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Advanced Spatial Shape Strategies for Apache Lucene
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/*
 * 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 java.util.Collection;
import org.apache.lucene.util.BytesRef;
import org.apache.lucene.util.StringHelper;
import org.locationtech.spatial4j.shape.Point;
import org.locationtech.spatial4j.shape.Shape;
import org.locationtech.spatial4j.shape.SpatialRelation;

/**
 * The base for the original two SPT's: Geohash and Quad. Don't subclass this for new SPTs.
 *
 * @lucene.internal
 */
// public for RPT pruneLeafyBranches code
public abstract class LegacyCell implements CellCanPrune {

  // Important: A LegacyCell doesn't share state for getNextLevelCells(), and
  //  LegacySpatialPrefixTree assumes this in its simplify tree logic.

  private static final byte LEAF_BYTE = '+'; // NOTE: must sort before letters & numbers

  // Arguably we could simply use a BytesRef, using an extra Object.
  protected byte[] bytes; // generally bigger to potentially hold a leaf
  protected int b_off;
  protected int b_len; // doesn't reflect leaf; same as getLevel()

  protected boolean isLeaf;

  /**
   * When set via getSubCells(filter), it is the relationship between this cell and the given shape
   * filter. Doesn't participate in shape equality.
   */
  protected SpatialRelation shapeRel;

  protected Shape shape; // cached

  /**
   * Warning: Refers to the same bytes (no copy). If {@link #setLeaf()} is subsequently called then
   * it may modify bytes.
   */
  protected LegacyCell(byte[] bytes, int off, int len) {
    this.bytes = bytes;
    this.b_off = off;
    this.b_len = len;
    readLeafAdjust();
  }

  protected void readCell(BytesRef bytes) {
    shapeRel = null;
    shape = null;
    this.bytes = bytes.bytes;
    this.b_off = bytes.offset;
    this.b_len = (short) bytes.length;
    readLeafAdjust();
  }

  protected void readLeafAdjust() {
    isLeaf = (b_len > 0 && bytes[b_off + b_len - 1] == LEAF_BYTE);
    if (isLeaf) b_len--;
    if (getLevel() == getMaxLevels()) isLeaf = true;
  }

  protected abstract SpatialPrefixTree getGrid();

  protected abstract int getMaxLevels();

  @Override
  public SpatialRelation getShapeRel() {
    return shapeRel;
  }

  @Override
  public void setShapeRel(SpatialRelation rel) {
    this.shapeRel = rel;
  }

  @Override
  public boolean isLeaf() {
    return isLeaf;
  }

  @Override
  public void setLeaf() {
    isLeaf = true;
  }

  @Override
  public BytesRef getTokenBytesWithLeaf(BytesRef result) {
    result = getTokenBytesNoLeaf(result);
    if (!isLeaf || getLevel() == getMaxLevels()) return result;
    if (result.bytes.length < result.offset + result.length + 1) {
      assert false : "Not supposed to happen; performance bug";
      byte[] copy = new byte[result.length + 1];
      System.arraycopy(result.bytes, result.offset, copy, 0, result.length - 1);
      result.bytes = copy;
      result.offset = 0;
    }
    result.bytes[result.offset + result.length++] = LEAF_BYTE;
    return result;
  }

  @Override
  public BytesRef getTokenBytesNoLeaf(BytesRef result) {
    if (result == null) return new BytesRef(bytes, b_off, b_len);
    result.bytes = bytes;
    result.offset = b_off;
    result.length = b_len;
    return result;
  }

  @Override
  public int getLevel() {
    return b_len;
  }

  @Override
  public CellIterator getNextLevelCells(Shape shapeFilter) {
    assert getLevel() < getGrid().getMaxLevels();
    if (shapeFilter instanceof Point) {
      LegacyCell cell = getSubCell((Point) shapeFilter);
      cell.shapeRel = SpatialRelation.CONTAINS;
      return new SingletonCellIterator(cell);
    } else {
      return new FilterCellIterator(getSubCells().iterator(), shapeFilter);
    }
  }

  /**
   * Performant implementations are expected to implement this efficiently by considering the
   * current cell's boundary.
   *
   * 
   *   Precondition: Never called when getLevel() == maxLevel.
   *   
Precondition: this.getShape().relate(p) != DISJOINT.
   * 
   */
  protected abstract LegacyCell getSubCell(Point p);

  /**
   * Gets the cells at the next grid cell level that covers this cell. Precondition: Never called
   * when getLevel() == maxLevel.
   *
   * @return A set of cells (no dups), sorted, modifiable, not empty, not null.
   */
  protected abstract Collection getSubCells();

  @Override
  public boolean isPrefixOf(Cell c) {
    // Note: this only works when each level uses a whole number of bytes.
    LegacyCell cell = (LegacyCell) c;
    boolean result = sliceEquals(cell.bytes, cell.b_off, cell.b_len, bytes, b_off, b_len);
    assert result
        == StringHelper.startsWith(c.getTokenBytesNoLeaf(null), getTokenBytesNoLeaf(null));
    return result;
  }

  /**
   * Copied from {@link org.apache.lucene.util.StringHelper#startsWith(BytesRef, BytesRef)} which
   * calls this. This is to avoid creating a BytesRef.
   */
  private static boolean sliceEquals(
      byte[] sliceToTest_bytes,
      int sliceToTest_offset,
      int sliceToTest_length,
      byte[] other_bytes,
      int other_offset,
      int other_length) {
    if (sliceToTest_length < other_length) {
      return false;
    }
    int i = sliceToTest_offset;
    int j = other_offset;
    final int k = other_offset + other_length;

    while (j < k) {
      if (sliceToTest_bytes[i++] != other_bytes[j++]) {
        return false;
      }
    }

    return true;
  }

  @Override
  public int compareToNoLeaf(Cell fromCell) {
    LegacyCell b = (LegacyCell) fromCell;
    return compare(bytes, b_off, b_len, b.bytes, b.b_off, b.b_len);
  }

  /** Copied from {@link BytesRef#compareTo(BytesRef)}. This is to avoid creating a BytesRef. */
  protected static int compare(
      byte[] aBytes, int aUpto, int a_length, byte[] bBytes, int bUpto, int b_length) {
    final int aStop = aUpto + Math.min(a_length, b_length);
    while (aUpto < aStop) {
      int aByte = aBytes[aUpto++] & 0xff;
      int bByte = bBytes[bUpto++] & 0xff;

      int diff = aByte - bByte;
      if (diff != 0) {
        return diff;
      }
    }

    // One is a prefix of the other, or, they are equal:
    return a_length - b_length;
  }

  @Override
  public boolean equals(Object obj) {
    // this method isn't "normally" called; just in asserts/tests
    if (obj instanceof Cell) {
      Cell cell = (Cell) obj;
      return getTokenBytesWithLeaf(null).equals(cell.getTokenBytesWithLeaf(null));
    } else {
      return false;
    }
  }

  @Override
  public int hashCode() {
    return getTokenBytesWithLeaf(null).hashCode();
  }

  @Override
  public String toString() {
    // this method isn't "normally" called; just in asserts/tests
    return getTokenBytesWithLeaf(null).utf8ToString();
  }
}