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package water;

import water.fvec.*;
import water.serial.AutoBufferSerializer;

import java.util.Collections;
import java.util.List;

/** Iced, with a Key.  Support for DKV removal. */
public abstract class Keyed extends Iced {
  /** Key mapping a Value which holds this object; may be null  */
  public Key _key;
  public Keyed() { _key = null; } // NOTE: every Keyed that can come out of the REST API has to have a no-arg constructor.
  public Keyed( Key key ) { _key = key; }

  /** Remove this Keyed object, and all subparts; blocking. */
  public final void remove( ) { remove(new Futures()).blockForPending(); }
  /** Remove this Keyed object, and all subparts.  */
  public final Futures remove( Futures fs ) {
    if( _key != null ) DKV.remove(_key,fs);
    return remove_impl(fs);
  }

  /** Override to remove subparts, but not self, of composite Keyed objects.  
   *  Examples include {@link Vec} (removing associated {@link Chunk} keys)
   *  and {@link Frame} (removing associated {@link Vec} keys.) */
  protected Futures remove_impl( Futures fs ) { return fs; }

  /** Remove this Keyed object, and all subparts; blocking. */
  public static void remove( Key k ) {
    Value val = DKV.get(k);
    if( val==null ) return;
    ((Keyed)val.get()).remove();
  }
  /** Remove this Keyed object, and all subparts. */
  public static void remove( Key k, Futures fs ) {
    Value val = DKV.get(k);
    if( val==null ) return;
    ((Keyed)val.get()).remove(fs);
  }

  /**
   * High-quality 64-bit checksum of the content of the
   * object.  Similar to hashcode(), but a long to reduce the
   * chance of hash clashes.  For composite objects this should
   * be defined using the subcomponents' checksums (or hashcodes
   * if not available).  If two Keyed objects have the same
   * checksum() there should be a 1 - 1/2^64 chance that they
   * are the same object by value.
   */
  abstract protected long checksum_impl();
  private long _checksum;
  // Efficiently fetch the checksum, setting on first access
  public final long checksum() {
    if( _checksum!=0 ) return _checksum;
    long x = checksum_impl();
    if( x==0 ) x=1;
    return (_checksum=x);
  }

  protected static class BinarySerializer extends AutoBufferSerializer {
  }

  /** Returns a model serializer into AutoBuffer. */
  public AutoBufferSerializer getBinarySerializer() {
    return new BinarySerializer<>();
  }

  public static final List EMPTY_KEY_LIST = Collections.emptyList();

  /**
   * Returns a list of keys which are published by this object.
   * @return key list
   */
  public List getPublishedKeys() {
    return EMPTY_KEY_LIST;
  }
}