protected function getFilesFromDirectory(string $mappingDirectory): array
    {
        $mappingPaths = [];

        $filePattern = \sprintf('/^.+\.(%s)$/i', \implode('|', $this->extensions));
        $recursiveIterator = new \RecursiveIteratorIterator(new \RecursiveDirectoryIterator($mappingDirectory));
        $regexIterator = new \RegexIterator($recursiveIterator, $filePattern, \RecursiveRegexIterator::GET_MATCH);

        foreach ($regexIterator as $mappingFile) {
            $mappingPaths[] = $mappingFile[0];
        }

        \sort($mappingPaths);

        return $mappingPaths;
    }