=head1 NAME

Term::ReadLine - Perl interface to various C<readline> packages. If
no real package is found, substitutes stubs instead of basic functions.

=head1 SYNOPSIS

  use Term::ReadLine;
  $term = new Term::ReadLine 'Simple Perl calc';
  $prompt = "Enter your arithmetic expression: ";
  $OUT = $term->OUT || STDOUT;
  while ( defined ($_ = $term->readline($prompt)) ) {
    $res = eval($_), "\n";
    warn $@ if $@;
    print $OUT $res, "\n" unless $@;
    $term->addhistory($_) if /\S/;
  }

=head1 DESCRIPTION

This package is just a front end to some other packages. At the moment
this description is written, the only such package is Term-ReadLine,
available on CPAN near you. The real target of this stub package is to
set up a common interface to whatever Readline emerges with time.

=head1 Minimal set of supported functions

All the supported functions should be called as methods, i.e., either as 

  $term = new Term::ReadLine 'name';

or as 

  $term->addhistory('row');

where $term is a return value of Term::ReadLine-E<gt>Init.

=over 12

=item C<ReadLine>

returns the actual package that executes the commands. Among possible
values are C<Term::ReadLine::Gnu>, C<Term::ReadLine::Perl>,
C<Term::ReadLine::Stub Exporter>.

=item C<new>

returns the handle for subsequent calls to following
functions. Argument is the name of the application. Optionally can be
followed by two arguments for C<IN> and C<OUT> filehandles. These
arguments should be globs.

=item C<readline>

gets an input line, I<possibly> with actual C<readline>
support. Trailing newline is removed. Returns C<undef> on C<EOF>.

=item C<addhistory>

adds the line to the history of input, from where it can be used if
the actual C<readline> is present.

=item C<IN>, $C<OUT>

return the filehandles for input and output or C<undef> if C<readline>
input and output cannot be used for Perl.

=item C<MinLine>

If argument is specified, it is an advice on minimal size of line to
be included into history.  C<undef> means do not include anything into
history. Returns the old value.

=item C<findConsole>

returns an array with two strings that give most appropriate names for
files for input and output using conventions C<"E<lt>$in">, C<"E<gt>out">.

=item Attribs

returns a reference to a hash which describes internal configuration
of the package. Names of keys in this hash conform to standard
conventions with the leading C<rl_> stripped.

=item C<Features>

Returns a reference to a hash with keys being features present in
current implementation. Several optional features are used in the
minimal interface: C<appname> should be present if the first argument
to C<new> is recognized, and C<minline> should be present if
C<MinLine> method is not dummy.  C<autohistory> should be present if
lines are put into history automatically (maybe subject to
C<MinLine>), and C<addhistory> if C<addhistory> method is not dummy.

If C<Features> method reports a feature C<attribs> as present, the
method C<Attribs> is not dummy.

=back

=head1 Additional supported functions

Actually C<Term::ReadLine> can use some other package, that will
support reacher set of commands.

All these commands are callable via method interface and have names
which conform to standard conventions with the leading C<rl_> stripped.

=head1 EXPORTS

None

=head1 ENVIRONMENT

The variable C<PERL_RL> governs which ReadLine clone is loaded. If the
value is false, a dummy interface is used. If the value is true, it
should be tail of the name of the package to use, such as C<Perl> or
C<Gnu>. 

If the variable is not set, the best available package is loaded.

