VariableCaseFixer.php

protected function applyFix(\SplFileInfo $file, Tokens $tokens)
{
    $predefinedVariables = [
        '$GLOBALS',
        '$_SERVER',
        '$_GET',
        '$_POST',
        '$_FILES',
        '$_REQUEST',
        '$_SESSION',
        '$_ENV',
        '$_COOKIE',
        '$php_errormsg',
        '$HTTP_RAW_POST_DATA',
        '$http_response_header',
        '$argc',
        '$argv'
    ];

    foreach ($tokens as $index => $token) {
        if ((T_VARIABLE === $token->getId()) || (T_STRING_VARNAME === $token->getId())) {
            if (in_array($token->getContent(), $predefinedVariables)) {
                continue;
            }
            $tokens[$index] = new Token([$token->getId(), $this->updateVariableCasing($token->getContent())]);
        }
    }
}

private function updateVariableCasing($variableName)
{
    if (self::CAMEL_CASE === $this->configuration['case']) {
        return $this->camelCase($variableName);
    }

    return $this->snakeCase($variableName);
}

private function camelCase($string)
{
    if(strtoupper($string) == $string){
        return $string;
    }

    $string = Preg::replace('/_/i', ' ', $string);
    $string = trim($string);
    // uppercase the first character of each word
    $string = ucwords($string);
    $string = str_replace(' ', '', $string);

    return lcfirst($string);
}

private function snakeCase($string, $separator = '_')
{
    if(strtoupper($string) == $string){
        return $string;
    }

    if(strtolower($string) == $string){
        return $string;
    }

    // insert separator between any letter and the beginning of a numeric chain
    $string = Preg::replace('/([a-z]+)([0-9]+)/i', '$1'.$separator.'$2', $string);
    // insert separator between any lower-to-upper-case letter chain
    $string = Preg::replace('/([a-z]+)([A-Z]+)/', '$1'.$separator.'$2', $string);
    // insert separator between the end of a numeric chain and the beginning of an alpha chain
    $string = Preg::replace('/([0-9]+)([a-z]+)/i', '$1'.$separator.'$2', $string);

    // Lowercase
    return strtolower($string);
}