/*
 * 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 org.apache.solr.client.solrj.io.eval;

import org.apache.solr.client.solrj.io.eval.OneValueWorker;
import org.apache.solr.client.solrj.io.eval.RecursiveObjectEvaluator;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;

import org.apache.commons.math3.stat.StatUtils;

import java.io.IOException;
import java.util.List;
import java.util.Locale;

public class VarianceEvaluator extends RecursiveObjectEvaluator implements OneValueWorker {
    protected static final long serialVersionUID = 1L;

    public VarianceEvaluator(StreamExpression expression, StreamFactory factory) throws IOException {
        super(expression, factory);

        if(1 != containedEvaluators.size()){
            throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - expecting exactly 1 value but found %d",expression,containedEvaluators.size()));
        }
    }

    @Override
    public Object doWork(Object value) throws IOException{
        if(null == value){
            throw new IOException(String.format(Locale.ROOT, "Unable to find %s(...) because the value is null", constructingFactory.getFunctionName(getClass())));
        }
        else if(value instanceof List){
            List<Number> c = (List<Number>) value;
            double[] data = new double[c.size()];
            for(int i=0; i< c.size(); i++) {
                data[i] = c.get(i).doubleValue();
            }

            return StatUtils.variance(data);
        }
        else{
            throw new IOException(String.format(Locale.ROOT, "Unable to find %s(...) because the value is not a collection, instead a %s was found", constructingFactory.getFunctionName(getClass()), value.getClass().getSimpleName()));
        }
    }
}