Text::FindIndent - Heuristically determine the indent style

  use Text::FindIndent;
  my $indentation_type = Text::FindIndent->parse($text, skip_pod => 1);
  if ($indentation_type =~ /^s(\d+)/) {
    print "Indentation with $1 spaces\n";
  }
  elsif ($indentation_type =~ /^t(\d+)/) {
    print "Indentation with tabs, a tab should indent by $1 characters\n";
  }
  elsif ($indentation_type =~ /^m(\d+)/) {
    print "Indentation with $1 characters in tab/space mixed mode\n";
  }
  else {
    print "Indentation style unknown\n";
  }

  my $mode = Text::FindIndent->parse(\$text, skip_pod => 1);

  map <F5> <Esc> :perl use Text::FindIndent;VIM::DoCommand($_) for
  Text::FindIndent->to_vim_commands(join "\n", $curbuf->Get(1..$curbuf->Count()));<CR>

package Text::FindIndent;

use 5.00503;
use strict;

use vars qw{$VERSION};
BEGIN {
  $VERSION = '0.10';
}

use constant MAX_LINES => 500;

sub parse {
  my $class = shift;
  my $text  = shift;

  my %opts = @_;
  my $textref = ref($text) ? $text : \$text; # accept references, too

  my $skip_pod = $opts{skip_pod};
  my $first_level_indent_only = $opts{first_level_indent_only}?1:0;

  my %modeline_settings;

  my %indentdiffs;
  my $lines                 = 0;
  my $prev_indent           = undef;
  my $skip                  = 0;
  my $in_pod                = 0;

  # Do we have emacs smart comments?
  $class->_check_emacs_local_variables_at_file_end($textref, \%modeline_settings);
  if (exists $modeline_settings{softtabstop} and exists $modeline_settings{usetabs}) {
    $modeline_settings{mixedmode} = $modeline_settings{usetabs}
      if not defined $modeline_settings{mixedmode};
    return(
      ($modeline_settings{mixedmode} ? "m" : "s")
      . $modeline_settings{softtabstop}
    );
  }
  elsif (exists $modeline_settings{tabstop} and $modeline_settings{usetabs}) {
    return( ($modeline_settings{mixedmode} ? "m" : "t") . $modeline_settings{tabstop} );
  }
  elsif (exists $modeline_settings{tabstop} and exists $modeline_settings{usetabs}) {
    return( "s" . $modeline_settings{tabstop} );
  }

  my $next_line_braces_pos_plus_1;
  my $prev_indent_type = undef;
  while ($$textref =~ /\G([ \t]*)([^\r\n]*)[\r\n]+/cgs) {
    my $ws       = $1;
    my $rest     = $2;
    my $fullline = "$ws$rest";
    $lines++;
    
    # check emacs start line stuff with some slack (shebang)
    my $changed_modelines;
    if ($lines < 3) {
      $changed_modelines = $class->_check_emacs_local_variables_first_line($fullline, \%modeline_settings);
    }

    # Do we have emacs smart comments?
    # ==> Done once at start
    #$class->_check_emacs_local_variables($fullline, \%modeline_settings);

    # Do we have vim smart comments?
    if ($class->_check_vim_modeline($fullline, \%modeline_settings) || $changed_modelines) {
      if (exists $modeline_settings{softtabstop} and exists $modeline_settings{usetabs}) {
        $modeline_settings{mixedmode} = $modeline_settings{usetabs}
          if not defined $modeline_settings{mixedmode};
        return(
          ($modeline_settings{mixedmode} ? "m" : "s")
          . $modeline_settings{softtabstop}
        );
      }
      elsif (exists $modeline_settings{tabstop} and $modeline_settings{usetabs}) {
        return( ($modeline_settings{mixedmode} ? "m" : "t") . $modeline_settings{tabstop} );
      }
      elsif (exists $modeline_settings{tabstop} and exists $modeline_settings{usetabs}) {
        return( "s" . $modeline_settings{tabstop} );
      }
    }

    if ($lines > MAX_LINES) {
      next;
    }

    if ($skip) {
      $skip--;
      next;
    }

    if ($skip_pod and $ws eq '' and substr($rest, 0, 1) eq '=') {
      if (not $in_pod and $rest =~ /^=(?:head\d|over|item|back|pod|begin|for|end)/ ) {
        $in_pod = 1;
      }
      elsif ($in_pod and $rest =~ /^=cut/) {
        $in_pod = 0;
      }

