document writing event

Init.cs

using System.Collections.Generic;
using System.Globalization;
using Examine;
using Examine.LuceneEngine;
using Examine.LuceneEngine.Providers;
using ExamineContrib.Spatial.Model;
using Lucene.Net.Documents;
using Lucene.Net.Spatial.Tier.Projectors;
using Lucene.Net.Util;
using Umbraco.Core;

namespace ExamineContrib
{
    public class Init : IApplicationEventHandler
    {
        readonly Dictionary<int, CartesianTierPlotter> _plotters = new Dictionary<int, CartesianTierPlotter>();
        private readonly int _startTier;
        private readonly int _endTier;

        /// <summary>
        /// cartesian stuff nicked from 
        /// https://www.leapinggorilla.com/Blog/Read/1010/spatial-search-in-lucenenet---worked-example
        /// </summary>
        public Init()
        {

            IProjector projector = new SinusoidalProjector();
            var plotter = new CartesianTierPlotter(0, projector,
                                               Constants.Fields.LocationTierPrefix);

            _startTier = plotter.BestFit(Constants.MaxKms);
            _endTier = plotter.BestFit(Constants.MinKms);

            for (var tier = _startTier; tier <= _endTier; tier++)
            {
                _plotters.Add(tier, new CartesianTierPlotter(tier, projector, Constants.Fields.LocationTierPrefix));
            }
        }

        public void OnApplicationInitialized(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            
        }

        public void OnApplicationStarting(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            
        }

        public void OnApplicationStarted(UmbracoApplicationBase umbracoApplication, ApplicationContext applicationContext)
        {
            WireupSpatialInjection();
        }

        private void WireupSpatialInjection()
        {
            //note difference here compared to ExamineEvents line 33
            var locationIndexer = (SimpleDataIndexer)ExamineManager.Instance.IndexProviderCollection["TownIndexer"];

            locationIndexer.DocumentWriting += locationIndexer_DocumentWriting;
        }

        private void locationIndexer_DocumentWriting(object sender, DocumentWritingEventArgs e)
        {
            if (IsSpatialAndHasGeoCodeValues(e))
            {
                
                double latitude = double.Parse(e.Fields["latitude"], CultureInfo.InvariantCulture);
                double longitude = double.Parse(e.Fields["longitude"], CultureInfo.InvariantCulture);
                
                var location = new Location(e.NodeId,e.Fields["name"],new Coordinate(latitude,longitude));

                if (location.Coordinates != null)
                {
                    e.Document.Add(new Field(Constants.Fields.HasGeoCode, Constants.FieldFlags.HasField, Field.Store.NO, Field.Index.NOT_ANALYZED));
                    e.Document.Add(new Field(Constants.Fields.Latitude, NumericUtils.DoubleToPrefixCoded(location.Coordinates.Latitude), Field.Store.YES, Field.Index.NOT_ANALYZED));
                    e.Document.Add(new Field(Constants.Fields.Longitude, NumericUtils.DoubleToPrefixCoded(location.Coordinates.Longitude), Field.Store.YES, Field.Index.NOT_ANALYZED));

                    AddCartesianTiers(location.Coordinates, e.Document);

                }
            }
        }

        private static bool IsSpatialAndHasGeoCodeValues(DocumentWritingEventArgs e)
        {
            return e.Fields.ContainsKey("latitude") && !string.IsNullOrEmpty(e.Fields["longitude"]);
        }

        private void AddCartesianTiers(Coordinate cord, Document document)
        {

            for (var tier = _startTier; tier <= _endTier; tier++)
            {
                var ctp = _plotters[tier];
                var boxId = ctp.GetTierBoxId(cord.Latitude, cord.Longitude);
                document.Add(new Field(ctp.GetTierFieldName(),
                                NumericUtils.DoubleToPrefixCoded(boxId),
                                Field.Store.YES,
                                Field.Index.NOT_ANALYZED_NO_NORMS));
            }
        }
    }
}