NAME

       File::Monitor::Delta - Encapsulate a change to a file or directory

VERSION

       This document describes File::Monitor::Delta version 1.00

SYNOPSIS

           use File::Monitor;

           my $monitor = File::Monitor->new();

           # Watch some files
           for my $file (qw( myfile.txt yourfile.txt otherfile.txt some_directory )) {
               $monitor->watch( $file );
           }

           # First scan just finds out about the monitored files. No changes
           # will be reported.
           $object->scan;

           # After the first scan we get a list of File::Monitor::Delta objects
           # that describe any changes
           my @changes = $object->scan;

           for my $change (@changes) {
               # Call methods on File::Monitor::Delta to discover what changed
               if ($change->is_size) {
                   my $name     = $change->name;
                   my $old_size = $change->old_size;
                   my $new_size = $change->new_size;
                   print "$name has changed size from $old_size to $new_size\n";
               }
           }

DESCRIPTION

       When File::Monitor or File::Monitor::Object detects a change to a file or directory it packages the
       details of the change in a "File::Monitor::Delta" object.

       Methods exist to discover the nature of the change ("is_event" et al.), retrieve the attributes of the
       file or directory before and after the change ("old_mtime", "old_mode", "new_mtime", "new_mode" etc),
       retrieve details of the change in a convenient form ("files_created", "files_deleted") and gain access to
       the File::Monitor::Object for which the change was observed ("object").

       Unless you are writing a subclass of "File::Monitor::Object" it isn't normally necessary to instantiate
       "File::Monitor::Delta" objects directly.

   Changes Classified
       Various types of change are identified and classified into the following hierarchy:

           change
               created
               deleted
               metadata
                   time
                       mtime
                       ctime
                   perms
                       uid
                       gid
                       mode
                   size
               directory
                   files_created
                   files_deleted

       The terminal nodes of that tree ("created", "deleted", "mtime", "ctime", "uid", "gid", "mode", "size",
       "files_created" and "files_deleted") represent actual change events. Non terminal nodes represent broader
       classifications of events. For example if a file's mtime changes the resulting "File::Monitor::Delta"
       object will return true for each of

           $delta->is_mtime;       # The actual change
           $delta->is_time;        # One of the file times changed
           $delta->is_metadata;    # The file's metadata changed
           $delta->is_change;      # This is true for any change

       This event classification is used to target callbacks at specific events or categories of events. See
       File::Monitor and File::Monitor::Object for more information about callbacks.

   Accessors
       Various accessors allow the state of the object before and after the change and the details of the change
       to be queried.

       These accessors return information about the state of the file or directory before the detected change:

           old_dev old_inode old_mode old_num_links old_uid old_gid
           old_rdev old_size old_mtime old_ctime old_blk_size old_blocks
           old_error old_files

       For example:

           my $mode_was = $delta->old_mode;

       These accessors return information about the state of the file or directory after the detected change:

           new_dev new_inode new_mode new_num_links new_uid new_gid
           new_rdev new_size new_mtime new_ctime new_blk_size new_blocks
           new_error new_files

       For example:

           my $new_size = $delta->new_size;

       These accessors return a value that reflects the change in the corresponding attribute:

           created deleted mtime ctime uid gid mode size

       With the exception of "mode", "created" and "deleted" they return the difference between the old value
       and the new value. This is only really useful in the case of "size":

           my $grown_by = $delta->size;

       Is equivalent to

           my $grown_by = $delta->new_size - $delta->old_size;

       For the other values the subtraction is performed merely to ensure that these values are non-zero.

           # Get the difference between the old and new UID. Unlikely to be
           # interesting.
           my $delta_uid = $delta->uid;

       As a special case the delta value for "mode" is computed as old_mode ^ new_mode. The old mode is XORed
       with the new mode so that

           my $bits_changed = $delta->mode;

       gets a bitmask of the mode bits that have changed.

