Extending patTemplate:
----------------------
$Id: extending-pattemplate.txt 97 2004-04-06 19:21:32Z schst $

1. Variable Modifiers
---------------------
Variable modifiers will be applied to the value of a variable when
parsing the template. There two types of modfifiers:

1.a) You may use any PHP function as a variable modifier.
The modifier must accept only a string as a parameter and also return
a string. Perfect examples for variable modifiers are nl2br() or
htmlentities().

2.b) You may create custom modifiers. To do this, create a new file in

  PATTEMPLATE_ROOT/patTemplate/Modifier
  
or any of its sub-folders. In this file, you have to create a new class
that's called

  patTemplate_Modifier_FILENAME
  
where FILENAME is the name of your file (and thus also of your modifier).
If your modifier is located in a subfolder, you have to include the folder
name in the class name, e.g. patTemplate_Modifier_Html_Image.

Your class should inherit from patTemplate_Modifier and provide the following
method:

  string modify( string value, array params )
  
In the method you may modify the value and return it to the templating enginge.

2. Template Readers
-------------------
patTemplate 3.0 allows you to read templates from any source,
may it be the filesystem, databases or shared memory.
To read from a datasource that's not yet supported, you'll have to
implement a new template reader. To do this, create a new PHP file in:

  PATTEMPLATE_ROOT/patTemplate/Reader
  
Let's say you want to create a reader that reads data from shared memory.
Then you'd create a new file in the mentioned folder called

  SHM.php
  
In this file you place a create a new class that extends patTemplate_Reader
and that is called patTemplate_Reader_SHM. There you'll have to implement only
one method that reads templates from the source:

<?PHP
class patTemplate_Reader_SHM extends patTemplate_Reader
{
	function readTemplates( $input, $options = array() )
	{
		/**
		 * somehow access shared memory
		 */
		$content	= shm_get( $shm, $input );
		$templates	= $this->parseString( $content );
		
		return	$templates;
	}
}

Options is currently not used, so this may change until patTemplate 3.0
stable is released.

If your reader should support the parse="off" attribute you'll have to
implement a second method loadTemplate(), that accepts exactly the same
parameters as readTemplates() and will just load the template content from
a datasource and return it as a string.

In order to use template caches (see 7), you'll have to implement
to other methods:

string  getKey( string input )
integer getModificationTime( string input )

getKey() should return a unique identification key for the template that
is referenced by input, a common way to achive this is to use md5().
getModificationTime() should return a timestamp of the time the file was
modified on, for a lot of readers this is not possible. In that case, you do not
need to implement the method, as it's already implemented in the base class.

You can als use the String reader if you need to parse templates that are
read from strange datasources, but you will loose the template caching feature.

Of course it's also possible to use the file reader and PHP's stream_wrappers.

3. Custom Template Tags (functions)
-----------------------------------
Custom Tags allow you to extend patTemplate. You may define classes that
are instantiated and evaluated,, when patTemplate finds a tag that is not
supported by the engine. Custom functions are evaluated by the template reader.
To create your own template function, create a new class that inherits from
patTemplate_Function and place it into

  PATTEMPLATE_ROOT/patTemplate/Function
  
In this class you have to implement on function:

  string call( array params, string content )
  
This method will be called on the closing tag with the same name as
your file (and class). patTemplate_Reader will pass the attributes
and the content of the tag to your method. You will then have to
compute the data you want to insert to the template and return the
string. This will be inserted instead of your custom tag.

Custom Template Functions allow to do things like:
 - Modify parts of the template while reading it
 - Insert the current date/time
 - Get request variables and insert them into the template
 - ...

Custom template functions (or tags) can also be called Horst. If you want to
know, why they are called Horst, you could contact gERD or Argh.

4. Output Filters
-----------------
Output filters allow you to modfiy the data that is sent to
the browser, after _all_ templates have been parsed. Output filters
are applied, when patTemplate::displayParsedTemplate() is called.
Examples for output filtering are the removal of all whitespace prior
to sending data to the browser or even compressing the data using gzip,
if the client supports gzip encoding. In fact these two examples already
accompany the patTemplate distributions.

Of course there are infinite possibilities of what an output filter
could to, and that's why I implemented it as a plugin to patTemplate.
To build your own output filter you simply have to create a new file in

  PATTEMPLATE_ROOT/patTemplate/OutputFilter
  
Let's say you want to create a filter that obfuscates email addresses in the
output. Then you'd create a new file in the mentioned folder called

  EmailObfuscator.php
  
In this file you place a create a new class that extends patTemplate_OutputFilter
and that is called patTemplate_OutputFilter_EmailObfuscator. There you'll have to
implement only one method that filters the output and this method has to be called
apply() and should only accept a string a sole parameter. So your file should look
like this:

<?PHP
class patTemplate_OutputFilter_EmailObfuscator extends patTemplate_OutputFilter
{
	function apply( $data )
	{
		/**
		 * somehow obfuscate emails here
		 */
		return $data;
	}
}
?> 

Now if you want to use this output filter, all you have to do is:

$tmpl->applyOutputFilter( 'EmailObfuscator' );
$tmpl->displayParsedTemplate();

And patTemplate will do the rest.

5. Input Filters
----------------
Input filters are used to modify the templates _before_ the patTemplate
tags are analyzed. This allows you to strip comments and improve performance
while parsing the templates.
They are implemented in exactly the same way as an output filter, they just
have to be place in the InputFilter directory and should extend the
patTemplate_InputFilter class.
You could use an input filter to:
 - strip HTML comments
 - unzip the templates
 - ...

6. Dumpers
----------
Dumpers are used for debugging purposes. To write your own dumper, create a new
class that is inherited from patTemplate_Dump and place it into the
patTemplate/Dump folder. The file has to be called exactly like the last
portion of the class name.
That means if you create a text dumper, call the file
/patTemplate/Dump/Text.php and the class patTemplate_Dump_Text.

You have to create four methods in this class:
void displayHeader()
void displayFooter()
void dumpGlobals( array globals )
void dumpTemplates( array templates, array vars )

In this methods you should only output data.
'globals' is an associative array containing all global variables,
'templates' is an associative array containing all templates. Each entry
is an array that contains all template properties. The 'vars' parameter
is an array that contains the variables of the templates.

7. Template Caches
------------------
A template cache is invoked when patTemplate::readTemplatesFromInput() is
called. It stores the serialized template so it does not have to be parsed
on every request. A template cache needs to implement to methods:

array load( int key[, array modificationTime] )
boolean write( int key, array templates )

When calling load, the template cache should read and unserialize the templates
from the storage container and return the array. The modification time will
only be passed, if the reader supports this feature (e.g. there's no modification
time when reading from a string).

The write method has to work just the other way round. It should serialize the
templates and write them to the storage container.

8. Output Caches
----------------
Output caches are not implemented, yet.
They will be part of patTemplate 3.1.0