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/*******************************************************************************
 * Copyright (c) 2015-2018 Skymind, Inc.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Apache License, Version 2.0 which is available at
 * https://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.
 *
 * SPDX-License-Identifier: Apache-2.0
 ******************************************************************************/

package org.datavec.api.writable;

import org.datavec.api.io.WritableComparable;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

/**
 * NullWritable. Typically only used in very limited circumstances, to signify that a value is missing.
 * Attempts to convert the NullWritable to some other value (using toInt(), toDouble() etc) will result in an
 * UnsupportedOperationException being thrown
 */
public class NullWritable implements WritableComparable {

    public static final NullWritable INSTANCE = new NullWritable();


    @Override
    public int compareTo(Object o) {
        if (this == o)
            return 0;
        if (!(o instanceof NullWritable))
            throw new IllegalArgumentException("Cannot compare NullWritable to " + o.getClass());
        return 0;
    }

    public boolean equals(Object o) {
        return o instanceof NullWritable;
    }

    @Override
    public void write(DataOutput out) throws IOException {
        //No op
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        //No op
    }

    @Override
    public void writeType(DataOutput out) throws IOException {
        out.writeShort(WritableType.Null.typeIdx());
    }

    @Override
    public double toDouble() {
        throw new UnsupportedOperationException("Cannot convert NullWritable to other values");
    }

    @Override
    public float toFloat() {
        throw new UnsupportedOperationException("Cannot convert NullWritable to other values");
    }

    @Override
    public int toInt() {
        throw new UnsupportedOperationException("Cannot convert NullWritable to other values");
    }

    @Override
    public long toLong() {
        throw new UnsupportedOperationException("Cannot convert NullWritable to other values");
    }

    @Override
    public WritableType getType() {
        return WritableType.Null;
    }

    @Override
    public String toString() {
        return "NullWritable";
    }
}