=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;
  my $term = new Term::ReadLine 'Simple Perl calc';
  my $prompt = "Enter your arithmetic expression: ";
  my $OUT = $term->OUT || \*STDOUT;
  while ( defined ($_ = $term->readline($prompt)) ) {
    my $res = eval($_), "\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>.

=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.

The stub package included with the perl distribution allows some
additional methods: 

=over 12

=item C<tkRunning>

makes Tk event loop run when waiting for user input (i.e., during
C<readline> method).

=item C<ornaments>

makes the command line stand out by using termcap data.  The argument
to C<ornaments> should be 0, 1, or a string of a form
C<"aa,bb,cc,dd">.  Four components of this string should be names of
I<terminal capacities>, first two will be issued to make the prompt
standout, last two to make the input line standout.

=item C<newTTY>

takes two arguments which are input filehandle and output filehandle.
Switches to use these filehandles.

=back

One can check whether the currently loaded ReadLine package supports
these methods by checking for corresponding C<Features>.

=head1 EXPORTS

None

=head1 ENVIRONMENT

The environment 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>.  

As a special case, if the value of this variable is space-separated,
the tail might be used to disable the ornaments by setting the tail to
be C<o=0> or C<ornaments=0>.  The head should be as described above, say

If the variable is not set, or if the head of space-separated list is
empty, the best available package is loaded.

  export "PERL_RL=Perl o=0"	# Use Perl ReadLine without ornaments
  export "PERL_RL= o=0"		# Use best available ReadLine without ornaments

(Note that processing of C<PERL_RL> for ornaments is in the discretion of the 
particular used C<Term::ReadLine::*> package).

=head1 CAVEATS

It seems that using Term::ReadLine from Emacs minibuffer doesn't work
quite right and one will get an error message like

    Cannot open /dev/tty for read at ...

One possible workaround for this is to explicitly open /dev/tty like this

    open (FH, "/dev/tty" )
      or eval 'sub Term::ReadLine::findConsole { ("&STDIN", "&STDERR") }';
    die $@ if $@;
    close (FH);

or you can try using the 4-argument form of Term::ReadLine->new().

=cut

use strict;

package Term::ReadLine::Stub;
our @ISA = qw'Term::ReadLine::Tk Term::ReadLine::TermCap';

$DB::emacs = $DB::emacs;	# To peacify -w
our @rl_term_set;
*rl_term_set = \@Term::ReadLine::TermCap::rl_term_set;

sub ReadLine {'Term::ReadLine::Stub'}
sub readline {
  my $self = shift;
  my ($in,$out,$str) = @$self;
  my $prompt = shift;
  print $out $rl_term_set[0], $prompt, $rl_term_set[1], $rl_term_set[2]; 
  $self->register_Tk 
     if not $Term::ReadLine::registered and $Term::ReadLine::toloop
	and defined &Tk::DoOneEvent;
  #$str = scalar <$in>;
  $str = $self->get_line;
  $str =~ s/^\s*\Q$prompt\E// if ($^O eq 'MacOS');
  print $out $rl_term_set[3]; 
  # bug in 5.000: chomping empty string creats length -1:
  chomp $str if defined $str;
  $str;
}
sub addhistory {}

sub findConsole {
    my $console;

    if ($^O eq 'MacOS') {
        $console = "Dev:Console";
    } elsif (-e "/dev/tty") {
	$console = "/dev/tty";
    } elsif (-e "con" or $^O eq 'MSWin32') {
	$console = "con";
    } else {
	$console = "sys\$command";
    }

    if (($^O eq 'amigaos') || ($^O eq 'beos') || ($^O eq 'epoc')) {
	$console = undef;
    }
    elsif ($^O eq 'os2') {
      if ($DB::emacs) {
	$console = undef;
      } else {
	$console = "/dev/con";
      }
    }

    my $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, $ret);
  if (@_==2) {
    my($console, $consoleOUT) = $_[0]->findConsole;

    open(FIN, "<$console"); 
    open(FOUT,">$consoleOUT");
    #OUT->autoflush(1);		# Conflicts with debugger?
    my $sel = select(FOUT);
    $| = 1;				# for DB::OUT
    select($sel);
    $ret = bless [\*FIN, \*FOUT];
  } else {			# Filehandles supplied
    $FIN = $_[2]; $FOUT = $_[3];
    #OUT->autoflush(1);		# Conflicts with debugger?
    my $sel = select($FOUT);
    $| = 1;				# for DB::OUT
    select($sel);
    $ret = bless [$FIN, $FOUT];
  }
  if ($ret->Features->{ornaments} 
      and not ($ENV{PERL_RL} and $ENV{PERL_RL} =~ /\bo\w*=0/)) {
    local $Term::ReadLine::termcap_nowarn = 1;
    $ret->ornaments(1);
  }
  return $ret;
}

sub newTTY {
  my ($self, $in, $out) = @_;
  $self->[0] = $in;
  $self->[1] = $out;
  my $sel = select($out);
  $| = 1;				# for DB::OUT
  select($sel);
}

sub IN { shift->[0] }
sub OUT { shift->[1] }
sub MinLine { undef }
sub Attribs { {} }

my %features = (tkRunning => 1, ornaments => 1, 'newTTY' => 1);
sub Features { \%features }

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

our $VERSION = '1.00';

my ($which) = exists $ENV{PERL_RL} ? split /\s+/, $ENV{PERL_RL} : undef;
if ($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 and $which ne '') {	# 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).
our @ISA;
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);
} elsif (defined $which && defined &{"Term::ReadLine::$which\::readline"}) {
  @ISA = "Term::ReadLine::$which";
} else {
  @ISA = qw(Term::ReadLine::Stub);
}

package Term::ReadLine::TermCap;

# Prompt-start, prompt-end, command-line-start, command-line-end
#     -- zero-width beautifies to emit around prompt and the command line.
our @rl_term_set = ("","","","");
# string encoded:
our $rl_term_set = ',,,';

our $terminal;
sub LoadTermCap {
  return if defined $terminal;
  
  require Term::Cap;
  $terminal = Tgetent Term::Cap ({OSPEED => 9600}); # Avoid warning.
}

sub ornaments {
  shift;
  return $rl_term_set unless @_;
  $rl_term_set = shift;
  $rl_term_set ||= ',,,';
  $rl_term_set = 'us,ue,md,me' if $rl_term_set eq '1';
  my @ts = split /,/, $rl_term_set, 4;
  eval { LoadTermCap };
  unless (defined $terminal) {
    warn("Cannot find termcap: $@\n") unless $Term::ReadLine::termcap_nowarn;
    $rl_term_set = ',,,';
    return;
  }
  @rl_term_set = map {$_ ? $terminal->Tputs($_,1) || '' : ''} @ts;
  return $rl_term_set;
}


package Term::ReadLine::Tk;

our($count_handle, $count_DoOne, $count_loop);
$count_handle = $count_DoOne = $count_loop = 0;

our($giveup);
sub handle {$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 = $self->IN;
  local ($/) = "\n";
  return scalar <$in>;
}

1;