How to make a Rust server info panel plugin (CUI tabs)

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("InfoPanel", "RustPluginGenerator", "1.0.0")]
    [Description("Shows a configurable tabbed server information window built with CUI.")]
    public class InfoPanel : RustPlugin
    {
        private const string PermUse = "infopanel.use";
        private const string PanelName = "InfoPanel.Panel";

        private PluginConfig config;
        private readonly Dictionary<ulong, string> activeTab = new Dictionary<ulong, string>();
        private StoredData stored;

        private class PluginConfig
        {
            [JsonProperty("Panel title")]
            public string Title { get; set; } = "Server Information";

            [JsonProperty("Tab label - Rules")]
            public string TabRules { get; set; } = "Rules";

            [JsonProperty("Tab label - Commands")]
            public string TabCommands { get; set; } = "Commands";

            [JsonProperty("Tab label - Wipe")]
            public string TabWipe { get; set; } = "Wipe info";

            [JsonProperty("Close button label")]
            public string CloseButton { get; set; } = "Close";

            [JsonProperty("Rules text")]
            public string RulesText { get; set; } = "1. No cheating or exploits.\n2. No raiding before 24h after wipe.\n3. Respect other players.\n4. Do not block monuments.";

            [JsonProperty("Commands text")]
            public string CommandsText { get; set; } = "/info - open this panel\n/help - server help\n/kit - list your kits\n/report <player> - report a rule break";

            [JsonProperty("Wipe text")]
            public string WipeText { get; set; } = "Wipe: every first Thursday of the month.\nMap wipes with server wipe, blueprints wipe too.\nCheck the Discord for the exact time.";

            [JsonProperty("Auto open on first connect")]
            public bool AutoOpenOnFirstConnect { get; set; } = true;
        }

        private class StoredData
        {
            [JsonProperty("Players that have seen the panel")]
            public HashSet<ulong> Seen { get; set; } = new HashSet<ulong>();
        }

        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 OnServerInitialized()
        {
            stored = Interface.Oxide.DataFileSystem.ReadObject<StoredData>(Name) ?? new StoredData();
        }

        private void OnPlayerConnected(BasePlayer player)
        {
            if (player == null || !config.AutoOpenOnFirstConnect) return;
            if (stored == null) stored = new StoredData();
            if (stored.Seen.Contains(player.userID.Get())) return;

            stored.Seen.Add(player.userID.Get());
            Interface.Oxide.DataFileSystem.WriteObject(Name, stored);

            timer.Once(2f, () =>
            {
                if (player != null && player.IsConnected)
                    OpenPanel(player, "rules");
            });
        }

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

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

        [ConsoleCommand("infopanel.tab")]
        private void CcmdTab(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermUse))
            {
                SendReply(player, Msg("NoPermission", player.UserIDString));
                return;
            }
            string tab = arg.GetString(0, "rules");
            if (tab != "rules" && tab != "commands" && tab != "wipe") tab = "rules";
            OpenPanel(player, tab);
        }

        private void OpenPanel(BasePlayer player, string tab)
        {
            activeTab[player.userID.Get()] = tab;
            CuiHelper.DestroyUi(player, PanelName);

            var container = new CuiElementContainer();
            container.Add(new CuiPanel
            {
                Image = { Color = "0.08 0.08 0.08 0.94" },
                RectTransform = { AnchorMin = "0.3 0.25", AnchorMax = "0.7 0.75" },
                CursorEnabled = true
            }, "Overlay", PanelName);

            container.Add(new CuiLabel
            {
                Text = { Text = config.Title, FontSize = 22, Align = TextAnchor.MiddleCenter, Color = "0.95 0.85 0.5 1" },
                RectTransform = { AnchorMin = "0 0.86", AnchorMax = "1 1" }
            }, PanelName);

            AddTab(container, "rules", config.TabRules, 0.02f, 0.2f, tab == "rules");
            AddTab(container, "commands", config.TabCommands, 0.23f, 0.41f, tab == "commands");
            AddTab(container, "wipe", config.TabWipe, 0.44f, 0.62f, tab == "wipe");

            string body;
            switch (tab)
            {
                case "commands": body = config.CommandsText; break;
                case "wipe": body = config.WipeText; break;
                default: body = config.RulesText; break;
            }

            container.Add(new CuiLabel
            {
                Text = { Text = body, FontSize = 13, Align = TextAnchor.UpperLeft, Color = "0.9 0.9 0.9 1" },
                RectTransform = { AnchorMin = "0.04 0.16", AnchorMax = "0.76 0.82" }
            }, PanelName);

            container.Add(new CuiButton
            {
                Button = { Command = "infopanel.close", Color = "0.55 0.15 0.15 1" },
                RectTransform = { AnchorMin = "0.8 0.03", AnchorMax = "0.96 0.13" },
                Text = { Text = config.CloseButton, FontSize = 14, Align = TextAnchor.MiddleCenter, Color = "1 1 1 1" }
            }, PanelName);

            CuiHelper.AddUi(player, container);
        }

        private void AddTab(CuiElementContainer container, string key, string label, float minX, float maxX, bool selected)
        {
            container.Add(new CuiButton
            {
                Button =
                {
                    Command = "infopanel.tab " + key,
                    Color = selected ? "0.25 0.45 0.25 1" : "0.18 0.18 0.18 1"
                },
                RectTransform =
                {
                    AnchorMin = minX.ToString("0.00", System.Globalization.CultureInfo.InvariantCulture) + " 0.74",
                    AnchorMax = maxX.ToString("0.00", System.Globalization.CultureInfo.InvariantCulture) + " 0.84"
                },
                Text = { Text = label, FontSize = 13, Align = TextAnchor.MiddleCenter, Color = "1 1 1 1" }
            }, PanelName);
        }

        private void Unload()
        {
            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null)
                    CuiHelper.DestroyUi(player, PanelName);
            }
            if (stored != null)
                Interface.Oxide.DataFileSystem.WriteObject(Name, stored);
        }
    }
}