#  You may distribute under the terms of either the GNU General Public License
#  or the Artistic License (the same terms as Perl itself)
#
#  (C) Paul Evans, 2011-2015 -- leonerd@leonerd.org.uk

package IO::Async::Process;

use strict;
use warnings;
use base qw( IO::Async::Notifier );

our $VERSION = '0.67';

use Carp;

use Socket qw( SOCK_STREAM );

use Future;

use IO::Async::OS;

=head1 NAME

C<IO::Async::Process> - start and manage a child process

=head1 SYNOPSIS

 use IO::Async::Process;

 use IO::Async::Loop;
 my $loop = IO::Async::Loop->new;

 my $process = IO::Async::Process->new(
    command => [ "tr", "a-z", "n-za-m" ],
    stdin => {
       from => "hello world\n",
    },
    stdout => {
       on_read => sub {
          my ( $stream, $buffref ) = @_;
          while( $$buffref =~ s/^(.*)\n// ) {
             print "Rot13 of 'hello world' is '$1'\n";
          }

          return 0;
       },
    },

    on_finish => sub {
       $loop->stop;
    },
 );

 $loop->add( $process );

 $loop->run;

=head1 DESCRIPTION

This subclass of L<IO::Async::Notifier> starts a child process, and invokes a
callback when it exits. The child process can either execute a given block of
code (via C<fork(2)>), or a command.

=cut

=head1 EVENTS

The following events are invoked, either using subclass methods or CODE
references in parameters:

=head2 on_finish $exitcode

Invoked after the process has exited by normal means (i.e. an C<exit(2)>
syscall from a process, or C<return>ing from the code block), and has closed
all its file descriptors.

=head2 on_exception $exception, $errno, $exitcode

Invoked when the process exits by an exception from C<code>, or by failing to
C<exec(2)> the given command. C<$errno> will be a dualvar, containing both
number and string values. After a successful C<exec()> call, this condition
can no longer happen.

Note that this has a different name and a different argument order from
C<< Loop->open_child >>'s C<on_error>.

If this is not provided and the process exits with an exception, then
C<on_finish> is invoked instead, being passed just the exit code.

Since this is just the results of the underlying C<< $loop->spawn_child >>
C<on_exit> handler in a different order it is possible that the C<$exception>
field will be an empty string. It will however always be defined. This can be
used to distinguish the two cases:

 on_exception => sub {
    my ( $self, $exception, $errno, $exitcode ) = @_;

    if( length $exception ) {
       print STDERR "The process died with the exception $exception " .
          "(errno was $errno)\n";
    }
    elsif( ( my $status = W_EXITSTATUS($exitcode) ) == 255 ) {
       print STDERR "The process failed to exec() - $errno\n";
    }
    else {
       print STDERR "The process exited with exit status $status\n";
    }
 }

=cut

=head1 CONSTRUCTOR

=cut

=head2 $process = IO::Async::Process->new( %args )

Constructs a new C<IO::Async::Process> object and returns it.

Once constructed, the C<Process> will need to be added to the C<Loop> before
the child process is started.

=cut

sub _init
{
   my $self = shift;
   $self->SUPER::_init( @_ );

   $self->{to_close}   = {};
   $self->{finish_futures} = [];
}

=head1 PARAMETERS

The following named parameters may be passed to C<new> or C<configure>:

=head2 on_finish => CODE

=head2 on_exception => CODE

CODE reference for the event handlers.

Once the C<on_finish> continuation has been invoked, the C<IO::Async::Process>
object is removed from the containing C<IO::Async::Loop> object.

The following parameters may be passed to C<new>, or to C<configure> before
the process has been started (i.e. before it has been added to the C<Loop>).
Once the process is running these cannot be changed.

=head2 command => ARRAY or STRING

Either a reference to an array containing the command and its arguments, or a
plain string containing the command. This value is passed into perl's
C<exec(2)> function.

=head2 code => CODE

A block of code to execute in the child process. It will be called in scalar
context inside an C<eval> block.

