/*******************************************************************************
 * 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.nd4j.shade.jackson.annotation.JsonTypeInfo;

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

/**
 * A serializable object which implements a simple, efficient, serialization 
 * protocol, based on {@link DataInput} and {@link DataOutput}.
 *
 * <p>Any <code>key</code> or <code>value</code> type in the Hadoop Map-Reduce
 * framework implements this interface.</p>
 *
 * <p>Implementations typically implement a static <code>read(DataInput)</code>
 * method which constructs a new instance, calls {@link #readFields(DataInput)}
 * and returns the instance.</p>
 *
 * <p>Example:</p>
 * <p><blockquote><pre>
 *     public class MyWritable implements Writable {
 *       // Some data     
 *       private int counter;
 *       private long timestamp;
 *
 *       public void write(DataOutput out) throws IOException {
 *         out.writeInt(counter);
 *         out.writeLong(timestamp);
 *       }
 *
 *       public void readFields(DataInput in) throws IOException {
 *         counter = in.readInt();
 *         timestamp = in.readLong();
 *       }
 *
 *       public static MyWritable read(DataInput in) throws IOException {
 *         MyWritable w = new MyWritable();
 *         w.readFields(in);
 *         return w;
 *       }
 *     }
 * </pre></blockquote></p>
 */
@JsonTypeInfo(use = JsonTypeInfo.Id.CLASS, include = JsonTypeInfo.As.PROPERTY, property = "@class")
public interface Writable extends Serializable {
    /**
     * Serialize the fields of this object to <code>out</code>.
     *
     * @param out <code>DataOuput</code> to serialize this object into.
     * @throws IOException
     */
    void write(DataOutput out) throws IOException;

    /**
     * Deserialize the fields of this object from <code>in</code>.
     *
     * <p>For efficiency, implementations should attempt to re-use storage in the
     * existing object where possible.</p>
     *
     * @param in <code>DataInput</code> to deseriablize this object from.
     * @throws IOException
     */
    void readFields(DataInput in) throws IOException;

    /**
     * Write the type (a single short value) to the DataOutput. See {@link WritableFactory} for details.
     *
     * @param out DataOutput to write to
     * @throws IOException For errors during writing
     */
    void writeType(DataOutput out) throws IOException;

    /** Convert Writable to double. Whether this is supported depends on the specific writable. */
    double toDouble();

    /** Convert Writable to float. Whether this is supported depends on the specific writable. */
    float toFloat();

    /** Convert Writable to int. Whether this is supported depends on the specific writable. */
    int toInt();

    /** Convert Writable to long. Whether this is supported depends on the specific writable. */
    long toLong();

    /**
     * Get the type of the writable.
     * @return
     */
    WritableType getType();

}
