Chapter 1, Ecosystem Overview, gives a gentle introduction to the current state of the PHP ecosystem. It looks into the latest features of PHP 7, some of which open a door to the new concepts of use in modular development. Furthermore, this chapter glosses over the popular PHP frameworks.

Chapter 2, GoF Design Patterns, describes recurring solutions to common problems in software design. Practical PHP examples are given for each of the following patterns: creation pattern types, structural patterns, and behavioral patterns.

Chapter 3, SOLID Design Principles, dives into the five basic principles of object-oriented programming and design under the acronym SOLID (single responsibility, open-closed, Liskov substitution, Interface Segregation, and dependency inversion).It gives practical examples and explains the importance of these principles in modular development.

Chapter 4, Requirement Specification for a Modular Web Shop App, guides a reader through the process of defining overall application requirements. It starts by defining actual application feature requirements and progresses all the way to the technology stack selection.

Chapter 5, Symfony at a Glance, gives a high-level overview of Symfony as a framework, a set of tools, and a development methodology. It focuses on the building blocks that we will need to build our modular application.

Chapter 6, Building the Core Module, guides you through setting up a core module based on the Symfony bundle. The core module is then used to set the structure and dependencies for other modules to use.

Chapter 7, Building the Catalog Module, guides us through building a self-sufficient module that matches the web shop catalog-only feature set. It shows us how to set up entities relevant to the module functionality and how to manage those entities and their interactions using the existing framework.

Chapter 8, Building the Customer Module, guides us through building a self-sufficient module that matches the web shop customer-related feature set. It shows us how to set up entities relevant to the module's functionality and how to manage those entities and their interactions using the existing framework. It further shows us how to create a register and login systems.

Chapter 9, Building the Payment Module, guides us through building a self-sufficient module that matches the web shop payment-related feature set. It shows us how to integrate with a third-party payment provider. It further shows us how to expose a payment provider as service for other modules to use.

Chapter 10, Building the Shipment Module, guides us through building a self-sufficient module that matches the web shop shipment-related feature set. It shows us how to define several flat methods that yield different shipment pricing based on various cart product attributes. It further shows us how to expose a shipment method as service for other modules to use.

Chapter 11, Building the Sales Module, guides us through building a self-sufficient module that matches the web shop sales-only feature set. It shows us how to set up cart, cart item, order, and order item entities relevant to the module functionality and how to manage those entities and their interactions using the existing framework.

Chapter 12, Integrating and Distributing Modules, integrates all the modules built in the preceding chapters into a single functioning application. Moving on, it guides us through the modern PHP module distribution techniques. These include Git and Composer, which in turn indirectly include GitHub and Packagist.

In order to successfully run all the examples provided in this book, you will need either your own web server or a third-party web-hosting solution. The high-level technology stack includes PHP 7.0 or greater, Apache/Nginx, and MySQL.

The Symfony framework itself comes with a detailed list of system requirements that can be found at http://symfony.com/doc/current/reference/requirements.html.

This book assumes that the reader is familiar with setting up the complete development environment.

This book is primarily intended for intermediate-level PHP developers, with little to no knowledge of modular programming who want to understand design patterns and principles in order to better utilize the existing framework for modular application development.

The modular web-shop application developed as a part of this book uses the Symfony framework. However, no previous knowledge of the Symfony framework is assumed or required.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "We can include other contexts through the use of the include directive."

A block of code is set as follows:

function hint (int $A, float $B, string $C, bool $D)
{
    var_dump($A, $B, $C, $D);
}

Any command-line input or output is written as follows:

sudo curl -LsS https://symfony.com/installer -o /usr/local/bin/symfony
sudo chmod a+x /usr/local/bin/symfony

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Clicking the Next button moves you to the next screen."

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