package Encode::MIME::Header;
use strict;
use warnings;
no warnings 'redefine';

our $VERSION = do { my @r = ( q$Revision: 2.13 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r };
use Encode qw(find_encoding encode_utf8 decode_utf8);
use MIME::Base64;
use Carp;

my %seed = (
decode_b => '1', # decodes 'B' encoding ?
decode_q => '1', # decodes 'Q' encoding ?
encode => 'B', # encode with 'B' or 'Q' ?
bpl => 75, # bytes per line
);

$Encode::Encoding{'MIME-Header'} =
bless { %seed, Name => 'MIME-Header', } => __PACKAGE__;

$Encode::Encoding{'MIME-B'} = bless {
%seed,
decode_q => 0,
Name => 'MIME-B',
} => __PACKAGE__;

$Encode::Encoding{'MIME-Q'} = bless {
%seed,
decode_q => 1,
encode => 'Q',
Name => 'MIME-Q',
} => __PACKAGE__;

use base qw(Encode::Encoding);

sub needs_lines { 1 }
sub perlio_ok { 0 }

sub decode($$;$) {
use utf8;
my ( $obj, $str, $chk ) = @_;

# zap spaces between encoded words
$str =~ s/\?=\s+=\?/\?==\?/gos;

# multi-line header to single line
$str =~ s/(?:\r\n|[\r\n])[ \t]//gos;

1 while ( $str =~
s/(=\?[-0-9A-Za-z_]+\?[Qq]\?)(.*?)\?=\1(.*?\?=)/$1$2$3/ )
; # Concat consecutive QP encoded mime headers
# Fixes breaking inside multi-byte characters

$str =~ s{
=\? # begin encoded word
([-0-9A-Za-z_]+) # charset (encoding)
(?:\*[A-Za-z]{1,8}(?:-[A-Za-z]{1,8})*)? # language (RFC 2231)
\?([QqBb])\? # delimiter
(.*?) # Base64-encodede contents
\?= # end encoded word
}{
if (uc($2) eq 'B'){
$obj->{decode_b} or croak qq(MIME "B" unsupported);
decode_b($1, $3, $chk);
} elsif (uc($2) eq 'Q'){
$obj->{decode_q} or croak qq(MIME "Q" unsupported);
decode_q($1, $3, $chk);
} else {
croak qq(MIME "$2" encoding is nonexistent!);
}
}egox;
$_[1] = $str if $chk;
return $str;
}

sub decode_b {
my $enc = shift;
my $d = find_encoding($enc) or croak qq(Unknown encoding "$enc");
my $db64 = decode_base64(shift);
my $chk = shift;
return $d->name eq 'utf8'
? Encode::decode_utf8($db64)
: $d->decode( $db64, $chk || Encode::FB_PERLQQ );
}

sub decode_q {
my ( $enc, $q, $chk ) = @_;
my $d = find_encoding($enc) or croak qq(Unknown encoding "$enc");
$q =~ s/_/ /go;
$q =~ s/=([0-9A-Fa-f]{2})/pack("C", hex($1))/ego;
return $d->name eq 'utf8'
? Encode::decode_utf8($q)
: $d->decode( $q, $chk || Encode::FB_PERLQQ );
}

my $especials =
join( '|' => map { quotemeta( chr($_) ) }
unpack( "C*", qq{()<>,;:"'/[]?=} ) );

my $re_encoded_word = qr{
=\? # begin encoded word
(?:[-0-9A-Za-z_]+) # charset (encoding)
(?:\*[A-Za-z]{1,8}(?:-[A-Za-z]{1,8})*)? # language (RFC 2231)
\?(?:[QqBb])\? # delimiter
(?:.*?) # Base64-encodede contents
\?= # end encoded word
}xo;

my $re_especials = qr{$re_encoded_word|$especials}xo;

