The src of the image.
	 *
	 * @return array $sources
	 */
	private function set_additional_srcset( $sources, $size_array, $url, $image_meta, $image_src = '' ) {
		$content_width = $this->max_content_width();

		// If url is empty, try to get from src.
		if ( empty( $url ) ) {
			$url = $this->get_url_without_dimensions( $image_src );
		}

		// We need to add additional dimensions.
		$full_width     = $image_meta['width'];
		$full_height    = $image_meta['height'];
		$current_width  = $size_array[0];
		$current_height = $size_array[1];
		// Get width and height calculated by WP.
		list( $constrained_width, $constrained_height ) = wp_constrain_dimensions( $full_width, $full_height, $current_width, $current_height );

		// Calculate base width.
		// If $constrained_width sizes are smaller than current size, set maximum content width.
		if ( abs( $constrained_width - $current_width ) <= 1 && abs( $constrained_height - $current_height ) <= 1 ) {
			$base_width = $content_width;
		} else {
			$base_width = $current_width;
		}

		$current_widths = array_keys( $sources );
		$new_sources    = array();

		/**
		 * Filter to add/update/bypass additional srcsets.
		 *
		 * If empty value or false is retured, additional srcset
		 * will not be generated.
		 *
		 * @param array|bool $additional_multipliers Additional multipliers.
		 */
		$additional_multipliers = apply_filters(
			'smush_srcset_additional_multipliers',
			array(
				0.2,
				0.4,
				0.6,
				0.8,
				1,
				2,
				3,
			)
		);

		// Continue only if additional multipliers found or not skipped.
		// Filter already documented in class-cdn.php.
		if ( apply_filters( 'smush_skip_image_from_cdn', false, $url, false ) || empty( $additional_multipliers ) ) {
			return $sources;
		}

		// Loop through each multipliers and generate image.
		foreach ( $additional_multipliers as $multiplier ) {
			// New width by multiplying with original size.
			$new_width = (int) ( $base_width * $multiplier );

			// In most cases - going over the current width is not recommended and probably not what the user is expecting.
			if ( $new_width > $current_width ) {
				continue;
			}

			// If a nearly sized image already exist, skip.
			foreach ( $current_widths as $_width ) {
				// If +- 50 pixel difference - skip.
				if ( abs( $_width - $new_width ) < 50 || ( $new_width > $full_width ) ) {
					continue 2;
				}
			}

			// We need the width as well...
			$dimensions = wp_constrain_dimensions( $current_width, $current_height, $new_width );

			// Arguments for cdn url.
			$args = array(
				'size' => "{$new_width}x{$dimensions[1]}",
			);

			// Add new srcset item.
			$new_sources[ $new_width ] = array(
				'url'        => $this->generate_cdn_url( $url, $args ),
				'descriptor' => 'w',
				'value'      => $new_width,
			);
		}

		// Assign new srcset items to existing ones.
		if ( ! empty( $new_sources ) ) {
			// Loop through each items and replace/add.
			foreach ( $new_sources as $_width_key => $_width_values ) {
				$sources[ $_width_key ] = $_width_values;
			}
		}

		return $sources;
	}

	/**
	 * Try to generate the srcset for the image.
	 *
	 * @since 3.0
	 *
	 * @param string $src  Image source.
	 *
	 * @return array|bool
	 */
	private function generate_srcset( $src ) {
		/**
		 * Try to get the attachment URL.
		 *
		 * TODO: attachment_url_to_postid() can be resource intensive and cause 100% CPU spikes.
		 *
		 * @see https://core.trac.wordpress.org/ticket/41281
		 */
		$attachment_id = attachment_url_to_postid( $src );

		// Try to get width and height from image.
		if ( $attachment_id ) {
			list( $src, $width, $height ) = wp_get_attachment_image_src( $attachment_id, 'full' );

			// Revolution slider fix: images will always return 0 height and 0 width.
			if ( 0 === $width && 0 === $height ) {
				// Try to get the dimensions directly from the file.
				list( $width, $height ) = $this->get_image_size( $src );
			}

			$image_meta = wp_get_attachment_metadata( $attachment_id );
		} else {
			// Try to get the dimensions directly from the file.
			list( $width, $height ) = $this->get_image_size( $src );

			// This is an image placeholder - do not generate srcset.
			if ( $width === $height && 1 === $width ) {
				return false;
			}

			$image_meta = array(
				'width'  => $width,
				'height' => $height,
			);
		}

		$size_array = array( absint( $width ), absint( $height ) );
		$srcset     = wp_calculate_image_srcset( $size_array, $src, $image_meta, $attachment_id );

		/**
		 * In some rare cases, the wp_calculate_image_srcset() will not generate any srcset, because there are
		 * not image sizes defined. If that is the case, try to revert to our custom maybe_generate_srcset() to
		 * generate the srcset string.
		 *
		 * Also srcset will not be generated for images that are not part of the media library (no $attachment_id).
		 */
		if ( ! $srcset ) {
			$srcset = $this->maybe_generate_srcset( $width, $height, $src, $image_meta );
		}

		$sizes = $srcset ? wp_calculate_image_sizes( $size_array, $src, $image_meta, $attachment_id ) : false;

		return array( $srcset, $sizes );
	}

	/**
	 * Try to generate srcset.
	 *
	 * @since 3.0
	 *
	 * @param int    $width   Attachment width.
	 * @param int    $height  Attachment height.
	 * @param string $src     Image source.
	 * @param array  $meta    Image meta.
	 *
	 * @return bool|string
	 */
	private function maybe_generate_srcset( $width, $height, $src, $meta ) {
		$sources[ $width ] = array(
			'url'        => $this->generate_cdn_url( $src ),
			'descriptor' => 'w',
			'value'      => $width,
		);

