===== Create A Plugin =====
This wiki entry documents the creation of a plugin, ''geo_kit'', that is still under development.  While it is believed to be complete, this document is subject to revision.

Writing a plugin is much like creating a project with the exception that you must provide for installation and uninstallation of the plugin.  There are some other differences that will be documented.

To write a plugin, create a project to hold it.  I'm calling my project ''app_home''.  I am creating a port of the Rails Geo-Kit to Akelos.  I don't know just how the Rails plugin works, but I assume that if the tests written for it are successful, then the plugin is working.  I am going to translate the tests from Ruby to PHP.  As I make each test, I'll make sure that it runs successfully.  This procedure makes this a TDD (Test Driven Development) project.

The first thing we need to do is to create the main plugin directory, which will be referred to as ''plugin_home''.  In our case, this will be ''geo_kit''.  From the ''app_home'' directory, we write:<code>cd app/vendor/plugins
mkdir geo_kit</code>

==== Documentation Files ====
The first files we need to create are plugin documentation.  They will be placed in the plugin home directory.  Details about them are [[plugin-documentation-files|here]].

==== Plugin Specific Files ====
These are files that are not required by an ordinary application that are needed by a plugin.  Details about them are [[plugin-specific-files|here]].




==== Plugin Application Files ====
=== config.php ===
Applications all contain a config.php in ''app_home/config''.  Some plugins, like geo_kit, need to add additional lines to it.  The file that modifies it should be in ''plugin_home/config''.  This plugin will name it config.php, too.  ''plugin_home/installer/geo_kit_installer.php'' needs to be able to find it.  We'll illustrate this with the first two lines of the geo_kit script:<code php>
<?php
defined('GEOKIT_DEFAULT_UNITS') ? null : define('GEOKIT_DEFAULT_UNITS', 'miles');
defined('GEOKIT_DEFAULT_FORMULA') ? null : define('GEOKIT_DEFAULT_FORMULA', 'sphere');
?>
</code>
=== Plugin Code Scripts ===
The php scripts that do the work of the plugin are written in ''plugin_home/lib/geo_kit'', where ''geo_kit'' is the name of your plugin.



==== Plugin Test Scripts ====
These scripts are for testing your plugin.  Details about them are [[plugin-test-files|here]].