    }
    next if $in_pod or $rest eq '';

    if ($ws eq '') {
      $prev_indent = $ws;
      next;
    }

    # skip next line if the last char is a backslash.
    # Doesn't matter for Perl, but let's be generous!
    $skip = 1 if $rest =~ /\\$/;
    
    # skip single-line comments
    next if $rest =~ /^(?:#|\/\/|\/\*)/; # TODO: parse /* ... */!

    if ($next_line_braces_pos_plus_1) {
      if ($next_line_braces_pos_plus_1==_length_with_tabs_converted($ws)) {
        next;
      }
      $next_line_braces_pos_plus_1=0;
    } else {
      if ($rest=~/=> {$/) { #handle case where hash keys and values are indented by braces pos + 1
        $next_line_braces_pos_plus_1=_length_with_tabs_converted($ws)+length($rest);
      }
    }

    if ($first_level_indent_only and $prev_indent ne '') {
      next;
    }

    if ($prev_indent eq $ws) {
      if ($prev_indent_type) {
        $indentdiffs{$prev_indent_type}+=0.01;
        #coefficient is not based on data, so change if you think it should be different
      }
      next;
    }

    # prefix-matching higher indentation level
    if ($ws =~ /^\Q$prev_indent\E(.+)$/) {
      my $diff = $1;
      my $indent_type=_analyse_indent_diff($diff);
      $indentdiffs{$indent_type}++;
      $prev_indent_type=$indent_type;
      $prev_indent = $ws;
      next;
    }

    # prefix-matching lower indentation level
    if ($prev_indent =~ /^\Q$ws\E(.+)$/) {
      my $diff = $1;
      #_grok_indent_diff($diff, \%indentdiffs);
      my $indent_type=_analyse_indent_diff($diff);
      $indentdiffs{$indent_type}++;
      $prev_indent_type=$indent_type;
      $prev_indent = $ws;
      next;
    }

    # at this point, we're desperate!
    my $prev_spaces = $prev_indent;
    $prev_spaces =~ s/[ ]{0,7}\t/        /g;
    my $spaces = $ws;
    $spaces =~ s/[ ]{0,7}\t/        /g;
    my $len_diff = length($spaces) - length($prev_spaces);
    if ($len_diff) {
      $len_diff = abs($len_diff);
      $indentdiffs{"m$len_diff"}++;
    }
    $prev_indent = $ws;
        
  } # end while lines

  # nothing found
  return 'u' if not keys %indentdiffs;

  my $max = 0;
  my $maxkey = undef;
  while (my ($key, $value) = each %indentdiffs) {
    $maxkey = $key, $max = $value if $value > $max;
  }

  if ($maxkey =~ /^s(\d+)$/) {
    my $mixedkey = "m" . $1;
    my $mixed = $indentdiffs{$mixedkey};
    if (defined($mixed) and $mixed >= $max * 0.2) {
      $maxkey = $mixedkey;
    }
  }

  # fallback to emacs styles which are guesses only
  foreach my $key (qw(softtabstop tabstop usetabs)) {
    if (not exists $modeline_settings{$key}
        and exists $modeline_settings{"style_$key"}) {
      $modeline_settings{$key} = $modeline_settings{"style_$key"};
    }
  }

  if (exists $modeline_settings{softtabstop}) {
    $maxkey =~ s/\d+/$modeline_settings{softtabstop}/;
  }
  elsif (exists $modeline_settings{tabstop}) {
    $maxkey =~ s/\d+/$modeline_settings{tabstop}/;
  }
  if (exists $modeline_settings{usetabs}) {
    if ($modeline_settings{usetabs}) {
      $maxkey =~ s/^(.)(\d+)$/$1 eq 'u' ? "t8" : ($2 == 8 ? "t8" : "m$2")/e;
    }
    else {
      $maxkey =~ s/^./m/;
    }
  }

