package VCP::Patch ;

=head1 NAME

VCP::Patch - Apply the (almost) unified diffs used in RevML

=head1 SYNOPSIS

    use VCP::Patch ;

    vcp_patch( \$patch, $source_file_name, $result_file_name ) ;

=head1 DESCRIPTION

Applies a patch (in $patch) to $source_file in order to build $result_file.

The patches are in a "unified diff" format, but without the filename headers
(these are passed as other data fields in VCP and the actual filenames are just
working files and are not important).  Some example patches:

=item *

For a one line file:

   @@ -1 +1 @@
   -a/deeply/buried/file, revision 1, char 0x01="<char code="0x01" />"
   +a/deeply/buried/file, revision 2, char 0x09="  "

=item *

For a several line file with multiple changes:

Here are the source and result files side-by-side:

   Source	Result
   ======	======

   1            1
   2		2
   3		3
   4		4
   5d		5a
   6		6
   7		7
   8		8
   9		9
   10		9a
   11		10
   11d		11
   12		12
   13		13

The "patch" to transform the source in to the result can be expressed in
several ways, depending on the amount of context.  VCP requires no context
since the result is checked with an MD5 checksum.  Context is, however,
sometimes used to make the RevML a bit more human readable, though this can
vary.

=over

=item 0 context (C<diff -U 0>):

   @@ -5 +5 @@
   -5d
   +5a
   @@ -9,0 +10 @@
   +9a
   @@ -12 +12,0 @@
   -11d

=item 1 line of context (C<diff -U 1>):

   --- A   Sat Aug 25 00:05:26 2001
   +++ B   Sat Aug 25 00:05:26 2001
   @@ -4,3 +4,3 @@
    4
   -5d
   +5a
    6
   @@ -9,5 +9,5 @@
    9
   +9a
    10
    11
   -11d
    12

=item 3 lines of context (C<diff -U 3 ...> or C<diff -u ...>)

   --- A   Sat Aug 25 00:05:26 2001
   +++ B   Sat Aug 25 00:05:26 2001
   @@ -2,13 +2,13 @@
    2
    3
    4
   -5d
   +5a
    6
    7
    8
    9
   +9a
    10
    11
   -11d
    12
    13

=back

=back

=head1 Functions

=over

=cut

@ISA    = qw( Exporter ) ;
@EXPORT = qw( vcp_patch ) ;

use strict ;
use Carp ;
use VCP::Debug ':debug' ;
use Exporter ;

=item vcp_patch

Takes a patch, a source file name, and a result file name and performs the
patch.  Called from VCP::Source::revml to reconstitute revisions given by delta
records.

The patch is passed by reference in order to not copy it, it is not altered.

Will die on error, always returns true.

=cut

sub vcp_patch {
    my ( $patch_ref, $source_fn, $result_fn ) = @_ ;

    debug "patching $source_fn -> $result_fn" if debugging ;

    open SOURCE, "<$source_fn"    or croak "$!: $source_fn" ;
    open RESULT, ">$result_fn"    or croak "$!: $result_fn" ;

    ## FUDGE
    print RESULT <SOURCE> ;

    close SOURCE or croak "$!: $source_fn" ;
    close RESULT or croak "$!: $result_fn" ;
    return 1 ;
}

=head1 COPYRIGHT

Copyright 2000, Perforce Software, Inc.  All Rights Reserved.

This module and the VCP package are licensed according to the terms given in
the file LICENSE accompanying this distribution, a copy of which is included in
L<vcp>.

=head1 AUTHOR

Sean McCune <sean@sean-mccune.com>

=cut

1 ;