package open;
use warnings;

our $VERSION = '1.11';

require 5.008001; # for PerlIO::get_layers()

my $locale_encoding;

sub _get_encname {
return ($1, Encode::resolve_alias($1)) if $_[0] =~ /^:?encoding\((.+)\)$/;
return;
}

sub croak {
require Carp; goto &Carp::croak;
}

sub _drop_oldenc {
# If by the time we arrive here there already is at the top of the
# perlio layer stack an encoding identical to what we would like
# to push via this open pragma, we will pop away the old encoding
# (+utf8) so that we can push ourselves in place (this is easier
# than ignoring pushing ourselves because of the way how ${^OPEN}
# works). So we are looking for something like
#
# stdio encoding(xxx) utf8
#
# in the existing layer stack, and in the new stack chunk for
#
# :encoding(xxx)
#
# If we find a match, we pop the old stack (once, since
# the utf8 is just a flag on the encoding layer)
my ($h, @new) = @_;
return unless @new >= 1 && $new[-1] =~ /^:encoding\(.+\)$/;
my @old = PerlIO::get_layers($h);
return unless @old >= 3 &&
$old[-1] eq 'utf8' &&
$old[-2] =~ /^encoding\(.+\)$/;
require Encode;
my ($loname, $lcname) = _get_encname($old[-2]);
unless (defined $lcname) { # Should we trust get_layers()?
croak("open: Unknown encoding '$loname'");
}
my ($voname, $vcname) = _get_encname($new[-1]);
unless (defined $vcname) {
croak("open: Unknown encoding '$voname'");
}
if ($lcname eq $vcname) {
binmode($h, ":pop"); # utf8 is part of the encoding layer
}
}

sub import {
my ($class,@args) = @_;
croak("open: needs explicit list of PerlIO layers") unless @args;
my $std;
my ($in,$out) = split(/\0/,(${^OPEN} || "\0"), -1);
while (@args) {
my $type = shift(@args);
my $dscp;
if ($type =~ /^:?(utf8|locale|encoding\(.+\))$/) {
$type = 'IO';
$dscp = ":$1";
} elsif ($type eq ':std') {
$std = 1;
next;
} else {
$dscp = shift(@args) || '';
}
my @val;
foreach my $layer (split(/\s+/,$dscp)) {
$layer =~ s/^://;
if ($layer eq 'locale') {
require Encode;
require encoding;
$locale_encoding = encoding::_get_locale_encoding()
unless defined $locale_encoding;
(warnings::warnif("layer", "Cannot figure out an encoding to use"), last)
unless defined $locale_encoding;
$layer = "encoding($locale_encoding)";
$std = 1;
} else {
my $target = $layer; # the layer name itself
$target =~ s/^(\w+)\(.+\)$/$1/; # strip parameters

unless(PerlIO::Layer::->find($target,1)) {
warnings::warnif("layer", "Unknown PerlIO layer '$target'");
}
}
push(@val,":$layer");
if ($layer =~ /^(crlf|raw)$/) {
$^H{"open_$type"} = $layer;
}
}
if ($type eq 'IN') {
_drop_oldenc(*STDIN, @val) if $std;
$in = join(' ', @val);
}
elsif ($type eq 'OUT') {
if ($std) {
_drop_oldenc(*STDOUT, @val);
_drop_oldenc(*STDERR, @val);
}
$out = join(' ', @val);
}
elsif ($type eq 'IO') {
if ($std) {
_drop_oldenc(*STDIN, @val);
_drop_oldenc(*STDOUT, @val);
_drop_oldenc(*STDERR, @val);
}
$in = $out = join(' ', @val);
}
else {
croak "Unknown PerlIO layer class '$type' (need IN, OUT or IO)";
}
}
${^OPEN} = join("\0", $in, $out);
if ($std) {
if ($in) {
if ($in =~ /:utf8\b/) {
binmode(STDIN, ":utf8");
} elsif ($in =~ /(\w+\(.+\))/) {
binmode(STDIN, ":$1");
}
}
if ($out) {
if ($out =~ /:utf8\b/) {
binmode(STDOUT, ":utf8");
binmode(STDERR, ":utf8");
} elsif ($out =~ /(\w+\(.+\))/) {
binmode(STDOUT, ":$1");
binmode(STDERR, ":$1");
}
}
}
}

1;
__END__

=head1 NAME

open - perl pragma to set default PerlIO layers for input and output

=head1 SYNOPSIS

use open IN => ":crlf", OUT => ":bytes";
use open OUT => ':utf8';
use open IO => ":encoding(iso-8859-7)";

use open IO => ':locale';

use open ':encoding(UTF-8)';
use open ':locale';
use open ':encoding(iso-8859-7)';

use open ':std';

=head1 DESCRIPTION

Full-fledged support for I/O layers is now implemented provided
Perl is configured to use PerlIO as its IO system (which is now the
default).

