Add custom Examine FileSystemDirectoryFactory using Umbraco SiteName

src/Umbraco.Examine.Lucene/ConfigurationEnabledDirectoryFactory.cs

@@ -54,7 +54,7 @@ private IDirectoryFactory CreateFactory()
             case LuceneDirectoryFactory.SyncedTempFileSystemDirectoryFactory:
                 return _services.GetRequiredService<SyncedFileSystemDirectoryFactory>();
             case LuceneDirectoryFactory.TempFileSystemDirectoryFactory:
-                return _services.GetRequiredService<TempEnvFileSystemDirectoryFactory>();
+                return _services.GetRequiredService<UmbracoTempEnvFileSystemDirectoryFactory>();
             case LuceneDirectoryFactory.Default:
             default:
                 return _services.GetRequiredService<FileSystemDirectoryFactory>();

src/Umbraco.Examine.Lucene/DependencyInjection/UmbracoBuilderExtensions.cs

@@ -1,8 +1,10 @@
 using Examine;
 using Examine.Lucene.Directories;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.DependencyInjection.Extensions;
 using Umbraco.Cms.Core;
 using Umbraco.Cms.Core.DependencyInjection;
+using Umbraco.Cms.Core.Hosting;
 
 namespace Umbraco.Cms.Infrastructure.Examine.DependencyInjection;
 
@@ -22,8 +24,26 @@ public static IUmbracoBuilder AddExamineIndexes(this IUmbracoBuilder umbracoBuil
 
         services.AddExamine();
 
-        // Create the indexes
-        services
+        services.AddSingleton<UmbracoTempEnvFileSystemDirectoryFactory>();
+        services.RemoveAll<SyncedFileSystemDirectoryFactory>();
+        services.AddSingleton<SyncedFileSystemDirectoryFactory>(
+            s =>
+            {
+                var baseDir = s.GetRequiredService<IApplicationRoot>().ApplicationRoot;
+
+                var tempDir = UmbracoTempEnvFileSystemDirectoryFactory.GetTempPath(
+                    s.GetRequiredService<IApplicationIdentifier>(), s.GetRequiredService<IHostingEnvironment>());
+
+                return ActivatorUtilities.CreateInstance<SyncedFileSystemDirectoryFactory>(
+                    s,
+                    new object[]
+                    {
+                        new DirectoryInfo(tempDir), s.GetRequiredService<IApplicationRoot>().ApplicationRoot
+                    });
+            });
+
+    // Create the indexes
+    services
             .AddExamineLuceneIndex<UmbracoContentIndex, ConfigurationEnabledDirectoryFactory>(Constants.UmbracoIndexes
                 .InternalIndexName)
             .AddExamineLuceneIndex<UmbracoContentIndex, ConfigurationEnabledDirectoryFactory>(Constants.UmbracoIndexes

src/Umbraco.Examine.Lucene/UmbracoTempEnvFileSystemDirectoryFactory.cs

@@ -0,0 +1,36 @@
+using Examine;
+using Examine.Lucene.Directories;
+using IHostingEnvironment = Umbraco.Cms.Core.Hosting.IHostingEnvironment;
+
+namespace Umbraco.Cms.Infrastructure.Examine
+{
+    /// <summary>
+    /// Custom version of https://github.com/Shazwazza/Examine/blob/release/3.0/src/Examine.Lucene/Directories/TempEnvFileSystemDirectoryFactory.cs that includes the Umbraco SiteName property in the path hash
+    /// </summary>
+    public class UmbracoTempEnvFileSystemDirectoryFactory : FileSystemDirectoryFactory
+    {
+        public UmbracoTempEnvFileSystemDirectoryFactory(
+            IApplicationIdentifier applicationIdentifier,
+            ILockFactory lockFactory,
+            IHostingEnvironment hostingEnvironment)
+            : base(new DirectoryInfo(GetTempPath(applicationIdentifier, hostingEnvironment)), lockFactory)
+        {
+        }
+
+        public static string GetTempPath(IApplicationIdentifier applicationIdentifier, IHostingEnvironment hostingEnvironment)
+        {
+            var hashString = hostingEnvironment.SiteName + "::" + applicationIdentifier.GetApplicationUniqueIdentifier();
+            var appDomainHash = hashString.GenerateHash();
+
+            var cachePath = Path.Combine(
+                Path.GetTempPath(),
+                "ExamineIndexes",
+                //include the appdomain hash is just a safety check, for example if a website is moved from worker A to worker B and then back
+                // to worker A again, in theory the %temp%  folder should already be empty but we really want to make sure that its not
+                // utilizing an old index
+                appDomainHash);
+
+            return cachePath;
+        }
+    }
+}