/*
 *  RapidMiner
 *
 *  Copyright (C) 2001-2011 by Rapid-I and the contributors
 *
 *  Complete list of developers available at our web site:
 *
 *       http://rapid-i.com
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see http://www.gnu.org/licenses/.
 */
package com.rapidminer.tools.math.function.aggregation;

import java.util.Map;
import java.util.TreeMap;

import com.rapidminer.example.Attribute;


/**
 * Calculates the (weighted) median of some values.
 * 
 * @author Tobias Malbrecht
 *
 */
public class MedianFunction extends AbstractAggregationFunction {

    private TreeMap<Double, Double> valueWeightMap = new TreeMap<Double, Double>();

    private double totalWeight;

    public MedianFunction() {
        this(DEFAULT_IGNORE_MISSINGS);
    }

    public MedianFunction(Boolean ignoreMissings) {
        super(ignoreMissings);
    }

    @Override
    public String getName() { return "median"; }

    @Override
    protected void reset() {
        foundMissing = false;
        totalWeight = 0;
        if (valueWeightMap != null) {
            valueWeightMap.clear();
        }
    }

    @Override
    public void update(double value, double weight) {
        if (Double.isNaN(value)) {
            foundMissing = true;
            return;
        }
        Double totalValueWeight = valueWeightMap.get(value);
        if (totalValueWeight != null) {
            totalValueWeight += weight;
        } else {
            totalValueWeight = new Double(weight);
        }
        valueWeightMap.put(value, totalValueWeight);
        totalWeight += weight;
    }

    @Override
    public void update(double value) {
        if (Double.isNaN(value)) {
            foundMissing = true;
            return;
        }
        Double totalValueWeight = valueWeightMap.get(value);
        if (totalValueWeight != null) {
            totalValueWeight++;
        } else {
            totalValueWeight = new Double(1);
        }
        valueWeightMap.put(value, totalValueWeight);
        totalWeight++;
    }

    @Override
    public double getValue() {
        if (foundMissing && !ignoreMissings) {
            return Double.NaN;
        }
        double valueWeightSum = 0;
        double lastValue = Double.NaN;
        double lastWeight = Double.NaN;
        // TODO: check weighted median calculation: Middle treatment seems suspicious. Sorted arrays might be much more memory efficient
        for (Map.Entry<Double, Double> entry : valueWeightMap.entrySet()) {
            if (!Double.isNaN(lastValue) && !Double.isNaN(lastWeight)) {
                double thisWeight = entry.getValue().doubleValue();
                return (lastValue * lastWeight + entry.getKey().doubleValue() * thisWeight) / (lastWeight + thisWeight);
            }
            valueWeightSum += entry.getValue().doubleValue();
            if (valueWeightSum > totalWeight / 2) {
                return entry.getKey().doubleValue();
            }
            // Now check for the case that we are EXACTLY on the middle. Then we have to average with the next value
            if (valueWeightSum == totalWeight / 2) {
                lastWeight = entry.getValue().doubleValue();
                lastValue = entry.getKey().doubleValue();
            }
        }
        return Double.NaN;
    }

    @Override
    public boolean supportsAttribute(Attribute attribute) {
        return attribute.isNumerical();
    }
}