=cut

package Term::ReadLine::Stub;
@ISA = 'Term::ReadLine::Tk';

$DB::emacs = $DB::emacs;	# To peacify -w

sub ReadLine {'Term::ReadLine::Stub'}
sub readline {
  my $self = shift;
  my ($in,$out,$str) = @$self;
  print $out shift; 
  $self->register_Tk 
     if not $Term::ReadLine::registered and $Term::ReadLine::toloop
	and defined &Tk::DoOneEvent;
  #$str = scalar <$in>;
  $str = $self->get_line;
  # bug in 5.000: chomping empty string creats length -1:
  chomp $str if defined $str;
  $str;
}
sub addhistory {}

sub findConsole {
    my $console;

    if (-e "/dev/tty") {
	$console = "/dev/tty";
    } elsif (-e "con") {
	$console = "con";
    } else {
	$console = "sys\$command";
    }

    if (defined $ENV{'OS2_SHELL'}) { # In OS/2
      if ($DB::emacs) {
	$console = undef;
      } else {
	$console = "/dev/con";
      }
    }

    $consoleOUT = $console;
    $console = "&STDIN" unless defined $console;
    if (!defined $consoleOUT) {
      $consoleOUT = defined fileno(STDERR) ? "&STDERR" : "&STDOUT";
    }
    ($console,$consoleOUT);
}

sub new {
  die "method new called with wrong number of arguments" 
    unless @_==2 or @_==4;
  #local (*FIN, *FOUT);
  my ($FIN, $FOUT);
  if (@_==2) {
    ($console, $consoleOUT) = findConsole;

    open(FIN, "<$console"); 
    open(FOUT,">$consoleOUT");
    #OUT->autoflush(1);		# Conflicts with debugger?
    $sel = select(FOUT);
    $| = 1;				# for DB::OUT
    select($sel);
    bless [\*FIN, \*FOUT];
  } else {			# Filehandles supplied
    $FIN = $_[2]; $FOUT = $_[3];
    #OUT->autoflush(1);		# Conflicts with debugger?
    $sel = select($FOUT);
    $| = 1;				# for DB::OUT
    select($sel);
    bless [$FIN, $FOUT];
  }
}
sub IN { shift->[0] }
sub OUT { shift->[1] }
sub MinLine { undef }
sub Attribs { {} }

my %features = (tkRunning => 1);
sub Features { \%features }

package Term::ReadLine;		# So late to allow the above code be defined?

my $which = $ENV{PERL_RL};
if ($which) {
  if ($which =~ /\bgnu\b/i){
    eval "use Term::ReadLine::Gnu;";
  } elsif ($which =~ /\bperl\b/i) {
    eval "use Term::ReadLine::Perl;";
  } else {
    eval "use Term::ReadLine::$which;";
  }
} elsif (defined $which) {	# Defined but false
  # Do nothing fancy
} else {
  eval "use Term::ReadLine::Gnu; 1" or eval "use Term::ReadLine::Perl; 1";
}

#require FileHandle;

# To make possible switch off RL in debugger: (Not needed, work done
# in debugger).

if (defined &Term::ReadLine::Gnu::readline) {
  @ISA = qw(Term::ReadLine::Gnu Term::ReadLine::Stub);
} elsif (defined &Term::ReadLine::Perl::readline) {
  @ISA = qw(Term::ReadLine::Perl Term::ReadLine::Stub);
} else {
  @ISA = qw(Term::ReadLine::Stub);
}

package Term::ReadLine::Tk;

$count_handle = $count_DoOne = $count_loop = 0;

sub handle {$giveup = 1; $count_handle++}

sub Tk_loop {
  # Tk->tkwait('variable',\$giveup);	# needs Widget
  $count_DoOne++, Tk::DoOneEvent(0) until $giveup;
  $count_loop++;
  $giveup = 0;
}

sub register_Tk {
  my $self = shift;
  $Term::ReadLine::registered++ 
    or Tk->fileevent($self->IN,'readable',\&handle);
}

sub tkRunning {
  $Term::ReadLine::toloop = $_[1] if @_ > 1;
  $Term::ReadLine::toloop;
}

sub get_c {
  my $self = shift;
  $self->Tk_loop if $Term::ReadLine::toloop && defined &Tk::DoOneEvent;
  return getc $self->IN;
}

sub get_line {
  my $self = shift;
  $self->Tk_loop if $Term::ReadLine::toloop && defined &Tk::DoOneEvent;
  my $in = $self->IN;
  return scalar <$in>;
}

1;

