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.\" ========================================================================
.\"
.IX Title "Template::Plugin::Filter 3pm"
.TH Template::Plugin::Filter 3pm "2012-01-24" "perl v5.14.2" "User Contributed Perl Documentation"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.nh
.SH "NAME"
Template::Plugin::Filter \- Base class for plugin filters
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 1
\&    package MyOrg::Template::Plugin::MyFilter;
\&    
\&    use Template::Plugin::Filter;
\&    use base qw( Template::Plugin::Filter );
\&    
\&    sub filter {
\&        my ($self, $text) = @_;
\&        
\&        # ...mungify $text...
\&        
\&        return $text;
\&    }
\&
\&    # now load it...
\&    [% USE MyFilter %]
\&    
\&    # ...and use the returned object as a filter
\&    [% FILTER $MyFilter %]
\&      ...
\&    [% END %]
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This module implements a base class for plugin filters.  It hides
the underlying complexity involved in creating and using filters
that get defined and made available by loading a plugin.
.PP
To use the module, simply create your own plugin module that is 
inherited from the \f(CW\*(C`Template::Plugin::Filter\*(C'\fR class.
.PP
.Vb 1
\&    package MyOrg::Template::Plugin::MyFilter;
\&    
\&    use Template::Plugin::Filter;
\&    use base qw( Template::Plugin::Filter );
.Ve
.PP
Then simply define your \f(CW\*(C`filter()\*(C'\fR method.  When called, you get
passed a reference to your plugin object (\f(CW$self\fR) and the text
to be filtered.
.PP
.Vb 2
\&    sub filter {
\&        my ($self, $text) = @_;
\&        
\&        # ...mungify $text...
\&        
\&        return $text;
\&    }
.Ve
.PP
To use your custom plugin, you have to make sure that the Template
Toolkit knows about your plugin namespace.
.PP
.Vb 3
\&    my $tt2 = Template\->new({
\&        PLUGIN_BASE => \*(AqMyOrg::Template::Plugin\*(Aq,
\&    });
.Ve
.PP
Or for individual plugins you can do it like this:
.PP
.Vb 5
\&    my $tt2 = Template\->new({
\&        PLUGINS => {
\&            MyFilter => \*(AqMyOrg::Template::Plugin::MyFilter\*(Aq,
\&        },
\&    });
.Ve
.PP
Then you \f(CW\*(C`USE\*(C'\fR your plugin in the normal way.
.PP
.Vb 1
\&    [% USE MyFilter %]
.Ve
.PP
The object returned is stored in the variable of the same name,
\&'\f(CW\*(C`MyFilter\*(C'\fR'.  When you come to use it as a \f(CW\*(C`FILTER\*(C'\fR, you should add
a dollar prefix.  This indicates that you want to use the filter 
stored in the variable '\f(CW\*(C`MyFilter\*(C'\fR' rather than the filter named 
\&'\f(CW\*(C`MyFilter\*(C'\fR', which is an entirely different thing (see later for 
information on defining filters by name).
.PP
.Vb 3
\&    [% FILTER $MyFilter %]
\&       ...text to be filtered...
\&    [% END %]
.Ve
.PP
You can, of course, assign it to a different variable.
.PP
.Vb 1
\&    [% USE blat = MyFilter %]
\&    
\&    [% FILTER $blat %]
\&       ...text to be filtered...
\&    [% END %]
.Ve
.PP
Any configuration parameters passed to the plugin constructor from the
\&\f(CW\*(C`USE\*(C'\fR directive are stored internally in the object for inspection by
the \f(CW\*(C`filter()\*(C'\fR method (or indeed any other method).  Positional
arguments are stored as a reference to a list in the \f(CW\*(C`_ARGS\*(C'\fR item while
named configuration parameters are stored as a reference to a hash
array in the \f(CW\*(C`_CONFIG\*(C'\fR item.
.PP
For example, loading a plugin as shown here:
.PP
.Vb 1
\&    [% USE blat = MyFilter \*(Aqfoo\*(Aq \*(Aqbar\*(Aq baz = \*(Aqblam\*(Aq %]
.Ve
.PP
would allow the \f(CW\*(C`filter()\*(C'\fR method to do something like this:
.PP
.Vb 2
\&    sub filter {
\&        my ($self, $text) = @_;
\&        
\&        my $args = $self\->{ _ARGS   };  # [ \*(Aqfoo\*(Aq, \*(Aqbar\*(Aq ]
\&        my $conf = $self\->{ _CONFIG };  # { baz => \*(Aqblam\*(Aq }
\&        
\&        # ...munge $text...
\&        
\&        return $text;
\&    }
.Ve
.PP
By default, plugins derived from this module will create static
filters.  A static filter is created once when the plugin gets 
loaded via the \f(CW\*(C`USE\*(C'\fR directive and re-used for all subsequent
\&\f(CW\*(C`FILTER\*(C'\fR operations.  That means that any argument specified with
the \f(CW\*(C`FILTER\*(C'\fR directive are ignored.
.PP
Dynamic filters, on the other hand, are re-created each time 
they are used by a \f(CW\*(C`FILTER\*(C'\fR directive.  This allows them to act
on any parameters passed from the \f(CW\*(C`FILTER\*(C'\fR directive and modify
their behaviour accordingly.
.PP
There are two ways to create a dynamic filter.  The first is to
define a \f(CW$DYNAMIC\fR class variable set to a true value.