  # mixedmode explicitly asked for
  if ($modeline_settings{mixedmode}) {
    $maxkey =~ s/^./m/;
  }

  return $maxkey;
}

sub _length_with_tabs_converted {
    my $str=shift;
    my $tablen=shift || 8;
    $str =~ s/( +)$//;
    my $trailing_spaces = $1||0;
    $str =~ s/ +//g; #  assume the spaces are all contained in tabs!
    return length($str)*$tablen+length($trailing_spaces);
}

sub _grok_indent_diff {
  my $diff = shift;
  my $indentdiffs = shift;

  if ($diff =~ /^ +$/) {
    $indentdiffs->{"s" . length($diff)}++;
  }
  elsif ($diff =~ /^\t+$/) {
    $indentdiffs->{"t8"}++; # we can't infer what a tab means. Or rather, we need smarter code to do it
  }
  else { # mixed!
    $diff =~ s/( +)$//;
    my $trailing_spaces = $1||0;
    $diff =~ s/ +//g; #  assume the spaces are all contained in tabs!
    $indentdiffs->{"m" . (length($diff)*8+length($trailing_spaces))}++;
  }
}

sub _analyse_indent_diff {
  my $diff = shift;

  if ($diff =~ /^ +$/) {
    return "s" . length($diff);
  }
  elsif ($diff =~ /^\t+$/) {
    return "t8"; # we can't infer what a tab means. Or rather, we need smarter code to do it
  }
  else { # mixed!
    $diff =~ s/( +)$//;
    my $trailing_spaces = $1||0;
    $diff =~ s/ +//g; #  assume the spaces are all contained in tabs!
    return "m" . (length($diff)*8+length($trailing_spaces));
  }
}

{
  # the vim modeline regexes
  my $VimTag = qr/(?:ex|vim?(?:[<=>]\d+)?):/;
  my $OptionArg = qr/[^\s\\]*(?:\\[\s\\][^\s\\]*)*/;
  my $VimOption = qr/
        \w+(?:=)?$OptionArg
    /xo;

  my $VimModeLineStart = qr/(?:^|\s+)$VimTag/o;

  # while technically, we match against $VimModeLineStart before,
  # IF there is a vim modeline, we don't need to optimize
  my $VimModelineTypeOne = qr/
        $VimModeLineStart
        \s*
        ($VimOption
            (?:
                (?:\s*:\s*|\s+)
                $VimOption
            )*
        )
        \s*$
    /xo;
  
  my $VimModelineTypeTwo = qr/
        $VimModeLineStart
        \s*
        set?\s+
        ($VimOption
            (?:\s+$VimOption)*
        )
        \s*
        :
    /xo;

  sub _check_vim_modeline {
    my $class = shift;
    my $line = shift;
    my $settings = shift;

# Quoting the vim docs:
# There are two forms of modelines.  The first form:
#	[text]{white}{vi:|vim:|ex:}[white]{options}
#
#[text]		any text or empty
#{white}		at least one blank character (<Space> or <Tab>)
#{vi:|vim:|ex:}	the string "vi:", "vim:" or "ex:"
#[white]		optional white space
#{options}	a list of option settings, separated with white space or ':',
#		where each part between ':' is the argument for a ":set"
#		command (can be empty)
#
#Example:
#   vi:noai:sw=3 ts=6 ~
#   The second form (this is compatible with some versions of Vi):
#
#	[text]{white}{vi:|vim:|ex:}[white]se[t] {options}:[text]
#
#[text]		any text or empty
#{white}		at least one blank character (<Space> or <Tab>)
#{vi:|vim:|ex:}	the string "vi:", "vim:" or "ex:"
#[white]		optional white space
#se[t]		the string "set " or "se " (note the space)
#{options}	a list of options, separated with white space, which is the
#		argument for a ":set" command
#:		a colon
#[text]		any text or empty
#
#Example:
#   /* vim: set ai tw=75: */ ~
#
   
    my @options;
    return if $line !~ $VimModeLineStart;

    if ($line =~ $VimModelineTypeOne) {
      push @options, split /(?!<\\)[:\s]+/, $1;
    }
    elsif ($line =~ $VimModelineTypeTwo) {
      push @options, split /(?!<\\)\s+/, $1;
    }
    else {
      return;
    }

    return if not @options;

    my $changed = 0;
    foreach (@options) {
      /s(?:ts|ofttabstop)=(\d+)/i and $settings->{softtabstop} = $1, $changed = 1, next;
      /t(?:s|abstop)=(\d+)/i and $settings->{tabstop} = $1, $changed = 1,  next;
      /((?:no)?)(?:expandtab|et)/i and $settings->{usetabs} = (defined $1 and $1 =~ /no/i ? 1 : 0), $changed = 1, next;
    }
    return $changed;
  }
}




