/*
 * 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.sysml.runtime.compress;

import org.apache.sysml.runtime.compress.utils.DblArray;
import org.apache.sysml.runtime.matrix.data.MatrixBlock;

/**
 * 
 * considers only a subset of row indexes
 */
public class ReaderColumnSelectionDenseSample extends ReaderColumnSelection 
{
	protected MatrixBlock _data;
	
	private int[] _sampleIndexes;
	private int lastIndex = -1;

	// reusable return
	private DblArray nonZeroReturn;
	private DblArray reusableReturn;
	private double[] reusableArr;

	public ReaderColumnSelectionDenseSample(MatrixBlock data, int[] colIndexes, int[] sampleIndexes, boolean skipZeros) 
	{
		super(colIndexes, -1, skipZeros);
		_data = data;
		_sampleIndexes = sampleIndexes;
		reusableArr = new double[colIndexes.length];
		reusableReturn = new DblArray(reusableArr);
	}

	@Override
	public DblArray nextRow() {
		if (_skipZeros) {
			while ((nonZeroReturn = getNextRow()) != null
					&& DblArray.isZero(nonZeroReturn));
			return nonZeroReturn;
		} else {
			return getNextRow();
		}
	}

	private DblArray getNextRow() {
		if (lastIndex == _sampleIndexes.length - 1)
			return null;
		lastIndex++;
		for (int i = 0; i < _colIndexes.length; i++) {
			reusableArr[i] = CompressedMatrixBlock.TRANSPOSE_INPUT ? 
					_data.quickGetValue(_colIndexes[i], _sampleIndexes[lastIndex]) :
					_data.quickGetValue(_sampleIndexes[lastIndex], _colIndexes[i]);
		}
		return reusableReturn;
	}

	@Override
	public int getCurrentRowIndex() {
		return _sampleIndexes[lastIndex];
	}
	
	@Override
	public void reset() {
		lastIndex = -1;
	}
}