strbetween for PHP

/**
 * Extract a string inside of a larger string, case sensitive.
 *
 * @param string      $haystack
 * @param null|string $startStr
 * @param null|string $endStr
 * @param bool        $includeStart
 * @param bool        $includeEnd
 * @return string|false
 */
function strbetween(
    string $haystack,
    ?string $startStr,
    ?string $endStr = null,
    bool $includeStart = false,
    bool $includeEnd = false) : ?string
{
    if (empty($haystack))
        return '';

    if (empty($startStr))
        $start = 0;
    else
    {
        $startPos = strpos($haystack, $startStr, 0);
        if ($startPos === false)
            return null;
        $start = $startPos + ($includeStart ? 0 : strlen($startStr));
    }

    if (empty($endStr))
        $end = strlen($haystack);
    else
    {
        $endPos = strpos($haystack, $endStr, $start);
        if ($endPos === false)
            return null;
        $end = $endPos + ($includeEnd ? strlen($endStr) : 0);
    }

    return substr($haystack, $start, $end - $start);
}