The C<open> pragma serves as one of the interfaces to declare default
"layers" (also known as "disciplines") for all I/O. Any two-argument
open(), readpipe() (aka qx//) and similar operators found within the
lexical scope of this pragma will use the declared defaults.
Even three-argument opens may be affected by this pragma
when they don't specify IO layers in MODE.

With the C<IN> subpragma you can declare the default layers
of input streams, and with the C<OUT> subpragma you can declare
the default layers of output streams. With the C<IO> subpragma
you can control both input and output streams simultaneously.

If you have a legacy encoding, you can use the C<:encoding(...)> tag.

If you want to set your encoding layers based on your
locale environment variables, you can use the C<:locale> tag.
For example:

$ENV{LANG} = 'ru_RU.KOI8-R';
# the :locale will probe the locale environment variables like LANG
use open OUT => ':locale';
open(O, ">koi8");
print O chr(0x430); # Unicode CYRILLIC SMALL LETTER A = KOI8-R 0xc1
close O;
open(I, "<koi8");
printf "%#x\n", ord(<I>), "\n"; # this should print 0xc1
close I;

These are equivalent

use open ':encoding(UTF-8)';
use open IO => ':encoding(UTF-8)';

as are these

use open ':locale';
use open IO => ':locale';

and these

use open ':encoding(iso-8859-7)';
use open IO => ':encoding(iso-8859-7)';

The matching of encoding names is loose: case does not matter, and
many encodings have several aliases. See L<Encode::Supported> for
details and the list of supported locales.

When open() is given an explicit list of layers (with the three-arg
syntax), they override the list declared using this pragma. open() can
also be given a single colon (:) for a layer name, to override this pragma
and use the default (C<:raw> on Unix, C<:crlf> on Windows).

The C<:std> subpragma on its own has no effect, but if combined with
the C<:utf8> or C<:encoding> subpragmas, it converts the standard
filehandles (STDIN, STDOUT, STDERR) to comply with encoding selected
for input/output handles. For example, if both input and out are
chosen to be C<:encoding(UTF-8)>, a C<:std> will mean that STDIN, STDOUT,
and STDERR are also in C<:encoding(UTF-8)>. On the other hand, if only
output is chosen to be in C<< :encoding(koi8r) >>, a C<:std> will cause
only the STDOUT and STDERR to be in C<koi8r>. The C<:locale> subpragma
implicitly turns on C<:std>.

The logic of C<:locale> is described in full in L<encoding>,
but in short it is first trying nl_langinfo(CODESET) and then
guessing from the LC_ALL and LANG locale environment variables.

Directory handles may also support PerlIO layers in the future.

=head1 NONPERLIO FUNCTIONALITY

If Perl is not built to use PerlIO as its IO system then only the two
pseudo-layers C<:bytes> and C<:crlf> are available.

The C<:bytes> layer corresponds to "binary mode" and the C<:crlf>
layer corresponds to "text mode" on platforms that distinguish
between the two modes when opening files (which is many DOS-like
platforms, including Windows). These two layers are no-ops on
platforms where binmode() is a no-op, but perform their functions
everywhere if PerlIO is enabled.

=head1 IMPLEMENTATION DETAILS

There is a class method in C<PerlIO::Layer> C<find> which is
implemented as XS code. It is called by C<import> to validate the
layers:

PerlIO::Layer::->find("perlio")

The return value (if defined) is a Perl object, of class
C<PerlIO::Layer> which is created by the C code in F<perlio.c>. As
yet there is nothing useful you can do with the object at the perl
level.

=head1 SEE ALSO

L<perlfunc/"binmode">, L<perlfunc/"open">, L<perlunicode>, L<PerlIO>,
L<encoding>

=cut