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Java library to initiate VWo instance for server side a/b testing
There is a newer version: 1.66.0
package com.vwo.bucketing;

import com.vwo.enums.LoggerMessagesEnum;
import com.vwo.logger.LoggerManager;
import com.vwo.models.Campaign;
import com.vwo.models.Variation;
import javafx.util.Pair;

public class Bucketer {

  private static final LoggerManager LOGGER = LoggerManager.getLogger(Bucketer.class);

  private static final int MAX_TRAFFIC_VALUE = 10000;
  private static final int MAX_PERCENT_TRAFFIC = 100;
  private static final int MURMUR_HASH_SEED = 1;

  public static long getUserHashForCampaign(Campaign campaign, String userId) {
    int murmurHash = Murmur3.hash32(userId.getBytes(), 0, userId.length(), MURMUR_HASH_SEED);
    Long signedMurmurHash = (murmurHash & 0xFFFFFFFFL);
    int bucketValueOfUser = Bucketer.getBucketValueForUser(signedMurmurHash, MAX_PERCENT_TRAFFIC, 1);

    LOGGER.debug(LoggerMessagesEnum.DEBUG_MESSAGES.USER_HASH_BUCKET_VALUE.value(
        new Pair<>("bucketValue", String.valueOf(bucketValueOfUser)),
        new Pair<>("userId", userId),
        new Pair<>("hashValue", String.valueOf(signedMurmurHash))
    ));

    if (bucketValueOfUser > campaign.getPercentTraffic()) {
      LOGGER.debug(LoggerMessagesEnum.DEBUG_MESSAGES.USER_NOT_PART_OF_CAMPAIGN.value(new Pair<>("userId", userId), new Pair<>("campaignTestKey", campaign.getKey())));
      return -1;
    } else {
      return signedMurmurHash;
    }
  }

  private static int getBucketValueForUser(long murmurHash, int maxTrafficValue, double multiplier) {
    double ratio = (double) murmurHash / Math.pow(2, 32);
    int multipliedValue = (int) (ratio * maxTrafficValue * multiplier);
    return multipliedValue + 1;
  }

  public Variation bucketUserToVariation(Campaign campaign, String userId) {
    if (!campaign.getStatus().equalsIgnoreCase("RUNNING")) {
      LOGGER.error(LoggerMessagesEnum.ERROR_MESSAGES.CAMPAIGN_NOT_RUNNING.value());
      return null;
    }

    long murmurHash = Bucketer.getUserHashForCampaign(campaign, userId);

    if (murmurHash != -1) {
      double multiplier = ((double) MAX_TRAFFIC_VALUE) / campaign.getPercentTraffic() / 100;
      int bucketValueForVariation = Bucketer.getBucketValueForUser(murmurHash, MAX_TRAFFIC_VALUE, multiplier);

      LOGGER.debug(LoggerMessagesEnum.DEBUG_MESSAGES.VARIATION_HASH_BUCKET_VALUE.value(
          new Pair<>("bucketValue", String.valueOf(bucketValueForVariation)),
          new Pair<>("userId", userId),
          new Pair<>("campaignTestKey", campaign.getKey()),
          new Pair<>("traffic", String.valueOf(campaign.getPercentTraffic())),
          new Pair<>("hashValue", String.valueOf(murmurHash))
      ));

      for (Variation variation : campaign.getVariations()) {
        if (bucketValueForVariation >= variation.getStartRangeVariation() && bucketValueForVariation <= variation.getEndRangeVariation()) {
          return variation;
        }
      }

    }
    return null;
  }

}