Creates an anonymous id for analytics specifically for play-services devices. This can be derived from advertising-id or even the fem token.

FirebaseId.java

import android.content.Context;
import android.support.annotation.Nullable;

import com.google.android.gms.ads.identifier.AdvertisingIdClient;
import com.google.android.gms.common.GooglePlayServicesNotAvailableException;
import com.google.android.gms.common.GooglePlayServicesRepairableException;
import com.google.firebase.iid.FirebaseInstanceId;

import java.io.IOException;

/**
 * Generates an ID for play-services powered devices
 */
public class FirebaseId extends Id {
    /**
     * Get an analytics ID for play-services powered devices, we will try the following
     * 1. get the advertising id if possible
     * 2. get the fcm token if possible
     * 3. get the UUID id
     * @param context
     * @return
     */
    @Override
    public String getId(final Context context) {
        // try to get an advertising id
        String adId = getAdvertisingIdIfApplicable(context);
        if (adId != null) return adId;
        // try to get the fcm token
        String firebaseToken = getFirebaseTokenIfPossible();
        if (firebaseToken != null) return firebaseToken;
        // get an id from UUID
        return getUUIDPoweredId();
    }

    /**
     * Get the advertising id if it is enabled
     * Found in play-services-basement
     * @param context
     * @return
     */
    @Nullable
    private String getAdvertisingIdIfApplicable(final Context context) {
        try {
            AdvertisingIdClient.Info info = AdvertisingIdClient.getAdvertisingIdInfo(context);
            if (info.isLimitAdTrackingEnabled()) {
                return info.getId();
            }
        } catch (IOException e) {
            e.printStackTrace();
        } catch (GooglePlayServicesNotAvailableException e) {
            e.printStackTrace();
        } catch (GooglePlayServicesRepairableException e) {
            e.printStackTrace();
        }
        return null;
    }

    /**
     * Get the FCM token if possible
     * @return
     */
    @Nullable
    private String getFirebaseTokenIfPossible() {
        try {
            return FirebaseInstanceId.getInstance().getToken();
        } catch (Exception exception) {
            exception.printStackTrace();
        }
        return null;
    }
}