package Encode::CN::HZ;

use strict;
use warnings;
use utf8 ();

use vars qw($VERSION);
$VERSION = do { my @r = ( q$Revision: 2.5 $ =~ /\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 = '';
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 not found
}

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

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

no warnings 'utf8'; # $str may be malformed UTF8 at the end of a chunk.

while ( length $str ) {
if ( $str =~ s/^([[:ascii:]]+)// ) {
my $tmp = $1;
$tmp =~ s/~/~~/g; # escapes tildes
if ( !$in_ascii ) {
$ret .= "\x7E\x7D"; # '~}'
$in_ascii = 1;
}
$ret .= pack 'a*', $tmp; # remove UTF8 flag.
}
elsif ( $str =~ s/(.)// ) {
my $s = $1;
my $tmp = $GB->encode( $s, $chk );
last if !defined $tmp;
if ( length $tmp == 2 ) { # maybe a valid GB char (XXX)
if ($in_ascii) {
$ret .= "\x7E\x7B"; # '~{'
$in_ascii = 0;
}
$ret .= $tmp;
}
elsif ( length $tmp ) { # maybe FALLBACK in ASCII (XXX)
if ( !$in_ascii ) {
$ret .= "\x7E\x7D"; # '~}'
$in_ascii = 1;
}
$ret .= $tmp;
}
}
else { # if $str is malformed UTF8 *and* if length $str != 0.
last;
}
}
$_[1] = $str if $chk;

# The state at the end of the chunk is discarded, even if in GB mode.
# That results in the combination of GB-OUT and GB-IN, i.e. "~}~{".
# Parhaps it is harmless, but further investigations may be required...

if ( !$in_ascii ) {
$ret .= "\x7E\x7D"; # '~}'
$in_ascii = 1;
}
utf8::encode($ret); # https://rt.cpan.org/Ticket/Display.html?id=35120
return $ret;
}

1;
__END__

=head1 NAME

Encode::CN::HZ -- internally used by Encode::CN

=cut