feat(indexing): support typed virtual stream routing

src/EventStore.Core.XUnit.Tests/Services/Storage/Indexing/IndexVirtualStreamReaderTests.cs

@@ -0,0 +1,69 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using EventStore.Core.Messages;
+using EventStore.Core.Services.Storage.Indexing;
+using Xunit;
+
+namespace EventStore.Core.XUnit.Tests.Services.Storage.Indexing;
+
+public class IndexVirtualStreamReaderTests
+{
+	[Fact]
+	public void constructor_rejects_missing_stream_id()
+	{
+		var exception = Assert.Throws<ArgumentNullException>(() => new TestIndexVirtualStreamReader(null!));
+
+		Assert.Equal("streamId", exception.ParamName);
+	}
+
+	[Fact]
+	public void exposes_stream_id()
+	{
+		var streamId = new IndexStreamId("$index-stream");
+		var reader = new TestIndexVirtualStreamReader(streamId);
+
+		Assert.Same(streamId, reader.StreamId);
+	}
+
+	[Fact]
+	public void can_read_stream_when_candidate_matches()
+	{
+		var reader = new TestIndexVirtualStreamReader(new IndexStreamId("$index-stream"));
+
+		Assert.True(reader.CanReadStream("$index-stream"));
+	}
+
+	[Fact]
+	public void cannot_read_stream_when_candidate_differs()
+	{
+		var reader = new TestIndexVirtualStreamReader(new IndexStreamId("$index-stream"));
+
+		Assert.False(reader.CanReadStream("other-stream"));
+	}
+
+	[Fact]
+	public void cannot_read_stream_when_candidate_is_null()
+	{
+		var reader = new TestIndexVirtualStreamReader(new IndexStreamId("$index-stream"));
+
+		Assert.False(reader.CanReadStream(null!));
+	}
+
+	private sealed class TestIndexVirtualStreamReader(IndexStreamId streamId) : IndexVirtualStreamReader(streamId)
+	{
+		public override ValueTask<ClientMessage.ReadStreamEventsForwardCompleted> ReadForwards(
+			ClientMessage.ReadStreamEventsForward msg,
+			CancellationToken token) =>
+			throw new NotSupportedException();
+
+		public override ValueTask<ClientMessage.ReadStreamEventsBackwardCompleted> ReadBackwards(
+			ClientMessage.ReadStreamEventsBackward msg,
+			CancellationToken token) =>
+			throw new NotSupportedException();
+
+		public override long GetLastEventNumber(string streamId) => throw new NotSupportedException();
+
+		public override long GetLastIndexedPosition(string streamId) => throw new NotSupportedException();
+	}
+}

src/EventStore.Core/Services/Storage/Indexing/IndexVirtualStreamReader.cs

@@ -0,0 +1,32 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using EventStore.Core.Messages;
+using EventStore.Core.Services.Storage.InMemory;
+
+namespace EventStore.Core.Services.Storage.Indexing;
+
+public abstract class IndexVirtualStreamReader : IVirtualStreamReader
+{
+	protected IndexVirtualStreamReader(IndexStreamId streamId)
+	{
+		ArgumentNullException.ThrowIfNull(streamId);
+		StreamId = streamId;
+	}
+
+	public IndexStreamId StreamId { get; }
+
+	public abstract ValueTask<ClientMessage.ReadStreamEventsForwardCompleted> ReadForwards(
+		ClientMessage.ReadStreamEventsForward msg,
+		CancellationToken token);
+
+	public abstract ValueTask<ClientMessage.ReadStreamEventsBackwardCompleted> ReadBackwards(
+		ClientMessage.ReadStreamEventsBackward msg,
+		CancellationToken token);
+
+	public abstract long GetLastEventNumber(string streamId);
+
+	public abstract long GetLastIndexedPosition(string streamId);
+
+	public bool CanReadStream(string streamId) => streamId == StreamId.Value;
+}