#!/usr/bin/env perl
# SPDX-License-Identifier: GPL-2.0
#
# Clean a patch file -- or directory of patch files -- of stealth whitespace.
# WARNING: this can be a highly destructive operation.  Use with caution.
#

use warnings;
use bytes;
use File::Basename;

# Default options
$max_width = 79;

# Clean up space-tab sequences, either by removing spaces or
# replacing them with tabs.
sub clean_space_tabs($)
{
    no bytes;			# Tab alignment depends on characters

    my($li) = @_;
    my($lo) = '';
    my $pos = 0;
    my $nsp = 0;
    my($i, $c);

    for ($i = 0; $i < length($li); $i++) {
	$c = substr($li, $i, 1);
	if ($c eq "\t") {
	    my $npos = ($pos+$nsp+8) & ~7;
	    my $ntab = ($npos >> 3) - ($pos >> 3);
	    $lo .= "\t" x $ntab;
	    $pos = $npos;
	    $nsp = 0;
	} elsif ($c eq "\n" || $c eq "\r") {
	    $lo .= " " x $nsp;
	    $pos += $nsp;
	    $nsp = 0;
	    $lo .= $c;
	    $pos = 0;
	} elsif ($c eq " ") {
	    $nsp++;
	} else {
	    $lo .= " " x $nsp;
	    $pos += $nsp;
	    $nsp = 0;
	    $lo .= $c;
	    $pos++;
	}
    }
    $lo .= " " x $nsp;
    return $lo;
}

# Compute the visual width of a string
sub strwidth($) {
    no bytes;			# Tab alignment depends on characters

    my($li) = @_;
    my($c, $i);
    my $pos = 0;
    my $mlen = 0;

    for ($i = 0; $i < length($li); $i++) {
	$c = substr($li,$i,1);
	if ($c eq "\t") {
	    $pos = ($pos+8) & ~7;
	} elsif ($c eq "\n") {
	    $mlen = $pos if ($pos > $mlen);
	    $pos = 0;
	} else {
	    $pos++;
	}
    }

    $mlen = $pos if ($pos > $mlen);
    return $mlen;
}

$name = basename($0);

@files = ();

while (defined($a = shift(@ARGV))) {
    if ($a =~ /^-/) {
	if ($a eq '-width' || $a eq '-w') {
	    $max_width = shift(@ARGV)+0;
	} else {
	    print STDERR "Usage: $name [-width #] files...\n";
	    exit 1;
	}
    } else {
	push(@files, $a);
    }
}

foreach $f ( @files ) {
    print STDERR "$name: $f\n";

    if (! -f $f) {
	print STDERR "$f: not a file\n";
	next;
    }

    if (!open(FILE, '+<', $f)) {
	print STDERR "$name: Cannot open file: $f: $!\n";
	next;
    }

    binmode FILE;

    # First, verify that it is not a binary file; consider any file
    # with a zero byte to be a binary file.  Is there any better, or
    # additional, heuristic that should be applied?
    $is_binary = 0;

    while (read(FILE, $data, 65536) > 0) {
	if ($data =~ /\0/) {
	    $is_binary = 1;
	    last;
	}
    }

    if ($is_binary) {
	print STDERR "$name: $f: binary file\n";
	next;
    }

    seek(FILE, 0, 0);

    $in_bytes = 0;
    $out_bytes = 0;
    $lineno = 0;

    @lines  = ();

    $in_hunk = 0;
    $err = 0;

    while ( defined($line = <FILE>) ) {
	$lineno++;
	$in_bytes += length($line);

	if (!$in_hunk) {
	    if ($line =~
		/^\@\@\s+\-([0-9]+),([0-9]+)\s+\+([0-9]+),([0-9]+)\s\@\@/) {
		$minus_lines = $2;
		$plus_lines = $4;
		if ($minus_lines || $plus_lines) {
		    $in_hunk = 1;
		    @hunk_lines = ($line);
		}
	    } else {
		push(@lines, $line);
		$out_bytes += length($line);
	    }
	} else {
	    # We're in a hunk

	    if ($line =~ /^\+/) {
		$plus_lines--;

		$text = substr($line, 1);
		$text =~ s/[ \t\r]*$//;		# Remove trailing spaces
		$text = clean_space_tabs($text);

		$l_width = strwidth($text);
		if ($max_width && $l_width > $max_width) {
		    print STDERR
			"$f:$lineno: adds line exceeds $max_width ",
			"characters ($l_width)\n";
		}

		push(@hunk_lines, '+'.$text);
	    } elsif ($line =~ /^\-/) {
		$minus_lines--;
		push(@hunk_lines, $line);
	    } elsif ($line =~ /^ /) {
		$plus_lines--;
		$minus_lines--;
		push(@hunk_lines, $line);
	    } else {
		print STDERR "$name: $f: malformed patch\n";
		$err = 1;
		last;
	    }

	    if ($plus_lines < 0 || $minus_lines < 0) {
		print STDERR "$name: $f: malformed patch\n";
		$err = 1;
		last;
	    } elsif ($plus_lines == 0 && $minus_lines == 0) {
		# End of a hunk.  Process this hunk.
		my $i;
		my $l;
		my @h = ();
		my $adj = 0;
		my $done = 0;

		for ($i = scalar(@hunk_lines)-1; $i > 0; $i--) {
		    $l = $hunk_lines[$i];
		    if (!$done && $l eq "+\n") {
			$adj++; # Skip this line
		    } elsif ($l =~ /^[ +]/) {
			$done = 1;
			unshift(@h, $l);
		    } else {
			unshift(@h, $l);
		    }
		}

		$l = $hunk_lines[0];  # Hunk header
		undef @hunk_lines;    # Free memory

		if ($adj) {
		    die unless
			($l =~ /^\@\@\s+\-([0-9]+),([0-9]+)\s+\+([0-9]+),([0-9]+)\s\@\@(.*)$/);
		    my $mstart = $1;
		    my $mlin = $2;
		    my $pstart = $3;
		    my $plin = $4;
		    my $tail = $5; # doesn't include the final newline

		    $l = sprintf("@@ -%d,%d +%d,%d @@%s\n",
				 $mstart, $mlin, $pstart, $plin-$adj,
				 $tail);
		}
		unshift(@h, $l);

		# Transfer to the output array
		foreach $l (@h) {
		    $out_bytes += length($l);
		    push(@lines, $l);
		}

		$in_hunk = 0;
	    }
	}
    }

    if ($in_hunk) {
	print STDERR "$name: $f: malformed patch\n";
	$err = 1;
    }

    if (!$err) {
	if ($in_bytes != $out_bytes) {
	    # Only write to the file if changed
	    seek(FILE, 0, 0);
	    print FILE @lines;

	    if ( !defined($where = tell(FILE)) ||
		 !truncate(FILE, $where) ) {
		die "$name: Failed to truncate modified file: $f: $!\n";
	    }
	}
    }

    close(FILE);
}