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feat(discovery): add ParticipantTracker with rename heuristic
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Zac Gaetano 2026-05-07 15:13:42 +00:00
parent c07a668672
commit cef9018b6d
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104
src/TeamsISO.Engine/Discovery/ParticipantTracker.cs Normal file
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using TeamsISO.Engine.Domain;
namespace TeamsISO.Engine.Discovery;
/// <summary>
/// Maintains the operator-facing participant list, applying the rename heuristic
/// from the v1 spec: if a participant source disappears and another participant
/// source with the same MachineName appears within <see cref="_renameWindow"/>,
/// the existing <see cref="Participant.Id"/> transfers to the new source.
/// </summary>
public sealed class ParticipantTracker
{
private readonly TimeSpan _renameWindow;
private readonly Func<DateTimeOffset> _now;
private readonly List<MutableParticipant> _participants = new();
private readonly List<RecentlyRemoved> _recentlyRemoved = new();
public ParticipantTracker(TimeSpan renameWindow, Func<DateTimeOffset> now)
{
_renameWindow = renameWindow;
_now = now;
}
public IReadOnlyList<Participant> Participants =>
_participants.Select(m => m.ToRecord()).ToList();
public void Apply(DiscoveryEvent ev)
{
switch (ev)
{
case DiscoveryEvent.Added a when a.Source.Kind == NdiSourceKind.Participant:
HandleAdded(a.Source);
break;
case DiscoveryEvent.Removed r when r.Source.Kind == NdiSourceKind.Participant:
HandleRemoved(r.Source);
break;
}
}
private void HandleAdded(NdiSource source)
{
var now = _now();
PruneRecentlyRemoved(now);
var match = _recentlyRemoved.FirstOrDefault(rr => rr.MachineName == source.MachineName);
if (match is not null)
{
var existing = _participants.First(p => p.Id == match.Id);
existing.DisplayName = source.DisplayName!;
existing.CurrentSource = source;
existing.LastSeen = now;
_recentlyRemoved.Remove(match);
return;
}
_participants.Add(new MutableParticipant(
Id: Guid.NewGuid(),
DisplayName: source.DisplayName!,
CurrentSource: source,
FirstSeen: now,
LastSeen: now));
}
private void HandleRemoved(NdiSource source)
{
var now = _now();
var existing = _participants.FirstOrDefault(p =>
p.CurrentSource is not null && p.CurrentSource.FullName == source.FullName);
if (existing is null)
return;
existing.CurrentSource = null;
_recentlyRemoved.Add(new RecentlyRemoved(existing.Id, source.MachineName, now));
}
private void PruneRecentlyRemoved(DateTimeOffset now)
{
_recentlyRemoved.RemoveAll(rr => now - rr.RemovedAt > _renameWindow);
}
private sealed class MutableParticipant
{
public Guid Id { get; init; }
public string DisplayName { get; set; }
public NdiSource? CurrentSource { get; set; }
public DateTimeOffset FirstSeen { get; init; }
public DateTimeOffset LastSeen { get; set; }
public MutableParticipant(Guid Id, string DisplayName, NdiSource? CurrentSource,
DateTimeOffset FirstSeen, DateTimeOffset LastSeen)
{
this.Id = Id;
this.DisplayName = DisplayName;
this.CurrentSource = CurrentSource;
this.FirstSeen = FirstSeen;
this.LastSeen = LastSeen;
}
public Participant ToRecord() =>
new(Id, DisplayName, CurrentSource, FirstSeen, LastSeen);
}
private sealed record RecentlyRemoved(Guid Id, string MachineName, DateTimeOffset RemovedAt);
}

103
src/tests/TeamsISO.Engine.Tests/Discovery/ParticipantTrackerTests.cs Normal file
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using TeamsISO.Engine.Discovery;
using TeamsISO.Engine.Domain;
namespace TeamsISO.Engine.Tests.Discovery;
public class ParticipantTrackerTests
{
private static NdiSource Source(string machine, string display) =>
new($"{machine} (Teams - {display})", machine, NdiSourceKind.Participant, display);
private static DateTimeOffset T0 => DateTimeOffset.UnixEpoch;
[Fact]
public void Added_CreatesParticipant()
{
var tracker = new ParticipantTracker(renameWindow: TimeSpan.FromSeconds(5), now: () => T0);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane")));
tracker.Participants.Should().HaveCount(1);
var p = tracker.Participants[0];
p.DisplayName.Should().Be("Jane");
p.CurrentSource!.MachineName.Should().Be("PC1");
}
[Fact]
public void Removed_NullsCurrentSourceButKeepsParticipant()
{
var time = T0;
var tracker = new ParticipantTracker(TimeSpan.FromSeconds(5), () => time);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane")));
time = T0.AddSeconds(1);
tracker.Apply(new DiscoveryEvent.Removed(Source("PC1", "Jane")));
tracker.Participants.Should().HaveCount(1);
tracker.Participants[0].CurrentSource.Should().BeNull();
}
[Fact]
public void RenameWithinWindow_TransfersParticipantId()
{
var time = T0;
var tracker = new ParticipantTracker(TimeSpan.FromSeconds(5), () => time);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane")));
var originalId = tracker.Participants[0].Id;
time = T0.AddSeconds(1);
tracker.Apply(new DiscoveryEvent.Removed(Source("PC1", "Jane")));
time = T0.AddSeconds(3);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane (PM)")));
tracker.Participants.Should().HaveCount(1);
tracker.Participants[0].Id.Should().Be(originalId);
tracker.Participants[0].DisplayName.Should().Be("Jane (PM)");
}
[Fact]
public void RenameAfterWindow_TreatsAsNewParticipant()
{
var time = T0;
var tracker = new ParticipantTracker(TimeSpan.FromSeconds(5), () => time);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane")));
var originalId = tracker.Participants[0].Id;
time = T0.AddSeconds(1);
tracker.Apply(new DiscoveryEvent.Removed(Source("PC1", "Jane")));
time = T0.AddSeconds(20);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Bob")));
tracker.Participants.Should().HaveCount(2);
tracker.Participants.Should().Contain(p => p.Id == originalId);
tracker.Participants.Should().Contain(p => p.DisplayName == "Bob" && p.Id != originalId);
}
[Fact]
public void DifferentMachine_DoesNotInheritIdentity()
{
var time = T0;
var tracker = new ParticipantTracker(TimeSpan.FromSeconds(5), () => time);
tracker.Apply(new DiscoveryEvent.Added(Source("PC1", "Jane")));
time = T0.AddSeconds(1);
tracker.Apply(new DiscoveryEvent.Removed(Source("PC1", "Jane")));
time = T0.AddSeconds(2);
tracker.Apply(new DiscoveryEvent.Added(Source("PC2", "Jane (PM)")));
tracker.Participants.Should().HaveCount(2);
}
[Fact]
public void NonParticipantSources_AreIgnored()
{
var tracker = new ParticipantTracker(TimeSpan.FromSeconds(5), () => T0);
var screen = new NdiSource("PC1 (Teams Screen Share)", "PC1", NdiSourceKind.ScreenShare, null);
tracker.Apply(new DiscoveryEvent.Added(screen));
tracker.Participants.Should().BeEmpty();
}
}