<?php
/**
 * Class AMP_Img_Sanitizer.
 *
 * @package AMP
 */

/**
 * Class AMP_Img_Sanitizer
 *
 * Converts <img> tags to <amp-img> or <amp-anim>
 */
class AMP_Img_Sanitizer extends AMP_Base_Sanitizer {

	/**
	 * Value used for width attribute when $attributes['width'] is empty.
	 *
	 * @since 0.2
	 *
	 * @const int
	 */
	const FALLBACK_WIDTH = 600;

	/**
	 * Value used for height attribute when $attributes['height'] is empty.
	 *
	 * @since 0.2
	 *
	 * @const int
	 */
	const FALLBACK_HEIGHT = 400;

	/**
	 * Tag.
	 *
	 * @var string HTML <img> tag to identify and replace with AMP version.
	 *
	 * @since 0.2
	 */
	public static $tag = 'img';

	/**
	 * Animation extension.
	 *
	 * @var string
	 */
	private static $anim_extension = '.gif';

	/**
	 * Script slug.
	 *
	 * @var string AMP HTML tag to use in place of HTML's <img> tag.
	 *
	 * @since 0.2
	 */
	private static $script_slug = 'amp-anim';

	/**
	 * Script src.
	 *
	 * @var string URL to AMP Project's Image element's JavaScript file found at cdn.ampproject.org
	 *
	 * @since 0.2
	 */
	private static $script_src = 'https://cdn.ampproject.org/v0/amp-anim-0.1.js';

	/**
	 * Return one element array containing AMP HTML image tag and respective Javascript URL
	 *
	 * HTML tags and Javascript URLs found at cdn.ampproject.org
	 *
	 * @since 0.2
	 *
	 * @return string[] Returns AMP HTML image tag as array key and Javascript URL
	 *                  as array value, respectively. Will return an empty array
	 *                  if sanitization has yet to be run or if it did not find any
	 *                  HTML image elements to convert to AMP equivalents.
	 */
	public function get_scripts() {
		if ( ! $this->did_convert_elements ) {
			return array();
		}
		return array( self::$script_slug => self::$script_src );
	}

	/**
	 * Sanitize the <img> elements from the HTML contained in this instance's DOMDocument.
	 *
	 * @since 0.2
	 */
	public function sanitize() {

		/**
		 * Node list.
		 *
		 * @var DOMNodeList $node
		 */
		$nodes           = $this->dom->getElementsByTagName( self::$tag );
		$need_dimensions = array();

		$num_nodes = $nodes->length;

		if ( 0 === $num_nodes ) {
			return;
		}

		for ( $i = $num_nodes - 1; $i >= 0; $i-- ) {
			$node = $nodes->item( $i );
			if ( ! $node instanceof DOMElement ) {
				continue;
			}

			if ( ! $node->hasAttribute( 'src' ) || '' === $node->getAttribute( 'src' ) ) {
				$node->parentNode->removeChild( $node );
				continue;
			}

			// Determine which images need their dimensions determined/extracted.
			if ( '' === $node->getAttribute( 'width' ) || '' === $node->getAttribute( 'height' ) ) {
				$need_dimensions[ $node->getAttribute( 'src' ) ][] = $node;
			} else {
				$this->adjust_and_replace_node( $node );
			}
		}

		$this->determine_dimensions( $need_dimensions );
		$this->adjust_and_replace_nodes_in_array_map( $need_dimensions );
	}

	/**
	 * "Filter" HTML attributes for <amp-anim> elements.
	 *
	 * @since 0.2
	 *
	 * @param string[] $attributes {
	 *      Attributes.
	 *
	 *      @type string $src Image URL - Pass along if found
	 *      @type string $alt <img> `alt` attribute - Pass along if found
	 *      @type string $class <img> `class` attribute - Pass along if found
	 *      @type string $srcset <img> `srcset` attribute - Pass along if found
	 *      @type string $sizes <img> `sizes` attribute - Pass along if found
	 *      @type string $on <img> `on` attribute - Pass along if found
	 *      @type string $attribution <img> `attribution` attribute - Pass along if found
	 *      @type int $width <img> width attribute - Set to numeric value if px or %
	 *      @type int $height <img> width attribute - Set to numeric value if px or %
	 * }
	 * @return array Returns HTML attributes; removes any not specifically declared above from input.
	 */
	private function filter_attributes( $attributes ) {
		$out = array();

