class ResponsiveImageBuilder

class ResponsiveImageBuilder {
  public function __construct(protected EntityTypeManagerInterface $entityTypeManager, protected MimeTypeMapInterface $mimeTypeMap, protected ImageFactory $imageFactory, protected FileUrlGeneratorInterface $fileUrlGenerator) {
  }
  
  /**
   * Helper function for template_preprocess_responsive_image().
   *
   * Builds an array of attributes for <source> tags to be used in a <picture>
   * tag. In other words, this function provides the attributes for each
   * <source> tag in a <picture> tag.
   *
   * In a responsive image style, each breakpoint has an image style mapping for
   * each of its multipliers. An image style mapping can be either of two types:
   * 'sizes' (meaning it will output a <source> tag with the 'sizes' attribute)
   * or 'image_style' (meaning it will output a <source> tag based on the
   * selected image style for this breakpoint and multiplier). A responsive
   * image style can contain image style mappings of mixed types (both
   * 'image_style' and 'sizes'). For example:
   * @code
   * $responsive_img_style = ResponsiveImageStyle::create([
   *   'id' => 'style_one',
   *   'label' => 'Style One',
   *   'breakpoint_group' => 'responsive_image_test_module',
   * ]);
   * $responsive_img_style->addImageStyleMapping('responsive_image_test_module.mobile', '1x', [
   *   'image_mapping_type' => 'image_style',
   *   'image_mapping' => 'thumbnail',
   * ])
   * ->addImageStyleMapping('responsive_image_test_module.narrow', '1x', [
   *   'image_mapping_type' => 'sizes',
   *   'image_mapping' => [
   *     'sizes' => '(min-width: 700px) 700px, 100vw',
   *     'sizes_image_styles' => [
   *       'large' => 'large',
   *       'medium' => 'medium',
   *     ],
   *   ],
   * ])
   * ->save();
   * @endcode
   * The above responsive image style will result in a <picture> tag like this:
   * @code
   * <picture>
   *   <source media="(min-width: 0px)" srcset="sites/default/files/styles/thumbnail/image.jpeg" />
   *   <source media="(min-width: 560px)" sizes="(min-width: 700px) 700px, 100vw" srcset="sites/default/files/styles/large/image.jpeg 480w, sites/default/files/styles/medium/image.jpeg 220w" />
   *   <img src="fallback.jpeg" />
   * </picture>
   * @endcode
   *
   * When all the images in the 'srcset' attribute of a <source> tag have the
   * same MIME type, the source tag will get a 'mime-type' attribute as well.
   * This way we can gain some front-end performance because browsers can select
   * which image (<source> tag) to load based on the MIME types they support
   * (which, for instance, can be beneficial for browsers supporting WebP).
   * For example:
   * A <source> tag can contain multiple images:
   * @code
   * <source [...] srcset="image1.jpeg 1x, image2.jpeg 2x, image3.jpeg 3x" />
   * @endcode
   * In the above example we can add the 'mime-type' attribute ('image/jpeg')
   * since all images in the 'srcset' attribute of the <source> tag have the
   * same MIME type.
   * If a <source> tag were to look like this:
   * @code
   * <source [...] srcset="image1.jpeg 1x, image2.webp 2x, image3.jpeg 3x" />
   * @endcode
   * We can't add the 'mime-type' attribute ('image/jpeg' vs 'image/webp').
   * So in order to add the 'mime-type' attribute to the <source> tag all images
   * in the 'srcset' attribute of the <source> tag need to be of the same MIME
   * type. This way, a <picture> tag could look like this:
   * @code
   * <picture>
   *   <source [...] mime-type="image/webp" srcset="image1.webp 1x, image2.webp 2x, image3.webp 3x"/>
   *   <source [...] mime-type="image/jpeg" srcset="image1.jpeg 1x, image2.jpeg 2x, image3.jpeg 3x"/>
   *   <img src="fallback.jpeg" />
   * </picture>
   * @endcode
   * This way a browser can decide which <source> tag is preferred based on the
   * MIME type. In other words, the MIME types of all images in one <source> tag
   * need to be the same in order to set the 'mime-type' attribute but not all
   * MIME types within the <picture> tag need to be the same.
   *
   * For image style mappings of the type 'sizes', a width descriptor is added
   * to each source. For example:
   * @code
   * <source media="(min-width: 0px)" srcset="image1.jpeg 100w" />
   * @endcode
   * The width descriptor here is "100w". This way the browser knows this image
   * is 100px wide without having to load it. According to the spec, a
   * multiplier can not be present if a width descriptor is.
   * For example:
   * Valid:
   * @code
   * <source media="(min-width:0px)" srcset="img1.jpeg 50w, img2.jpeg=100w" />
   * @endcode
   * Invalid:
   * @code
   * <source media="(min-width:0px)" srcset="img1.jpeg 50w 1x, img2.jpeg=100w 1x" />
   * @endcode
   *
   * Note: Since the specs do not allow width descriptors and multipliers
   * combined inside one 'srcset' attribute, we either have to use something
   * like
   * @code
   * <source [...] srcset="image1.jpeg 1x, image2.webp 2x, image3.jpeg 3x" />
   * @endcode
   * to support multipliers or
   * @code
   * <source [...] sizes"(min-width: 40em) 80vw, 100vw" srcset="image1.jpeg 300w, image2.webp 600w, image3.jpeg 1200w" />
   * @endcode
   * to support the 'sizes' attribute.
