# -*- mode: perl -*-

package Text::ScriptTemplate;

=head1 NAME

 Text::ScriptTemplate - Standalone ASP/JSP/PHP-style template processor

=head1 SYNOPSIS

 use Text::ScriptTemplate;

 $text = <<'EOF';            # PHP/JSP/ASP-style template
 <% for (1..3) { %>          # - any Perl expression is supported
 Message is: <%= $TEXT %>.   # - also supports variable expansion
 <% } %>
 EOF

 $tmpl = new Text::ScriptTemplate;    # create processor object
 $tmpl->setq(TEXT => "hello, world"); # export data to template

 # load, fill, and print expanded result in single action
 print $tmpl->pack($text)->fill;

=head1 DESCRIPTION

This is a successor of Text::SimpleTemplate, a module for template-
based text generation.

Template-based text generation is a way to separate program code and
data, so non-programmer can control final result (like HTML) as desired
without tweaking the program code itself. By doing so, jobs like website
maintenance is much easier because you can leave program code unchanged
even if page redesign was needed.

The idea of this module is simple. Whenever a block of text surrounded
by '<%' and '%>' (or any pair of delimiters you specify) is found, it
will be taken as Perl expression, and will be handled specially by
template processing engine. With this module, Perl script and text
can be intermixed closely.

Major goal of this library is to provide support of powerful PHP-style
template with smaller resource. This is useful when PHP, Java/JSP,
or Apache::ASP is overkill, but their template style is still desired.

=head1 INSTALLATION / REQUIREMENTS

No other module is needed to use this module.
All you need is perl itself.

For installation, standard procedure of

    perl Makefile.PL
    make
    make test
    make install

should work just fine.

=head1 TEMPLATE SYNTAX AND USAGE

Any block surrounded by '<%=' and '%>' will be replaced with
its evaluated result. So,

  <%= $message %>

will expand to "hello" if $message variable contains "hello"
at the time of evaluation (when "fill" method is called).

For block surrounded by '<%' and '%>, it will be taken as a
part of control structure. After all parts are merged into
one big script, it get evaluated and its result will become
expanded result. This means,

  <% for my $i (1..3) { %>
  i = <%= %i %>
  <% } %>

will generate

  i = 1
  i = 2
  i = 3

as a resulting output.

Now, let's continue with more practical example.
Suppose you have a following template named "sample.tmpl":

    === Module Information ===
    <% if ($HAS->{Text::ScriptTemplate}) { %>
    Name: <%= $INFO->{Name}; %>
    Description: <%= $INFO->{Description}; %>
    Author: <%= $INFO->{Author}; %> <<%= $INFO->{Email}; %>>
    <% } else { %>
    Text::ScriptTemplate is not installed.
    <% } %>

With the following script...

    #!/usr/bin/perl

    use Safe;
    use Text::ScriptTemplate;

    $tmpl = new Text::ScriptTemplate;
    $tmpl->setq(INFO => {
        Name        => "Text::ScriptTemplate",
        Description => "Lightweight processor for full-featured template",
        Author      => "Taisuke Yamada",
        Email       => "tyamadajp\@spam.rakugaki.org",
    });
    $tmpl->setq(HAS => { Text::ScriptTemplate => 1 }); # installed
    $tmpl->load("sample.tmpl");

    print $tmpl->fill(PACKAGE => new Safe);

...you will get following result:

    === Module Information ===

    Name: Text::ScriptTemplate
    Description: Lightweight processor for full-featured template
    Author: Taisuke Yamada <tyamadajp@spam.rakugaki.org>

If you change

    $tmpl->setq(HAS => { Text::ScriptTemplate => 1 }); # installed

to

    $tmpl->setq(HAS => { Text::ScriptTemplate => 0 }); # not installed

, then you will get

    === Module Information ===

    Text::ScriptTemplate is not installed.

You can embed any control structure as long as intermixed text
block is surround by set of braces. This means

    hello world<% if ($firsttime); %>

must be written as

    <% do { %>hello world<% } if ($firsttime); %>

to ensure surrounding block. If you want to know more on this
internal, please read TEMPLATE INTERNAL section for the detail.

Also, as you might have noticed, any scalar data can be exported
to template namespace, even hash reference or code reference.

