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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package hivemall.knn.distance;

import hivemall.model.FeatureValue;
import hivemall.utils.hadoop.HiveUtils;

import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.hive.ql.exec.Description;
import org.apache.hadoop.hive.ql.exec.UDFArgumentException;
import org.apache.hadoop.hive.ql.metadata.HiveException;
import org.apache.hadoop.hive.ql.udf.UDFType;
import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;
import org.apache.hadoop.hive.serde2.objectinspector.ListObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;
import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;
import org.apache.hadoop.io.FloatWritable;

@Description(name = "euclid_distance",
        value = "_FUNC_(ftvec1, ftvec2) - Returns the square root of the sum of the squared differences"
                + ": sqrt(sum((x - y)^2))")
@UDFType(deterministic = true, stateful = false)
public final class EuclidDistanceUDF extends GenericUDF {

    private ListObjectInspector arg0ListOI, arg1ListOI;

    @Override
    public ObjectInspector initialize(ObjectInspector[] argOIs) throws UDFArgumentException {
        if (argOIs.length != 2) {
            throw new UDFArgumentException("euclid_distance takes 2 arguments");
        }
        this.arg0ListOI = HiveUtils.asListOI(argOIs[0]);
        this.arg1ListOI = HiveUtils.asListOI(argOIs[1]);

        return PrimitiveObjectInspectorFactory.writableFloatObjectInspector;
    }

    @Override
    public FloatWritable evaluate(DeferredObject[] arguments) throws HiveException {
        List ftvec1 = HiveUtils.asStringList(arguments[0], arg0ListOI);
        List ftvec2 = HiveUtils.asStringList(arguments[1], arg1ListOI);
        float d = (float) euclidDistance(ftvec1, ftvec2);
        return new FloatWritable(d);
    }

    public static double euclidDistance(final List ftvec1, final List ftvec2) {
        final FeatureValue probe = new FeatureValue();
        final Map map = new HashMap(ftvec1.size() * 2 + 1);
        for (String ft : ftvec1) {
            if (ft == null) {
                continue;
            }
            FeatureValue.parseFeatureAsString(ft, probe);
            float v1 = probe.getValueAsFloat();
            String f1 = probe.getFeature();
            map.put(f1, v1);
        }
        double d = 0.d;
        for (String ft : ftvec2) {
            if (ft == null) {
                continue;
            }
            FeatureValue.parseFeatureAsString(ft, probe);
            String f2 = probe.getFeature();
            float v2f = probe.getValueAsFloat();
            Float v1 = map.remove(f2);
            if (v1 == null) {
                d += (v2f * v2f);
            } else {
                float v1f = v1.floatValue();
                float diff = v1f - v2f;
                d += (diff * diff);
            }
        }
        for (Map.Entry e : map.entrySet()) {
            float v1f = e.getValue();
            d += (v1f * v1f);
        }
        return Math.sqrt(d);
    }

    @Override
    public String getDisplayString(String[] children) {
        return "euclid_distance(" + Arrays.toString(children) + ")";
    }

}