/*
 * 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
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package hivemall.knn.similarity;

import hivemall.knn.distance.EuclidDistanceUDF;
import hivemall.utils.hadoop.HiveUtils;

import java.util.Arrays;
import java.util.List;

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_similarity",
        value = "_FUNC_(ftvec1, ftvec2) - Returns a euclid distance based similarity"
                + ", which is `1.0 / (1.0 + distance)`, of the given two vectors")
@UDFType(deterministic = true, stateful = false)
public final class EuclidSimilarity extends GenericUDF {

    private ListObjectInspector arg0ListOI, arg1ListOI;

    @Override
    public ObjectInspector initialize(ObjectInspector[] argOIs) throws UDFArgumentException {
        if (argOIs.length != 2) {
            throw new UDFArgumentException("euclid_similarity 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<String> ftvec1 = HiveUtils.asStringList(arguments[0], arg0ListOI);
        List<String> ftvec2 = HiveUtils.asStringList(arguments[1], arg1ListOI);
        float d = (float) EuclidDistanceUDF.euclidDistance(ftvec1, ftvec2);
        float sim = 1.0f / (1.0f + d);
        return new FloatWritable(sim);
    }

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

}