Finally, although I had used "Safe" module in example above,
this is not a requirement. Either of

    print $tmpl->fill(PACKAGE => new Safe);
    print $tmpl->fill(PACKAGE => new MyPackage);
    print $tmpl->fill(PACKAGE => 'MyOtherPackage');
    print $tmpl->fill; # uses calling context as package namespace

will work. However, if you want to limit priviledge of program
logic embedded in template, using Safe module as sandbox is
recommended.

=head1 RESERVED NAMES

Currently, only reserved name pattern is the one starting
with "_" (underscore).

Since template can be evaluated in separate namespace using
PACKAGE option (see "fill" method), this module does not have
much restriction on variable or function name you define in
theory. However, if you choose existing module namespace
as evaluating namespace, there could be some other predefined
names that may interfere with the symbols you have exported.

Also, if you don't specify PACKAGE option, namespace of
calling context is used as default namespace. This means
all defined functions and variables in calling script
are visible from template, even if they weren't exported
by "setq" method.

=head1 METHODS

Following methods are currently available.

=over 4

=cut

use Carp;
use FileHandle;

use strict;
use vars qw($DEBUG $VERSION);

$DEBUG   = 0;
$VERSION = '0.08';

=item $tmpl = new Text::ScriptTemplate;

Constructor. Returns newly created object.

If this method was called through existing object, cloned object
will be returned. This cloned instance inherits all properties
except for internal buffer which holds template data. Cloning is
useful for chained template processing.

=cut
sub new {
    my $name = shift;
    my $self = bless { hash => {} }, ref($name) || $name;

    return $self unless ref($name);

    ## inherit parent configuration
    while (my($k, $v) = each %{$name}) {
        $self->{$k} = $v unless $k eq 'buff';
    }
    $self;
}

=item $tmpl->setq($name => $data, $name => $data, ...);

Exports scalar data ($data) to template namespace,
with $name as a scalar variable name to be used in template.
You can repeat the pair to export multiple sets in one operation.

Returns object reference to itself.

=cut
sub setq {
    my $self = shift;
    my %pair = @_;

    while (my($key, $val) = each %pair) {
        $self->{hash}->{$key} = $val;
    }
    $self;
}

=item $tmpl->load($file, %opts);

Loads template file ($file) for later evaluation.
File can be specified in either form of pathname or fileglob.

This method accepts DELIM option, used to specify delimiter
for parsing template. It is speficied by passing reference
to array containing delimiter pair, just like below:

    $tmpl->load($file, DELIM => [qw(<? ?>)]);

Returns object reference to itself.

=cut
sub load {
    my $self = shift;
    my $file = shift;

    $file = new FileHandle($file) || croak($!) unless ref($file);
    $self->pack(join("", <$file>), @_);
}

=item $tmpl->pack($data, %opts);

Loads in-memory data ($data) for later evaluation.
Except for this difference, works just like $tmpl->load.

=cut
sub pack {
    my $self = shift;
    my $buff = shift;
    my %opts = @_;
    my $temp;

    $self->{DELIM}   = [map { quotemeta } @{$opts{DELIM}}] if $opts{DELIM};
    $self->{DELIM} ||= [qw(<% %>)];

    my $L = $self->{DELIM}->[0];
    my $R = $self->{DELIM}->[1];

    undef $self->{buff};

    while ($buff) {
        ## match: <%= ... %>
        if ($buff =~ s|^$L=(.*?)$R||s) {
            $self->{buff} .= qq{\$_handle->(do { $1 \n});} if $1;
        }
        ## match: <% ... %>
        elsif ($buff =~ s|^$L(.*?)$R||s) {
            $self->{buff} .= qq{$1\n} if $1;
        }
        ## match: ... <% or ...
        elsif ($buff =~ s|^(.*?)(?=$L)||s) {
            if ($temp = $1) {
                $temp =~ s|[\{\}]|\\$&|g;
                $self->{buff} .= qq{\$_handle->(q{$temp});};
            }
        }
        ## match: ... (EOF) or <% ... (EOF)
        else {
            last;
        }

        #print STDERR "Remaining:\n<buff>$buff</buff>\n" if $DEBUG;
        #print STDERR "Converted:\n<buff>$self->{buff}</buff>\n" if $DEBUG;
    }

    if ($temp = $buff) {
        $temp =~ s|[\{\}\\]|\\$&|g;
        $self->{buff} .= qq{\$_handle->(q{$temp});};
    }

    print STDERR "Converted:\n<buff>$self->{buff}</buff>\n" if $DEBUG;

    $self;
}

=item $text = $tmpl->fill(%opts);

Returns evaluated result of template, which was
preloaded by either $tmpl->pack or $tmpl->load method.

