/*
 * 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.commons.math.linear;

import org.apache.commons.math.Field;
import org.apache.commons.math.FieldElement;
import org.apache.commons.math.util.OpenIntToFieldHashMap;

/**
 * Sparse matrix implementation based on an open addressed map.
 * 
 * @param <T>
 *            the type of the field elements
 * @version $Revision: 762117 $ $Date: 2009-04-05 09:53:35 -0700 (Sun, 05 Apr
 *          2009) $
 * @since 2.0
 */
public class SparseFieldMatrix<T extends FieldElement<T>> extends AbstractFieldMatrix<T> {
	/**
	 * Serial id
	 */
	private static final long serialVersionUID = 9078068119297757342L;
	/** Storage for (sparse) matrix elements. */
	private final OpenIntToFieldHashMap<T> entries;
	/**
	 * row dimension
	 */
	private final int rowDimension;
	/**
	 * column dimension
	 */
	private final int columnDimension;

	/**
	 * Creates a matrix with no data.
	 * 
	 * @param field
	 *            field to which the elements belong
	 */
	public SparseFieldMatrix(final Field<T> field) {
		super(field);
		rowDimension = 0;
		columnDimension = 0;
		entries = new OpenIntToFieldHashMap<T>(field);
	}

	/**
	 * Create a new SparseFieldMatrix<T> with the supplied row and column
	 * dimensions.
	 *
	 * @param field
	 *            field to which the elements belong
	 * @param rowDimension
	 *            the number of rows in the new matrix
	 * @param columnDimension
	 *            the number of columns in the new matrix
	 * @throws IllegalArgumentException
	 *             if row or column dimension is not positive
	 */
	public SparseFieldMatrix(final Field<T> field, final int rowDimension, final int columnDimension)
			throws IllegalArgumentException {
		super(field, rowDimension, columnDimension);
		this.rowDimension = rowDimension;
		this.columnDimension = columnDimension;
		entries = new OpenIntToFieldHashMap<T>(field);
	}

	/**
	 * Copy constructor.
	 * 
	 * @param other
	 *            The instance to copy
	 */
	public SparseFieldMatrix(SparseFieldMatrix<T> other) {
		super(other.getField(), other.getRowDimension(), other.getColumnDimension());
		rowDimension = other.getRowDimension();
		columnDimension = other.getColumnDimension();
		entries = new OpenIntToFieldHashMap<T>(other.entries);
	}

	/**
	 * Generic copy constructor.
	 * 
	 * @param other
	 *            The instance to copy
	 */
	public SparseFieldMatrix(FieldMatrix<T> other) {
		super(other.getField(), other.getRowDimension(), other.getColumnDimension());
		rowDimension = other.getRowDimension();
		columnDimension = other.getColumnDimension();
		entries = new OpenIntToFieldHashMap<T>(getField());
		for (int i = 0; i < rowDimension; i++) {
			for (int j = 0; j < columnDimension; j++) {
				setEntry(i, j, other.getEntry(i, j));
			}
		}
	}

	/** {@inheritDoc} */
	@Override
	public void addToEntry(int row, int column, T increment) throws MatrixIndexException {
		checkRowIndex(row);
		checkColumnIndex(column);
		final int key = computeKey(row, column);
		final T value = entries.get(key).add(increment);
		if (getField().getZero().equals(value)) {
			entries.remove(key);
		} else {
			entries.put(key, value);
		}

	}

	/** {@inheritDoc} */
	@Override
	public FieldMatrix<T> copy() {
		return new SparseFieldMatrix<T>(this);
	}

	/** {@inheritDoc} */
	@Override
	public FieldMatrix<T> createMatrix(int rowDimension, int columnDimension) throws IllegalArgumentException {
		return new SparseFieldMatrix<T>(getField(), rowDimension, columnDimension);
	}

	/** {@inheritDoc} */
	@Override
	public int getColumnDimension() {
		return columnDimension;
	}

	/** {@inheritDoc} */
	@Override
	public T getEntry(int row, int column) throws MatrixIndexException {
		checkRowIndex(row);
		checkColumnIndex(column);
		return entries.get(computeKey(row, column));
	}

	/** {@inheritDoc} */
	@Override
	public int getRowDimension() {
		return rowDimension;
	}

	/** {@inheritDoc} */
	@Override
	public void multiplyEntry(int row, int column, T factor) throws MatrixIndexException {
		checkRowIndex(row);
		checkColumnIndex(column);
		final int key = computeKey(row, column);
		final T value = entries.get(key).multiply(factor);
		if (getField().getZero().equals(value)) {
			entries.remove(key);
		} else {
			entries.put(key, value);
		}

	}

	/** {@inheritDoc} */
	@Override
	public void setEntry(int row, int column, T value) throws MatrixIndexException {
		checkRowIndex(row);
		checkColumnIndex(column);
		if (getField().getZero().equals(value)) {
			entries.remove(computeKey(row, column));
		} else {
			entries.put(computeKey(row, column), value);
		}

	}

	/**
	 * Compute the key to access a matrix element
	 * 
	 * @param row
	 *            row index of the matrix element
	 * @param column
	 *            column index of the matrix element
	 * @return key within the map to access the matrix element
	 */
	private int computeKey(int row, int column) {
		return row * columnDimension + column;
	}

}
