/*
 * This file is part of ELKI:
 * Environment for Developing KDD-Applications Supported by Index-Structures
 *
 * Copyright (C) 2022
 * ELKI Development Team
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
package elki.clustering.optics;

import elki.database.ids.DBID;
import elki.database.ids.DBIDUtil;

/**
 * Entry in the priority heap.
 * 
 * @author Elke Achtert
 * @since 0.1
 */
public class OPTICSHeapEntry implements Comparable<OPTICSHeapEntry> {
  /**
   * The id of the entry.
   */
  DBID objectID;

  /**
   * The id of the entry's predecessor.
   */
  DBID predecessorID;

  /**
   * The reachability of the entry.
   */
  double reachability;

  /**
   * Creates a new entry in a cluster order with the specified parameters.
   * 
   * @param objectID the id of the entry
   * @param predecessorID the id of the entry's predecessor
   * @param reachability the reachability of the entry
   */
  public OPTICSHeapEntry(DBID objectID, DBID predecessorID, double reachability) {
    this.objectID = objectID;
    this.predecessorID = predecessorID;
    this.reachability = reachability;
  }

  /**
   * Indicates whether some other object is "equal to" this one.
   * <p>
   * NOTE: for the use in an UpdatableHeap, only the ID is compared!
   * <p>
   * @param o the reference object with which to compare.
   * @return <code>true</code> if this object has the same attribute values as
   *         the o argument; <code>false</code> otherwise.
   */
  @Override
  public boolean equals(Object o) {
    return this == o || (o instanceof OPTICSHeapEntry) && DBIDUtil.equal(objectID, ((OPTICSHeapEntry) o).objectID);
  }

  /**
   * Returns a hash code value for the object.
   * 
   * @return the object id if this entry
   */
  @Override
  public int hashCode() {
    return objectID.hashCode();
  }

  /**
   * Returns a string representation of the object.
   * 
   * @return a string representation of the object.
   */
  @Override
  public String toString() {
    return objectID + "(" + predecessorID + "," + reachability + ")";
  }

  @Override
  public int compareTo(OPTICSHeapEntry o) {
    return this.reachability < o.reachability ? -1 : //
        this.reachability > o.reachability ? +1 : //
            DBIDUtil.compare(objectID, o.objectID);
  }
}
