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use strict;
use warnings;
use utf8 ();

use vars qw($VERSION);
$VERSION = do { my @r = ( q$Revision: 2.6 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r };

use Encode qw(:fallbacks);

use base qw(Encode::Encoding);
__PACKAGE__->Define('hz');

# HZ is a combination of ASCII and escaped GB, so we implement it
# with the GB2312(raw) encoding here. Cf. RFCs 1842 & 1843.

# not ported for EBCDIC.  Which should be used, "~" or "\x7E"?

sub needs_lines { 1 }

sub decode ($$;$) {
    my ( $obj, $str, $chk ) = @_;

    my $GB  = Encode::find_encoding('gb2312-raw');
    my $ret = substr($str, 0, 0); # to propagate taintedness
    my $in_ascii = 1;    # default mode is ASCII.

    while ( length $str ) {
        if ($in_ascii) {    # ASCII mode
            if ( $str =~ s/^([\x00-\x7D\x7F]+)// ) {    # no '~' => ASCII
                $ret .= $1;

                # EBCDIC should need ascii2native, but not ported.
            }
            elsif ( $str =~ s/^\x7E\x7E// ) {           # escaped tilde
                $ret .= '~';
            }
            elsif ( $str =~ s/^\x7E\cJ// ) {    # '\cJ' == LF in ASCII
                1;                              # no-op
            }
            elsif ( $str =~ s/^\x7E\x7B// ) {    # '~{'
                $in_ascii = 0;                   # to GB
            }
            else {    # encounters an invalid escape, \x80 or greater
                last;
            }
        }
        else {        # GB mode; the byte ranges are as in RFC 1843.
            no warnings 'uninitialized';
            if ( $str =~ s/^((?:[\x21-\x77][\x21-\x7E])+)// ) {
                $ret .= $GB->decode( $1, $chk );
            }
            elsif ( $str =~ s/^\x7E\x7D// ) {    # '~}'
                $in_ascii = 1;
            }
            else {                               # invalid
                last;
            }
        }
    }
    $_[1] = '' if $chk;    # needs_lines guarantees no partial character
    return $ret;
}

sub cat_decode {
    my ( $obj, undef, $src, $pos, $trm, $chk ) = @_;
    my ( $rdst, $rsrc, $rpos ) = \@_[ 1 .. 3 ];

    my $GB  = Encode::find_encoding('gb2312-raw');
    my $ret = '';
    my $in_ascii = 1;      # default mode is ASCII.

    my $ini_pos = pos($$rsrc);

    substr( $src, 0, $pos ) = '';

    my $ini_len = bytes::length($src);

    # $trm is the first of the pair '~~', then 2nd tilde is to be removed.
    # XXX: Is better C<$src =~ s/^\x7E// or die if ...>?
    $src =~ s/^\x7E// if $trm eq "\x7E";

    while ( length $src ) {
        my $now;
        if ($in_ascii) {    # ASCII mode
            if ( $src =~ s/^([\x00-\x7D\x7F])// ) {    # no '~' => ASCII
                $now = $1;
            }
            elsif ( $src =~ s/^\x7E\x7E// ) {          # escaped tilde
                $now = '~';
            }
            elsif ( $src =~ s/^\x7E\cJ// ) {    # '\cJ' == LF in ASCII
                next;
            }
            elsif ( $src =~ s/^\x7E\x7B// ) {    # '~{'
                $in_ascii = 0;                   # to GB
                next;
            }
            else {    # encounters an invalid escape, \x80 or greater
                last;
            }
        }
        else {        # GB mode; the byte ranges are as in RFC 1843.
            if ( $src =~ s/^((?:[\x21-\x77][\x21-\x7F])+)// ) {
                $now = $GB->decode( $1, $chk );
            }
            elsif ( $src =~ s/^\x7E\x7D// ) {    # '~}'
                $in_ascii = 1;
                next;
            }
            else {                               # invalid
                last;
            }
        }

        next if !defined $now;

        $ret .= $now;

        if ( $now eq $trm ) {
            $$rdst .= $ret;
            $$rpos = $ini_pos + $pos + $ini_len - bytes::length($src);
            pos($$rsrc) = $ini_pos;
            return 1;
        }
    }

    $$rdst .= $ret;
    $$rpos = $ini_pos + $pos + $ini_len - bytes::length($src);
    pos($$rsrc) = $ini_pos;
    return '';    # terminator no