#!/usr/bin/perl
# -*- perl -*-
#
# Pretty-print diff outputs with GNU enscript.
# Copyright (c) 1996-1998 Markku Rossi
#
# Author: Markku Rossi <mtr@iki.fi>
#

#
# This file is part of GNU Enscript.
#
# Enscript is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# Enscript 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.
#
# You should have received a copy of the GNU General Public License
# along with Enscript.  If not, see <http://www.gnu.org/licenses/>.
#

#
# Original idea by Trent Fisher <trent@informix.com>
# Thanks to:
#  - Tero Kivinen <kivinen@iki.fi> for the first prototype
#  - Tait Cyrus <tait.cyrus@mci.com> for fixes and cleanups
#

$file = shift(@ARGV);
$add_gray = ".80";
$del_gray = ".60";

$program = $0;
$program =~ s/.*\///g;

sub usage {
    warn "Usage: $program ORIGINAL_FILE < DIFF\n\n";
    warn "Program reads a diff file from its standard input and annotates
ORIGINAL_FILE to show the changes made to the file.  The easiest way to use
this program is to use it as an input filter for GNU enscript:

  \$ enscript -G2re --filter='rcsdiff %s | diffpp %s' *.c *.h
  \$ enscript -G2re --filter='diff %s~ %s | diffpp %s' *.c *.h

";
}

if (!defined($file) || defined($ARGV[0])) {
    &usage;
    exit 1;
}

if ($file eq "--help") {
    &usage;
    exit 0;
}

if ($file eq "--version") {
    warn "diffpp 1.0\n";
    exit 0;
}

# Read in original file into internal array.
open(FP, $file) || die "$program: couldn't open file `$file' for input: $!\n";
@orig_file = <FP>;
close(FP);
$[ = 1;
$orig_line_num = 1;
$orig_num_lines = @orig_file;

# Now read in file of diffs into internal array.
@diffs = <STDIN>;
$diff_line_num = 1;
$diff_num_lines = @diffs;

while ($diff_line_num <= $diff_num_lines) {
    $_ = $diffs[$diff_line_num];
    if (/a/) {
	do_add($_);
    } elsif (/d/) {
	do_delete($_);
    } elsif (/c/) {
	do_change($_);
    }
}

while ($orig_line_num <= $orig_num_lines) {
    print $orig_file[$orig_line_num++];
}

# Handle new/added lines
#
# Formats used:
#	#a#
#	#a#,#
sub do_add {
    ($line) = @_;
    if ($line =~ /(\d+)a(\d+),(\d+)/) {
	$insert_at_line = $1;
	$num_new_lines = $3 - $2 + 1;
    } elsif ($line =~ /(\d+)a(\d+)/) {
	$insert_at_line = $1;
	$num_new_lines = 1;
    }
    &skip_to_line($insert_at_line);
    printf("\000shade{$add_gray}");
    &mark_to_line($num_new_lines, "+");
    printf("\000shade{1.0}");
}

# Handle deleted/removed lines
#
# Formats used:
#	#d#
#	#,#d#
sub do_delete {
    ($line) = @_;
    if ($line =~ /(\d+),(\d+)d(\d+)/) {
	$num_del_lines = $2 - $1 + 1;
    } elsif ($line =~ /(\d+)d(\d+)/) {
	$num_del_lines = 1;
    }
    $del_from = $1;
    &skip_to_line($del_from - 1);
    printf("\000shade{$del_gray}");
    &mark_to_line($num_del_lines, "-");
    printf("\000shade{1.0}");
    $orig_line_num += $num_del_lines;
}

# Handle changed/modified lines
#
# Formats used:
#	#,#c#,#
#	#,#c#
#	#c#,#
#	#c#
sub do_change {
    ($line) = @_;
    if ($line =~ /(\d+),(\d+)c(\d+),(\d+)/) {
	$num_old_lines = $2 - $1 + 1;
	$num_new_lines = $4 - $3 + 1;
	$change_at_line = $1;
    } elsif ($line =~ /(\d+),(\d+)c(\d+)/) {
	$num_old_lines = $2 - $1 + 1;
	$num_new_lines = 1;
	$change_at_line = $1;
    } elsif ($line =~ /(\d+)c(\d+),(\d+)/) {
	$num_old_lines = 1;
	$num_new_lines = $3 - $2 + 1;
	$change_at_line = $1;
    } elsif ($line =~ /(\d+)c(\d+)/) {
	$num_old_lines = 1;
	$num_new_lines = 1;
	$change_at_line = $1;
    }
    # Mark old lines
    &skip_to_line($change_at_line - 1);
    $orig_line_num += $num_old_lines;	# skip over changed lines
    printf("\000shade{$del_gray}");
    &mark_to_line($num_old_lines, "-");
    printf("\000shade{1.0}");
    # Mark new lines
    printf("\000shade{$add_gray}");
    &mark_to_line($num_new_lines, "+");
    printf("\000shade{1.0}");
}

sub skip_to_line {
    ($line) = @_;

    while ($orig_line_num <= $line) {
	print $orig_file[$orig_line_num];
	$orig_line_num++;
    }
}

sub mark_to_line {
    ($num_lines, $marker) = @_;

    $diff_line_num++;		# skip over diff command
    while ($num_lines > 0) {
	$diff_line = substr($diffs[$diff_line_num++],3);
	print "\000ps{gsave -5 0 rmoveto ($marker) show grestore}";
	print $diff_line;
	$num_lines--;
    }
}