		foreach ( $attributes as $name => $value ) {
			switch ( $name ) {
				case 'src':
				case 'alt':
				case 'class':
				case 'srcset':
				case 'sizes':
				case 'on':
				case 'attribution':
					$out[ $name ] = $value;
					break;

				case 'width':
				case 'height':
					$out[ $name ] = $this->sanitize_dimension( $value, $name );
					break;

				default:
					break;
			}
		}

		return $out;
	}

	/**
	 * Determine width and height attribute values for images without them.
	 *
	 * Attempt to determine actual dimensions, otherwise set reasonable defaults.
	 *
	 * @param DOMElement[][] $need_dimensions Map <img> @src URLs to node for images with missing dimensions.
	 */
	private function determine_dimensions( $need_dimensions ) {

		$dimensions_by_url = AMP_Image_Dimension_Extractor::extract( array_keys( $need_dimensions ) );

		foreach ( $dimensions_by_url as $url => $dimensions ) {
			foreach ( $need_dimensions[ $url ] as $node ) {
				if ( ! $node instanceof DOMElement ) {
					continue;
				}

				// Provide default dimensions for images whose dimensions we couldn't fetch.
				if ( false !== $dimensions ) {
					$node->setAttribute( 'width', $dimensions['width'] );
					$node->setAttribute( 'height', $dimensions['height'] );
				} else {
					$width  = isset( $this->args['content_max_width'] ) ? $this->args['content_max_width'] : self::FALLBACK_WIDTH;
					$height = self::FALLBACK_HEIGHT;
					$node->setAttribute( 'width', $width );
					$node->setAttribute( 'height', $height );
					$class = $node->hasAttribute( 'class' ) ? $node->getAttribute( 'class' ) . ' amp-wp-unknown-size' : 'amp-wp-unknown-size';
					$node->setAttribute( 'class', $class );
				}
			}
		}
	}

	/**
	 * Now that all images have width and height attributes, make final tweaks and replace original image nodes
	 *
	 * @param DOMNodeList[] $node_lists Img DOM nodes (now with width and height attributes).
	 */
	private function adjust_and_replace_nodes_in_array_map( $node_lists ) {
		foreach ( $node_lists as $node_list ) {
			foreach ( $node_list as $node ) {
				$this->adjust_and_replace_node( $node );
			}
		}
	}

	/**
	 * Make final modifications to DOMNode
	 *
	 * @param DOMNode $node The DOMNode to adjust and replace.
	 */
	private function adjust_and_replace_node( $node ) {
		$old_attributes = AMP_DOM_Utils::get_node_attributes_as_assoc_array( $node );
		$new_attributes = $this->filter_attributes( $old_attributes );
		$new_attributes = $this->enforce_sizes_attribute( $new_attributes );
		if ( $this->is_gif_url( $new_attributes['src'] ) ) {
			$this->did_convert_elements = true;

			$new_tag = 'amp-anim';
		} else {
			$new_tag = 'amp-img';
		}
		$new_node = AMP_DOM_Utils::create_node( $this->dom, $new_tag, $new_attributes );
		$node->parentNode->replaceChild( $new_node, $node );
	}

	/**
	 * Determines is a URL is considered a GIF URL
	 *
	 * @since 0.2
	 *
	 * @param string $url URL to inspect for GIF vs. JPEG or PNG.
	 *
	 * @return bool Returns true if $url ends in `.gif`
	 */
	private function is_gif_url( $url ) {
		$ext  = self::$anim_extension;
		$path = AMP_WP_Utils::parse_url( $url, PHP_URL_PATH );
		return substr( $path, -strlen( $ext ) ) === $ext;
	}
}