=head2 setup => ARRAY

Optional reference to an array to pass to the underlying C<Loop>
C<spawn_child> method.

=head2 fdI<n> => HASH

A hash describing how to set up file descriptor I<n>. The hash may contain the
following keys:

=over 4

=item via => STRING

Configures how this file descriptor will be configured for the child process.
Must be given one of the following mode names:

=over 4

=item pipe_read

The child will be given the writing end of a C<pipe(2)>; the parent may read
from the other.

=item pipe_write

The child will be given the reading end of a C<pipe(2)>; the parent may write
to the other. Since an EOF condition of this kind of handle cannot reliably be
detected, C<on_finish> will not wait for this type of pipe to be closed.

=item pipe_rdwr

Only valid on the C<stdio> filehandle. The child will be given the reading end
of one C<pipe(2)> on STDIN and the writing end of another on STDOUT. A single
Stream object will be created in the parent configured for both filehandles.

=item socketpair

The child will be given one end of a C<socketpair(2)>; the parent will be
given the other. The family of this socket may be given by the extra key
called C<family>; defaulting to C<unix>. The socktype of this socket may be
given by the extra key called C<socktype>; defaulting to C<stream>. If the
type is not C<SOCK_STREAM> then a L<IO::Async::Socket> object will be
constructed for the parent side of the handle, rather than
C<IO::Async::Stream>.

=back

Once the filehandle is set up, the C<fd> method (or its shortcuts of C<stdin>,
C<stdout> or C<stderr>) may be used to access the
C<IO::Async::Handle>-subclassed object wrapped around it.

The value of this argument is implied by any of the following alternatives.

=item on_read => CODE

The child will be given the writing end of a pipe. The reading end will be
wrapped by an C<IO::Async::Stream> using this C<on_read> callback function.

=item into => SCALAR

The child will be given the writing end of a pipe. The referenced scalar will
be filled by data read from the child process. This data may not be available
until the pipe has been closed by the child.

=item from => STRING

The child will be given the reading end of a pipe. The string given by the
C<from> parameter will be written to the child. When all of the data has been
written the pipe will be closed.

=back

=head2 stdin => ...

=head2 stdout => ...

=head2 stderr => ...

Shortcuts for C<fd0>, C<fd1> and C<fd2> respectively.

=head2 stdio => ...

Special filehandle to affect STDIN and STDOUT at the same time. This
filehandle supports being configured for both reading and writing at the same
time.

=cut

sub configure
{
   my $self = shift;
   my %params = @_;

   foreach (qw( on_finish on_exception )) {
      $self->{$_} = delete $params{$_} if exists $params{$_};
   }

   # All these parameters can only be configured while the process isn't
   # running
   my %setup_params;
   foreach (qw( code command setup stdin stdout stderr stdio ), grep { m/^fd\d+$/ } keys %params ) {
      $setup_params{$_} = delete $params{$_} if exists $params{$_};
   }

   if( $self->is_running ) {
      keys %setup_params and croak "Cannot configure a running Process with " . join ", ", keys %setup_params;
   }

   defined( exists $setup_params{code} ? $setup_params{code} : $self->{code} ) +
      defined( exists $setup_params{command} ? $setup_params{command} : $self->{command} ) <= 1 or
      croak "Cannot have both 'code' and 'command'";

   foreach (qw( code command setup )) {
      $self->{$_} = delete $setup_params{$_} if exists $setup_params{$_};
   }

   $self->configure_fd( 0, %{ delete $setup_params{stdin}  } ) if $setup_params{stdin};
   $self->configure_fd( 1, %{ delete $setup_params{stdout} } ) if $setup_params{stdout};
   $self->configure_fd( 2, %{ delete $setup_params{stderr} } ) if $setup_params{stderr};

   $self->configure_fd( 'io', %{ delete $setup_params{stdio} } ) if $setup_params{stdio};

   # All the rest are fd\d+
   foreach ( keys %setup_params ) {
      my ( $fd ) = m/^fd(\d+)$/ or croak "Expected 'fd\\d+'";
      $self->configure_fd( $fd, %{ $setup_params{$_} } );
   }

