package Encode::Guess;
use strict;

use Encode qw(:fallbacks find_encoding);
our $VERSION = do { my @r = (q$Revision: 2.0 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r };

my $Canon = 'Guess';
sub DEBUG () { 0 }
our %DEF_SUSPECTS = map { $_ => find_encoding($_) } qw(ascii utf8);
$Encode::Encoding{$Canon} = 
    bless { 
	   Name       => $Canon,
	   Suspects => { %DEF_SUSPECTS },
	  } => __PACKAGE__;

use base qw(Encode::Encoding);
sub needs_lines { 1 }
sub perlio_ok { 0 }

our @EXPORT = qw(guess_encoding);
our $NoUTFAutoGuess = 0;
our $UTF8_BOM = pack("C3", 0xef, 0xbb, 0xbf);

sub import { # Exporter not used so we do it on our own
    my $callpkg = caller;
    for my $item (@EXPORT){
	no strict 'refs';
	*{"$callpkg\::$item"} = \&{"$item"};
    }
    set_suspects(@_);
}

sub set_suspects{
    my $class = shift;
    my $self = ref($class) ? $class : $Encode::Encoding{$Canon};
    $self->{Suspects} = { %DEF_SUSPECTS };
    $self->add_suspects(@_);
}

sub add_suspects{
    my $class = shift;
    my $self = ref($class) ? $class : $Encode::Encoding{$Canon};
    for my $c (@_){
	my $e = find_encoding($c) or die "Unknown encoding: $c";
	$self->{Suspects}{$e->name} = $e;
	DEBUG and warn "Added: ", $e->name;
    }
}

sub decode($$;$){
    my ($obj, $octet, $chk) = @_;
    my $guessed = guess($obj, $octet);
    unless (ref($guessed)){
	require Carp;
	Carp::croak($guessed);
    }
    my $utf8 = $guessed->decode($octet, $chk);
    $_[1] = $octet if $chk;
    return $utf8;
}

sub guess_encoding{
    guess($Encode::Encoding{$Canon}, @_);
}

sub guess {
    my $class = shift;
    my $obj   = ref($class) ? $class : $Encode::Encoding{$Canon};
    my $octet = shift;

    # sanity check
    return unless defined $octet and length $octet;

    # cheat 0: utf8 flag;
    if ( Encode::is_utf8($octet) ) {
	return find_encoding('utf8') unless $NoUTFAutoGuess;
	Encode::_utf8_off($octet);
    }
    # cheat 1: BOM
    use Encode::Unicode;
    unless ($NoUTFAutoGuess) {
	my $BOM = pack('C3', unpack("C3", $octet));
	return find_encoding('utf8')
	    if (defined $BOM and $BOM eq $UTF8_BOM);
	$BOM = unpack('N', $octet);
	return find_encoding('UTF-32')
	    if (defined $BOM and ($BOM == 0xFeFF or $BOM == 0xFFFe0000));
	$BOM = unpack('n', $octet);
	return find_encoding('UTF-16')
	    if (defined $BOM and ($BOM == 0xFeFF or $BOM == 0xFFFe));
	if ($octet =~ /\x00/o){ # if \x00 found, we assume UTF-(16|32)(BE|LE)
	    my $utf;
	    my ($be, $le) = (0, 0);
	    if ($octet =~ /\x00\x00/o){ # UTF-32(BE|LE) assumed
		$utf = "UTF-32";
		for my $char (unpack('N*', $octet)){
		    $char & 0x0000ffff and $be++;
		    $char & 0xffff0000 and $le++;
		}
	    }else{ # UTF-16(BE|LE) assumed
		$utf = "UTF-16";
		for my $char (unpack('n*', $octet)){
		    $char & 0x00ff and $be++;
		    $char & 0xff00 and $le++;
		}
	    }
	    DEBUG and warn "$utf, be == $be, le == $le";
	    $be == $le 
		and return
		    "Encodings ambiguous between $utf BE and LE ($be, $le)";
	    $utf .= ($be > $le) ? 'BE' : 'LE';
	    return find_encoding($utf);
	}
    }
    my %try =  %{$obj->{Suspects}};
    for my $c (@_){
	my $e = find_encoding($c) or die "Unknown encoding: $c";
	$try{$e->name} = $e;
	DEBUG and warn "Added: ", $e->name;
    }
    my $nline = 1;
    for my $line (split /\r\n?|\n/, $octet){
	# cheat 2 -- \e in the string
	if ($line =~ /\e/o){
	    my @keys = keys %try;
	    delete @try{qw/utf8 ascii/};
	    for my $k (@keys){
		ref($try{$k}) eq 'Encode::XS' and delete $try{$k};
	    }
	}
	my %ok = %try;
	# warn join(",", keys %try);
	for my $k (keys %try){
	    my $scratch = $line;
	    $try{$k}->decode($scratch, FB_QUIET);
	    if ($scratch eq ''){
		DEBUG and warn sprintf("%4d:%-24s ok\n", $nline, $k);
	    }else{
		use bytes ();
		DEBUG and 
		    warn sprintf("%4d:%-24s not ok; %d bytes left\n", 
				 $nline, $k, bytes::length($scratch));
		delete $ok{$k};
	    }
	}
	%ok or return "No appropriate encodings found!";
	if (scalar(keys(%ok)) == 1){
	    my ($retval) = values(%ok);
	    return $retval;
	}
	%try = %ok; $nline++;
    }
    $try{ascii} or 
	return  "Encodings too ambiguous: ", join(" or ", keys %try);
    return $try{ascii};
}



1;
__END__

=head1 NAME

Encode::Guess -- Guesses encoding from data

=head1 SYNOPSIS

  # if you are sure $data won't contain anything bogus

  use Encode;
  use Encode::Guess qw/euc-jp shiftjis 7bit-jis/;
  my $utf8 = decode("Guess", $data);
  my $data = encode("Guess", $utf8);   # this doesn't work!

