// calculation result
float cruise_time = 39.123;

DateTimeFormatter formatter = DateTimeFormatter.ISO_OFFSET_DATE_TIME;
OffsetDateTime departure_at = OffsetDateTime.parse(params.departure_at, formatter);
OffsetDateTime arrive_at = OffsetDateTime.from(departure_at).plusMinutes((long)cruise_time);
boolean is_available = true;

for(int i = 0; i < doc['unavailability'].length; i++) {
    if(doc['unavailability'][i].starts_at !== null) {
        OffsetDateTime starts_at = OffsetDateTime.parse(doc['unavailability'][i].starts_at, formatter);
        OffsetDateTime ends_at = OffsetDateTime.parse(doc['unavailability'][i].ends_at, formatter);

        if(
            (starts_at.isAfter(departure_at) && starts_at.isBefore(arrive_at))
            || (ends_at.isAfter(departure_at) && ends_at.isBefore(arrive_at))
            || (starts_at.isAfter(departure_at) && ends_at.isBefore(arrive_at))
            || (starts_at.isBefore(departure_at) && ends_at.isAfter(arrive_at))
        ) {
            is_available = false;
        }
    }
}

return is_available;