   $self->SUPER::configure( %params );
}

# These are from the perspective of the parent
use constant FD_VIA_PIPEREAD  => 1;
use constant FD_VIA_PIPEWRITE => 2;
use constant FD_VIA_PIPERDWR  => 3; # Only valid for stdio pseudo-fd
use constant FD_VIA_SOCKETPAIR => 4;

my %via_names = (
   pipe_read  => FD_VIA_PIPEREAD,
   pipe_write => FD_VIA_PIPEWRITE,
   pipe_rdwr  => FD_VIA_PIPERDWR,
   socketpair => FD_VIA_SOCKETPAIR,
);

sub configure_fd
{
   my $self = shift;
   my ( $fd, %args ) = @_;

   $self->is_running and croak "Cannot configure fd $fd in a running Process";

   if( $fd eq "io" ) {
      exists $self->{fd_opts}{$_} and croak "Cannot configure stdio since fd$_ is already defined" for 0 .. 1;
   }
   elsif( $fd == 0 or $fd == 1 ) {
      exists $self->{fd_opts}{io} and croak "Cannot configure fd$fd since stdio is already defined";
   }

   my $opts = $self->{fd_opts}{$fd} ||= {};
   my $via = $opts->{via};

   my ( $wants_read, $wants_write );

   if( my $via_name = delete $args{via} ) {
      defined $via and
         croak "Cannot change the 'via' mode of fd$fd now that it is already configured";

      $via = $via_names{$via_name} or
         croak "Unrecognised 'via' name of '$via_name'";
   }

   if( my $on_read = delete $args{on_read} ) {
      $opts->{handle}{on_read} = $on_read;

      $wants_read++;
   }
   elsif( my $into = delete $args{into} ) {
      $opts->{handle}{on_read} = sub {
         my ( undef, $buffref, $eof ) = @_;
         $$into .= $$buffref if $eof;
         return 0;
      };

      $wants_read++;
   }

   if( defined( my $from = delete $args{from} ) ) {
      $opts->{from} = $from;

      $wants_write++;
   }

   if( defined $via and $via == FD_VIA_SOCKETPAIR ) {
      $self->{fd_opts}{$fd}{$_} = delete $args{$_} for qw( family socktype );
   }

   keys %args and croak "Unexpected extra keys for fd $fd - " . join ", ", keys %args;

   if( !defined $via ) {
      $via = FD_VIA_PIPEREAD  if  $wants_read and !$wants_write;
      $via = FD_VIA_PIPEWRITE if !$wants_read and  $wants_write;
      $via = FD_VIA_PIPERDWR  if  $wants_read and  $wants_write;
   }
   elsif( $via == FD_VIA_PIPEREAD ) {
      $wants_write and $via = FD_VIA_PIPERDWR;
   }
   elsif( $via == FD_VIA_PIPEWRITE ) {
      $wants_read and $via = FD_VIA_PIPERDWR;
   }
   elsif( $via == FD_VIA_PIPERDWR or $via == FD_VIA_SOCKETPAIR ) {
      # Fine
   }
   else {
      die "Need to check fd_via{$fd}\n";
   }

   $via == FD_VIA_PIPERDWR and $fd ne "io" and
      croak "Cannot both read and write simultaneously on fd$fd";

   defined $via and $opts->{via} = $via;
}

sub _prepare_fds
{
   my $self = shift;
   my ( $loop ) = @_;

   my $fd_handle = $self->{fd_handle};
   my $fd_opts   = $self->{fd_opts};

   my $finish_futures = $self->{finish_futures};

   my @setup;

   foreach my $fd ( keys %$fd_opts ) {
      my $opts   = $fd_opts->{$fd};
      my $via    = $opts->{via};

      my $handle = $self->fd( $fd );

      my $key = $fd eq "io" ? "stdio" : "fd$fd";
      my $write_only;

      if( $via == FD_VIA_PIPEREAD ) {
         my ( $myfd, $childfd ) = IO::Async::OS->pipepair or croak "Unable to pipe() - $!";