  # more elaborate way
  use Encode::Guess;
  my $enc = guess_encoding($data, qw/euc-jp shiftjis 7bit-jis/);
  ref($enc) or die "Can't guess: $enc"; # trap error this way
  $utf8 = $enc->decode($data);
  # or
  $utf8 = decode($enc->name, $data)

=head1 ABSTRACT

Encode::Guess enables you to guess in what encoding a given data is
encoded, or at least tries to.  

=head1 DESCRIPTION

By default, it checks only ascii, utf8 and UTF-16/32 with BOM.

  use Encode::Guess; # ascii/utf8/BOMed UTF

To use it more practically, you have to give the names of encodings to
check (I as follows).  The name of suspects can either be
canonical names or aliases.

CAVEAT: Unlike UTF-(16|32), BOM in utf8 is NOT AUTOMATICALLY STRIPPED.

 # tries all major Japanese Encodings as well
  use Encode::Guess qw/euc-jp shiftjis 7bit-jis/;

If the C<$Encode::Guess::NoUTFAutoGuess> variable is set to a true
value, no heuristics will be applied to UTF8/16/32, and the result
will be limited to the suspects and C.

=over 4

=item Encode::Guess->set_suspects

You can also change the internal suspects list via C
method. 

  use Encode::Guess;
  Encode::Guess->set_suspects(qw/euc-jp shiftjis 7bit-jis/);

=item Encode::Guess->add_suspects

Or you can use C method.  The difference is that
C flushes the current suspects list while
C adds.

  use Encode::Guess;
  Encode::Guess->add_suspects(qw/euc-jp shiftjis 7bit-jis/);
  # now the suspects are euc-jp,shiftjis,7bit-jis, AND
  # euc-kr,euc-cn, and big5-eten
  Encode::Guess->add_suspects(qw/euc-kr euc-cn big5-eten/);

=item Encode::decode("Guess" ...)

When you are content with suspects list, you can now

  my $utf8 = Encode::decode("Guess", $data);

=item Encode::Guess->guess($data)

But it will croak if:

=over

=item *

Two or more suspects remain

=item *

No suspects left

=back

So you should instead try this;

  my $decoder = Encode::Guess->guess($data);

On success, $decoder is an object that is documented in
L.  So you can now do this;

  my $utf8 = $decoder->decode($data);

On failure, $decoder now contains an error message so the whole thing
would be as follows;

  my $decoder = Encode::Guess->guess($data);
  die $decoder unless ref($decoder);
  my $utf8 = $decoder->decode($data);

=item guess_encoding($data, [, I])

You can also try C function which is exported by
default.  It takes $data to check and it also takes the list of
suspects by option.  The optional suspect list is I to
the internal suspects list.

  my $decoder = guess_encoding($data, qw/euc-jp euc-kr euc-cn/);
  die $decoder unless ref($decoder);
  my $utf8 = $decoder->decode($data);
  # check only ascii and utf8
  my $decoder = guess_encoding($data);

=back

=head1 CAVEATS

=over 4

=item *

Because of the algorithm used, ISO-8859 series and other single-byte
encodings do not work well unless either one of ISO-8859 is the only
one suspect (besides ascii and utf8).

  use Encode::Guess;
  # perhaps ok
  my $decoder = guess_encoding($data, 'latin1');
  # definitely NOT ok
  my $decoder = guess_encoding($data, qw/latin1 greek/);

The reason is that Encode::Guess guesses encoding by trial and error.
It first splits $data into lines and tries to decode the line for each
suspect.  It keeps it going until all but one encoding is eliminated
out of suspects list.  ISO-8859 series is just too successful for most
cases (because it fills almost all code points in \x00-\xff).

=item *

Do not mix national standard encodings and the corresponding vendor
encodings.

  # a very bad idea
  my $decoder
     = guess_encoding($data, qw/shiftjis MacJapanese cp932/);

The reason is that vendor encoding is usually a superset of national
standard so it becomes too ambiguous for most cases.

=item *

On the other hand, mixing various national standard encodings
automagically works unless $data is too short to allow for guessing.

 # This is ok if $data is long enough
 my $decoder =  
  guess_encoding($data, qw/euc-cn
                           euc-jp shiftjis 7bit-jis
                           euc-kr
                           big5-eten/);

=item *

DO NOT PUT TOO MANY SUSPECTS!  Don't you try something like this!

  my $decoder = guess_encoding($data, 
                               Encode->encodings(":all"));

=back

It is, after all, just a guess.  You should alway be explicit when it
comes to encodings.  But there are some, especially Japanese,
environment that guess-coding is a must.  Use this module with care. 

=head1 TO DO

Encode::Guess does not work on EBCDIC platforms.

=head1 SEE ALSO

L, L

=cut