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package se.leap.bitmaskclient.eip;
import java.util.Calendar;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.TreeMap;
public class GatewaySelector {
List<Gateway> gateways;
public GatewaySelector(List<Gateway> gateways) {
this.gateways = gateways;
}
public Gateway select() {
return closestGateway();
}
private Gateway closestGateway() {
TreeMap<Integer, Set<Gateway>> offsets = calculateOffsets();
return offsets.isEmpty() ? null : offsets.firstEntry().getValue().iterator().next();
}
private TreeMap<Integer, Set<Gateway>> calculateOffsets() {
TreeMap<Integer, Set<Gateway>> offsets = new TreeMap<Integer, Set<Gateway>>();
int localOffset = Calendar.getInstance().get(Calendar.ZONE_OFFSET) / 3600000;
for(Gateway gateway : gateways) {
int dist = timezoneDistance(localOffset, gateway.getTimezone());
Set<Gateway> set = (offsets.get(dist) != null) ?
offsets.get(dist) : new HashSet<Gateway>();
set.add(gateway);
offsets.put(dist, set);
}
return offsets;
}
private int timezoneDistance(int local_timezone, int remote_timezone) {
// Distance along the numberline of Prime Meridian centric, assumes UTC-11 through UTC+12
int dist = Math.abs(local_timezone - remote_timezone);
// Farther than 12 timezones and it's shorter around the "back"
if (dist > 12)
dist = 12 - (dist -12); // Well i'll be. Absolute values make equations do funny things.
return dist;
}
}
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