   *
   * In theory people could add an image style mapping for the same breakpoint
   * (but different multiplier) so the array contains an entry for
   * breakpointA.1x and breakpointA.2x. If we would output those we will end up
   * with something like
   * @code
   * <source [...] sizes="(min-width: 40em) 80vw, 100vw" srcset="a1.jpeg 300w 1x, a2.jpeg 600w 1x, a3.jpeg 1200w 1x, b1.jpeg 250w 2x, b2.jpeg 680w 2x, b3.jpeg 1240w 2x" />
   * @endcode
   * which is illegal. So the solution is to merge both arrays into one and
   * disregard the multiplier. Which, in this case, would output
   * @code
   * <source [...] sizes="(min-width: 40em) 80vw, 100vw" srcset="b1.jpeg 250w, a1.jpeg 300w, a2.jpeg 600w, b2.jpeg 680w, a3.jpeg 1200w,  b3.jpeg 1240w" />
   * @endcode
   * See https://www.w3.org/html/wg/drafts/html/master/embedded-content.html#image-candidate-string
   * for further information.
   *
   * @param array $variables
   *   An array with the following keys:
   *     - responsive_image_style_id: The
   *       \Drupal\responsive_image\Entity\ResponsiveImageStyle ID.
   *     - width: The width of the image (if known).
   *     - height: The height of the image (if known).
   *     - uri: The URI of the image file.
   * @param \Drupal\breakpoint\BreakpointInterface $breakpoint
   *   The breakpoint for this source tag.
   * @param array $multipliers
   *   An array with multipliers as keys and image style mappings as values.
   *
   * @return \Drupal\Core\Template\Attribute
   *   An object of attributes for the source tag.
   */
  public function buildSourceAttributes(array $variables, BreakpointInterface $breakpoint, array $multipliers) : Attribute {
    if (empty($variables['width']) || empty($variables['height'])) {
      $image = $this->imageFactory
        ->get($variables['uri']);
      $width = $image->getWidth();
      $height = $image->getHeight();
    }
    else {
      $width = $variables['width'];
      $height = $variables['height'];
    }
    $extension = pathinfo($variables['uri'], PATHINFO_EXTENSION);
    $sizes = [];
    $srcset = [];
    $derivative_mime_types = [];
    // Traverse the multipliers in reverse so the largest image is processed
    // last./ The last image's dimensions are used for img.srcset height and
    // width.
    foreach (array_reverse($multipliers) as $multiplier => $image_style_mapping) {
      switch ($image_style_mapping['image_mapping_type']) {
        // Create a <source> tag with the 'sizes' attribute.
        case 'sizes':
          // Loop through the image styles for this breakpoint and multiplier.
          foreach ($image_style_mapping['image_mapping']['sizes_image_styles'] as $image_style_name) {
            // Get the dimensions.
            $dimensions = $this->getImageDimensions($image_style_name, [
              'width' => $width,
              'height' => $height,
            ], $variables['uri']);
            // Get MIME type.
            $derivative_mime_type = $this->getMimeType($image_style_name, $extension);
            $derivative_mime_types[] = $derivative_mime_type;
            // Add the image source with its width descriptor. When a width
            // descriptor is used in a srcset, we can't add a multiplier to
            // it. Because of this, the image styles for all multipliers of
            // this breakpoint should be merged into one srcset and the sizes
            // attribute should be merged as well.
            if (is_null($dimensions['width'])) {
              throw new \LogicException("Could not determine image width for '{$variables['uri']}' using image style with ID: {$image_style_name}. This image style can not be used for a responsive image style mapping using the 'sizes' attribute.");
            }
            // Use the image width as key so we can sort the array later on.
            // Images within a srcset should be sorted from small to large,
            // since the first matching source will be used.
            $srcset[intval($dimensions['width'])] = $this->getImageStyleUrl($image_style_name, $variables['uri']) . ' ' . $dimensions['width'] . 'w';
            $sizes = array_merge(explode(',', $image_style_mapping['image_mapping']['sizes']), $sizes);
          }
          break;

        case 'image_style':
          // Get MIME type.
          $derivative_mime_type = $this->getMimeType($image_style_mapping['image_mapping'], $extension);
          $derivative_mime_types[] = $derivative_mime_type;
          // Add the image source with its multiplier. Use the multiplier as
          // key so we can sort the array later on. Multipliers within a srcset
          // should be sorted from small to large, since the first matching
          // source will be used. We multiply it by 100 so multipliers with up
          // to two decimals can be used.
          $srcset[intval(mb_substr($multiplier, 0, -1) * 100)] = $this->getImageStyleUrl($image_style_mapping['image_mapping'], $variables['uri']) . ' ' . $multiplier;
          $dimensions = $this->getImageDimensions($image_style_mapping['image_mapping'], [
            'width' => $width,
            'height' => $height,
          ], $variables['uri']);
          break;

