lucene/spatial-extras/src/java/org/apache/lucene/spatial/prefix/tree/S2PrefixTreeCell.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 java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

import com.google.common.geometry.S2CellId;
import org.apache.lucene.util.BytesRef;
import org.locationtech.spatial4j.shape.Shape;
import org.locationtech.spatial4j.shape.SpatialRelation;

/**
 * This class represents a S2 pixel in the RPT.
 *
 * @lucene.internal
 */
class S2PrefixTreeCell implements CellCanPrune {

    //Faces of S2 Geometry
    private static S2CellId[] FACES = new S2CellId[6];

    static {
        FACES[0] = S2CellId.fromFacePosLevel(0, 0, 0);
        FACES[1] = S2CellId.fromFacePosLevel(1, 0, 0);
        FACES[2] = S2CellId.fromFacePosLevel(2, 0, 0);
        FACES[3] = S2CellId.fromFacePosLevel(3, 0, 0);
        FACES[4] = S2CellId.fromFacePosLevel(4, 0, 0);
        FACES[5] = S2CellId.fromFacePosLevel(5, 0, 0);
    }

    /*Special character to define a cell leaf*/
    private static final byte LEAF = '+';
    /*Tokens are used to serialize cells*/
    private static final byte[] TOKENS = {'.', '/', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
        'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'};
    /*Map containing mapping between tokens and integer values*/
    private static final Map<Byte, Integer> PIXELS;

    static {
        PIXELS = new HashMap<>(TOKENS.length);
        for (int i = 0; i < TOKENS.length; i++) {
            PIXELS.put(TOKENS[i], i);
        }
    }

    S2CellId cellId;
    int level; //cache level
    S2PrefixTree tree;

    SpatialRelation shapeRel = null;
    boolean isLeaf;
    Shape shape = null;

    S2PrefixTreeCell(S2PrefixTree tree, S2CellId cellId) {
        this.cellId = cellId;
        this.tree = tree;
        setLevel();
        if (getLevel() == tree.getMaxLevels()) {
            setLeaf();
        }
    }

    void readCell(S2PrefixTree tree, BytesRef ref) {
        isLeaf = false;
        shape = null;
        shapeRel = null;
        this.tree = tree;
        cellId = getS2CellIdFromBytesRef(ref);
        setLevel();
        if (isLeaf(ref) || getLevel() == tree.getMaxLevels()) {
            setLeaf();
        }
    }

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

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

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

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

    @Override
    public BytesRef getTokenBytesWithLeaf(BytesRef result) {
        result = getTokenBytesNoLeaf(result);
        //max levels do not have leaf
        if (isLeaf() && !(getLevel() == tree.getMaxLevels())) {
            //Add leaf byte
            result.bytes[result.offset + result.length] = LEAF;
            result.length++;
        }
        return result;
    }

    @Override
    public BytesRef getTokenBytesNoLeaf(BytesRef result) {
        if (result == null) {
            result = new BytesRef();
        }
        getBytesRefFromS2CellId(cellId, result);
        return result;
    }

    @Override
    public int getLevel() {
        return this.level;
    }

    /**
     * Cache level of cell.
     */
    private void setLevel() {
        if (this.cellId == null) {
            this.level = 0;
        } else {
            assert cellId.level() % tree.arity == 0;
            this.level = (this.cellId.level() / tree.arity) + 1;
        }
    }

    @Override
    public CellIterator getNextLevelCells(Shape shapeFilter) {
        S2CellId[] children;
        if (cellId == null) { // this is the world cell
            children = FACES;
        } else {
            int nChildren = (int) Math.pow(4, tree.arity);
            children = new S2CellId[nChildren];
            children[0] = cellId.childBegin(cellId.level() + tree.arity);
            for (int i = 1; i < nChildren; i++) {
                children[i] = children[i - 1].next();
            }
        }
        List<Cell> cells = new ArrayList<>(children.length);
        for (S2CellId pixel : children) {
            cells.add(new S2PrefixTreeCell(tree, pixel));
        }
        return new FilterCellIterator(cells.iterator(), shapeFilter);
    }

    @Override
    public Shape getShape() {
        if (shape == null) {
            if (cellId == null) { //World cell
                shape = tree.getSpatialContext().getWorldBounds();
            } else {
                shape = tree.s2ShapeFactory.getS2CellShape(cellId);
            }
        }
        return shape;
    }

    @Override
    public boolean isPrefixOf(Cell c) {
        if (cellId == null) {
            return true;
        }
        S2PrefixTreeCell cell = (S2PrefixTreeCell) c;
        return cellId.contains(cell.cellId);
    }

    @Override
    public int compareToNoLeaf(Cell fromCell) {
        if (cellId == null) {
            return 1;
        }
        S2PrefixTreeCell cell = (S2PrefixTreeCell) fromCell;
        return cellId.compareTo(cell.cellId);
    }

    /**
     * Check if a cell is a leaf.
     *
     * @param ref The Byteref of the leaf
     * @return true if it is a leaf, e.g last byte is the special Character.
     */
    private boolean isLeaf(BytesRef ref) {
        return (ref.bytes[ref.offset + ref.length - 1] == LEAF);
    }

    /**
     * Get the {@link S2CellId} from the {@link BytesRef} representation.
     *
     * @param ref The bytes.
     * @return the corresponding S2 cell.
     */
    private S2CellId getS2CellIdFromBytesRef(BytesRef ref) {
        int length = ref.length;
        if (isLeaf(ref)) {
            length--;
        }
        if (length == 0) {
            return null; //world cell
        }
        int face = PIXELS.get(ref.bytes[ref.offset]);
        S2CellId cellId = FACES[face];
        long id = cellId.id();
        for (int i = ref.offset + 1; i < ref.offset + length; i++) {
            int thisLevel = i - ref.offset;
            int pos = PIXELS.get(ref.bytes[i]);
            // first child at level
            id  = id - (id & -id) + (1L << (2 * (S2CellId.MAX_LEVEL -  thisLevel * tree.arity)));
            // next until pos
            id  = id + pos * ((id & -id) << 1);
        }
        return new S2CellId(id);
    }

    /**
     * Codify a {@link S2CellId} into its {@link BytesRef} representation.
     *
     * @param cellId The S2 Cell id to codify.
     * @param bref   The byteref representation.
     */
    private void getBytesRefFromS2CellId(S2CellId cellId, BytesRef bref) {
        if (cellId == null) {//world cell
            bref.length = 0;
            return;
        }
        int length = getLevel() + 1;
        byte[] b = bref.bytes.length >= length ? bref.bytes : new byte[length];
        b[0] = TOKENS[cellId.face()];
        for (int i = 1; i < getLevel(); i++) {
            int offset = 0;
            int level = tree.arity * i;
            for (int j = 1; j < tree.arity; j++) {
                offset = 4 * offset + cellId.childPosition(level - tree.arity + j);
            }
            b[i] = TOKENS[4 * offset + cellId.childPosition(level)];
        }
        bref.bytes = b;
        bref.length = getLevel();
        bref.offset = 0;
    }

    @Override
    public int getSubCellsSize() {
        if (cellId == null) { //root node
            return 6;
        }
        return  (int) Math.pow(4, tree.arity);
    }

    @Override
    public int hashCode() {
        if (cellId == null) {
            return super.hashCode();
        }
        return this.cellId.hashCode();
    }

    @Override
    public boolean equals(Object o) {
        S2PrefixTreeCell cell = (S2PrefixTreeCell) o;
        return Objects.equals(cellId, cell.cellId);
    }

    @Override
    public String toString() {
        if (cellId == null) {
            return "0";
        }
        return cellId.toString();
    }
}