Custom Joomla! form field to generate extensions (components, modules, plugins, libraries) dropdown list

extensions.php

<?php
/**
 * Custom Joomla! form field to generate extensions dropdown list
 *
 * @author Rene Korss <rene.korss@gmail.com>
 * @copyright 2016 All rights reserved.
 * @license MIT
 *
 * Usage examples:
 *
 *	<field
 *		name="componentpicker"
 *		type="extensions"
 *		label="Choose component"
 *		>
 *		<option value="">Please choose component</option>
 *	</field>
 *
 *	<field
 *		name="modulepicker"
 *		type="extensions"
 *		extensiontype="module"
 *		clientid="1"
 *		label="Choose module"
 *		>
 *		<option value="">Please choose module</option>
 *	</field>
 *
 *	<field
 *		name="pluginpicker"
 *		type="extensions"
 *		extensiontype="plugin"
 *		clientid="1"
 *		label="Choose plugin"
 *		>
 *		<option value="">Please choose plugin</option>
 *	</field>
 *
 */

defined('JPATH_PLATFORM') or die;

JFormHelper::loadFieldClass('list');

/**
 * Form Field class for the Joomla Framework.
 */
class JFormFieldExtensions extends JFormFieldList
{
	/**
	 * The field type.
	 *
	 * @var    string
	 */
	protected $type = 'Extensions';

	/**
	 * The extension type to seaarch for.
	 *
	 * @var    string
	 */
	protected $extensionType = 'component';

	/**
	 * The path to folder for plugins.
	 *
	 * @var    string
	 */
	protected $folder;

	/**
	 * The client if to search extensions.
	 *
	 * 1 - backend, 0 - frontend
	 *
	 * @var    int
	 */
	protected $clientId;

	/**
	 * Method to get certain otherwise inaccessible properties from the form field object.
	 *
	 * @param   string  $name  The property name for which to the the value.
	 *
	 * @return  mixed  The property value or null.
	 */
	public function __get($name)
	{
		switch ($name)
		{
			case 'folder':
			case 'clientId':
				return $this->{$name};
			case 'extensiontype':
				return $this->extensionType;
		}

		return parent::__get($name);
	}

	/**
	 * Method to set certain otherwise inaccessible properties of the form field object.
	 *
	 * @param   string  $name   The property name for which to the the value.
	 * @param   mixed   $value  The value of the property.
	 *
	 * @return  void
	 */
	public function __set($name, $value)
	{
		switch ($name)
		{
			case 'folder':
				$this->folder = (string) $value;
				break;

			case 'extensiontype':
				$this->extensionType = (string) $value;
				break;

			case 'clientId':
				$this->clientId = (int) $value;
				break;

			default:
				parent::__set($name, $value);
		}
	}

	/**
	 * Method to attach a JForm object to the field.
	 *
	 * @param   SimpleXMLElement  $element  The SimpleXMLElement object representing the `<field>` tag for the form field object.
	 * @param   mixed             $value    The form field value to validate.
	 * @param   string            $group    The field name group control value. This acts as as an array container for the field.
	 *                                      For example if the field has name="foo" and the group value is set to "bar" then the
	 *                                      full field name would end up being "bar[foo]".
	 *
	 * @return  boolean  True on success.
	 *
	 * @see     JFormField::setup()
	 */
	public function setup(SimpleXMLElement $element, $value, $group = null)
	{
		$return = parent::setup($element, $value, $group);

		if ($return)
		{
			$this->folder        = (string) $this->element['folder'];
			$this->extensionType = $this->element['extensiontype'] ? (string) $this->element['extensiontype'] : 'component';
			$this->clientId      = $this->element['clientid'] ? (int) $this->element['clientid'] : 1;

			// Force client id to be 0 for plugins and libraries
			if ($this->extensiontype === 'plugin' || $this->extensiontype == 'library')
			{
				$this->clientId = 0;
			}
		}

		return $return;
	}

	/**
	 * Method to get a list of options for a list input.
	 *
	 * @return	array  An array of JHtml options.
	 */
	protected function getOptions()
	{
		$folder   = $this->folder;
		$type     = $this->extensionType;
		$clientId = $this->clientId;
		$options = array();

		if (!empty($type))
		{
			// Get list of plugins
			$db    = JFactory::getDbo();
			$query = $db->getQuery(true)
				->select('element AS value, name AS text, folder')
				->from('#__extensions')
				->where('enabled = 1')
				->order('ordering, name');

			if (strlen($type) > 0)
			{
				$query->where('type = ' . $db->quote($type));
			}

			if ($type === 'plugin' && !empty($folder))
			{
				$query->where('folder = ' . $db->quote($folder));
			}

			if (in_array($clientId, array(0, 1)))
			{
				$query->where('client_id = ' . $db->quote($clientId));
			}

			$db->setQuery($query);
			$options = $db->loadObjectList();

			$lang = JFactory::getLanguage();

			foreach ($options as $i => $item)
			{
				if ($type === 'plugin')
				{
					$extension = 'plg_' . $item->folder . '_' . $item->value;
				}
				else
				{
					$extension = $item->text;
				}

				if ($type === 'plugin')
				{
					$source = JPATH_PLUGINS . '/' . $item->folder . '/' . $item->value;
					$lang->load($extension . '.sys', JPATH_ADMINISTRATOR, null, false, true) || $lang->load($extension, $source, null, false, true);
				}
				else
				{
					$lang->load($extension . '.sys', $clientId === 1 ? JPATH_ADMINISTRATOR : JPATH_SITE, null, false, true) || $lang->load($extension . '.sys', JPATH_ADMINISTRATOR, null, false, true);
				}

				$options[$i]->text = JText::_($item->text);
			}
		}
		else
		{
			JLog::add(JText::_('No extensions found.'), JLog::WARNING, 'jerror');
		}

		// Merge any additional options in the XML definition.
		$options = array_merge(parent::getOptions(), (array) $options);

		return $options;
	}
}