Updatedededed...? Still needs testing.

RelayServer/Services/Rtc/RtcChannelPresenceService.cs

@@ -0,0 +1,55 @@
+using System.Collections.Concurrent;
+
+namespace RelayServer.Services.Rtc;
+
+public static class RtcChannelPresenceService
+{
+    private static readonly ConcurrentDictionary<string, string> SessionToChannel = new();
+    private static readonly ConcurrentDictionary<string, string> SessionToUsername = new();
+
+    public static void SetUser(string sessionId, string username)
+    {
+        SessionToUsername[sessionId] = username;
+    }
+
+    public static void JoinChannel(string sessionId, string channelId)
+    {
+        SessionToChannel[sessionId] = channelId;
+    }
+
+    public static void LeaveChannel(string sessionId)
+    {
+        SessionToChannel.TryRemove(sessionId, out _);
+    }
+
+    public static void RemoveSession(string sessionId)
+    {
+        SessionToChannel.TryRemove(sessionId, out _);
+        SessionToUsername.TryRemove(sessionId, out _);
+    }
+
+    public static IReadOnlyList<string> GetSessionsInChannel(string channelId)
+    {
+        return SessionToChannel
+            .Where(x => x.Value == channelId)
+            .Select(x => x.Key)
+            .ToList();
+    }
+
+    public static IReadOnlyList<string> GetUsersInChannel(string channelId)
+    {
+        var sessionIds = GetSessionsInChannel(channelId);
+
+        return sessionIds
+            .Where(id => SessionToUsername.ContainsKey(id))
+            .Select(id => SessionToUsername[id])
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList();
+    }
+
+    public static bool IsInChannel(string sessionId, string channelId)
+    {
+        return SessionToChannel.TryGetValue(sessionId, out var currentChannel) &&
+               string.Equals(currentChannel, channelId, StringComparison.Ordinal);
+    }
+}