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/**
 * A {@link Sink} with a stateful {@link SinkWriter}.
 *
 * <p>The {@link StatefulSink} needs to be serializable. All configuration should be validated
 * eagerly. The respective sink writers are transient and will only be created in the subtasks on
 * the taskmanagers.
 *
 * @param <InputT> The type of the sink's input
 * @param <WriterStateT> The type of the sink writer's state
 */
@PublicEvolving
public interface StatefulSink<InputT, WriterStateT> extends Sink<InputT> {

    /**
     * Create a {@link StatefulSinkWriter}.
     *
     * @param context the runtime context.
     * @return A sink writer.
     * @throws IOException for any failure during creation.
     */
    StatefulSinkWriter<InputT, WriterStateT> createWriter(InitContext context) throws IOException;

    /**
     * Create a {@link StatefulSinkWriter} from a recovered state.
     *
     * @param context the runtime context.
     * @return A sink writer.
     * @throws IOException for any failure during creation.
     */
    StatefulSinkWriter<InputT, WriterStateT> recoverWriterrestoreWriter(
            InitContext context, Collection<WriterStateT> recoveredState) throws IOException;

    /**
     * Any stateful sink needs to provide this state serializer and implement {@link
     * StatefulSinkWriter#snapshotState(long)} properly. The respective state is used in {@link
     * #recoverWriter(InitContext, Collection)} on recovery.
     *
     * @return the serializer of the writer's state type.
     */
    SimpleVersionedSerializer<WriterStateT> getWriterStateSerializer();

    interface StateCompatible {
        /**
         * A list of state names of sinks from which the state can be restored. For example, the new
         * {@code FileSink} can resume from the state of an old {@code StreamingFileSink} as a
         * drop-in replacement when resuming from a checkpoint/savepoint.
         */
        Collection<String> getCompatibleWriterStateNames();
    }

    /**
     * A {@link SinkWriter} whose state needs to be checkpointed.
     *
     * @param <InputT> The type of the sink writer's input
     * @param <WriterStateT> The type of the writer's state
     */
    @PublicEvolving
    interface StatefulSinkWriter<InputT, WriterStateT> extends SinkWriter<InputT> {
        /**
         * @return The writer's state.
         * @throws IOException if fail to snapshot writer's state.
         */
        Collection<WriterStateT> snapshotState(long checkpointId) throws IOException;
    }
}