OnTeamUpdated

using System.Linq;
using Oxide.Game.Rust.Cui;
using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;

namespace Oxide.Plugins
{
    [Info("Team Join Notifier", "RustPluginGenerator", "1.0.0")]
    [Description("Announces in team chat when a member joins a team")]
    public class TeamJoinNotifier : RustPlugin
    {
        private const string PermUse = "teamjoinnotifier.use";

        private PluginConfig config;
        private readonly Dictionary<ulong, HashSet<ulong>> membersByTeam = new Dictionary<ulong, HashSet<ulong>>();
        private readonly Dictionary<ulong, Timer> debounceTimers = new Dictionary<ulong, Timer>();

        private class PluginConfig
        {
            [JsonProperty("Notify team in chat")]
            public bool NotifyTeam { get; set; } = true;

            [JsonProperty("Log joins to admins")]
            public bool LogToAdmins { get; set; } = true;
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new Exception();
            }
            catch
            {
                PrintWarning("Configuration file is invalid, using defaults");
                LoadDefaultConfig();
            }
            SaveConfig();
        }

        protected override void SaveConfig() => Config.WriteObject(config);

        protected override void LoadDefaultMessages()
        {
            lang.RegisterMessages(new Dictionary<string, string>
            {
                ["Team.Joined"] = "{0} joined the team",
                ["Admin.Joined"] = "{0} joined team {1}"
            }, this);
        }

        private string Msg(string key, string userId = null, params object[] args) => string.Format(lang.GetMessage(key, this, userId), args);

        private void Init()
        {
            permission.RegisterPermission(PermUse, this);
        }

        private List<ulong> GetMemberIds(ProtoBuf.PlayerTeam teamData)
        {
            var ids = new List<ulong>();
            foreach (var member in teamData.members)
            {
                if (member != null) ids.Add(member.userID);
            }
            return ids;
        }

        private object OnTeamUpdated(ulong teamId, ProtoBuf.PlayerTeam teamData, BasePlayer player)
        {
            if (teamData?.members == null || player == null || teamId == 0) return null;

            List<ulong> currentMembers = GetMemberIds(teamData);

            HashSet<ulong> previous;
            if (!membersByTeam.TryGetValue(teamId, out previous))
            {
                previous = new HashSet<ulong>();
                foreach (ulong member in currentMembers) previous.Add(member);
                membersByTeam[teamId] = previous;
                return null;
            }

            ulong joined = 0;
            foreach (ulong member in currentMembers)
            {
                if (!previous.Contains(member)) joined = member;
            }

            if (joined == 0) return null;

            previous.Clear();
            foreach (ulong member in currentMembers) previous.Add(member);

            if (config.NotifyTeam)
            {
                var newMember = BasePlayer.FindByID(joined);
                string name = newMember != null ? newMember.displayName : joined.ToString();
                foreach (ulong member in currentMembers)
                {
                    BasePlayer memberPlayer = BasePlayer.FindByID(member);
                    if (memberPlayer != null && memberPlayer.IsConnected)
                    {
                        memberPlayer.ChatMessage(Msg("Team.Joined", memberPlayer.UserIDString, name));
                    }
                }
            }

            if (config.LogToAdmins)
            {
                var newMember = BasePlayer.FindByID(joined);
                string name = newMember != null ? newMember.displayName : joined.ToString();
                foreach (BasePlayer admin in BasePlayer.activePlayerList)
                {
                    if (admin.IsAdmin && permission.UserHasPermission(admin.UserIDString, PermUse))
                    {
                        admin.ChatMessage(Msg("Admin.Joined", admin.UserIDString, name, teamId));
                    }
                }
            }

            return null;
        }

        private void Unload()
        {
            foreach (Timer timer in debounceTimers.Values) timer?.Destroy();
            debounceTimers.Clear();
            membersByTeam.Clear();

            foreach (BasePlayer player in BasePlayer.activePlayerList)
            {
                if (player != null && !player.IsDestroyed) CuiHelper.DestroyUi(player, "TeamJoinNotifierPanel");
            }
        }
    }
}