#!/usr/bin/env perl

# Copyright (c) 2009, Douglas Haber
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#     * Redistributions of source code must retain the above copyright
#       notice, this list of conditions and the following disclaimer.
#     * Redistributions in binary form must reproduce the above 
#       copyright notice, this list of conditions and the following
#       disclaimer in the documentation and/or other materials provided
#       with the distribution.
#     * The names names of the authors may not be used to endorse or
#       promote products derived from this software without specific
#       prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER AND ITS
# CONTRIBUTERS ''AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
# INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
# MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
# DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR ITS
# CONTRIBUTERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
# SUCH DAMAGE.

# diffgrep
# USAGE diffgrep [regex] [filename]
#    Display sections of the diff file that match the regex.

# WARNING:  This is slop.  It will work, but there are many cases
#           where it is unreliable.

use strict;

my $COLORS = 1;   # Don't like colors, turn it off

sub color {
# scary hardcoded xterm escape sequence for color changes
    my ($color) = @_; # number  (1=red,2=green,3=yellow,etc...)
    if($COLORS) { print sprintf("%c[3${color}m", 27); }
}

sub verify_regex {
# Check the validity of a regular expression
    eval
    {   "" =~ /$_[0]/; 
	return(1);    
    } or die "ERROR: Invalid regex '$_[0]'\n";
}

sub read_args {
# Read args
    if($#ARGV != 1) { die "USAGE:  diffgrep [regex] [filename]\n"; }
    verify_regex($ARGV[0]);
    return($ARGV[0], $ARGV[1]);
}

sub process_line {
    my($print, $line, $regex) = @_;

    if($$print) {
	if($line =~ /^Only in/ || $line =~ /^diff/) {
	    $$print = 0;
	} 
	else 
	{
	    if($line =~ /^< /)    { color(1); }
	    elsif($line =~ /^> /) { color(2); }
	    print $line; 
	    color(9); # Turn off colors
	}
    }
   
    if(!$$print)
    {
	if(($line =~ /Only in/ || $line =~ /^diff/)
	   && ($line !~ /\/CVS(\/|:)/ )) {
	    if($line =~ /$regex/)
	    { 
		    print $line;
		    $$print = 1;
	    }
	}
    }
}

sub main
{
    my ($regex, $filename) = read_args();
    my $print = 0;  # boolean to determine if printing is on
    my $line;

    if(! open(FD,"<$filename")) {
	die "ERROR:  Can not open file '$filename'\n";
    }

    foreach $line (<FD>) {
	process_line(\$print, $line, $regex);
    }

    close(FD);    
}

main();