#!/usr/bin/env perl

  # SPDX-License-Identifier: GPL-2.0

  #
  # Clean a text file -- or directory of text 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 "
  " || $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 "
  ") {
  	    $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...
  ";
  	    exit 1;
  	}
      } else {
  	push(@files, $a);
      }
  }
  
  foreach $f ( @files ) {

      print STDERR "$name: $f
  ";
  
      if (! -f $f) {
  	print STDERR "$f: not a file
  ";
  	next;
      }
  
      if (!open(FILE, '+<', $f)) {
  	print STDERR "$name: Cannot open file: $f: $!
  ";
  	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
  ";
  	next;
      }
  
      seek(FILE, 0, 0);
  
      $in_bytes = 0;
      $out_bytes = 0;
      $blank_bytes = 0;
  
      @blanks = ();
      @lines  = ();

      $lineno = 0;

  
      while ( defined($line = <FILE>) ) {

  	$lineno++;

  	$in_bytes += length($line);
  	$line =~ s/[ \t\r]*$//;		# Remove trailing spaces
  	$line = clean_space_tabs($line);
  
  	if ( $line eq "
  " ) {
  	    push(@blanks, $line);
  	    $blank_bytes += length($line);
  	} else {
  	    push(@lines, @blanks);
  	    $out_bytes += $blank_bytes;
  	    push(@lines, $line);
  	    $out_bytes += length($line);
  	    @blanks = ();
  	    $blank_bytes = 0;
  	}

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

      }
  
      # Any blanks at the end of the file are discarded
  
      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: $!
  ";
  	}
      }
  
      close(FILE);
  }