File : agpl-safe_file.adb


------------------------------------------------------------------------------

--                         ADAGIO - ADALID - AENEA.                         --

--                                                                          --

--                            Copyright (C) 2003                            --

--                                 A. Mosteo.                               --

--                                                                          --

--  Authors: A. Mosteo. (adagio@mosteo.com)                                 --

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--  This program is free software; you can redistribute it and/or modify    --

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--  your option) any later version.                                         --

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--  This program 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.                                --

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--  You should have received a copy of the GNU General Public License       --

--  along with this library; if not, write to the Free Software Foundation, --

--  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.          --

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--  You are not allowed to use any part of this code to develop a program   --

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------------------------------------------------------------------------------

--  $Id: agpl-safe_file.adb,v 1.3 2004/01/21 21:05:25 Jano Exp $


--  Facilities for saving/loading from a file in a way that it doesn't 

--  overwrite the previous version.

--  When opening for writing, a temporary is used. After completion, the

--  original file is removed and the temporary renamed.

--  When opening for reading, regular filename is tried. If missing, a check

--  for a temporary is made, and if it exists, it is renamed to the regular

--  name and opened. If neither regular and temporary exists, error.


with Ada.Streams.Stream_IO;
use  Ada.Streams.Stream_IO;

with Gnat.Os_lib;
use  Gnat;

package body Agpl.Safe_file is

   ------------------------------------------------------------------------

   -- Exists_for_reading                                                 --

   ------------------------------------------------------------------------

   function Exists_for_reading (Name : in String) return Boolean is
   begin
      return Os_lib.Is_regular_file (Name) or else
             Os_lib.Is_regular_file (Name & ".tmp");
   end Exists_for_reading;

   ------------------------------------------------------------------------

   -- Get_Real_Name                                                      --

   ------------------------------------------------------------------------

   -- Gets the real name found (i.e. the supplied or the backup one

   function Get_Real_Name (Name : in String) return String is
   begin
      if Os_Lib.Is_Regular_File (Name) then
         return Name;
      elsif Os_Lib.Is_Regular_File (Name & ".tmp") then
         return Name & ".tmp";
      else
         raise File_Not_Found;
      end if;
   end Get_Real_Name;

   ------------------------------------------------------------------------

   -- Open                                                               --

   ------------------------------------------------------------------------

   -- Accepts In_file and Out_file

   procedure Open (
      File : in out Stream_IO.File_type;
      Mode : in     Stream_IO.File_mode;
      Name : in     String := "";
      Form : in     String := "") 
   is
      Success : Boolean;
   begin
      case Mode is
         when In_file =>
            if Os_lib.Is_regular_file (Name & ".tmp") and 
               not Os_lib.Is_regular_file (Name) 
            then
               Os_lib.Rename_file (Name & ".tmp", Name, Success);
               if not Success then
                  raise Storage_error;
               end if;
            end if;
            Stream_io.Open (File, Mode, Name, Form);
         when Out_file =>
            Stream_io.Create (File, Mode, Name & ".tmp", Form);
         when Append_file =>
            raise Unimplemented;
      end case;
   end Open;

   ------------------------------------------------------------------------

   -- Close                                                              --

   ------------------------------------------------------------------------

   procedure Close (File : in out Stream_IO.File_type) is
      Filename : String := Stream_IO.Name (File);
      Success  : Boolean;
   begin
      case Mode (File) is
         when In_file =>
            Stream_IO.Close (File);
         when Out_file =>
            Stream_IO.Close (File);
            -- Delete previous, if exists:

            if Os_lib.Is_regular_file (
               Filename (Filename'First .. Filename'Last - 4))
            then
               Os_lib.Delete_file (
                  Filename (Filename'First .. Filename'Last - 4), Success);
               if not Success then
                  raise Storage_error;
               end if;
            end if;
            -- Rename file:

            Os_lib.Rename_file (
               Filename,
               Filename (Filename'First .. Filename'Last - 4),
               Success);
            if not Success then
               raise Storage_error;
            end if;
         when Append_file =>
            raise Unimplemented;
      end case;
   end Close;

end Agpl.Safe_file;