		$sources = $this->set_additional_srcset(
			$sources,
			array( absint( $width ), absint( $height ) ),
			$src,
			$meta
		);

		$srcsets = array();

		if ( 1 < count( $sources ) ) {
			foreach ( $sources as $source ) {
				$srcsets[] = str_replace( ' ', '%20', $source['url'] ) . ' ' . $source['value'] . $source['descriptor'];
			}
			return implode( ',', $srcsets );
		}

		return false;
	}

	/**
	 * Check if the image path is supported by the CDN.
	 *
	 * @since 3.0
	 * @since 3.3.0 Changed access to public.
	 *
	 * @param string $src  Image path.
	 *
	 * @return bool|string
	 */
	public function is_supported_path( $src ) {
		// Remove whitespaces.
		$src = trim( $src );

		// No image? Return.
		if ( empty( $src ) ) {
			return false;
		}

		// Allow only these extensions in CDN.
		$path = wp_parse_url( $src, PHP_URL_PATH );
		$ext  = strtolower( pathinfo( $path, PATHINFO_EXTENSION ) );
		if ( ! in_array( $ext, $this->supported_extensions, true ) ) {
			return false;
		}

		$url_parts = wp_parse_url( $src );

		// Unsupported scheme.
		if ( isset( $url_parts['scheme'] ) && 'http' !== $url_parts['scheme'] && 'https' !== $url_parts['scheme'] ) {
			return false;
		}

		if ( ! isset( $url_parts['scheme'] ) && 0 === strpos( $src, '//' ) ) {
			$src = is_ssl() ? 'https:' . $src : 'http:' . $src;
		}

		// This is a relative path, try to get the URL.
		if ( ! isset( $url_parts['host'] ) && ! isset( $url_parts['scheme'] ) ) {
			$src = site_url( $src );
		}

		$mapped_domain = $this->check_mapped_domain();

		/**
		 * There are chances for a custom uploads directory using UPLOADS constant.
		 *
		 * But some security plugins (for example, WP Hide & Security Enhance) will allow replacing paths via Nginx/Apache
		 * rules. So for this reason, we don't want the path to be replaced everywhere with the custom UPLOADS constant,
		 * we just want to let the user redefine it here, in the CDN.
		 *
		 * @since 3.4.0
		 *
		 * @param array $uploads {
		 *     Array of information about the upload directory.
		 *
		 *     @type string       $path    Base directory and subdirectory or full path to upload directory.
		 *     @type string       $url     Base URL and subdirectory or absolute URL to upload directory.
		 *     @type string       $subdir  Subdirectory if uploads use year/month folders option is on.
		 *     @type string       $basedir Path without subdir.
		 *     @type string       $baseurl URL path without subdir.
		 *     @type string|false $error   False or error message.
		 * }
		 *
		 * Usage (replace /wp-content/uploads/ with /media/ directory):
		 *
		 * add_filter(
		 *     'smush_cdn_custom_uploads_dir',
		 *     function( $uploads ) {
		 *         $uploads['baseurl'] = 'https://example.com/media';
		 *         return $uploads;
		 *     }
		 * );
		 */
		$uploads = apply_filters( 'smush_cdn_custom_uploads_dir', wp_get_upload_dir() );
		// Check if the src is within custom uploads directory.
		$uploads = isset( $uploads['baseurl'] ) ? false !== strpos( $src, $uploads['baseurl'] ) : true;

		if ( ( false === strpos( $src, content_url() ) && ! $uploads ) || ( is_multisite() && $mapped_domain && false === strpos( $src, $mapped_domain ) ) ) {
			return false;
		}

		return $src;
	}

	/**
	 * Support for domain mapping plugin.
	 *
	 * @since 3.1.1
	 */
	private function check_mapped_domain() {
		if ( ! is_multisite() ) {
			return false;
		}

		if ( ! defined( 'DOMAINMAP_BASEFILE' ) ) {
			return false;
		}

		$domain = wp_cache_get( 'smush_mapped_site_domain', 'smush' );

		if ( ! $domain ) {
			global $wpdb;

			$domain = $wpdb->get_var(
				$wpdb->prepare(
					"SELECT domain FROM {$wpdb->base_prefix}domain_mapping WHERE blog_id = %d ORDER BY id LIMIT 1",
					get_current_blog_id()
				)
			); // Db call ok.

			if ( null !== $domain ) {
				wp_cache_add( 'smush_mapped_site_domain', $domain, 'smush' );
			}
		}

		return $domain;
	}

	/**
	 * Init the page parser.
	 */
	private function init_parser() {
		$background_images = $this->settings->get( 'background_images' );

		if ( $background_images ) {
			$this->parser->enable( 'background_images' );
		}

		$this->parser->enable( 'cdn' );
	}

	/**
	 * Try to get the image dimensions from a local file.
	 *
	 * @since 3.4.0
	 * @param string $url  Image URL.
	 *
	 * @return array|false
	 */
	private function get_image_size( $url ) {
		if ( $this->site_url !== $this->home_url ) {
			$url = str_replace( $this->site_url, $this->home_url, $url );
		}

		$path = wp_make_link_relative( $url );
		$path = wp_normalize_path( ABSPATH . $path );

		if ( ! file_exists( $path ) ) {
			return false;
		}

		return getimagesize( $path );
	}

}