/**                                                                                                                                                                                
 * Copyright (c) 2010 Yahoo! Inc. All rights reserved.                                                                                                                             
 *                                                                                                                                                                                 
 * Licensed 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. See accompanying                                                                                                                 
 * LICENSE file.                                                                                                                                                                   
 */

package com.yahoo.ycsb.generator;

import java.util.ArrayList;
import java.util.Collection;
import static java.util.Objects.requireNonNull;

import com.yahoo.ycsb.Utils;

/**
 * Generates a distribution by choosing from a discrete set of values.
 */
public class DiscreteGenerator extends Generator<String>
{
	private static class Pair
	{
		private double _weight;
		private String _value;

		Pair(double weight, String value)
		{
			_weight=weight;
			_value = requireNonNull(value);
		}
	}

	private final Collection<Pair> _values = new ArrayList<>();
	private String _lastvalue;

	public DiscreteGenerator()
	{
		_lastvalue=null;
	}

	/**
	 * Generate the next string in the distribution.
	 */
	@Override
    public String nextValue()
	{
		double sum=0;

		for (Pair p : _values)
		{
			sum+=p._weight;
		}

		double val=Utils.random().nextDouble();

		for (Pair p : _values)
		{
		    double pw = p._weight / sum;
			if (val < pw)
			{
				return p._value;
			}

			val -= pw;
		}

		throw new AssertionError("oops. should not get here.");

	}

	/**
	 * Return the previous string generated by the distribution; e.g., returned from the last nextString() call. 
	 * Calling lastString() should not advance the distribution or have any side effects. If nextString() has not yet 
	 * been called, lastString() should return something reasonable.
	 */
	@Override
    public String lastValue()
	{
		if (_lastvalue==null)
		{
			_lastvalue=nextValue();
		}
		return _lastvalue;
	}

	public void addValue(double weight, String value)
	{
		_values.add(new Pair(weight,value));
	}

}
