Extensions in SeedDMS
=====================

Since verson 5.0.0 SeedDMS can be extended by extensions. Extensions
can hook up functions into certain operations, e.g.
uploading, removing or displaying a document. They can also be
used to modify some of the internal variables like the list of
translations and they can even replace classes in the core of
seeddms and hook up functions into certain operations in the core.

All extensions are located in the folder 'ext'. Each extension
has its own folder named by the name of the extension. The central
configuration of an extension is stored in conf.php.
The configuration sets the file and classname which is loaded
during initialization of the extension. The class has to have
a method init() which is called with any page request. The
configuration itself is cached and must be updated within
the extension manager if it was changed.

The integration into SeedDMS is done by hooks, class and file
overloading. SeedDMS manages
a globally available array of hooks ($GLOBALS['SEEDDMS_HOOKS']).
This array has the elements 'view' and 'controller'. All entries
in those array elements contain instances of self defined classes
containing the hook methods. For setting up the hooks in the view
'viewFolder' the following code is needed.

$GLOBALS['SEEDDMS_HOOKS']['view']['viewFolder'][] = new SeedDMS_ExtExample_ViewFolder;

class SeedDMS_ExtExample_ViewFolder {
  ...
};

The same approach is implemented for hooks called from the controller
logic (the op/op.*.php files).

$GLOBALS['SEEDDMS_HOOKS']['controller']['removeFolder'][] = new SeedDMS_ExtExample_RemoveFolder;

class SeedDMS_ExtExample_RemoveFolder {
  ...
};

Based on these two variants of adding hooks to the seeddms application code,
the seeddms core can be extended by implementing the controller hook 'initDMS'
which is called right after the class SeedDMS_Core_DMS has been initiated.

Beside hooks and callbacks another way of modifying seeddms is given
by overloading the files in the directory 'views' and 'controllers'. Both
directories contain class files with a single class for either running
controller or view code. If an extension provides those file in its
own extension dir, they will be used instead of the files shipped with
seeddms.

