<?php
/**
 * Collects inline styles and outputs them in the amp-custom stylesheet.
 */
class AMP_Style_Sanitizer extends AMP_Base_Sanitizer {
	private $styles = array();

	public function get_styles() {
		return $this->styles;
	}

	public function sanitize() {
		$body = $this->get_body_node();
		$this->collect_styles_recursive( $body );
	}

	private function collect_styles_recursive( $node ) {
		if ( $node->nodeType !== XML_ELEMENT_NODE ) {
			return;
		}

		if ( $node->hasAttributes() && $node instanceof DOMElement ) {
			$style = $node->getAttribute( 'style' );
			$class = $node->getAttribute( 'class' );

			if ( $style ) {
				$style = $this->process_style( $style );
				if ( ! empty( $style ) ) {
					$class_name = $this->generate_class_name( $style );
					$new_class  = trim( $class . ' ' . $class_name );

					$node->setAttribute( 'class', $new_class );
					$this->styles[ '.' . $class_name ] = $style;
				}

				$node->removeAttribute( 'style' );
			}
		}

		$length = $node->childNodes->length;
		for ( $i = $length - 1; $i >= 0; $i -- ) {
			$child_node = $node->childNodes->item( $i );

			$this->collect_styles_recursive( $child_node );
		}
	}

	private function process_style( $string ) {
		// Filter properties
		$string = safecss_filter_attr( esc_html( $string ) );

		if ( ! $string ) {
			return array();
		}

		// Normalize order
		$styles = array_map( 'trim', explode( ';', $string ) );
		sort( $styles );

		$processed_styles = array();

		// Normalize whitespace and filter rules
		foreach ( $styles as $index => $rule ) {
			$arr2 = array_map( 'trim', explode( ':', $rule, 2 ) );
			if ( 2 !== count( $arr2 ) ) {
				continue;
			}

			list( $property, $value ) = $this->filter_style( $arr2[0], $arr2[1] );
			if ( empty( $property ) || empty( $value ) ) {
				continue;
			}

			$processed_styles[ $index ] = $property . ':' . $value;
		}

		return $processed_styles;
	}

	private function filter_style( $property, $value ) {
		// Handle overflow rule
		// https://www.ampproject.org/docs/reference/spec.html#properties
		if ( 0 === strpos( $property, 'overflow' )
			&& ( false !== strpos( $value, 'auto' ) || false !== strpos( $value, 'scroll' ) )
		) {
			return false;
		}

		if ( 'width' === $property ) {
			$property = 'max-width';
		}

		// !important is not allowed
		if ( false !== strpos( $value, 'important' ) ) {
			$value = preg_replace( '/\s*\!\s*important$/', '', $value );
		}

		return array( $property, $value );
	}

	private function generate_class_name( $data ) {
		$string = maybe_serialize( $data );
		return 'amp-wp-inline-' . md5( $string );
	}
}