PHP parsing for Nagios/Icinga threshold values

parser.php

/**
 * Return a normalized threshold value (floats are converted to ints)
 *
 * @param string $thresh The threshold specification
 * @return string The normalized threshold
 * @throws Exception In case of invalid format
 */
function parse_threshold(string $thresh): string
{
    if (preg_match("/^[0-9]+$/", $thresh)) {
        verbose("Threshold $thresh is an integer", 3);

        return $thresh;
    }
    if (preg_match("/^([0-9]+)\.[0-9]+$/", $thresh, $matches)) {
        verbose("Threshold $thresh is a float, returning integer", 3);

        return $matches[1];
    }
    if (preg_match("/^(@?(?:[0-9]+|~))(?:\\.[0-9]+)?(?::(?:([0-9]+)(?:\\.[0-9]+)?)?)?$/", $thresh, $matches)) {
        verbose("Threshold $thresh is a range '$matches[1]' to '$matches[2]'", 3);
        if (count($matches) !== 3) {

            return $matches[1];
        }
        if ($matches[1] === "~" || $matches[1] < $matches[2]) {

            return "$matches[1]:$matches[2]";
        }
    }

    throw new Exception("Invalid threshold format $thresh");
}

/**
 * Checks to see if a value should trigger an alert based on a given threshold
 * The threshold specification looks like [@][start:][end]
 * 'start:end' means to alert if value is *outside* of the range
 * 'start:' means end is infinity, effectively alert if below start
 * 'end' means start is negative infinity, effectively alert if value is above end
 * '~:end' is the same as omitting start
 * a leading '@' means to invert the above definitions
 *
 * @see https://nagios-plugins.org/doc/guidelines.html#THRESHOLDFORMAT
 * @see https://icinga.com/docs/icinga-2/2.11/doc/05-service-monitoring/#threshold-ranges
 * @param string $thresh The threshold specification
 * @param string|int $val The numeric value to compare against
 * @return bool Whether or not an alert should be raised
 */
function compare_threshold(string $thresh, string|int $val): bool
{
    verbose("Evaluating '$thresh' with '$val'", 2);
    $inverse = false;
    $start = null;
    $end = null;
	if (str_starts_with($thresh, "@")) {
        $inverse = true;
        $thresh = trim($thresh, "@");
    }
    if (!str_contains($thresh, ":")) {
        $end = (int)$thresh;
    } else {
        $vals = explode(":", $thresh);
        $start = $vals[0] === "~" ? -INF : (int)$vals[0];
        $end = $vals[1] === "" ? INF : (int)$vals[1];
    }

    return $inverse
        ? $val <= $end && (is_null($start) || $val >= $start)
        : $val > $end || (!is_null($start) && $val < $start);
}

/**
 * Output debug data
 * @param string $message The message to output to stderr
 * @param int $level The verbosity level
 */
function verbose(string $message, int $level = 1): void
{
    global $verbose;
    if ($verbose >= $level) {
        file_put_contents("php://stderr", "$message\n");
    }
}