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package AnyEvent::Handle::Writer;

use 5.8.8;
use common::sense 2;m{
use strict;
use warnings;
}x;
use AnyEvent::Handle;
use AnyEvent::Util;
BEGIN{ push our @ISA, 'AnyEvent::Handle'; }

=head1 NAME

AnyEvent::Handle::Writer - Extended version of AnyEvent::Handle with additional write options

=cut

our $VERSION = '0.02';

=head1 SYNOPSIS

   use AnyEvent;
   use AnyEvent::Handle::Writer;

   my $hdl; $hdl = AnyEvent::Handle::Writer->new(
      fh => $fh,
      on_error => sub {
         my ($hdl, $fatal, $msg) = @_;
         warn "got error $msg\n";
         $hdl->destroy;
      }
   );

   # Custom writer
   $hdl->push_write(sub {
      my $h = shift;
      if ($have_data) {
         $h->unshift_write($data);
         return 1; # Work done
      } else {
         return 0; # Work not done, call me again
      }
   });

   # sendfile
   $hdl->push_sendfile('/path/to/file', 1024);

=head1 RATIONALE

We have great l<AnyEvent::Handle>. But it have only raw write queue. This module extends it with
callbacks in write queue and adds a C<push_sendfile()> call, which would be processed at correct time

=head1 METHODS

=cut

=head2 push_write($data)

L<AnyEvent::Handle/WRITE_QUEUE>

=head2 push_write(type => @args)

L<AnyEvent::Handle/WRITE_QUEUE>

=head2 push_write($cb->($handle))

This version of call allow to push a callback, which will be invoked when the write queue before it became empty.

   Callback should return:
      true  - when there is no work to be done with this callback.
              it will be removed from queue and continue
      false - when it want to be called again (i.e. not all work was done)
              it will be kept in queue and called on next drain

This call allow us to implement such a thing:

   $handle->push_write("HTTP/1.1 200 OK\012\015\012\015");
   $handle->push_write(sub {
      # Manual work on handle
      my $h = shift;
      my $len = syswrite($h->{fh}, $data); # Here may be also sendfile work
      if (defined $len) {
         diag "written $len";
         substr $data, 0, $len, "";
         if (length $data) {
            return 0; # want be called again
         } else {
            return 1; # all done
         }
      } elsif (!$!{EAGAIN} and !$!{EINTR} and !$!{WSAEWOULDBLOCK}) {
         $h->_error ($!, 1);
         return 1; # No more requests to me, got an error
      }
      else { return 0; }
   });
   $handle->push_write("HTTP/1.1 200 OK\012\015\012\015");
   $handle->push_write("Common response");

=head2 unshift_write($data)
=head2 unshift_write(type => @args)
=head2 unshift_write($cb->($handle))

Analogically to C<unshift_read>, it unshift write data at the beginngin of queue. B<The only recommended usage is from write callback>

   $handle->push_write("1")
   $handle->push_write(sub {
      my $h = shift;
      $h->unshift_write("2");
      return 1;
   });
   $handle->push_write("3");