.PP
.Vb 3
\&    package MyOrg::Template::Plugin::MyFilter;
\&    use base \*(AqTemplate::Plugin::Filter\*(Aq;
\&    our $DYNAMIC = 1;
.Ve
.PP
The other way is to set the internal \f(CW\*(C`_DYNAMIC\*(C'\fR value within the \f(CW\*(C`init()\*(C'\fR
method which gets called by the \f(CW\*(C`new()\*(C'\fR constructor.
.PP
.Vb 5
\&    sub init {
\&        my $self = shift;
\&        $self\->{ _DYNAMIC } = 1;
\&        return $self;
\&    }
.Ve
.PP
When this is set to a true value, the plugin will automatically
create a dynamic filter.  The outcome is that the \f(CW\*(C`filter()\*(C'\fR method
will now also get passed a reference to an array of postional
arguments and a reference to a hash array of named parameters.
.PP
So, using a plugin filter like this:
.PP
.Vb 1
\&    [% FILTER $blat \*(Aqfoo\*(Aq \*(Aqbar\*(Aq baz = \*(Aqblam\*(Aq %]
.Ve
.PP
would allow the \f(CW\*(C`filter()\*(C'\fR method to work like this:
.PP
.Vb 2
\&    sub filter {
\&        my ($self, $text, $args, $conf) = @_;
\&        
\&        # $args = [ \*(Aqfoo\*(Aq, \*(Aqbar\*(Aq ]
\&        # $conf = { baz => \*(Aqblam\*(Aq }
\&    }
.Ve
.PP
In this case can pass parameters to both the \s-1USE\s0 and \s-1FILTER\s0 directives,
so your \fIfilter()\fR method should probably take that into account.
.PP
.Vb 1
\&    [% USE MyFilter \*(Aqfoo\*(Aq wiz => \*(Aqwaz\*(Aq %]
\&    
\&    [% FILTER $MyFilter \*(Aqbar\*(Aq biz => \*(Aqbaz\*(Aq %]
\&       ...
\&    [% END %]
.Ve
.PP
You can use the \f(CW\*(C`merge_args()\*(C'\fR and \f(CW\*(C`merge_config()\*(C'\fR methods to do a quick
and easy job of merging the local (e.g. \f(CW\*(C`FILTER\*(C'\fR) parameters with the
internal (e.g. \f(CW\*(C`USE\*(C'\fR) values and returning new sets of conglomerated
data.
.PP
.Vb 2
\&    sub filter {
\&        my ($self, $text, $args, $conf) = @_;
\&        
\&        $args = $self\->merge_args($args); 
\&        $conf = $self\->merge_config($conf);
\&        
\&        # $args = [ \*(Aqfoo\*(Aq, \*(Aqbar\*(Aq ]      
\&        # $conf = { wiz => \*(Aqwaz\*(Aq, biz => \*(Aqbaz\*(Aq }        
\&        ...
\&    }
.Ve
.PP
You can also have your plugin install itself as a named filter by
calling the \f(CW\*(C`install_filter()\*(C'\fR method from the \f(CW\*(C`init()\*(C'\fR method.  You 
should provide a name for the filter, something that you might 
like to make a configuration option.
.PP
.Vb 6
\&    sub init {
\&        my $self = shift;
\&        my $name = $self\->{ _CONFIG }\->{ name } || \*(Aqmyfilter\*(Aq;
\&        $self\->install_filter($name);
\&        return $self;
\&    }
.Ve
.PP
This allows the plugin filter to be used as follows:
.PP
.Vb 1
\&    [% USE MyFilter %]
\&    
\&    [% FILTER myfilter %] 
\&       ... 
\&    [% END %]
.Ve
.PP
or
.PP
.Vb 1
\&    [% USE MyFilter name = \*(Aqswipe\*(Aq %]
\&        
\&    [% FILTER swipe %] 
\&       ... 
\&    [% END %]
.Ve
.PP
Alternately, you can allow a filter name to be specified as the 
first positional argument.
.PP
.Vb 6
\&    sub init {
\&        my $self = shift;
\&        my $name = $self\->{ _ARGS }\->[0] || \*(Aqmyfilter\*(Aq;
\&        $self\->install_filter($name);
\&        return $self;
\&    }
\&
\&    [% USE MyFilter \*(Aqswipe\*(Aq %]
\&    
\&    [% FILTER swipe %]
\&       ...
\&    [% END %]
.Ve
.SH "EXAMPLE"
.IX Header "EXAMPLE"
Here's a complete example of a plugin filter module.
.PP
.Vb 3
\&    package My::Template::Plugin::Change;
\&    use Template::Plugin::Filter;
\&    use base qw( Template::Plugin::Filter );
\&    
\&    sub init {
\&        my $self = shift;
\&        
\&        $self\->{ _DYNAMIC } = 1;
\&        
\&        # first arg can specify filter name
\&        $self\->install_filter($self\->{ _ARGS }\->[0] || \*(Aqchange\*(Aq);
\&        
\&        return $self;
\&    }
\&    
\&    sub filter {
\&        my ($self, $text, $args, $config) = @_;
\&        
\&        $config = $self\->merge_config($config);
\&        my $regex = join(\*(Aq|\*(Aq, keys %$config);
\&        
\&        $text =~ s/($regex)/$config\->{ $1 }/ge;
\&        
\&        return $text;
\&    }
\&    
\&    1;
.Ve
.SH "AUTHOR"
.IX Header "AUTHOR"
Andy Wardley <abw@wardley.org> <http://wardley.org/>
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright (C) 1996\-2007 Andy Wardley.  All Rights Reserved.
.PP
This module is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Template::Plugin, Template::Filters, Template::Manual::Filters