re) ...)"
        stx))))

  ;; Lex buffer is NOT thread safe


  ;; c = char | eof
  ;; lex-buf = 
  ;;   (make-lex-buffer input-port (c list) (c list) int int int (int list) boolean)
  (define-struct lex-buffer (ip from to offset line col line-lengths tab-skips has-seen-eof?))

  ;; make-lex-buf: input-port -> lex-buf
  (define make-lex-buf
    (case-lambda 
     ((ip) 
      (cond
       ((not (input-port? ip))
	(raise-type-error 'make-lex-buf "input-port" 0 ip))
       (else
	(make-lex-buffer ip null null 1 1 1 null null #f))))
     ((ip offsets)
      (cond
       ((not (input-port? ip))
	(raise-type-error 'make-lex-buf "input-port" 0 ip offsets))
       ((or (not (= 3 (length offsets)))
	    (not (andmap integer? offsets))
	    (not (andmap exact? offsets))
	    (not (andmap (lambda (x) (>= x 0)) offsets)))
	(raise-type-error 'make-lex-buf "list of 3 non-negative exact integers" 1 ip offsets))
       (else
	(make-lex-buffer ip null null (caddr offsets) (car offsets) (cadr offsets) null null #f))))))

  (define (get-next lb)
    (cond
     ((null? (lex-buffer-from lb)) 
      (let ((res (read-char (lex-buffer-ip lb))))
        (if (eof-object? res)
            (if (lex-buffer-has-seen-eof? lb)
                (raise-read-error
                 (format "lex-buf: No characters left in input stream")
                 #f #f #f #f #f)
                (set-lex-buffer-has-seen-eof?! lb #t)))
        res))
     (else 
      (begin0
       (car (lex-buffer-from lb))
       (set-lex-buffer-from! lb (cdr (lex-buffer-from lb)))))))

  ;; next-char: lex-buf -> c
  ;; gets the next character from the buffer
  (define (next-char lb)
    (let ((char-in
	   (let ((real-char (get-next lb)))
	     (if (eq? #\return real-char)
		 (let ((second-char (get-next)))
		   (if (not (eq? second-char #\newline))
		       (set-lex-buffer-from! 
			lb 
			(cons second-char (lex-buffer-from lb))))
		   #\newline)
		 real-char))))
      (set-lex-buffer-to! lb (cons char-in (lex-buffer-to lb)))
      (cond 
       ((eq? #\tab char-in)
	(let ((skip-amt (- 8 (modulo (lex-buffer-col lb) 8))))
	  (set-lex-buffer-tab-skips! lb (cons skip-amt (lex-buffer-tab-skips lb)))
	  (set-lex-buffer-col! lb (+ skip-amt (lex-buffer-col lb)))))
       ((eq? #\newline char-in)
	(set-lex-buffer-line-lengths!
	 lb
	 (cons (lex-buffer-col lb)
	       (lex-buffer-line-lengths lb)))
	(set-lex-buffer-line! lb (add1 (lex-buffer-line lb)))
	(set-lex-buffer-col! lb 1))
       (else
	(set-lex-buffer-col! lb (add1 (lex-buffer-col lb)))))
      (set-lex-buffer-offset! lb (add1 (lex-buffer-offset lb)))
      char-in))
  
  ;; push-back: lex-buf * int -> c list
  ;; pushes the last read i characters back to be read again
  ;; returns the characters not pushed back and read after the last push-back
  ;; (in reverse order)
  (define (push-back lb i)
    (letrec (
	     ;; switch-buffers: c list * c list * int -> clist * clist
	     ;; moves num-to-add characters from from to to.
	     ;; (switch-buffers '(1 2 3 4) '(5 6 7 8) 2) =
	     ;;   (values '(3 4) '(2 1 5 6 7 8))
	     ;; (switch-buffers '(4 3 2 1) '(5 6 7 8) 2) =
	     ;;   (values '(2 1) '(3 4 5 6 7 8))
	     (switch-buffers
	      (lambda (from to num-to-add)
		(cond
		 ((= 0 num-to-add) (values from to))
		 (else
		  (cond
		   ((eq? #\newline (car from))
		    (set-lex-buffer-line! lb (sub1 (lex-buffer-line lb)))
		    (set-lex-buffer-col! lb (car (lex-buffer-line-lengths lb)))
		    (set-lex-buffer-line-lengths! lb (cdr (lex-buffer-line-lengths lb))))
                   ((eq? #\tab (car from))
                    (set-lex-buffer-col! lb (- (lex-buffer-col lb) 
                                               (car (lex-buffer-tab-skips lb))))
                    (set-lex-buffer-tab-skips! lb (cdr (lex-buffer-tab-skips lb))))
                   (else
                    (set-lex-buffer-col! lb (sub1 (lex-buffer-col lb)))))
                  (switch-buffers (cdr from) 
                                  (cons (car from) to) 
                                  (sub1 num-to-add)))))))
      (let-values (((ret new-from)
		    (switch-buffers (lex-buffer-to lb)
				    (lex-buffer-from lb)
				    i)))
        (set-lex-buffer-from! lb new-from)
        (set-lex-buffer-to! lb null)
        (set-lex-buffer-offset! lb (- (lex-buffer-offset lb) i))
        (set-lex-buffer-line-lengths! lb null)
        (set-lex-buffer-tab-skips! lb null)
        ret)))

  (define-struct position (offset line col))
  (define (get-position lb)
    (make-position (lex-buffer-offset lb)
		   (lex-buffer-line lb)
		   (lex-buffer-col lb)))


)