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One of the main interest of a module is to add functionalities to PrestaShop without having to edit its core files, thus making it easier to perform an update without having the transpose all core changes. Indeed, you should always strive to stay away from core files when building a module, even though this can prove hard to do in some situations...
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The PrestaShop file
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structure
The PrestaShop developers have done their best to clearly and intuitively separate the various parts of the software.
Here is how the files are organized:
/admin: contains all the PrestaShop files pertaining to the back-office. When accessing this folder with your browser, you will be asked to provide proper identification, for security reasons. Important: you should make sure to protect that folder with a.htaccessor.htpasswdfile!/cache: contains temporary folders that are generated and re-used in order to alleviate the server's load./classes: contains all the files pertaining to PrestaShop's object model. Each file represents (and contains) a PHP class, and its methods/properties./config: contains all of PrestaShop's configuration files. Unless asked to, you should never edit them, as they are directly handled by PrestaShop's installer and back-office./controllers: contains all the files pertaining to PrestaShop controllers – as in Model-View-Controller (or MVC), the software architecture used by PrestaShop. Each file controls a specific part of PrestaShop./css: contains all CSS files that are not attached to themes – hence, these are mostly used by the PrestaShop back-office./docs: contains some documentation. Note: it should be deleted in a production environment./download: contains your digital products, which can be downloaded: PDFs, MP3s, etc./img: contains all of PrestaShop's default images, icons and picture files – that, those that do not belong to the theme. This is where you can find the pictures for product categories (/csub-folder, those for the products (/psub-folder) and those for the back-office itself (/adminsub-folder)./install: contains all the files related to PrestaShop's installer. You will be required to delete it after installation, in order to increase security./js: contains all JavaScript files that are not attached to themes. Most of them belong to the back-office. This is also where you will find the jQuery framework./localization: contains all of PrestaShop's localization files – that is, files that contain local information, such as currency, language, tax rules and tax rules groups, states and the various units in use in the chosen country (i.e., volume in liter, weight in kilograms, etc.)./log: contains the log files generated by PrestaShop at various stages, for instance during the installation process./mails: contains all HTML and text files related to e-mails sent by PrestaShop. Each language has its specific folder, where you can manually edit their content if you wish./modules: contains all of PrestaShop's modules, each in its own folder. If you wish to definitely remove a module, first uninstall it from the back-office, then only can you delete its folder./override: this is a special folder that appeared with PrestaShop 1.4. By using PrestaShop's regular folder/filename convention, it is possible to create files that override PrestaShop's default classes or controllers. This enables you to change PrestaShop core behavior without touching to the original files, keeping them safe for the next update./pdf: contains all the template files (.tpl) pertaining to the PDF file generation (invoice, delivery slips, etc.). Change these files in order to change the look of the PDF files that PrestaShop generates./themes: contains all the currently-installed themes, each in its own folder./tools: contains external tools that were integrated into PrestaShop. For instance, this were you'll find Smarty (template/theme engine), FPDF (PDF file generator), Swift (mail sender), PEAR XML Parser (PHP tool)./translations: contains a sub-folder for each available language. However, if you wish to change the translation, you must do so using the PrestaShop internal tool, and not edit them directly in this folder./upload: contains the files that would be uploaded by clients for customizable products (for instance, a picture that a client wants printed on a mug)./webservice: contains files that enable third-party applications to access PrestaShop through its API.
Modules folder
PrestaShop's modules are most often found in the /modules folder, which is at the root of the PrestaShop main folder. This is true for both default modules (provided with PrestaShop) and 3rd-party modules that are subsequently installed.
Modules can also be part of a theme if they are really specific to it. In that case, they would be in the theme's own /modules folder, and therefore under the following path: /themes/mytheme/modules
Each module has its own sub-folder inside the /modules folder: /bankwire, /birthdaypresent, etc.
About the cache
The /cache/Class_index.php file contains the link between the class and the declaration file. It can be safely deleted.
The /cache/xml folder contains the list of all the base modules.
When the store's front-end doesn't quite reflect your changes and emptying the browser's cache is not effective, you should try emptying the following folders:
/cache/smarty/cache/cache/smarty/compile
Basic structure of a module
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