
# Time-stamp: "2004-06-20 21:47:55 ADT"

require 5;
package I18N::LangTags::Detect;
use strict;

use vars qw( @ISA $VERSION $MATCH_SUPERS $USING_LANGUAGE_TAGS
             $USE_LITERALS $MATCH_SUPERS_TIGHTLY);

BEGIN { unless(defined &DEBUG) { *DEBUG = sub () {0} } }
 # define the constant 'DEBUG' at compile-time

$VERSION = "1.03";
@ISA = ();
use I18N::LangTags qw(alternate_language_tags locale2language_tag);

sub _uniq { my %seen; return grep(!($seen{$_}++), @_); }
sub _normalize {
  my(@languages) =
    map lc($_),
    grep $_,
    map {; $_, alternate_language_tags($_) } @_;
  return _uniq(@languages) if wantarray;
  return $languages[0];
}

#---------------------------------------------------------------------------
# The extent of our functional interface:

sub detect () { return __PACKAGE__->ambient_langprefs; }

#===========================================================================

sub ambient_langprefs { # always returns things untainted
  my $base_class = $_[0];
  
  return $base_class->http_accept_langs
   if length( $ENV{'REQUEST_METHOD'} || '' ); # I'm a CGI
       # it's off in its own routine because it's complicated

  # Not running as a CGI: try to puzzle out from the environment
  my @languages;

  foreach my $envname (qw( LANGUAGE LC_ALL LC_MESSAGES LANG )) {
    next unless $ENV{$envname};
    DEBUG and print "Noting \$$envname: $ENV{$envname}\n";
    push @languages,
      map locale2language_tag($_),
        # if it's a lg tag, fine, pass thru (untainted)
        # if it's a locale ID, try converting to a lg tag (untainted),
        # otherwise nix it.

      split m/[,:]/,
      $ENV{$envname}
    ;
    last; # first one wins
  }
  
  if($ENV{'IGNORE_WIN32_LOCALE'}) {
    # no-op
  } elsif(&_try_use('Win32::Locale')) {
    # If we have that module installed...
    push @languages, Win32::Locale::get_language() || ''
     if defined &Win32::Locale::get_language;
  }
  return _normalize @languages;
}

#---------------------------------------------------------------------------

sub http_accept_langs {
  # Deal with HTTP "Accept-Language:" stuff.  Hassle.
  # This code is more lenient than RFC 3282, which you must read.
  # Hm.  Should I just move this into I18N::LangTags at some point?
  no integer;

  my $in = (@_ > 1) ? $_[1] : $ENV{'HTTP_ACCEPT_LANGUAGE'};
  # (always ends up untainting)

  return() unless defined $in and length $in;

  $in =~ s/\([^\)]*\)//g; # nix just about any comment
  
  if( $in =~ m/^\s*([a-zA-Z][-a-zA-Z]+)\s*$/s ) {
    # Very common case: just one language tag
    return _normalize $1;
  } elsif( $in =~ m/^\s*[a-zA-Z][-a-zA-Z]+(?:\s*,\s*[a-zA-Z][-a-zA-Z]+)*\s*$/s ) {
    # Common case these days: just "foo, bar, baz"
    return _normalize( $in =~ m/([a-zA-Z][-a-zA-Z]+)/g );
  }

  # Else it's complicated...

  $in =~ s/\s+//g;  # Yes, we can just do without the WS!
  my @in = $in =~ m/([^,]+)/g;
  my %pref;
  
  my $q;
  foreach my $tag (@in) {
    next unless $tag =~
     m/^([a-zA-Z][-a-zA-Z]+)
        (?:
         ;q=
         (
          \d*   # a bit too broad of a RE, but so what.
          (?:
            \.\d+
          )?
         )
        )?
       $
      /sx
    ;
    $q = (defined $2 and length $2) ? $2 : 1;
    #print "$1 with q=$q\n";
    push @{ $pref{$q} }, lc $1;
  }

  return _normalize(
    # Read off %pref, in descending key order...
    map @{$pref{$_}},
    sort {$b <=> $a}
    keys %pref
  );
}

#===========================================================================

my %tried = ();
  # memoization of whether we've used this module, or found it unusable.

sub _try_use {   # Basically a wrapper around "require Modulename"
  # "Many men have tried..."  "They tried and failed?"  "They tried and died."
  return $tried{$_[0]} if exists $tried{$_[0]};  # memoization

  my $module = $_[0];   # ASSUME sane module name!
  { no strict 'refs';
    return($tried{$module} = 1)
     if %{$module . "::Lexicon"} or @{$module . "::ISA"};
    # weird case: we never use'd it, but there it is!
  }

  print " About to use $module ...\n" if DEBUG;
  {
    local $SIG{'__DIE__'};
    eval "require $module"; # used to be "use $module", but no point in that.
  }
  if($@) {
    print "Error using $module \: $@\n" if DEBUG > 1;
    return $tried{$module} = 0;
  } else {
    print " OK, $module is used\n" if DEBUG;
    return $tried{$module} = 1;
  }
}

#---------------------------------------------------------------------------
1;
__END__


=head1 NAME

I18N::LangTags::Detect - detect the user's language preferences

=head1 SYNOPSIS

  use I18N::LangTags::Detect;
  my @user_wants = I18N::LangTags::Detect::detect();

=head1 DESCRIPTION

It is a common problem to want to detect what language(s) the user would
prefer output in.

=head1 FUNCTIONS

This module defines one public function,
C<I18N::LangTags::Detect::detect()>.  This function is not exported
(nor is even exportable), and it takes no parameters.

In scalar context, the function returns the most preferred language
tag (or undef if no preference was seen).

In list context (which is usually what you want),
the function returns a
(possibly empty) list of language tags representing (best first) what
languages the user apparently would accept output in.  You will
probably want to pass the output of this through
C<I18N::LangTags::implicate_supers_tightly(...)>
or
C<I18N::LangTags::implicate_supers(...)>, like so:

  my @languages =
    I18N::LangTags::implicate_supers_tightly(
      I18N::LangTags::Detect::detect()
    );


=head1 ENVIRONMENT

This module looks for several environment variables, including
REQUEST_METHOD, HTTP_ACCEPT_LANGUAGE,
LANGUAGE, LC_ALL, LC_MESSAGES, and LANG.

It will also use the L<Win32::Locale> module, if it's installed.


=head1 SEE ALSO

L<I18N::LangTags>, L<Win32::Locale>, L<Locale::Maketext>.

(This module's core code started out as a routine in Locale::Maketext;
but I moved it here once I realized it was more generally useful.)


=head1 COPYRIGHT

Copyright (c) 1998-2004 Sean M. Burke. All rights reserved.

This library is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

The programs and documentation in this dist are distributed in
the hope that they will be useful, but without any warranty; without
even the implied warranty of merchantability or fitness for a
particular purpose.


=head1 AUTHOR

Sean M. Burke C<sburke@cpan.org>

=cut

# a tip: Put a bit of chopped up pickled ginger in your salad. It's tasty!