{
# lookup for emacs tab modes
  my %tabmodelookup = (
   t   => sub {
     $_[0]->{mixedmode} = 1;
     $_[0]->{usetabs} = 1;
   },
   nil => sub {
     delete $_[0]->{mixedmode};
     $_[0]->{usetabs} = 0;
   },
  );

# lookup for emacs styles
  my %stylelookup = (
   kr => sub {
     $_[0]->{style_softtabstop} = 4;
     $_[0]->{style_tabstop} = 8;
     $_[0]->{style_usetabs} = 1;
   },
   linux => sub {
     $_[0]->{style_softtabstop} = 8;
     $_[0]->{style_tabstop} = 8;
     $_[0]->{style_usetabs} = 1;
   },
   'gnu' => sub {
     $_[0]->{style_softtabstop} = 2;
     $_[0]->{style_tabstop} = 8;
     $_[0]->{style_usetabs} = 1;
   },
   'bsd' => sub {
     $_[0]->{style_softtabstop} = 4;
     $_[0]->{style_tabstop} = 8;
     $_[0]->{style_usetabs} = 1;
   },
   'ellemtel' => sub {
     $_[0]->{style_softtabstop} = 3;
     $_[0]->{style_tabstop} = 3;
     $_[0]->{style_usetabs} = 0;
   },
   'java' => sub {
     $_[0]->{style_softtabstop} = 4;
     $_[0]->{style_tabstop} = 8;
   },
  );
  $stylelookup{'k&r'} = $stylelookup{kr};
  $stylelookup{'bsd'} = $stylelookup{kr};
  $stylelookup{'whitesmith'} = $stylelookup{kr};
  $stylelookup{'stroustrup'} = $stylelookup{kr};

  my $FirstLineVar = qr/[^\s:]+/;
  my $FirstLineValue = qr/[^;]+/; # dumb
  my $FirstLinePair = qr/\s*$FirstLineVar\s*:\s*$FirstLineValue;/o;
  my $FirstLineRegexp = qr/-\*-\s*mode:\s*[^\s;]+;\s*($FirstLinePair+)\s*-\*-/o;
  
  
  sub _check_emacs_local_variables_first_line {
    my $class = shift;
    my $line = shift;
    my $settings = shift;

# on first line (second if there is a shebang):
#     -*- mode: $MODENAME; $VARNAME: $VALUE; ... -*-
# ($FOO is not a literal)
# Example with a Lisp comment:
# ;; -*- mode: Lisp; fill-column: 75; comment-column: 50; -*-


    my $changed = 0;
    if ($line =~ $FirstLineRegexp) {
      my @pairs = split /\s*;\s*/, $1;
      foreach my $pair (@pairs) {
        my ($key, $value) = split /\s*:\s*/, $pair, 2;
        if ($key eq 'tab-width') {
          $settings->{tabstop} = $value;# FIXME: check var
          $changed = 1;
        }
        elsif ($key eq 'indent-tabs-mode') {
          $tabmodelookup{$value}->($settings), $changed = 1 if defined $tabmodelookup{$value};
        }
        elsif ($key eq 'c-basic-offset') {
          $settings->{tabstop} ||= $value; # tab-width takes precedence!?
          $changed = 1;
        }
        elsif ($key eq 'style') { # this is quite questionable practice...
          $stylelookup{$value}->($settings), $changed = 1 if defined $stylelookup{$value};
        }
      }
    }

    # do this only as a LAST resort!
    #$settings->{tabstop}     = $settings->{style_tabstop}     if not exists $settings->{tabstop};
    #$settings->{softtabstop} = $settings->{style_softtabstop} if not exists $settings->{softtabstop};
    #$settings->{usetabs}     = $settings->{style_usetabs}     if not exists $settings->{usetabs};

    return $changed;
  }

  sub _check_emacs_local_variables {
    my $class = shift;
    my $line = shift;
    my $settings = shift;

