How to make a Rust welcome panel plugin (CUI on spawn)

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

namespace Oxide.Plugins
{
    [Info("Welcome Panel", "RustPluginGenerator", "1.0.0")]
    [Description("Shows a configurable CUI welcome panel when a player wakes up.")]
    public class WelcomePanel : RustPlugin
    {
        private const string PanelName = "WelcomePanelUI";
        private const string PermUse = "welcomepanel.use";

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

        private class PluginConfig
        {
            [JsonProperty("Title")]
            public string Title = "WELCOME TO OUR SERVER";

            [JsonProperty("Lines")]
            public List<string> Lines = new List<string>
            {
                "Wipe schedule: first Thursday of every month",
                "Group limit: 4 players",
                "No cheating, no exploit abuse"
            };

            [JsonProperty("Links")]
            public List<string> Links = new List<string>
            {
                "Discord: discord.gg/example",
                "Website: example.com"
            };

            [JsonProperty("Auto Close Seconds")]
            public float AutoCloseSeconds = 15f;

            [JsonProperty("Cursor Enabled")]
            public bool CursorEnabled = true;

            [JsonProperty("Panel Anchor Min")]
            public string AnchorMin = "0.28 0.30";

            [JsonProperty("Panel Anchor Max")]
            public string AnchorMax = "0.72 0.70";

            [JsonProperty("Background Color")]
            public string BackgroundColor = "0.10 0.10 0.10 0.92";

            [JsonProperty("Title Color")]
            public string TitleColor = "1.00 0.78 0.30 1.00";

            [JsonProperty("Text Color")]
            public string TextColor = "0.92 0.92 0.92 1.00";

            [JsonProperty("Title Font Size")]
            public int TitleFontSize = 22;

            [JsonProperty("Text Font Size")]
            public int TextFontSize = 14;
        }

        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>
            {
                ["NoPermission"] = "You do not have permission to use this command."
            }, 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 void OnPlayerSleepEnded(BasePlayer player)
        {
            if (player == null || player.IsNpc || !player.IsConnected) return;
            ulong id = player.userID.Get();
            if (!shown.Add(id)) return;
            ShowPanel(player);
        }

        private void OnPlayerDisconnected(BasePlayer player, string reason)
        {
            if (player == null) return;
            ulong id = player.userID.Get();
            shown.Remove(id);
            DestroyTimer(id);
            CuiHelper.DestroyUi(player, PanelName);
        }

        private void ShowPanel(BasePlayer player)
        {
            DestroyTimer(player.userID.Get());
            CuiHelper.DestroyUi(player, PanelName);

            var c = new CuiElementContainer();
            string panel = c.Add(new CuiPanel
            {
                Image = { Color = config.BackgroundColor },
                RectTransform = { AnchorMin = config.AnchorMin, AnchorMax = config.AnchorMax },
                CursorEnabled = config.CursorEnabled
            }, "Overlay", PanelName);

            c.Add(new CuiLabel
            {
                Text = { Text = config.Title, FontSize = config.TitleFontSize, Color = config.TitleColor, Align = TextAnchor.MiddleCenter },
                RectTransform = { AnchorMin = "0.02 0.82", AnchorMax = "0.98 0.97" }
            }, panel);

            string body = config.Lines != null ? string.Join("\n", config.Lines.ToArray()) : "";
            c.Add(new CuiLabel
            {
                Text = { Text = body, FontSize = config.TextFontSize, Color = config.TextColor, Align = TextAnchor.UpperLeft },
                RectTransform = { AnchorMin = "0.05 0.45", AnchorMax = "0.95 0.80" }
            }, panel);

            string links = config.Links != null ? string.Join("\n", config.Links.ToArray()) : "";
            c.Add(new CuiLabel
            {
                Text = { Text = links, FontSize = config.TextFontSize, Color = config.TextColor, Align = TextAnchor.UpperLeft },
                RectTransform = { AnchorMin = "0.05 0.22", AnchorMax = "0.95 0.43" }
            }, panel);

            c.Add(new CuiButton
            {
                Button = { Command = "welcomepanel.close", Color = "0.70 0.20 0.20 1.00" },
                RectTransform = { AnchorMin = "0.38 0.05", AnchorMax = "0.62 0.18" },
                Text = { Text = "CLOSE", FontSize = 16, Align = TextAnchor.MiddleCenter }
            }, panel);

            CuiHelper.AddUi(player, c);

            if (config.AutoCloseSeconds > 0f)
            {
                ulong id = player.userID.Get();
                closeTimers[id] = timer.Once(config.AutoCloseSeconds, () =>
                {
                    closeTimers.Remove(id);
                    if (player != null && player.IsConnected)
                        CuiHelper.DestroyUi(player, PanelName);
                });
            }
        }

        [ConsoleCommand("welcomepanel.close")]
        private void CmdClose(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player == null) return;
            DestroyTimer(player.userID.Get());
            CuiHelper.DestroyUi(player, PanelName);
        }

        [ChatCommand("welcome")]
        private void CmdWelcome(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermUse))
            {
                SendReply(player, Msg("NoPermission", player.UserIDString));
                return;
            }
            ShowPanel(player);
        }

        private void DestroyTimer(ulong id)
        {
            Timer existing;
            if (closeTimers.TryGetValue(id, out existing))
            {
                existing?.Destroy();
                closeTimers.Remove(id);
            }
        }

        private void Unload()
        {
            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null)
                    CuiHelper.DestroyUi(player, PanelName);
            }
            foreach (var entry in closeTimers)
                entry.Value?.Destroy();
            closeTimers.Clear();
            shown.Clear();
        }
    }
}