Presence can send both a `Leave` and `Join` event that cancel each other out.

Start with the client handling for the presence_diff event and the phx_ref/phx_ref_prev values shown in the report. Reproduce a manual Track Event while already joined, then verify that a matching join and leave are treated as a sync rather than separate Join and Leave events.

I noticed that sending a Track Event manually whilst already joined to the channel causes both a Join and Leave eventto be raised. However, the Leave event is raised after the join making it appear as though I left when I didn't.

29 May 2023 12:08:29 Sending Track Event
29 May 2023 12:08:29 Realtime Client Debug Message: Socket Push [topic: realtime:11111111111111111111111111111111, event: presence, ref: 5d6df879-afa3-4961-8eea-c8f548630ad9]:	{  "event": "track",  "payload": {    "LastSeen": "2023-05-29T11:08:29.1576795Z",    "Email": "xxx@gmail.com",    "Name": "Daz Kuffs",    "ComputerName": "RAGE",    "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a",    "ConnectID": "00000000-0000-0000-0000-000000000000",    "SharedInstances": [      {        "InstanceID": "409f44f0-0542-49bc-bec5-47de2b59be48",        "InstanceName": "Ruffster",        "ComputerName": "RAGE",        "RemoteComputerID": "1a796a13-bd00-4a35-835e-648682a2601b",        "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"      }    ]  }}
29 May 2023 12:08:29 Realtime Client Debug Message: Socket Message Received:	{"event":"phx_reply","payload":{"response":{},"status":"ok"},"ref":"5d6df879-afa3-4961-8eea-c8f548630ad9","topic":"realtime:11111111111111111111111111111111"}
29 May 2023 12:08:29 Realtime Client Debug Message: Socket Message Received:	{"event":"presence_diff","payload":{"joins":{"145bacf8-fe11-11ed-9abb-6a2047d90b67":{"metas":[{"phx_ref":"F2OYoo6yrtA9v9zm","phx_ref_prev":"F2OYnFmge_Q9v3RI","ComputerName":"RAGE","ConnectID":"00000000-0000-0000-0000-000000000000","Email":"kuffs2205@gmail.com","LastSeen":"2023-05-29T11:08:29.1576795Z","Name":"Daz Kuffs","SharedInstances":[{"ComputerName":"RAGE","InstanceID":"409f44f0-0542-49bc-bec5-47de2b59be48","InstanceName":"Ruffster","RemoteComputerID":"1a796a13-bd00-4a35-835e-648682a2601b","UserID":"7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"}],"UserID":"7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"}]}},"leaves":{"145bacf8-fe11-11ed-9abb-6a2047d90b67":{"metas":[{"phx_ref":"F2OYnFmge_Q9v3RI","ComputerName":"RAGE","ConnectID":"00000000-0000-0000-0000-000000000000","Email":"xxx@gmail.com","LastSeen":"2023-05-29T11:08:02.5031865Z","Name":"Daz Kuffs","SharedInstances":[{"ComputerName":"RAGE","InstanceID":"409f44f0-0542-49bc-bec5-47de2b59be48","InstanceName":"Ruffster","RemoteComputerID":"1a796a13-bd00-4a35-835e-648682a2601b","UserID":"7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"}],"UserID":"7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"}]}}},"ref":null,"topic":"realtime:11111111111111111111111111111111"}
29 May 2023 12:08:29 Presence Sync: Daz Kuffs on RAGE
29 May 2023 12:08:29 Presence Join: Daz Kuffs on RAGE
29 May 2023 12:08:29 Presence Leave: Daz Kuffs on RAGE

I notice that the Json for the Join Event apparently (with my limited knowledge) contains a reference to the Leave event in the : phx_ref_prev field.

Maybe some internal magic needs to check for this and not raise events when they cancel each other out. Personally, I feel that this should only have raised a Sync event and neither a Join or Leave.

Here is the Json for easier viewing.

{
"event": "presence_diff",
"payload":
    {
    "joins":
        {
        "145bacf8-fe11-11ed-9abb-6a2047d90b67":
            {
            "metas":
                [
                    {
                    "ComputerName": "RAGE",
                    "ConnectID": "00000000-0000-0000-0000-000000000000",
                    "Email": "xxx@gmail.com",
                    "LastSeen": "2023-05-29T11:08:29.1576795Z",
                    "Name": "Daz Kuffs",
                    "phx_ref": "F2OYoo6yrtA9v9zm",
                    "phx_ref_prev": "F2OYnFmge_Q9v3RI", ' MATCH '
                    "SharedInstances":
                        [
                            {
                            "ComputerName": "RAGE",
                            "InstanceID": "409f44f0-0542-49bc-bec5-47de2b59be48",
                            "InstanceName": "Ruffster",
                            "RemoteComputerID": "1a796a13-bd00-4a35-835e-648682a2601b",
                            "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"
                            }
                        ],
                    "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"
                    }
                ]
            }
        },
    "leaves":
        {
        "145bacf8-fe11-11ed-9abb-6a2047d90b67":
            {
            "metas":
                [
                    {
                    "ComputerName": "RAGE",
                    "ConnectID": "00000000-0000-0000-0000-000000000000",
                    "Email": "xxx@gmail.com",
                    "LastSeen": "2023-05-29T11:08:02.5031865Z",
                    "Name": "Daz Kuffs",
                    "phx_ref": "F2OYnFmge_Q9v3RI", ' MATCH '
                    "SharedInstances":
                        [
                            {
                            "ComputerName": "RAGE",
                            "InstanceID": "409f44f0-0542-49bc-bec5-47de2b59be48",
                            "InstanceName": "Ruffster",
                            "RemoteComputerID": "1a796a13-bd00-4a35-835e-648682a2601b",
                            "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"
                            }
                        ],
                    "UserID": "7aaab6a9-fe93-47e9-a3d0-eb717389cf9a"
                    }
                ]
            }
        }
    },
"ref": null,
"topic": "realtime:11111111111111111111111111111111"
}

Originally posted by @Kuffs2205 in https://github.com/supabase-community/realtime-csharp/issues/29#issuecomment-1567024728