/*
 * Copyright (c) 2013 DataTorrent, 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.
 */
package com.datatorrent.lib.stream;

import java.util.Collection;

import javax.validation.constraints.Min;

import com.datatorrent.api.Context.OperatorContext;
import com.datatorrent.api.DefaultInputPort;
import com.datatorrent.api.DefaultOutputPort;
import com.datatorrent.api.Operator;
import com.datatorrent.api.annotation.OperatorAnnotation;

/**
 * 
 * A base implementation of an operator that aggregates tuples.&nbsp; Subclasses should provide the 
   implementation to get a new collection of a given size. 
 * <p>
 * If size of collection is 0 then all tuples till end window are aggregated, otherwise collection is emitted as
 * soon as collection size reaches to given size. <br>
 * <br>
 * <b>StateFull : Yes </b>, values are collected over application window. <br>
 * <b>Partitions : No</b>, will yield wrong results.
 * @displayName: Abstract Aggregator
 * @category: stream
 * @tag: aggregate
 * @param <T>
 *          Aggregate tuple type.
 * @since 0.3.3
 */
@OperatorAnnotation(partitionable = false)
public abstract class AbstractAggregator<T> implements Operator
{
	/**
	 * collection of input values.
	 */
	protected Collection<T> collection;
	@Min(0)
	/**
	 * size of output collection, all tuples till end window if set to 0.
	 */
	private int size = 0;

	/**
	 * Input port that takes data to be added to a collection.
	 */
	public final transient DefaultInputPort<T> input = new DefaultInputPort<T>()
	{
		@Override
		public void process(T tuple)
		{
			if (collection == null) {
				collection = getNewCollection(size);
			}
			collection.add(tuple);
			if (collection.size() == size) {
				output.emit(collection);
				collection = null;
			}
		}

	};

	/**
	 * Output port that emits a collection.
	 */
	public final transient DefaultOutputPort<Collection<T>> output = new DefaultOutputPort<Collection<T>>();

	/**
	 * Set the size of the collection.
	 * 
	 * If set to zero, the collection collects all the tuples within a window and
	 * emits the collection as 1 output tuple at the end of the window. If set to
	 * positive value, it collects the collection as soon as the size of the
	 * collection reaches the size.
	 * 
	 * @param size
	 *          the size to set
	 */
	public void setSize(int size)
	{
		this.size = size;
	}

	/**
	 * Size of collection.
	 * 
	 * @return size of collection
	 */
	@Min(0)
	public int getSize()
	{
		return size;
	}

	/**
	 * Abstract method to get collection of given size.
	 * 
	 * @param size
	 * @return collection
	 */
	public abstract Collection<T> getNewCollection(int size);

	@Override
	public void beginWindow(long windowId)
	{
	}

	@Override
	public void endWindow()
	{
		if (size == 0 && collection != null) {
			output.emit(collection);
			collection = null;
		}
	}

	@Override
	public void setup(OperatorContext context)
	{
	}

	@Override
	public void teardown()
	{
	}
}