         $handle->configure( read_handle => $myfd );

         push @setup, $key => [ dup => $childfd ];
         $self->{to_close}{$childfd->fileno} = $childfd;
      }
      elsif( $via == FD_VIA_PIPEWRITE ) {
         my ( $childfd, $myfd ) = IO::Async::OS->pipepair or croak "Unable to pipe() - $!";
         $write_only++;

         $handle->configure( write_handle => $myfd );

         push @setup, $key => [ dup => $childfd ];
         $self->{to_close}{$childfd->fileno} = $childfd;
      }
      elsif( $via == FD_VIA_PIPERDWR ) {
         $key eq "stdio" or croak "Oops - should only be FD_VIA_PIPERDWR on stdio";
         # Can't use pipequad here for now because we need separate FDs so we
         # can ->close them properly
         my ( $myread, $childwrite ) = IO::Async::OS->pipepair or croak "Unable to pipe() - $!";
         my ( $childread, $mywrite ) = IO::Async::OS->pipepair or croak "Unable to pipe() - $!";

         $handle->configure( read_handle => $myread, write_handle => $mywrite );

         push @setup, stdin => [ dup => $childread ], stdout => [ dup => $childwrite ];
         $self->{to_close}{$childread->fileno}  = $childread;
         $self->{to_close}{$childwrite->fileno} = $childwrite;
      }
      elsif( $via == FD_VIA_SOCKETPAIR ) {
         my ( $myfd, $childfd ) = IO::Async::OS->socketpair( $opts->{family}, $opts->{socktype} ) or croak "Unable to socketpair() - $!";

         $handle->configure( handle => $myfd );

         if( $key eq "stdio" ) {
            push @setup, stdin => [ dup => $childfd ], stdout => [ dup => $childfd ];
         }
         else {
            push @setup, $key => [ dup => $childfd ];
         }
         $self->{to_close}{$childfd->fileno} = $childfd;
      }
      else {
         croak "Unsure what to do with fd_via==$via";
      }

      $self->add_child( $handle );

      unless( $write_only ) {
         push @$finish_futures, $handle->new_close_future;
      }
   }

   return @setup;
}

sub _add_to_loop
{
   my $self = shift;
   my ( $loop ) = @_;

   $self->{code} or $self->{command} or
      croak "Require either 'code' or 'command' in $self";

   $self->can_event( "on_finish" ) or
      croak "Expected either an on_finish callback or to be able to ->on_finish";

   my @setup;
   push @setup, @{ $self->{setup} } if $self->{setup};

   push @setup, $self->_prepare_fds( $loop );

   my $finish_futures = delete $self->{finish_futures};

   my ( $exitcode, $dollarbang, $dollarat );
   push @$finish_futures, my $exit_future = $loop->new_future;

   $self->{pid} = $loop->spawn_child(
      code    => $self->{code},
      command => $self->{command},

      setup => \@setup,

      on_exit => $self->_capture_weakself( sub {
         ( my $self, undef, $exitcode, $dollarbang, $dollarat ) = @_;

         $self->debug_printf( "EXIT status=0x%04x", $exitcode ) if $self;
         $exit_future->done unless $exit_future->is_cancelled;
      } ),
   );
   $self->{running} = 1;

   $self->SUPER::_add_to_loop( @_ );

   $_->close for values %{ delete $self->{to_close} };

   my $is_code = defined $self->{code};

   $self->{finish_future} = Future->needs_all( @$finish_futures )
      ->on_done( $self->_capture_weakself( sub {
         my $self = shift or return;

         $self->{exitcode} = $exitcode;
         $self->{dollarbang} = $dollarbang;
         $self->{dollarat}   = $dollarat;

         undef $self->{running};

         if( $is_code ? $dollarat eq "" : $dollarbang == 0 ) {
            $self->invoke_event( on_finish => $exitcode );
         }
         else {
            $self->maybe_invoke_event( on_exception => $dollarat, $dollarbang, $exitcode ) or
               # Don't have a way to report dollarbang/dollarat
               $self->invoke_event( on_finish => $exitcode );
         }

