Implementing complex HTML Markup and overriding templates in Drupal

In Drupal, hook_theme_suggestions is a powerful hook that allows developers to define custom theme suggestions for rendering templates. It can significantly simplify the process of injecting complex HTML markup into your Drupal theme. By utilizing `hook_theme_suggestions`, you can create dynamic template suggestions based on various conditions, making your code more organized and maintainable. 

Here's how `hook_theme_suggestions` works and how it can make your life easier when injecting complex HTML markup: 

1. Dynamic template suggestions: `hook_theme_suggestions` enables you to generate template suggestions based on specific criteria. For example, you can create template suggestions based on content types, view modes, field values, paths, or any other contextual information. This means you can have different templates for different scenarios without cluttering your code with conditionals. 
2. Structured template files: When injecting complex HTML markup, it's crucial to keep your templates organized and maintainable. With `hook_theme_suggestions`, you can define template file names and folder structures that reflect the structure of your content, making it easier to locate and manage templates. 
3. Modularity and reusability: By using `hook_theme_suggestions`, you can create reusable templates that can be applied to multiple elements or sections on your site. This promotes modularity and reduces duplication of code, resulting in a more efficient and maintainable theme. 
4. Clear separation of concerns: Drupal follows the "Separation of Concerns" principle, which encourages dividing code into distinct parts based on their roles. `hook_theme_suggestions` helps you achieve this by keeping theme-related logic in the theme layer and away from business logic or data processing layers. 
5. Theming flexibility: Drupal's theme layer is known for its flexibility, allowing developers to modify the appearance of their sites without altering the underlying functionality. By using `hook_theme_suggestions`, you can customize the markup of specific elements without changing the core logic or structure of the site. 
6. Responsive design: Complex HTML markup often needs to be responsive to different devices and screen sizes. By utilizing theme suggestions, you can create templates optimized for various display contexts, improving the overall user experience. 
7. Collaboration and maintenance: When you follow Drupal's theming conventions and use `hook_theme_suggestions`, other developers working on the same project can easily understand and extend your theme. This promotes collaboration and makes maintenance and updates more manageable. 

When dealing with complex HTML markup and custom templates, you might have specific requirements to render content differently based on various factors like content types, node properties, user roles, or other contextual information. hook_theme_suggestions can simplify this process by providing a way to define custom theme suggestions based on these conditions.

Here's how you can use hook_theme_suggestions to make your life easier when injecting complex HTML markup with real code examples:

Implement hook_theme_suggestions in your module or theme's .module file:

/**
 * Implements hook_theme_suggestions_HOOK_alter() for block templates.
 */
function YOUR_MODULE_OR_THEME_NAME_theme_suggestions_block_alter(array &$suggestions, array $variables) {
  // Add custom theme suggestion for a specific block.
  if ($variables['elements']['#id'] === 'YOUR_BLOCK_ID') {
    $suggestions[] = 'block__custom_template';
  }
}

In the above example, we're adding a custom theme suggestion, 'block__custom_template', for a specific block with the ID 'YOUR_BLOCK_ID'. This means that whenever Drupal tries to render that specific block, it will check for the existence of block--custom-template.html.twig in your theme's templates folder.

Now, create the custom template file, block--custom-template.html.twig, in your theme's templates folder (if it doesn't already exist). In this template file, you can inject the complex HTML markup and use variables as needed:

{# Customize the markup for the block with the ID 'YOUR_BLOCK_ID' #}
<div class="custom-block">
  <h2>{{ content.title }}</h2>
  <div class="content">{{ content.body }}</div>
</div>

Clear the Drupal cache to ensure the new theme suggestion takes effect. By using hook_theme_suggestions, you have the flexibility to generate custom theme suggestions for various template levels based on your specific requirements. You can use any logic inside the hook_theme_suggestions implementation to determine which template should be used for a particular situation.

This approach allows you to organize your complex HTML markup into separate template files, making your code more manageable and easier to maintain. It's especially useful when dealing with different types of content or elements that require unique styling or rendering.