lucene/spatial-extras/src/java/org/apache/lucene/spatial/prefix/tree/Cell.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://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.
 */
package org.apache.lucene.spatial.prefix.tree;

import org.apache.lucene.util.BytesRef;
import org.locationtech.spatial4j.shape.Shape;
import org.locationtech.spatial4j.shape.SpatialRelation;

/**
 * Represents a grid cell. Cell instances are generally very transient and may be re-used
 * internally. To get an instance, you could start with {@link SpatialPrefixTree#getWorldCell()}.
 * And from there you could either traverse down the tree with {@link
 * #getNextLevelCells(org.locationtech.spatial4j.shape.Shape)}, or you could read an indexed term
 * via {@link SpatialPrefixTree#readCell(org.apache.lucene.util.BytesRef,Cell)}. When a cell is read
 * from a term, it is comprised of just the base bytes plus optionally a leaf flag.
 *
 * @lucene.experimental
 */
public interface Cell {

  //  If we bring this back; perhaps do so as a method that un-shares its internal state: void
  // unshare();
  //  /** Resets the state of this cell such that it is identical to {@code source}. This can be
  // used for
  //   * cloning a cell to have a safe copy, and it also might be used to position this cell
  //   * before calling {@link #readCell(org.apache.lucene.util.BytesRef)} in a loop if you know the
  // first term
  //   * is going to be close to some other cell, thereby saving some computations. */
  //  void copyFrom(Cell source);

  /**
   * Gets the relationship this cell has with the shape from which it was filtered from, assuming it
   * came from a {@link CellIterator}. Arguably it belongs there but it's very convenient here.
   */
  SpatialRelation getShapeRel();

  /**
   * See {@link #getShapeRel()}.
   *
   * @lucene.internal
   */
  void setShapeRel(SpatialRelation rel);

  /**
   * Some cells are flagged as leaves, which are indexed as such. A leaf cell is either within some
   * shape or it both intersects and the cell is at an accuracy threshold such that no smaller cells
   * for the shape will be represented.
   */
  boolean isLeaf();

  /**
   * Set this cell to be a leaf. Warning: never call on a cell initialized to reference the same
   * bytes from termsEnum, which should be treated as immutable. Note: not supported at level 0.
   *
   * @lucene.internal
   */
  void setLeaf();

  /**
   * Returns the bytes for this cell, with a leaf byte <em>if this is a leaf cell</em>. The result
   * param is used to save object allocation, though its bytes aren't used.
   *
   * @param result where the result goes, or null to create new
   */
  BytesRef getTokenBytesWithLeaf(BytesRef result);

  /**
   * Returns the bytes for this cell, without a leaf set. The bytes should sort before {@link
   * #getTokenBytesWithLeaf(org.apache.lucene.util.BytesRef)}. The result param is used to save
   * object allocation, though its bytes aren't used.
   *
   * @param result where the result goes, or null to create new
   */
  BytesRef getTokenBytesNoLeaf(BytesRef result);

  /**
   * Level 0 is the world (and has no parent), from then on a higher level means a smaller cell than
   * the level before it.
   */
  int getLevel();

  /**
   * Gets the cells at the next grid cell level underneath this one, optionally filtered by {@code
   * shapeFilter}. The returned cells should have {@link #getShapeRel()} set to their relation with
   * {@code shapeFilter}. In addition, for non-points {@link #isLeaf()} must be true when that
   * relation is WITHIN.
   *
   * <p>IMPORTANT: Cells returned from this iterator can be shared, as well as the bytes.
   *
   * <p>Precondition: Never called when getLevel() == maxLevel.
   *
   * @param shapeFilter an optional filter for the returned cells.
   * @return A set of cells (no dups), sorted. Not Modifiable.
   */
  CellIterator getNextLevelCells(Shape shapeFilter);

  /** Gets the shape for this cell; typically a Rectangle. */
  Shape getShape();

  /**
   * Returns if the target term is within/underneath this cell; not necessarily a direct descendant.
   *
   * @param c the term
   */
  boolean isPrefixOf(Cell c);

  /**
   * Equivalent to {@code
   * this.getTokenBytesNoLeaf(null).compareTo(fromCell.getTokenBytesNoLeaf(null))}.
   */
  int compareToNoLeaf(Cell fromCell);
}