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/*
 * Hibernate Search, full-text search for your domain model
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.search.spatial.impl;

import java.util.ArrayList;
import java.util.List;

import org.hibernate.search.spatial.Coordinates;

/**
 * Spatial fields, ids generator and geometric calculation methods for use in SpatialFieldBridge
 *
 * @author Nicolas Helleringer 
 * @author Mathieu Perez 
 * @see org.hibernate.search.spatial.SpatialFieldBridgeByHash
 * @see org.hibernate.search.spatial.SpatialFieldBridgeByRange
 */
public abstract class SpatialHelper {

	private static final double LOG2 = Math.log( 2 );

	/**
	 * Private constructor locking down utility class
	 */
	private SpatialHelper() { };

	/**
	 * Generate a Cell Index on one axis
	 *
	 * @param coordinate position to compute the Index for
	 * @param range range of the axis (-pi,pi)/(-90,90) => 2*pi/180 e.g
	 * @param spatialHashLevel Hox many time the range has been split in two
	 * @return the cell index on the axis
	 */
	public static int getCellIndex(double coordinate, double range, int spatialHashLevel) {
		return (int) Math.floor( Math.pow( 2, spatialHashLevel ) * coordinate / range );
	}

	/**
	 * Generate a spatial hash cell id (with both cell index on both dimension in it) for a position
	 *
	 * @param point position to compute the spatial hash cell id for
	 * @param spatialHashLevel Hox many time the dimensions have been split in two
	 * @return the cell id for the point at the given spatial hash level
	 */
	public static String getSpatialHashCellId(Point point, int spatialHashLevel) {
		double[] indexablesCoordinates = projectToIndexSpace( point );
		int longitudeCellIndex = getCellIndex(
				indexablesCoordinates[0],
				GeometricConstants.PROJECTED_LONGITUDE_RANGE,
				spatialHashLevel
		);
		int latitudeCellIndex = getCellIndex(
				indexablesCoordinates[1],
				GeometricConstants.PROJECTED_LATITUDE_RANGE,
				spatialHashLevel
		);
		return formatSpatialHashCellId( longitudeCellIndex, latitudeCellIndex );
	}

	/**
	 * Generate a spatial hash cell ids list covered by a bounding box
	 *
	 * @param lowerLeft lower left corner of the bounding box
	 * @param upperRight upper right corner of the bounding box
	 * @param spatialHashLevel spatial hash level of the wanted cell ids
	 * @return List of ids of the cells containing the point
	 */
	public static List getSpatialHashCellsIds(Point lowerLeft, Point upperRight, int spatialHashLevel) {
		double[] projectedLowerLeft = projectToIndexSpace( lowerLeft );
		int lowerLeftXIndex = getCellIndex(
				projectedLowerLeft[0],
				GeometricConstants.PROJECTED_LONGITUDE_RANGE,
				spatialHashLevel
		);
		int lowerLeftYIndex = getCellIndex(
				projectedLowerLeft[1],
				GeometricConstants.PROJECTED_LATITUDE_RANGE,
				spatialHashLevel
		);

		double[] projectedUpperRight = projectToIndexSpace( upperRight );
		int upperRightXIndex = getCellIndex(
				projectedUpperRight[0],
				GeometricConstants.PROJECTED_LONGITUDE_RANGE,
				spatialHashLevel
		);
		int upperRightYIndex = getCellIndex(
				projectedUpperRight[1],
				GeometricConstants.PROJECTED_LATITUDE_RANGE,
				spatialHashLevel
		);

		double[] projectedLowerRight = projectToIndexSpace( Point.fromDegrees( lowerLeft.getLatitude(), upperRight.getLongitude() ) );
		int lowerRightXIndex = getCellIndex(
				projectedLowerRight[0],
				GeometricConstants.PROJECTED_LONGITUDE_RANGE,
				spatialHashLevel
		);
		int lowerRightYIndex = getCellIndex(
				projectedLowerRight[1],
				GeometricConstants.PROJECTED_LATITUDE_RANGE,
				spatialHashLevel
		);

		double[] projectedUpperLeft = projectToIndexSpace( Point.fromDegrees( upperRight.getLatitude(), lowerLeft.getLongitude() ) );
		int upperLeftXIndex = getCellIndex(
				projectedUpperLeft[0],
				GeometricConstants.PROJECTED_LONGITUDE_RANGE,
				spatialHashLevel
		);
		int upperLeftYIndex = getCellIndex(
				projectedUpperLeft[1],
				GeometricConstants.PROJECTED_LATITUDE_RANGE,
				spatialHashLevel
		);

		final int startX = Math.min( Math.min( Math.min( lowerLeftXIndex, upperLeftXIndex ), upperRightXIndex ), lowerRightXIndex );
		final int endX = Math.max( Math.max( Math.max( lowerLeftXIndex, upperLeftXIndex ), upperRightXIndex ), lowerRightXIndex );

		final int startY = Math.min( Math.min( Math.min( lowerLeftYIndex, upperLeftYIndex ), upperRightYIndex ), lowerRightYIndex );
		final int endY = Math.max( Math.max( Math.max( lowerLeftYIndex, upperLeftYIndex ), upperRightYIndex ), lowerRightYIndex );

