<?php

/**
 * Validates the HTML attribute style, otherwise known as CSS.
 * @note We don't implement the whole CSS specification, so it might be
 *       difficult to reuse this component in the context of validating
 *       actual stylesheet declarations.
 * @note If we were really serious about validating the CSS, we would
 *       tokenize the styles and then parse the tokens. Obviously, we
 *       are not doing that. Doing that could seriously harm performance,
 *       but would make these components a lot more viable for a CSS
 *       filtering solution.
 */
class HTMLPurifier_AttrDef_CSS extends HTMLPurifier_AttrDef {
	
	/**
	 *
	 * @param string $css        	
	 * @param HTMLPurifier_Config $config        	
	 * @param HTMLPurifier_Context $context        	
	 * @return bool|string
	 */
	public function validate($css, $config, $context) {
		$css = $this->parseCDATA ( $css );
		
		$definition = $config->getCSSDefinition ();
		
		// we're going to break the spec and explode by semicolons.
		// This is because semicolon rarely appears in escaped form
		// Doing this is generally flaky but fast
		// IT MIGHT APPEAR IN URIs, see HTMLPurifier_AttrDef_CSSURI
		// for details
		
		$declarations = explode ( ';', $css );
		$propvalues = array ();
		
		/**
		 * Name of the current CSS property being validated.
		 */
		$property = false;
		$context->register ( 'CurrentCSSProperty', $property );
		
		foreach ( $declarations as $declaration ) {
			if (! $declaration) {
				continue;
			}
			if (! strpos ( $declaration, ':' )) {
				continue;
			}
			list ( $property, $value ) = explode ( ':', $declaration, 2 );
			$property = trim ( $property );
			$value = trim ( $value );
			$ok = false;
			do {
				if (isset ( $definition->info [$property] )) {
					$ok = true;
					break;
				}
				if (ctype_lower ( $property )) {
					break;
				}
				$property = strtolower ( $property );
				if (isset ( $definition->info [$property] )) {
					$ok = true;
					break;
				}
			} while ( 0 );
			if (! $ok) {
				continue;
			}
			// inefficient call, since the validator will do this again
			if (strtolower ( trim ( $value ) ) !== 'inherit') {
				// inherit works for everything (but only on the base property)
				$result = $definition->info [$property]->validate ( $value, $config, $context );
			} else {
				$result = 'inherit';
			}
			if ($result === false) {
				continue;
			}
			$propvalues [$property] = $result;
		}
		
		$context->destroy ( 'CurrentCSSProperty' );
		
		// procedure does not write the new CSS simultaneously, so it's
		// slightly inefficient, but it's the only way of getting rid of
		// duplicates. Perhaps config to optimize it, but not now.
		
		$new_declarations = '';
		foreach ( $propvalues as $prop => $value ) {
			$new_declarations .= "$prop:$value;";
		}
		
		return $new_declarations ? $new_declarations : false;
	}
}

// vim: et sw=4 sts=4