class OneClassPerFileSniff

class OneClassPerFileSniff implements Sniff {
    
    /**
     * Returns an array of tokens this test wants to listen for.
     *
     * @return array<int|string>
     */
    public function register() {
        return [
            T_CLASS,
        ];
    }
    
    //end register()
    
    /**
     * Processes this sniff, when one of its tokens is encountered.
     *
     * @param \PHP_CodeSniffer\Files\File $phpcsFile The file being scanned.
     * @param int                         $stackPtr  The position of the current token in
     *                                               the stack passed in $tokens.
     *
     * @return void
     */
    public function process(File $phpcsFile, $stackPtr) {
        $tokens = $phpcsFile->getTokens();
        $start = $stackPtr + 1;
        if (isset($tokens[$stackPtr]['scope_closer']) === true) {
            $start = $tokens[$stackPtr]['scope_closer'] + 1;
        }
        $nextClass = $phpcsFile->findNext($this->register(), $start);
        if ($nextClass !== false) {
            $error = 'Only one class is allowed in a file';
            $phpcsFile->addError($error, $nextClass, 'MultipleFound');
        }
    }
    
    //end process()

}