#!/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);
}