.. include:: ../Includes.txt

Create Folder Structure And Configuration Files
===============================================

Before we write the first line of code, we must arrange the
infrastructure of the extension. Beside the folder structure there are some
minimum needed configuration files counting. We put the unique identifier of
our extension (extension-key) as ``store_inventory``, and thus
we specify at the same time the name of the extension as
*Store Inventory*.

.. tip::

   The name of an extension is always written in
   *UpperCamelCase* (beginning with a capital letter, then
   upper and lower letters; no underscore), while the extension key may only
   contain small letters and underscore (lower_underscore). You will find an
   overview of the name conventions in appendix A, *Coding
   Guidelines*.

Extensions can be stored at different places in TYPO3. Locally
installed extensions are the rule. These are in the folder
:file:`typo3conf/ext/`. System extensions are delivered with the
TYPO3-distribution and are in the folder :file:`typo3/sysext/`.
Extbase or Fluid are examples of system extensions. The two paths are
below the installation folder of TYPO3, in which also lies the file
`index.php`.

Then, in the folder for local extensions
:file:`typo3conf/ext/` we create the folder
:file:`store_inventory`. The name of this folder
must be written like the extension key and therefore in lower-case letters,
and where appropriate, with underscores. On the uppermost level lie the
folders :file:`Classes` and :file:`Resources`. The
folder :file:`Classes` contains all PHP classes, with the exception of external PHP libraries. The folder
:file:`Resources` contains two directories named :file:`Private` and :file:`Public`.
The folder :file:`Resources/Private/` contains subfolders like :file:`Templates`, :file:`Layouts`, :file:`Partials`
and :file:`Language`. These files can only be accessed through the file system.
The folder :file:`Resources/Public/` contains subfolders like :file:`Icons`, :file:`Css`, :file:`Js`. These files can be accessed through the web browser.
Within the folder
:file:`Classes` are the folders
:file:`Controller` and
:file:`Domain`. In our example, the folder
:file:`Controller` contains only one class that will control
the entire process of listing creation later. The folder *Domain* again contains the two folders
:file:`Model` and
:file:`Repository`. Resulting from all this, the folder structure within the extension folder
:file:`store_inventory` should look as in image 4-1.

.. figure:: /Images/4-FirstExtension/figure-4-1.png
   :align: center

   Figure 4-1: The standard directory structure with the important files for the extension manager

A single configuration file named :file:`ext_emconf.php` is required by TYPO3
to allow for loading the extension. The file is located in the extension's
top level folder (:file:`store_inventory/`). You can copy and adapt this file
from an existing extension. Later on it is advisable to have it generated by
the *extension_builder* extension.

The file :file:`ext_emconf.php` contains the meta information for the
extension like title, description, status, name of the author and more. It
is not special in any way and does not differ from the one of any other
extension. Find a complete reference in chapter
:ref:`t3coreapi:extension-declaration` of the *Core Api Reference* manual.

.. code-block:: php

   <?php

   $EM_CONF[$_EXTKEY] = [
       'title' => 'Store Inventory',
       'description' => 'An extension to manage a stock.',
       'category' => 'plugin',
       'author' => 'John Doe',
       'author_company' => 'John Doe Inc.',
       'author_email' => 'john.doe@example.com',
       'state' => 'alpha',
       'clearCacheOnLoad' => true,
       'version' => '0.0.0',
       'constraints' => [
           'depends' => [
               'typo3' => '8.7.0-8.9.99',
           ],
       ],
       'autoload' => [
           'psr-4' => [
               'MyVendor\\StoreInventory\\' => 'Classes'
           ],
       ],
   ];

In previous versions of TYPO3 the extension icon was named
:file:`ext_icon.gif`. Starting with TYPO3 8 you can choose between PNG or SVG
format. The file must have the name
:file:`Extension.png` or :file:`Extension.svg` and must be stored in the
directory :file:`Resources/Public/Icons/`.
The icon will be displayed in the extension manager and in the TYPO3 extension
repository (TER).

If the extension has namespaced classes following the PSR-4 standard, then you
can add the autoload array to your :file:`ext_emconf.php` file.

After the basic structure was constructed, the extension can already be shown in the extension manager and
can be installed. But first we turn to our domain.