SpatialPrefixTreeFactory.cs

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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.
 */

using System;
using System.Collections.Generic;
using Spatial4n.Core.Context;
using Spatial4n.Core.Distance;

namespace Lucene.Net.Spatial.Prefix.Tree
{
    /// <summary>
    /// Abstract Factory for creating {@link SpatialPrefixTree} instances with useful
    /// defaults and passed on configurations defined in a Map.
    /// </summary>
    public abstract class SpatialPrefixTreeFactory
    {
        private const double DEFAULT_GEO_MAX_DETAIL_KM = 0.001; //1m
        public static readonly String PREFIX_TREE = "prefixTree";
        public static readonly String MAX_LEVELS = "maxLevels";
        public static readonly String MAX_DIST_ERR = "maxDistErr";

        protected Dictionary<String, String> args;
        protected SpatialContext ctx;
        protected int? maxLevels;

        /// <summary>
        /// The factory  is looked up via "prefixTree" in args, expecting "geohash" or "quad".
        /// If its neither of these, then "geohash" is chosen for a geo context, otherwise "quad" is chosen.
        /// </summary>
        /// <param name="args"></param>
        /// <param name="ctx"></param>
        /// <returns></returns>
        public static SpatialPrefixTree MakeSPT(Dictionary<String, String> args, SpatialContext ctx)
        {
            SpatialPrefixTreeFactory instance;
            String cname;
            if (!args.TryGetValue(PREFIX_TREE, out cname) || cname == null)
                cname = ctx.IsGeo() ? "geohash" : "quad";
            if ("geohash".Equals(cname, StringComparison.InvariantCultureIgnoreCase))
                instance = new GeohashPrefixTree.Factory();
            else if ("quad".Equals(cname, StringComparison.InvariantCultureIgnoreCase))
                instance = new QuadPrefixTree.Factory();
            else
            {
                Type t = Type.GetType(cname);
                instance = (SpatialPrefixTreeFactory)Activator.CreateInstance(t);
            }
            instance.Init(args, ctx);
            return instance.NewSPT();
        }

        protected void Init(Dictionary<String, String> args, SpatialContext ctx)
        {
            this.args = args;
            this.ctx = ctx;
            InitMaxLevels();
        }

        protected void InitMaxLevels()
        {
            String mlStr;
            if (args.TryGetValue(MAX_LEVELS, out mlStr) && mlStr != null)
            {
                maxLevels = int.Parse(mlStr);
                return;
            }

            double degrees;
            if (!args.TryGetValue(MAX_DIST_ERR, out mlStr) || mlStr == null)
            {
                if (!ctx.IsGeo())
                    return; //let default to max
                degrees = DistanceUtils.Dist2Degrees(DEFAULT_GEO_MAX_DETAIL_KM, DistanceUtils.EARTH_MEAN_RADIUS_KM);
            }
            else
            {
                degrees = Double.Parse(mlStr);
            }
            maxLevels = GetLevelForDistance(degrees);
        }

        /* Calls {@link SpatialPrefixTree#getLevelForDistance(double)}. */
        protected abstract int GetLevelForDistance(double degrees);

        protected abstract SpatialPrefixTree NewSPT();

    }
}