#| -*-Scheme-*-

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    2017, 2018, 2019, 2020, 2021, 2022 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,
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|#

;;;; Buffer Input Ports

(declare (usual-integrations))

(define (with-input-from-mark mark thunk #!optional receiver)
  (let ((port (make-buffer-input-port mark (group-end mark))))
    (let ((value
	   (parameterize ((current-input-port port))
	     (thunk))))
      (if (default-object? receiver)
	  value
	  (receiver value (input-port/mark port))))))

(define (with-input-from-region region thunk)
  (parameterize ((current-input-port
		  (make-buffer-input-port (region-start region)
					  (region-end region))))
    (thunk)))

(define (call-with-input-mark mark procedure)
  (procedure (make-buffer-input-port mark (group-end mark))))

(define (call-with-input-region region procedure)
  (procedure
   (make-buffer-input-port (region-start region) (region-end region))))

(define (make-buffer-input-port start end)
  ;; This uses indices, so it can only be used locally
  ;; where there is no buffer-modification happening.
  (make-port buffer-input-port-type
	     (make-bstate (mark-group start)
			  (mark-index start)
			  (mark-index end)
			  (mark-index start))))

(define (input-port/mark port)
  (let ((operation (textual-port-operation port 'BUFFER-MARK)))
    (if (not operation)
	(error:bad-range-argument port 'INPUT-PORT/MARK))
    (operation port)))

(define-structure bstate
  (group #f read-only #t)
  (start #f read-only #t)
  (end #f read-only #t)
  (index #f))

(define buffer-input-port-type
  (make-port-type
   `((BUFFER-MARK
      ,(lambda (port)
	(let ((state (port/state port)))
	  (make-mark (bstate-group state)
		     (bstate-index state)))))
     (CHAR-READY?
      ,(lambda (port)
	 (let ((state (port/state port)))
	   (fix:< (bstate-index state)
		  (bstate-end state)))))
     (PEEK-CHAR
      ,(lambda (port)
	 (let ((state (port/state port)))
	   (let ((index (bstate-index state)))
	     (if (fix:< index (bstate-end state))
		 (group-right-char (bstate-group state) index)
		 (eof-object))))))
     (READ-CHAR
      ,(lambda (port)
	 (let ((state (port/state port)))
	   (let ((index (bstate-index state)))
	     (if (fix:< index (bstate-end state))
		 (let ((char (group-right-char (bstate-group state) index)))
		   (set-bstate-index! state (fix:+ index 1))
		   char)
		 (eof-object))))))
     (UNREAD-CHAR
      ,(lambda (port char)
	 (let ((state (port/state port)))
	   (let ((index (bstate-index state)))
	     (if (fix:<= index (bstate-start state))
		 (error "No character to unread:" port))
	     (if (not (char=? (group-left-char (bstate-group state) index)
			      char))
		 (error "Incorrect char being unread:" char))
	     (set-bstate-index! state (fix:- index 1))))))
     (WRITE-SELF
      ,(lambda (port output)
	 (write-string " from buffer at " output)
	 (write (input-port/mark port) output))))
   #f))