		List spatialHashCellsIds = new ArrayList( ( endX + 1 - startX ) * ( endY + 1 - startY ) );
		for ( int xIndex = startX; xIndex <= endX; xIndex++ ) {
			for ( int yIndex = startY; yIndex <= endY; yIndex++ ) {
				spatialHashCellsIds.add( formatSpatialHashCellId( xIndex, yIndex ) );
			}
		}

		return spatialHashCellsIds;
	}

	/**
	 * Generate a spatial hash cell ids list for the bounding box of a circular search area
	 *
	 * @param center center of the search area
	 * @param radius radius of the search area
	 * @param spatialHashLevel spatial hash level of the wanted cell ids
	 * @return List of the ids of the cells covering the bounding box of the given search discus
	 */
	public static List getSpatialHashCellsIds(Coordinates center, double radius, int spatialHashLevel) {

		Rectangle boundingBox = Rectangle.fromBoundingCircle( center, radius );

		double lowerLeftLatitude = boundingBox.getLowerLeft().getLatitude();
		double lowerLeftLongitude = boundingBox.getLowerLeft().getLongitude();
		double upperRightLatitude = boundingBox.getUpperRight().getLatitude();
		double upperRightLongitude = boundingBox.getUpperRight().getLongitude();

		if ( upperRightLongitude < lowerLeftLongitude ) { // Box cross the 180 meridian
			final List spatialHashCellsIds;
			spatialHashCellsIds = getSpatialHashCellsIds(
					Point.fromDegreesInclusive( lowerLeftLatitude, lowerLeftLongitude ),
					Point.fromDegreesInclusive( upperRightLatitude, GeometricConstants.LONGITUDE_DEGREE_RANGE / 2 ),
					spatialHashLevel
			);
			spatialHashCellsIds.addAll(
					getSpatialHashCellsIds(
							Point.fromDegreesInclusive(
									lowerLeftLatitude,
									GeometricConstants.LONGITUDE_DEGREE_RANGE / 2
								), Point.fromDegreesInclusive( upperRightLatitude, upperRightLongitude ), spatialHashLevel
					)
			);
			return spatialHashCellsIds;
		}
		else {
			return getSpatialHashCellsIds(
					Point.fromDegreesInclusive( lowerLeftLatitude, lowerLeftLongitude ),
					Point.fromDegreesInclusive( upperRightLatitude, upperRightLongitude ),
					spatialHashLevel
				);
		}
	}

	/**
	 * If point are searched at d distance from a point, a certain spatial hash cell level will problem spatial hash
	 * cell that are big enough to contain the search area but the smallest possible. By returning this level we ensure
	 * 4 spatial hash cell maximum will be needed to cover the search area (2 max on each axis because of search area
	 * crossing fixed bonds of the spatial hash cells)
	 *
	 * @param searchRange
	 *            search range to be covered by the spatial hash cells
	 * @return Return the best spatial hash level for a given search radius.
	 */
	public static int findBestSpatialHashLevelForSearchRange(double searchRange) {

		double iterations = GeometricConstants.EARTH_EQUATOR_CIRCUMFERENCE_KM / ( 2.0d * searchRange );

		return (int) Math.max( 0, Math.ceil( Math.log( iterations ) / LOG2 ) );
	}

	/**
	 * Project a degree latitude/longitude point into a sinusoidal projection planar space for spatial hash cell ids
	 * computation
	 *
	 * @param point
	 *            point to be projected
	 * @return array of projected coordinates
	 */
	public static double[] projectToIndexSpace(Point point) {
		double[] projectedCoordinates = new double[2];

		projectedCoordinates[0] = point.getLongitudeRad() * Math.cos( point.getLatitudeRad() );
		projectedCoordinates[1] = point.getLatitudeRad();

		return projectedCoordinates;
	}

	public static String formatFieldName(final int spatialHashLevel, final String fieldName) {
		return fieldName + "_HSSI_" + spatialHashLevel;
	}

	public static String formatLatitude(final String fieldName) {
		return fieldName + "_HSSI_Latitude";
	}

	public static String formatLongitude(final String fieldName) {
		return fieldName + "_HSSI_Longitude";
	}

	public static String formatSpatialHashCellId(final int xIndex, final int yIndex) {
		return xIndex + "|" + yIndex;
	}
}