#lang scheme/base
(require (planet bzlib/base)
         (planet bzlib/port/port)
         "path.ss"
         "base.ss"
         "file.ss"
         scheme/file
         (planet bzlib/os)
         )

;; what does this do?
;; 1 - create the temp file.
;; 2 - write to the temp file...
;; 3 - when closing the temp file - we want the file to then be renamed to the original
;;     file...
;; is there a filter somewhere here?
;; 1 - write the port to the actual underlying file...
;;     when it is closed -
;; THIS IS NOT GUARANTEED TO WORK ON WINDOWS...
(define (open-output-atomic-file path)
  (let* ((temp (make-temporary-file ".gzlib-temp.~a" #f (parent-path path)))
         (out (open-output-file temp #:exists 'replace)))
    (make-output-port path
                      always-evt 
                      (lambda (bytes-out start end block? break?)
                        (if (= start end)
                            (flush-output out)
                            (write-bytes bytes-out out start end)))
                      (lambda () 
                        (begin0 (close-output-port out)
                                (+:windows (rename-file temp path) ;; this line can still fail in windows...
                                           (rename temp path #t))  
                                )))))

(define call-with-output-atomic-file
  (make-call-with-output-port open-output-atomic-file path))

(provide/contract 
 (open-output-atomic-file (-> path-string? output-port?))
 (call-with-output-atomic-file
     (-> path-string? (-> output-port? any) any))
 )