=cut

sub on_drain {
   my ($self, $cb) = @_;

   $self->{on_drain} = $cb;

   $cb->($self)
      if $cb && $self->{low_water_mark} >= length $self->{wbuf};
}

=item $handle->push_write ($data)

Queues the given scalar to be written. You can push as much data as you
want (only limited by the available memory), as C<AnyEvent::Handle>
buffers it independently of the kernel.

=cut

sub _drain_wbuf {
   my ($self) = @_;

   if (!$self->{_ww} && length $self->{wbuf}) {

      Scalar::Util::weaken $self;

      my $cb = sub {
         my $len = syswrite $self->{fh}, $self->{wbuf};

         if ($len >= 0) {
            substr $self->{wbuf}, 0, $len, "";

            $self->{_activity} = AnyEvent->now;

            $self->{on_drain}($self)
               if $self->{low_water_mark} >= length $self->{wbuf}
                  && $self->{on_drain};

            delete $self->{_ww} unless length $self->{wbuf};
         } elsif ($! != EAGAIN && $! != EINTR && $! != WSAEWOULDBLOCK) {
            $self->_error ($!, 1);
         }
      };

      # try to write data immediately
      $cb->();

      # if still data left in wbuf, we need to poll
      $self->{_ww} = AnyEvent->io (fh => $self->{fh}, poll => "w", cb => $cb)
         if length $self->{wbuf};
   };
}

our %WH;

sub register_write_type($$) {
   $WH{$_[0]} = $_[1];
}

sub push_write {
   my $self = shift;

   if (@_ > 1) {
      my $type = shift;

      @_ = ($WH{$type} or Carp::croak "unsupported type passed to AnyEvent::Handle::push_write")
           ->($self, @_);
   }

   if ($self->{filter_w}) {
      $self->{filter_w}($self, \$_[0]);
   } else {
      $self->{wbuf} .= $_[0];
      $self->_drain_wbuf;
   }
}

=item $handle->push_write (type => @args)

Instead of formatting your data yourself, you can also let this module do
the job by specifying a type and type-specific arguments.

Predefined types are (if you have ideas for additional types, feel free to
drop by and tell us):

=over 4

=item netstring => $string

Formats the given value as netstring
(http://cr.yp.to/proto/netstrings.txt, this is not a recommendation to use them).

=cut

register_write_type netstring => sub {
   my ($self, $string) = @_;

   sprintf "%d:%s,", (length $string), $string
};