         $self->remove_from_parent;
      } ),
   );
}

sub DESTROY
{
   my $self = shift;
   $self->{finish_future}->cancel if $self->{finish_future};
}

sub notifier_name
{
   my $self = shift;
   if( length( my $name = $self->SUPER::notifier_name ) ) {
      return $name;
   }

   return "nopid" unless my $pid = $self->pid;
   return "[$pid]" unless $self->is_running;
   return "$pid";
}

=head1 METHODS

=cut

=head2 $pid = $process->pid

Returns the process ID of the process, if it has been started, or C<undef> if
not. Its value is preserved after the process exits, so it may be inspected
during the C<on_finish> or C<on_exception> events.

=cut

sub pid
{
   my $self = shift;
   return $self->{pid};
}

=head2 $process->kill( $signal )

Sends a signal to the process

=cut

sub kill
{
   my $self = shift;
   my ( $signal ) = @_;

   kill $signal, $self->pid or croak "Cannot kill() - $!";
}

=head2 $running = $process->is_running

Returns true if the Process has been started, and has not yet finished.

=cut

sub is_running
{
   my $self = shift;
   return $self->{running};
}

=head2 $exited = $process->is_exited

Returns true if the Process has finished running, and finished due to normal
C<exit(2)>.

=cut

sub is_exited
{
   my $self = shift;
   return defined $self->{exitcode} ? ( $self->{exitcode} & 0x7f ) == 0 : undef;
}

=head2 $status = $process->exitstatus

If the process exited due to normal C<exit(2)>, returns the value that was
passed to C<exit(2)>. Otherwise, returns C<undef>.

=cut

sub exitstatus
{
   my $self = shift;
   return defined $self->{exitcode} ? ( $self->{exitcode} >> 8 ) : undef;
}

=head2 $exception = $process->exception

If the process exited due to an exception, returns the exception that was
thrown. Otherwise, returns C<undef>.

=cut

sub exception
{
   my $self = shift;
   return $self->{dollarat};
}

=head2 $errno = $process->errno

If the process exited due to an exception, returns the numerical value of
C<$!> at the time the exception was thrown. Otherwise, returns C<undef>.

=cut

sub errno
{
   my $self = shift;
   return $self->{dollarbang}+0;
}

=head2 $errstr = $process->errstr

If the process exited due to an exception, returns the string value of
C<$!> at the time the exception was thrown. Otherwise, returns C<undef>.

=cut

sub errstr
{
   my $self = shift;
   return $self->{dollarbang}."";
}

=head2 $stream = $process->fd( $fd )

Returns the L<IO::Async::Stream> or L<IO::Async::Socket> associated with the
given FD number. This must have been set up by a C<configure> argument prior
to adding the C<Process> object to the C<Loop>.

The returned object have its read or write handle set to the other end of a
pipe or socket connected to that FD number in the child process. Typically,
this will be used to call the C<write> method on, to write more data into the
child, or to set an C<on_read> handler to read data out of the child.

The C<on_closed> event for these streams must not be changed, or it will break
the close detection used by the C<Process> object and the C<on_finish> event
will not be invoked.

=cut

sub fd
{
   my $self = shift;
   my ( $fd ) = @_;

   return $self->{fd_handle}{$fd} ||= do {
      my $opts = $self->{fd_opts}{$fd} or
         croak "$self does not have an fd Stream for $fd";

      my $handle_class;
      if( defined $opts->{socktype} && IO::Async::OS->getsocktypebyname( $opts->{socktype} ) != SOCK_STREAM ) {
         require IO::Async::Socket;
         $handle_class = "IO::Async::Socket";
      }
      else {
         require IO::Async::Stream;
         $handle_class = "IO::Async::Stream";
      }

      my $handle = $handle_class->new(
         notifier_name => $fd eq "0"  ? "stdin" :
                          $fd eq "1"  ? "stdout" :
                          $fd eq "2"  ? "stderr" :
                          $fd eq "io" ? "stdio" : "fd$fd",
         %{ $opts->{handle} },
      );

      if( defined $opts->{from} ) {
         $handle->write( $opts->{from},
            on_flush => sub {
               my ( $handle ) = @_;
               $handle->close_write;
            },
         );
      }

