solr/solrj/src/java/org/apache/solr/client/solrj/io/stream/metrics/CountDistinctMetric.java

/*
 * 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.stream.metrics;

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

import org.apache.solr.client.solrj.io.Tuple;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpression;
import org.apache.solr.client.solrj.io.stream.expr.StreamExpressionParameter;
import org.apache.solr.client.solrj.io.stream.expr.StreamFactory;

public class CountDistinctMetric extends Metric {

    public static final String COUNT_DISTINCT = "countDist";
    public static final String APPROX_COUNT_DISTINCT = "hll";

    private String columnName;

    public CountDistinctMetric(String columnName){
        this(columnName, false);
    }

    public CountDistinctMetric(String columnName, boolean isApproximate){
        init(isApproximate ? APPROX_COUNT_DISTINCT : COUNT_DISTINCT, columnName);
    }

    public CountDistinctMetric(StreamExpression expression, StreamFactory factory) throws IOException{
        // grab all parameters out
        String functionName = expression.getFunctionName();
        String columnName = factory.getValueOperand(expression, 0);


        // validate expression contains only what we want.
        if(null == columnName){
            throw new IOException(String.format(Locale.ROOT,"Invalid expression %s - expected %s(columnName)", expression, functionName));
        }

        init(functionName, columnName);
    }

    private void init(String functionName, String columnName){
        this.columnName = columnName;
        this.outputLong = true;
        setFunctionName(functionName);
        setIdentifier(functionName, "(", columnName, ")");
    }

    public void update(Tuple tuple) {
        //Nop for now
    }

    public Metric newInstance() {
        return new CountDistinctMetric(columnName);
    }

    public String[] getColumns() {
        return new String[]{columnName};
    }

    public Number getValue() {
        //No op for now
        return null;
    }

    @Override
    public StreamExpressionParameter toExpression(StreamFactory factory) throws IOException {
        return new StreamExpression(getFunctionName()).withParameter(columnName).withParameter(Boolean.toString(outputLong));
    }
}