PHP_CodeSniffer sniff for CSS to find box model styles which can be optimised using shorthand

ShorthandBoxModelSniff.php

<?php

/**
 * Shorthand box model value sniffer
 *
 * @package SkylabCodeSniffer
 * @author  Jaik Dean
 **/

/**
 * Shorthand box model value sniffer
 *
 * @author Jaik Dean
 **/
class Skylab_Sniffs_CSS_ShorthandBoxModelSniff implements PHP_CodeSniffer_Sniff
{
    /**
     * A list of tokenizers this sniff supports.
     *
     * @var array
     **/
    public $supportedTokenizers = array('CSS');

    /**
     * A list of styles this rule applies to
     *
     * @var array
     **/
    protected $applicableStyles = array(
        'margin',
        'padding',
        'border-width',
        'border-color',
        'border-style',
    );

    /**
     * Returns the token types that this sniff is interested in.
     *
     * @return array(int)
     **/
    public function register()
    {
        return array(T_STYLE);
    }

    /**
     * Processes the tokens that this sniff is interested in.
     *
     * @param PHP_CodeSniffer_File $phpcsFile The file where the token was found.
     * @param int                  $stackPtr  The position in the stack where
     *                                        the token was found.
     *
     * @return void
     **/
    public function process(PHP_CodeSniffer_File $phpcsFile, $stackPtr)
    {
        $tokens = $phpcsFile->getTokens();

        // only apply to margin, padding and borders
        if (!in_array($tokens[$stackPtr]['content'], $this->applicableStyles)) {
            return;
        }

        // find the start and end of the value
        $valueStart = $phpcsFile->findNext(array(T_COLON, T_WHITESPACE), ($stackPtr + 1), null, true);
        $valueEnd   = $phpcsFile->findNext(array(T_SEMICOLON),           ($valueStart + 1));

        // concatenate the value into a string
        $value = '';
        for ($i = $valueStart; $i < $valueEnd; $i++) {
            $value .= $tokens[$i]['content'];
        }
        $value = trim($value);

        // exit if we don't have any whitespace to avoid expensive preg_match()ing
        if (!preg_match('/\\s/', $value)) {
            return;
        }

        // check if we aren't using the most compact shorthand
        $errorData = false;

        if (preg_match('/^([^\\s]+)(?:\\s+\\1){1,3}$/', $value, $matches)) {
            // one unique value
            $errorData = array(
                $matches[1],
                $value,
                $tokens[$stackPtr]['content'],
            );
        } elseif (preg_match('/^([^\\s]+)\\s+([^\\s]+)\\s+\\1(?:\\s+\\2)?$/', $value, $matches)) {
            // two unique values
            $errorData = array(
                $matches[1] . ' ' . $matches[2],
                $value,
                $tokens[$stackPtr]['content'],
            );
        } elseif (preg_match('/^([^\\s]+)\\s+([^\\s]+)\\s+([^\\s]+)\\s+\\2$/', $value, $matches)) {
            // three unique values
            $errorData = array(
                $matches[1] . ' ' . $matches[2] . ' ' . $matches[3],
                $value,
                $tokens[$stackPtr]['content'],
            );
        }

        if ($errorData !== false) {
            $phpcsFile->addError('Box model styles must be shorthand; expected "%s" but found "%s" (%s)', $i, 'Found', $errorData);
        }
    }
}