       If the detected change was the creation or deletion of a file "created" or "deleted" respectively will be
       true.

           if ( $delta->created ) {
               print "Yippee! We exist\n";
           }

           if ( $delta->deleted ) {
               print "Boo! We got deleted\n";
           }

       For a directory which is being monitored with the "recurse" or "files" options (see File::Monitor::Object
       for details) "files_created" and "files_deleted" will contain respectively the list of new files below
       this directory and the list of files that have been deleted.

           my @new_files = $delta->files_created;

           for my $file ( @new_files ) {
               print "$file created\n";
           }

           my @gone_away = $delta->files_deletedl

           for my $file ( @gone_away ) {
               print "$file deleted\n";
           }

INTERFACE

       "new( $args )"
           Create a new "File::Monitor::Delta" object. You don't normally need to do this; deltas are created as
           necessary by File::Monitor::Object.

           The single argument is a reference to a hash that must contain the following keys:

           object
               The File::Monitor::Object for which this change is being reported.

           old_info
               A hash describing the state of the file or directory before the change.

           new_info
               A hash describing the state of the file or directory after the change.

       "is_event( $event )"
           Returns true if this delta represents the specified event. For example, if a file's size changes the
           following will all return true:

               $delta->is_event('size');        # The actual change
               $delta->is_event('metadata');    # The file's metadata changed
               $delta->is_event('change');      # This is true for any change

           Valid eventnames are

               change created deleted metadata time mtime ctime perms uid gid
               mode size directory files_created files_deleted

           As an alternative interface you may call "is_"eventname directly.  For example

               $delta->is_size;
               $delta->is_metadata;
               $delta->is_change;

           Unless the event you wish to test for is variable this is a cleaner, less error prone interface.

           Normally your code won't see a "File::Monitor::Delta" for which "is_change" returns false. Any change
           causes "is_change" to be true and the "scan" methods of "File::Monitor" and "File::Monitor::Object"
           don't return deltas for unchanged files.

       "name"
           The name of the file for which the change is being reported. Read only.

       "object"
           The File::Monitor::Object for which this change is being reported.

   Other methods
       As mentioned above a large number of other accessors are provided to get the state of the object before
       and after the change and query details of the change:

           old_dev old_inode old_mode old_num_links old_uid old_gid old_rdev
           old_size old_mtime old_ctime old_blk_size old_blocks old_error
           old_files new_dev new_inode new_mode new_num_links new_uid new_gid
           new_rdev new_size new_mtime new_ctime new_blk_size new_blocks
           new_error new_files created deleted mtime ctime uid gid mode size
           files_created files_deleted name

       See "Accessors" for details of these.

DIAGNOSTICS

       "%s is read-only"
           "File::Monitor::Delta" is an immutable description of a change in a file's state. None of its
           accessors allow values to be changed.

       "You must supply a value for %s"
           The three options that "new" ("old_info", "new_info" and "object") are all mandatory.

CONFIGURATION AND ENVIRONMENT

       File::Monitor::Delta requires no configuration files or environment variables.

DEPENDENCIES

       None.

INCOMPATIBILITIES

       None reported.

BUGS AND LIMITATIONS

       No bugs have been reported.

       Please report any bugs or feature requests to "bug-file-monitor@rt.cpan.org", or through the web
       interface at <http://rt.cpan.org>.

AUTHOR

       Andy Armstrong  "<andy@hexten.net>"

       Faycal Chraibi originally registered the File::Monitor namespace and then kindly handed it to me.

LICENCE AND COPYRIGHT

       Copyright (c) 2007, Andy Armstrong "<andy@hexten.net>". All rights reserved.

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl
       itself. See perlartistic.

DISCLAIMER OF WARRANTY

       BECAUSE THIS SOFTWARE IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE SOFTWARE, TO THE EXTENT
       PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER
       PARTIES PROVIDE THE SOFTWARE "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED,
       INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
       PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE SOFTWARE IS WITH YOU. SHOULD THE
       SOFTWARE PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR, OR CORRECTION.

       IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY
       OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE SOFTWARE AS PERMITTED BY THE ABOVE LICENCE, BE LIABLE
       TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING OUT OF
       THE USE OR INABILITY TO USE THE SOFTWARE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING
       RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE SOFTWARE TO OPERATE
       WITH ANY OTHER SOFTWARE), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
       DAMAGES.