;;;
;;; file/filter.scm - utility to build filter programs
;;;  
;;;   Copyright (c) 2000-2007  Shiro Kawai  <shiro@acm.org>
;;;   
;;;   Redistribution and use in source and binary forms, with or without
;;;   modification, are permitted provided that the following conditions
;;;   are met:
;;;   
;;;   1. Redistributions of source code must retain the above copyright
;;;      notice, this list of conditions and the following disclaimer.
;;;  
;;;   2. Redistributions in binary form must reproduce the above copyright
;;;      notice, this list of conditions and the following disclaimer in the
;;;      documentation and/or other materials provided with the distribution.
;;;  
;;;   3. Neither the name of the authors nor the names of its contributors
;;;      may be used to endorse or promote products derived from this
;;;      software without specific prior written permission.
;;;  
;;;   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
;;;   "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
;;;   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
;;;   A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
;;;   OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
;;;   SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
;;;   TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
;;;   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
;;;   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
;;;   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
;;;   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
;;;  
;;;  $Id: filter.scm,v 1.7 2007/03/02 07:39:08 shirok Exp $
;;;

;;; This module provides utilities for a common pattern in
;;; filter-type commands, that is, to take an input, to process
;;; the content, and to write the result.   The common occurring
;;; pattern is:
;;; 
;;; - input may be a specified file, or stdin.
;;; - output may be a specified file, or stdout.
;;; - output may be a temporary file, which will be renamed
;;;   upon completion of the processing.
;;; - output file may be removed when an error occurs in the processing.
;;;

(define-module file.filter
  (use srfi-11)
  (use srfi-13)
  (export file-filter)
  )
(select-module file.filter)

(define (file-filter proc . options)
  (let-keywords options
      ((input  (current-input-port))
       (output (current-output-port))
       (temporary-file #f)
       (keep-output?   #f))

    (define (process-with-output oport)
      (cond
       ((input-port? input) (proc input oport))
       ((string? input)
        (call-with-input-file input (lambda (iport) (proc iport oport))))
       (else
        (error "input must be either an input port or a file name, but got"
               input))))

    (define (process-with-tempfile ofile)
      (let*-values (((tempfile) (cond ((string-prefix? "/" temporary-file)
                                       temporary-file)
                                      ((string-prefix? "./" temporary-file)
                                       temporary-file)
                                      ((string-prefix? "../" temporary-file)
                                       temporary-file)
                                      (else (string-append
                                             (sys-dirname ofile)
                                             "/"
                                             temporary-file))))
                    ((tport tfile) (sys-mkstemp tempfile)))
        (guard (e
                (else 
                 (unless keep-output? (sys-unlink tfile))
                 (raise e)))
          (receive r (process-with-output tport)
            (close-output-port tport)
            (sys-rename tfile ofile)
            (apply values r)))))

    (cond
     ((output-port? output) (process-with-output output))
     ((string? output)
      (if temporary-file
          (process-with-tempfile output)
          (with-error-handler
           (lambda (e)
             (unless keep-output? (sys-unlink output))
             (raise e))
           (lambda ()
             (call-with-output-file output process-with-output)))))
     (else
      (error "output must be either an output port or a file name, but got"
             output)))
    )
  )

(provide "file/filter")