sub encode($$;$) {
my ( $obj, $str, $chk ) = @_;
my @line = ();
for my $line ( split /\r\n|[\r\n]/o, $str ) {
my ( @word, @subline );
for my $word ( split /($re_especials)/o, $line ) {
if ( $word =~ /[^\x00-\x7f]/o
or $word =~ /^$re_encoded_word$/o )
{
push @word, $obj->_encode($word);
}
else {
push @word, $word;
}
}
my $subline = '';
for my $word (@word) {
use bytes ();
if ( bytes::length($subline) + bytes::length($word) >
$obj->{bpl} - 1 )
{
push @subline, $subline;
$subline = '';
}
$subline .= ' ' if ($subline =~ /\?=$/ and $word =~ /^=\?/);
$subline .= $word;
}
$subline and push @subline, $subline;
push @line, join( "\n " => @subline );
}
$_[1] = '' if $chk;
return join( "\n", @line );
}

use constant HEAD => '=?UTF-8?';
use constant TAIL => '?=';
use constant SINGLE => { B => \&_encode_b, Q => \&_encode_q, };

sub _encode {
my ( $o, $str ) = @_;
my $enc = $o->{encode};
my $llen = ( $o->{bpl} - length(HEAD) - 2 - length(TAIL) );

# to coerce a floating-point arithmetics, the following contains
# .0 in numbers -- dankogai
$llen *= $enc eq 'B' ? 3.0 / 4.0 : 1.0 / 3.0;
my @result = ();
my $chunk = '';
while ( length( my $chr = substr( $str, 0, 1, '' ) ) ) {
use bytes ();
if ( bytes::length($chunk) + bytes::length($chr) > $llen ) {
push @result, SINGLE->{$enc}($chunk);
$chunk = '';
}
$chunk .= $chr;
}
length($chunk) and push @result, SINGLE->{$enc}($chunk);
return @result;
}

sub _encode_b {
HEAD . 'B?' . encode_base64( encode_utf8(shift), '' ) . TAIL;
}

sub _encode_q {
my $chunk = shift;
$chunk = encode_utf8($chunk);
$chunk =~ s{
([^0-9A-Za-z])
}{
join("" => map {sprintf "=%02X", $_} unpack("C*", $1))
}egox;
return HEAD . 'Q?' . $chunk . TAIL;
}

1;
__END__

=head1 NAME

Encode::MIME::Header -- MIME 'B' and 'Q' header encoding

=head1 SYNOPSIS

use Encode qw/encode decode/;
$utf8 = decode('MIME-Header', $header);
$header = encode('MIME-Header', $utf8);

=head1 ABSTRACT

This module implements RFC 2047 Mime Header Encoding. There are 3
variant encoding names; C<MIME-Header>, C<MIME-B> and C<MIME-Q>. The
difference is described below

decode() encode()
----------------------------------------------
MIME-Header Both B and Q =?UTF-8?B?....?=
MIME-B B only; Q croaks =?UTF-8?B?....?=
MIME-Q Q only; B croaks =?UTF-8?Q?....?=

=head1 DESCRIPTION

When you decode(=?I<encoding>?I<X>?I<ENCODED WORD>?=), I<ENCODED WORD>
is extracted and decoded for I<X> encoding (B for Base64, Q for
Quoted-Printable). Then the decoded chunk is fed to
decode(I<encoding>). So long as I<encoding> is supported by Encode,
any source encoding is fine.

When you encode, it just encodes UTF-8 string with I<X> encoding then
quoted with =?UTF-8?I<X>?....?= . The parts that RFC 2047 forbids to
encode are left as is and long lines are folded within 76 bytes per
line.

=head1 BUGS

It would be nice to support encoding to non-UTF8, such as =?ISO-2022-JP?
and =?ISO-8859-1?= but that makes the implementation too complicated.
These days major mail agents all support =?UTF-8? so I think it is
just good enough.

Due to popular demand, 'MIME-Header-ISO_2022_JP' was introduced by
Makamaka. Thre are still too many MUAs especially cellular phone
handsets which does not grok UTF-8.

=head1 SEE ALSO

L<Encode>

RFC 2047, L<http://www.faqs.org/rfcs/rfc2047.html> and many other
locations.

=cut