      }
    }
    // Sort the srcset from small to large image width or multiplier.
    ksort($srcset);
    $source_attributes = new Attribute([
      'srcset' => implode(', ', array_unique($srcset)),
    ]);
    $media_query = trim($breakpoint->getMediaQuery());
    if (!empty($media_query)) {
      $source_attributes->setAttribute('media', $media_query);
    }
    if (count(array_unique($derivative_mime_types)) == 1) {
      $source_attributes->setAttribute('type', $derivative_mime_types[0]);
    }
    if (!empty($sizes)) {
      $source_attributes->setAttribute('sizes', implode(',', array_unique($sizes)));
    }
    // The images used in a particular srcset attribute should all have the same
    // aspect ratio. The sizes attribute paired with the srcset attribute
    // provides information on how much space these images take up within the
    // viewport at different breakpoints, but the aspect ratios should remain
    // the same across those breakpoints. Multiple source elements can be used
    // for art direction, where aspect ratios should change at particular
    // breakpoints. Each source element can still have srcset and sizes
    // attributes to handle variations for that particular aspect ratio. Because
    // the same aspect ratio is assumed for all images in a srcset, dimensions
    // are always added to the source attribute. Within srcset, images are
    // sorted from largest to smallest in terms of the real dimension of the
    // image.
    if (!empty($dimensions['width']) && !empty($dimensions['height'])) {
      $source_attributes->setAttribute('width', $dimensions['width']);
      $source_attributes->setAttribute('height', $dimensions['height']);
    }
    return $source_attributes;
  }
  
  /**
   * Determines the dimensions of an image.
   *
   * @param string $image_style_name
   *   The name of the style to be used to alter the original image.
   * @param array $dimensions
   *   An associative array containing:
   *   - width: The width of the source image (if known).
   *   - height: The height of the source image (if known).
   * @param string $uri
   *   The URI of the image file.
   *
   * @return array
   *   Dimensions to be modified - an array with components width and height, in
   *   pixels.
   */
  public function getImageDimensions(string $image_style_name, array $dimensions, string $uri) : array {
    // Determine the dimensions of the styled image.
    if ($image_style_name == ResponsiveImageStyleInterface::EMPTY_IMAGE) {
      $dimensions = [
        'width' => 1,
        'height' => 1,
      ];
    }
    elseif ($entity = $this->entityTypeManager
      ->getStorage('image_style')
      ->load($image_style_name)) {
      assert($entity instanceof ImageStyle);
      $entity->transformDimensions($dimensions, $uri);
    }
    return $dimensions;
  }
  
  /**
   * Determines the MIME type of an image.
   *
   * @param string $image_style_name
   *   The image style that will be applied to the image.
   * @param string $extension
   *   The original extension of the image (without the leading dot).
   *
   * @return string|null
   *   The MIME type of the image after the image style is applied, or NULL if
   *   not found.
   */
  public function getMimeType(string $image_style_name, string $extension) : ?string {
    $extension = match ($image_style_name) {  ResponsiveImageStyleInterface::EMPTY_IMAGE => 'gif',
      ResponsiveImageStyleInterface::ORIGINAL_IMAGE => $extension,
      default => $this->entityTypeManager
        ->getStorage('image_style')
        ->load($image_style_name)
        ->getDerivativeExtension($extension),
    
    };
    return $this->mimeTypeMap
      ->getMimeTypeForExtension($extension);
  }
  
  /**
   * Returns the given image style URL.
   *
   * Explicitly supports the special empty image as aa data: URL.
   *
   * @param string $style_name
   *   Name of the image style.
   * @param string $path
   *   The path or URI to the original image.
   *
   * @return string
   *   The image style URL.
   */
  public function getImageStyleUrl(string $style_name, string $path) : string {
    if ($style_name == ResponsiveImageStyleInterface::EMPTY_IMAGE) {
      // The smallest data URI for a 1px square transparent GIF image.
      // http://probablyprogramming.com/2009/03/15/the-tiniest-gif-ever
      return 'data:image/gif;base64,R0lGODlhAQABAIABAP///wAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==';
    }
    $entity = ImageStyle::load($style_name);
    if ($entity instanceof ImageStyle) {
      return $this->fileUrlGenerator
        ->transformRelative($entity->buildUrl($path));
    }
    return $this->fileUrlGenerator
      ->generateString($path);
  }

}