      $handle
   };
}

=head2 $stream = $process->stdin

=head2 $stream = $process->stdout

=head2 $stream = $process->stderr

=head2 $stream = $process->stdio

Shortcuts for calling C<fd> with 0, 1, 2 or C<io> respectively, to obtain the
L<IO::Async::Stream> representing the standard input, output, error, or
combined input/output streams of the child process.

=cut

sub stdin  { shift->fd( 0 ) }
sub stdout { shift->fd( 1 ) }
sub stderr { shift->fd( 2 ) }
sub stdio  { shift->fd( 'io' ) }

=head1 EXAMPLES

=head2 Capturing the STDOUT stream of a process

By configuring the C<stdout> filehandle of the process using the C<into> key,
data written by the process can be captured.

 my $stdout;
 my $process = IO::Async::Process->new(
    command => [ "writing-program", "arguments" ],
    stdout => { into => \$stdout },
    on_finish => sub {
       print "The process has finished, and wrote:\n";
       print $stdout;
    }
 );

 $loop->add( $process );

Note that until C<on_finish> is invoked, no guarantees are made about how much
of the data actually written by the process is yet in the C<$stdout> scalar.

See also the C<run_child> method of L<IO::Async::Loop>.

To handle data more interactively as it arrives, the C<on_read> key can
instead be used, to provide a callback function to invoke whenever more data
is available from the process.

 my $process = IO::Async::Process->new(
    command => [ "writing-program", "arguments" ],
    stdout => {
       on_read => sub {
          my ( $stream, $buffref ) = @_;
          while( $$buffref =~ s/^(.*)\n// ) {
             print "The process wrote a line: $1\n";
          }

          return 0;
       },
    },
    on_finish => sub {
       print "The process has finished\n";
    }
 );

 $loop->add( $process );

If the code to handle data read from the process isn't available yet when
the object is constructed, it can be supplied later by using the C<configure>
method on the C<stdout> filestream at some point before it gets added to the
Loop. In this case, C<stdin> should be configured using C<pipe_read> in the
C<via> key.

 my $process = IO::Async::Process->new(
    command => [ "writing-program", "arguments" ],
    stdout => { via => "pipe_read" },
    on_finish => sub {
       print "The process has finished\n";
    }
 );

 $process->stdout->configure(
    on_read => sub {
       my ( $stream, $buffref ) = @_;
       while( $$buffref =~ s/^(.*)\n// ) {
          print "The process wrote a line: $1\n";
       }

       return 0;
    },
 );

 $loop->add( $process );

=head2 Sending data to STDIN of a process

By configuring the C<stdin> filehandle of the process using the C<from> key,
data can be written into the C<STDIN> stream of the process.

 my $process = IO::Async::Process->new(
    command => [ "reading-program", "arguments" ],
    stdin => { from => "Here is the data to send\n" },
    on_finish => sub { 
       print "The process has finished\n";
    }
 );

 $loop->add( $process );

The data in this scalar will be written until it is all consumed, then the
handle will be closed. This may be useful if the program waits for EOF on
C<STDIN> before it exits.

To have the ability to write more data into the process once it has started.
the C<write> method on the C<stdin> stream can be used, when it is configured
using the C<pipe_write> value for C<via>:

 my $process = IO::Async::Process->new(
    command => [ "reading-program", "arguments" ],
    stdin => { via => "pipe_write" },
    on_finish => sub { 
       print "The process has finished\n";
    }
 );

 $loop->add( $process );

 $process->stdin->write( "Here is some more data\n" );

=cut

=head1 AUTHOR

Paul Evans <leonerd@leonerd.org.uk>

=cut

0x55AA;