This method accepts two options: PACKAGE and OHANDLE.

PACKAGE option specifies the namespace where template
evaluation takes place. You can either pass the name of
the package, or the package object itself. So either of

    $tmpl->fill(PACKAGE => new Safe);
    $tmpl->fill(PACKAGE => new Some::Module);
    $tmpl->fill(PACKAGE => 'Some::Package');
    $tmpl->fill; # uses calling context as evaluating namespace

works. In case Safe module (or its subclass) was passed,
its "reval" method will be used instead of built-in eval.

OHANDLE option is for output selection. By default, this
method returns the result of evaluation, but with OHANDLE
option set, you can instead make it print to given handle.
Either style of

    $tmpl->fill(OHANDLE => \*STDOUT);
    $tmpl->fill(OHANDLE => new FileHandle(...));

is supported.

=cut
sub fill {
    my $self = shift;
    my %opts = @_;
    my $from = $opts{PACKAGE} || caller;
    my $name;
    my $eval;

    no strict;

    ## dynamically create evaluation engine
    if (UNIVERSAL::isa($from, 'Safe')) {
        $name = $from->root;
        $eval = sub { my $v = $from->reval($_[0]); $@ ? $@ : $v; }
    }
    else {
        $name = ref($from) || $from;
        $eval = eval qq{
            package $name; sub { my \$v = eval(\$_[0]); \$@ ? \$@ : \$v; };
        };
    }

    ## export stored data to target namespace
    while (my($key, $val) = each %{$self->{hash}}) {
        if ($DEBUG) {
            print STDERR "Exporting to ${name}::${key}: $val\n";
        }
        $ {"${name}::${key}"} = $val;
    }

    ## dynamically create handler for buffered or unbuffered mode
    if ($ {"${name}::_OHANDLE"} = $opts{OHANDLE}) {
        $eval->(q{$_handle = sub { print $_OHANDLE $_[0]; };});
    }
    else {
        $eval->(q{$_handle = sub { $_OBUFFER .= $_[0]; };});
    }

    ##
    $eval->(qq{ undef \$_OBUFFER; $self->{buff}; \$_OBUFFER; });
}

=item $text = $tmpl->include($file, \%vars, @args);

This is a shortcut of doing

  $text = $tmpl->new->load($file)->setq(%vars)->fill(@args);

Why a shortcut? Because this will allow you to write

  <%= $tmpl->include("subtemplate.tmpl") %>

which is much (visually) cleaner way to include other
template fragment in current template.

Note: you need to export instance as $tmpl beforehand
in above example.

=cut
sub include {
    my $self = shift;
    my $file = shift;
    my $vars = shift || {};

    $self->new->load($file)->setq(%{$vars})->fill(@_);
}

=back

=head1 TEMPLATE INTERNAL

Internally, template processor converts template into one big
perl script, and then simply executes it. Conversion rule is
fairly simple - If you have following template,

    <% if ($bool) { %>
    hello, <%= $name; %>
    <% } %>

it will be converted into

    if ($bool) {
        $_handle->(q{
    hello, });
        $_handle->(do{ $name; });
        $_handle->(q{
    });
    }

Note line breaks are preserved. After all conversion is done, it
will be executed. And depending on existance of OHANDLE option,
$_handle (this is a code reference to predefined function) will
either print or buffer its argument.

=head1 NOTES / BUGS

Nested template delimiter will cause this module to fail.
In another word, don't do something like

  <%= "<%=" %>

as it'll fail template parsing engine.

=head1 SEE ALSO

L<Safe> and L<Text::SimpleTemplate>

=head1 CONTACT ADDRESS

Please send any bug reports/comments to <tyamadajp@spam.rakugaki.org>.

NOTE: You need to replace "spam" to "list" in above email address
      before sending.

=head1 AUTHORS / CONTRIBUTORS

 - Taisuke Yamada <tyamadajp@spam.rakugaki.org>

=head1 COPYRIGHT

Copyright 2001-2004. All rights reserved.

This library is free software; you can redistribute it
and/or modify it under the same terms as Perl itself.

=cut

1;