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A client library for Unleash
There is a newer version: 4.4.1
package no.finn.unleash.variant;

import java.util.List;
import java.util.Optional;
import java.util.function.Predicate;

import no.finn.unleash.FeatureToggle;
import no.finn.unleash.UnleashContext;
import no.finn.unleash.Variant;
import no.finn.unleash.strategy.StrategyUtils;

public final class VariantUtil {
    // Utility class
    private VariantUtil() {}

    private static Predicate overrideMatchesContext(UnleashContext context) {
        return (override) -> {
            Optional contextValue;
            switch (override.getContextName()) {
                case "userId": {
                    contextValue = context.getUserId();
                    break;
                } case "sessionId": {
                    contextValue = context.getSessionId();
                    break;
                } case "remoteAddress": {
                    contextValue = context.getRemoteAddress();
                    break;
                } default:
                    contextValue = Optional.ofNullable(context.getProperties().get(override.getContextName()));
                    break;
            }
            return override.getValues().contains(contextValue.orElse(""));
        };
    }

    private static Optional getOverride(List variants, UnleashContext context) {
        return variants.stream()
                .filter(variant -> variant.getOverrides().stream().anyMatch(overrideMatchesContext(context)))
                .findFirst();
    }

    private static String getIdentifier(UnleashContext context) {
        return context.getUserId()
                .orElse(context.getSessionId()
                .orElse(context.getRemoteAddress()
                .orElse(Double.toString(Math.random()))));
    }

    public static Variant selectVariant(FeatureToggle featureToggle, UnleashContext context, Variant defaultVariant) {
        List variants = featureToggle.getVariants();
        int totalWeight = variants.stream().mapToInt(VariantDefinition::getWeight).sum();
        if(totalWeight == 0) {
            return defaultVariant;
        }

        Optional variantOverride = getOverride(variants, context);
        if(variantOverride.isPresent()) {
            return variantOverride.get().toVariant();
        }

        int target = StrategyUtils.getNormalizedNumber(getIdentifier(context),featureToggle.getName(), totalWeight);

        int counter = 0;
        for (final VariantDefinition definition : featureToggle.getVariants()) {
            if (definition.getWeight() != 0) {
                counter += definition.getWeight();
                if (counter >= target) {
                    return definition.toVariant();
                }
            }
        }

        //Should not happen
        return defaultVariant;
    }
}