PrefixTreeStrategy.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;
#if !NET35
using System.Collections.Concurrent;
#else
using Lucene.Net.Support.Compatibility;
#endif
using System.Collections.Generic;
using Lucene.Net.Analysis;
using Lucene.Net.Analysis.Tokenattributes;
using Lucene.Net.Documents;
using Lucene.Net.Search.Function;
using Lucene.Net.Spatial.Prefix.Tree;
using Lucene.Net.Spatial.Queries;
using Lucene.Net.Spatial.Util;
using Spatial4n.Core.Shapes;

namespace Lucene.Net.Spatial.Prefix
{
    /// <summary>
    /// Abstract SpatialStrategy which provides common functionality for those 
    /// Strategys which use {@link SpatialPrefixTree}s
    /// </summary>
    public abstract class PrefixTreeStrategy : SpatialStrategy
    {
        protected readonly SpatialPrefixTree grid;

        private readonly IDictionary<String, PointPrefixTreeFieldCacheProvider> provider =
            new ConcurrentDictionary<string, PointPrefixTreeFieldCacheProvider>();

        protected int defaultFieldValuesArrayLen = 2;
        protected double distErrPct = SpatialArgs.DEFAULT_DISTERRPCT; // [ 0 TO 0.5 ]

        protected PrefixTreeStrategy(SpatialPrefixTree grid, String fieldName)
            : base(grid.GetSpatialContext(), fieldName)
        {
            this.grid = grid;
        }

        /* Used in the in-memory ValueSource as a default ArrayList length for this field's array of values, per doc. */

        public void SetDefaultFieldValuesArrayLen(int defaultFieldValuesArrayLen)
        {
            this.defaultFieldValuesArrayLen = defaultFieldValuesArrayLen;
        }

        /// <summary>
        /// The default measure of shape precision affecting indexed and query shapes.
        /// Specific shapes at index and query time can use something different.
        /// @see org.apache.lucene.spatial.query.SpatialArgs#getDistErrPct()
        /// </summary>
        public double DistErrPct { get; set; }

        public override AbstractField[] CreateIndexableFields(Shape shape)
        {
            double distErr = SpatialArgs.CalcDistanceFromErrPct(shape, distErrPct, ctx);
            return CreateIndexableFields(shape, distErr);
        }

        public AbstractField[] CreateIndexableFields(Shape shape, double distErr)
        {
            int detailLevel = grid.GetLevelForDistance(distErr);
            var cells = grid.GetNodes(shape, detailLevel, true);//true=intermediates cells
            //If shape isn't a point, add a full-resolution center-point so that
            // PointPrefixTreeFieldCacheProvider has the center-points.
            // TODO index each center of a multi-point? Yes/no?
            if (!(shape is Point))
            {
                Point ctr = shape.GetCenter();
                //TODO should be smarter; don't index 2 tokens for this in CellTokenStream. Harmless though.
                cells.Add(grid.GetNodes(ctr, grid.GetMaxLevels(), false)[0]);
            }

            //TODO is CellTokenStream supposed to be re-used somehow? see Uwe's comments:
            //  http://code.google.com/p/lucene-spatial-playground/issues/detail?id=4

            return new AbstractField[]
                    {
                        new Field(GetFieldName(), new CellTokenStream(cells.GetEnumerator()))
                            {OmitNorms = true, OmitTermFreqAndPositions = true}
                    };
        }

        /// <summary>
        /// Outputs the tokenString of a cell, and if its a leaf, outputs it again with the leaf byte.
        /// </summary>
        protected class CellTokenStream : TokenStream
        {
            private ITermAttribute termAtt;
            private readonly IEnumerator<Node> iter;

            public CellTokenStream(IEnumerator<Node> tokens)
            {
                this.iter = tokens;
                Init();
            }

            private void Init()
            {
                termAtt = AddAttribute<ITermAttribute>();
            }

            private string nextTokenStringNeedingLeaf;

            public override bool IncrementToken()
            {
                ClearAttributes();
                if (nextTokenStringNeedingLeaf != null)
                {
                    termAtt.Append(nextTokenStringNeedingLeaf);
                    termAtt.Append((char)Node.LEAF_BYTE);
                    nextTokenStringNeedingLeaf = null;
                    return true;
                }
                if (iter.MoveNext())
                {
                    Node cell = iter.Current;
                    var token = cell.GetTokenString();
                    termAtt.Append(token);
                    if (cell.IsLeaf())
                        nextTokenStringNeedingLeaf = token;
                    return true;
                }
                return false;
            }

            protected override void Dispose(bool disposing)
            {
            }
        }

        public ShapeFieldCacheProvider<Point> GetCacheProvider()
        {
            PointPrefixTreeFieldCacheProvider p;
            if (!provider.TryGetValue(GetFieldName(), out p) || p == null)
            {
                lock (this)
                {//double checked locking idiom is okay since provider is threadsafe
                    if (!provider.ContainsKey(GetFieldName()))
                    {
                        p = new PointPrefixTreeFieldCacheProvider(grid, GetFieldName(), defaultFieldValuesArrayLen);
                        provider[GetFieldName()] = p;
                    }
                }
            }
            return p;
        }

        public override ValueSource MakeDistanceValueSource(Point queryPoint)
        {
            var p = (PointPrefixTreeFieldCacheProvider)GetCacheProvider();
            return new ShapeFieldCacheDistanceValueSource(ctx, p, queryPoint);
        }

        public SpatialPrefixTree GetGrid()
        {
            return grid;
        }
    }
}