S2Manager.java

/*
 * Copyright 2010-2013 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 * 
 * http://aws.amazon.com/apache2.0
 * 
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.geo.s2.internal;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ConcurrentLinkedQueue;

import com.amazonaws.geo.model.GeoPoint;
import com.google.common.geometry.S2Cell;
import com.google.common.geometry.S2CellId;
import com.google.common.geometry.S2CellUnion;
import com.google.common.geometry.S2LatLng;
import com.google.common.geometry.S2LatLngRect;

public class S2Manager {

	public static S2CellUnion findCellIds(S2LatLngRect latLngRect) {

		ConcurrentLinkedQueue<S2CellId> queue = new ConcurrentLinkedQueue<S2CellId>();
		ArrayList<S2CellId> cellIds = new ArrayList<S2CellId>();

		for (S2CellId c = S2CellId.begin(0); !c.equals(S2CellId.end(0)); c = c.next()) {
			if (containsGeodataToFind(c, latLngRect)) {
				queue.add(c);
			}
		}

		processQueue(queue, cellIds, latLngRect);
		assert queue.size() == 0;
		queue = null;

		if (cellIds.size() > 0) {
			S2CellUnion cellUnion = new S2CellUnion();
			cellUnion.initFromCellIds(cellIds); // This normalize the cells.
			// cellUnion.initRawCellIds(cellIds); // This does not normalize the cells.
			cellIds = null;

			return cellUnion;
		}

		return null;
	}

	private static boolean containsGeodataToFind(S2CellId c, S2LatLngRect latLngRect) {
		if (latLngRect != null) {
			return latLngRect.intersects(new S2Cell(c));
		}

		return false;
	}

	private static void processQueue(ConcurrentLinkedQueue<S2CellId> queue, ArrayList<S2CellId> cellIds,
			S2LatLngRect latLngRect) {
		for (S2CellId c = queue.poll(); c != null; c = queue.poll()) {

			if (!c.isValid()) {
				break;
			}

			processChildren(c, latLngRect, queue, cellIds);
		}
	}

	private static void processChildren(S2CellId parent, S2LatLngRect latLngRect,
			ConcurrentLinkedQueue<S2CellId> queue, ArrayList<S2CellId> cellIds) {
		List<S2CellId> children = new ArrayList<S2CellId>(4);

		for (S2CellId c = parent.childBegin(); !c.equals(parent.childEnd()); c = c.next()) {
			if (containsGeodataToFind(c, latLngRect)) {
				children.add(c);
			}
		}

		/*
		 * TODO: Need to update the strategy!
		 * 
		 * Current strategy:
		 * 1 or 2 cells contain cellIdToFind: Traverse the children of the cell.
		 * 3 cells contain cellIdToFind: Add 3 cells for result.
		 * 4 cells contain cellIdToFind: Add the parent for result.
		 * 
		 * ** All non-leaf cells contain 4 child cells.
		 */
		if (children.size() == 1 || children.size() == 2) {
			for (S2CellId child : children) {
				if (child.isLeaf()) {
					cellIds.add(child);
				} else {
					queue.add(child);
				}
			}
		} else if (children.size() == 3) {
			cellIds.addAll(children);
		} else if (children.size() == 4) {
			cellIds.add(parent);
		} else {
			assert false; // This should not happen.
		}
	}

	public static long generateGeohash(GeoPoint geoPoint) {
		S2LatLng latLng = S2LatLng.fromDegrees(geoPoint.getLatitude(), geoPoint.getLongitude());
		S2Cell cell = new S2Cell(latLng);
		S2CellId cellId = cell.id();

		return cellId.id();
	}

	public static long generateHashKey(long geohash, int hashKeyLength) {
		if (geohash < 0) {
			// Counteract "-" at beginning of geohash.
			hashKeyLength++;
		}

		String geohashString = String.valueOf(geohash);
		long denominator = (long) Math.pow(10, geohashString.length() - hashKeyLength);
		return geohash / denominator;
	}
}