CssVariableEvaluator.php
<?php
declare(strict_types=1);
namespace Automattic\WooCommerce\Vendor\Pelago\Emogrifier\HtmlProcessor;
use Automattic\WooCommerce\Vendor\Pelago\Emogrifier\Utilities\DeclarationBlockParser;
use Automattic\WooCommerce\Vendor\Pelago\Emogrifier\Utilities\Preg;
/**
* This class can evaluate CSS custom properties that are defined and used in inline style attributes.
*/
final class CssVariableEvaluator extends AbstractHtmlProcessor
{
/**
* temporary collection used by {@see replaceVariablesInDeclarations} and callee methods
*
* @var array<non-empty-string, string>
*/
private $currentVariableDefinitions = [];
/**
* Replaces all CSS custom property references in inline style attributes with their corresponding values where
* defined in inline style attributes (either from the element itself or the nearest ancestor).
*
* @return $this
*
* @throws \UnexpectedValueException
*/
public function evaluateVariables(): self
{
return $this->evaluateVariablesInElementAndDescendants($this->getHtmlElement(), []);
}
/**
* @param array<non-empty-string, string> $declarations
*
* @return array<non-empty-string, string>
*/
private function getVariableDefinitionsFromDeclarations(array $declarations): array
{
return \array_filter(
$declarations,
static function (string $key): bool {
return \substr($key, 0, 2) === '--';
},
ARRAY_FILTER_USE_KEY
);
}
/**
* Callback function for {@see replaceVariablesInPropertyValue} performing regular expression replacement.
*
* @param array<int, string> $matches
*/
private function getPropertyValueReplacement(array $matches): string
{
$variableName = $matches[1];
if (isset($this->currentVariableDefinitions[$variableName])) {
$variableValue = $this->currentVariableDefinitions[$variableName];
} else {
$fallbackValueSeparator = $matches[2] ?? '';
if ($fallbackValueSeparator !== '') {
$fallbackValue = $matches[3];
// The fallback value may use other CSS variables, so recurse
$variableValue = $this->replaceVariablesInPropertyValue($fallbackValue);
} else {
$variableValue = $matches[0];
}
}
return $variableValue;
}
/**
* Regular expression based on {@see https://stackoverflow.com/a/54143883/2511031 a StackOverflow answer}.
*/
private function replaceVariablesInPropertyValue(string $propertyValue): string
{
return (new Preg())->replaceCallback(
'/
var\\(
\\s*+
# capture variable name including `--` prefix
(
--[^\\s\\),]++
)
\\s*+
# capture optional fallback value
(?:
# capture separator to confirm there is a fallback value
(,)\\s*
# begin capture with named group that can be used recursively
(?<recursable>
# begin named group to match sequence without parentheses, except in strings
(?<noparentheses>
# repeated zero or more times:
(?:
# sequence without parentheses or quotes
[^\\(\\)\'"]++
|
# string in double quotes
"(?>[^"\\\\]++|\\\\.)*"
|
# string in single quotes
\'(?>[^\'\\\\]++|\\\\.)*\'
)*+
)
# repeated zero or more times:
(?:
# sequence in parentheses
\\(
# using the named recursable pattern
(?&recursable)
\\)
# sequence without parentheses, except in strings
(?&noparentheses)
)*+
)
)?+
\\)
/x',
\Closure::fromCallable([$this, 'getPropertyValueReplacement']),
$propertyValue
);
}
/**
* @param array<non-empty-string, string> $declarations
*
* @return ?array<non-empty-string, string> `null` is returned if no substitutions were made.
*/
private function replaceVariablesInDeclarations(array $declarations): ?array
{
$substitutionsMade = false;
$result = \array_map(
function (string $propertyValue) use (&$substitutionsMade): string {
$newPropertyValue = $this->replaceVariablesInPropertyValue($propertyValue);
if ($newPropertyValue !== $propertyValue) {
$substitutionsMade = true;
}
return $newPropertyValue;
},
$declarations
);
return $substitutionsMade ? $result : null;
}
/**
* @param array<non-empty-string, string> $declarations
*/
private function getDeclarationsAsString(array $declarations): string
{
$declarationStrings = \array_map(
static function (string $key, string $value): string {
return $key . ': ' . $value;
},
\array_keys($declarations),
\array_values($declarations)
);
return \implode('; ', $declarationStrings) . ';';
}
/**
* @param array<non-empty-string, string> $ancestorVariableDefinitions
*
* @return $this
*/
private function evaluateVariablesInElementAndDescendants(
\DOMElement $element,
array $ancestorVariableDefinitions
): self {
$style = $element->getAttribute('style');
// Avoid parsing declarations if none use or define a variable
if ((new Preg())->match('/(?<![\\w\\-])--[\\w\\-]/', $style) !== 0) {
$declarations = (new DeclarationBlockParser())->parse($style);
$variableDefinitions = $this->currentVariableDefinitions
= $this->getVariableDefinitionsFromDeclarations($declarations) + $ancestorVariableDefinitions;
$newDeclarations = $this->replaceVariablesInDeclarations($declarations);
if ($newDeclarations !== null) {
$element->setAttribute('style', $this->getDeclarationsAsString($newDeclarations));
}
} else {
$variableDefinitions = $ancestorVariableDefinitions;
}
foreach ($element->childNodes as $child) {
if ($child instanceof \DOMElement) {
$this->evaluateVariablesInElementAndDescendants($child, $variableDefinitions);
}
}
return $this;
}
}