# A local variables list goes near the end of the file, in the last page.[...]
# The local variables list starts with a line containing the string `Local Variables:',
# and ends with a line containing the string `End:'. In between come the variable names
# and values, one set per line, as `variable: value'. The values are not evaluated;
# they are used literally. If a file has both a local variables list and a `-*-'
# line, Emacs processes everything in the `-*-' line first, and everything in the
# local variables list afterward.
# 
# Here is an example of a local variables list:
# 
#     ;; Local Variables: **
#     ;; mode:lisp **
#     ;; comment-column:0 **
#     ;; comment-start: ";; "  **
#     ;; comment-end:"**" **
#     ;; End: **
# 
# Each line starts with the prefix `;; ' and each line ends with the suffix ` **'.
# Emacs recognizes these as the prefix and suffix based on the first line of the
# list, by finding them surrounding the magic string `Local Variables:'; then it
# automatically discards them from the other lines of the list.
# 
# The usual reason for using a prefix and/or suffix is to embed the local variables
# list in a comment, so it won't confuse other programs that the file is intended as
# input for. The example above is for a language where comment lines start with `;; '
# and end with `**'; the local values for comment-start and comment-end customize the
# rest of Emacs for this unusual syntax. Don't use a prefix (or a suffix) if you don't need one. 
#
#
# Can it be any more annoying to parse? --Steffen

    if ($settings->{in_local_variables_section}) {
      my $prefix = $settings->{local_variable_prefix};
      $prefix = '' if not defined $prefix;
      $prefix = quotemeta($prefix);
      my $suffix = $settings->{local_variable_suffix};
      $suffix = '' if not defined $suffix;
      $suffix = quotemeta($suffix);

      if ($line =~ /^\s*$prefix\s*([^\s:]+):\s*(.+)$suffix\s*$/) {
        my $key = $1;
        my $value = $2;
        $value =~ s/\s+$//;
        if ($key eq 'tab-width') {
          $settings->{tabstop} = $value;
        }
        elsif ($key eq 'indent-tabs-mode') {
          $tabmodelookup{$value}->($settings) if defined $tabmodelookup{$value};
        }
        elsif ($key eq 'c-basic-offset') {
          $settings->{tabstop} ||= $value; # tab-width takes precedence!?
        }
        elsif ($key eq 'style') { # this is quite questionable practice...
          $stylelookup{$value}->($settings) if defined $stylelookup{$value};
        }
      } # end if variable line
      else {
        delete $settings->{in_local_variables_section};
        delete $settings->{local_variable_prefix};
        delete $settings->{local_variable_suffix};
      }
    }
    elsif ($line =~ /^\s*(\S*)\s*Local Variables:\s*(\S*)\s*$/) {
      $settings->{local_variable_prefix} = $1;
      $settings->{local_variable_suffix} = $2;
      $settings->{in_local_variables_section} = 1;
    }
  }

  sub _check_emacs_local_variables_at_file_end {
    my $class = shift;
    my $textref = shift;
    my $settings = shift;
    my $len = length($$textref);
    my $start = $len-3000;
    $start = 0 if $start < 0;
    my $text = substr($$textref, $start);

    while ($text =~ /\G[ \t]*([^\r\n]*)[\r\n]+/cgs) {
      $class->_check_emacs_local_variables($1, $settings);
    }
    return;
  }
} # end lexical block for emacs lookups


sub to_vim_commands {
  my $indent = shift;
  $indent = shift if $indent eq __PACKAGE__;
  $indent = __PACKAGE__->parse($indent) if ref($indent) or length($indent) > 5;

  my @cmd;
  if ( $indent =~ /^t(\d+)/ ) {
    my $chars = $1;
    push @cmd, ":set shiftwidth=$chars";
    push @cmd, ":set tabstop=$chars";
    push @cmd, ":set softtabstop=0";
    push @cmd, ":set noexpandtab";
  } elsif ( $indent =~ /^s(\d+)/ ) {
    my $spaces = $1;
    push @cmd, ":set shiftwidth=$spaces";
    push @cmd, ":set tabstop=8";
    push @cmd, ":set softtabstop=$spaces";
    push @cmd, ':set expandtab';
  } elsif ( $indent =~ /^m(\d+)/ ) {
    my $spaces = $1;
    push @cmd, ":set shiftwidth=$spaces";
    push @cmd, ":set tabstop=8";
    push @cmd, ":set softtabstop=$spaces";
    push @cmd, ':set noexpandtab';
  }
  return @cmd;
}

1;

__END__