MDL-55224 core: Import PHP-CSS-Parser into core

Part of MDL-55071

lib/php-css-parser/Property/Selector.php

@@ -0,0 +1,74 @@
+<?php
+
+namespace Sabberworm\CSS\Property;
+
+/**
+ * Class representing a single CSS selector. Selectors have to be split by the comma prior to being passed into this class.
+ */
+class Selector {
+
+	//Regexes for specificity calculations
+	const NON_ID_ATTRIBUTES_AND_PSEUDO_CLASSES_RX = '/
+	(\.[\w]+)                   # classes
+	|
+	\[(\w+)                     # attributes
+	|
+	(\:(                        # pseudo classes
+		link|visited|active
+		|hover|focus
+		|lang
+		|target
+		|enabled|disabled|checked|indeterminate
+		|root
+		|nth-child|nth-last-child|nth-of-type|nth-last-of-type
+		|first-child|last-child|first-of-type|last-of-type
+		|only-child|only-of-type
+		|empty|contains
+	))
+	/ix';
+
+	const ELEMENTS_AND_PSEUDO_ELEMENTS_RX = '/
+	((^|[\s\+\>\~]+)[\w]+   # elements
+	|
+	\:{1,2}(                # pseudo-elements
+		after|before|first-letter|first-line|selection
+	))
+	/ix';
+
+	private $sSelector;
+	private $iSpecificity;
+
+	public function __construct($sSelector, $bCalculateSpecificity = false) {
+		$this->setSelector($sSelector);
+		if ($bCalculateSpecificity) {
+			$this->getSpecificity();
+		}
+	}
+
+	public function getSelector() {
+		return $this->sSelector;
+	}
+
+	public function setSelector($sSelector) {
+		$this->sSelector = trim($sSelector);
+		$this->iSpecificity = null;
+	}
+
+	public function __toString() {
+		return $this->getSelector();
+	}
+
+	public function getSpecificity() {
+		if ($this->iSpecificity === null) {
+			$a = 0;
+			/// @todo should exclude \# as well as "#"
+			$aMatches = null;
+			$b = substr_count($this->sSelector, '#');
+			$c = preg_match_all(self::NON_ID_ATTRIBUTES_AND_PSEUDO_CLASSES_RX, $this->sSelector, $aMatches);
+			$d = preg_match_all(self::ELEMENTS_AND_PSEUDO_ELEMENTS_RX, $this->sSelector, $aMatches);
+			$this->iSpecificity = ($a * 1000) + ($b * 100) + ($c * 10) + $d;
+		}
+		return $this->iSpecificity;
+	}
+
+}