How to make a Rust rules acceptance screen plugin (CUI + persistent accept)

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("Rules Accept Panel", "RustPluginGenerator", "1.0.0")]
    [Description("Shows a one-time CUI rules window with Accept and Decline buttons to new players.")]
    public class RulesAcceptPanel : RustPlugin
    {
        private const string PermShow = "rulesacceptpanel.show";
        private const string PermAdmin = "rulesacceptpanel.admin";
        private const string PanelName = "RulesAcceptPanel.Main";
        private const string DimName = "RulesAcceptPanel.Dim";

        private PluginConfig config;
        private StoredData data;

        private class PluginConfig
        {
            [JsonProperty("Exempt admins")]
            public bool ExemptAdmins { get; set; } = true;

            [JsonProperty("Panel background color")]
            public string PanelColor { get; set; } = "0.08 0.08 0.08 0.96";

            [JsonProperty("Accept button color")]
            public string AcceptColor { get; set; } = "0.25 0.55 0.25 1";

            [JsonProperty("Decline button color")]
            public string DeclineColor { get; set; } = "0.65 0.2 0.2 1";
        }

        private class StoredData
        {
            [JsonProperty("Accepted steam ids")]
            public HashSet<string> Accepted = new HashSet<string>();
        }

        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>
            {
                ["RulesTitle"] = "SERVER RULES",
                ["Accept"] = "ACCEPT",
                ["Decline"] = "DECLINE",
                ["KickReason"] = "You must accept the server rules to play here.",
                ["RulesText"] = "1. No cheating or third-party software.\n2. No racism, harassment or spam in chat.\n3. Do not exploit bugs; report them instead.\n4. Raiding is allowed, griefing spawn areas is not.\n5. Admins have the final say on rule enforcement.",
                ["ResetUsage"] = "Usage: rules.reset <steamid>",
                ["ResetDone"] = "Removed {0} from the accepted list.",
                ["NoPermission"] = "You do not have permission to use this command."
            }, this);
        }

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

        private void Init()
        {
            permission.RegisterPermission(PermShow, this);
            permission.RegisterPermission(PermAdmin, this);
            data = Interface.Oxide.DataFileSystem.ReadObject<StoredData>(Name) ?? new StoredData();
        }

        private void SaveData() => Interface.Oxide.DataFileSystem.WriteObject(Name, data);

        private void Unload()
        {
            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null) CuiHelper.DestroyUi(player, PanelName);
            }
            SaveData();
        }

        private void OnPlayerSleepEnded(BasePlayer player)
        {
            if (player == null || player.IsNpc) return;
            if (config.ExemptAdmins && player.IsAdmin) return;
            if (data.Accepted.Contains(player.UserIDString)) return;

            ShowPanel(player);
        }

        private void ShowPanel(BasePlayer player)
        {
            if (player == null || !player.IsConnected) return;

            CuiHelper.DestroyUi(player, PanelName);

            var c = new CuiElementContainer();
            c.Add(new CuiPanel
            {
                Image = { Color = "0 0 0 0.65" },
                RectTransform = { AnchorMin = "0 0", AnchorMax = "1 1" },
                CursorEnabled = true
            }, "Overlay", DimName);

            c.Add(new CuiPanel
            {
                Image = { Color = config.PanelColor },
                RectTransform = { AnchorMin = "0.3 0.22", AnchorMax = "0.7 0.78" }
            }, DimName, PanelName);

            c.Add(new CuiLabel
            {
                Text = { Text = Msg("RulesTitle", player.UserIDString), FontSize = 24, Align = TextAnchor.MiddleCenter, Color = "1 1 1 1" },
                RectTransform = { AnchorMin = "0.05 0.86", AnchorMax = "0.95 0.98" }
            }, PanelName);

            string body = Msg("RulesText", player.UserIDString);
            c.Add(new CuiLabel
            {
                Text = { Text = body, FontSize = 14, Align = TextAnchor.UpperLeft, Color = "0.9 0.9 0.9 1" },
                RectTransform = { AnchorMin = "0.06 0.25", AnchorMax = "0.94 0.85" }
            }, PanelName);

            c.Add(new CuiButton
            {
                Button = { Command = "rules.accept", Color = config.AcceptColor },
                RectTransform = { AnchorMin = "0.06 0.06", AnchorMax = "0.47 0.18" },
                Text = { Text = Msg("Accept", player.UserIDString), FontSize = 16, Align = TextAnchor.MiddleCenter, Color = "1 1 1 1" }
            }, PanelName);

            c.Add(new CuiButton
            {
                Button = { Command = "rules.decline", Color = config.DeclineColor },
                RectTransform = { AnchorMin = "0.53 0.06", AnchorMax = "0.94 0.18" },
                Text = { Text = Msg("Decline", player.UserIDString), FontSize = 16, Align = TextAnchor.MiddleCenter, Color = "1 1 1 1" }
            }, PanelName);

            CuiHelper.AddUi(player, c);
        }

        [ConsoleCommand("rules.accept")]
        private void CcmdAccept(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player == null) return;

            data.Accepted.Add(player.UserIDString);
            SaveData();
            CuiHelper.DestroyUi(player, PanelName);
            CuiHelper.DestroyUi(player, DimName);
        }

        [ConsoleCommand("rules.decline")]
        private void CcmdDecline(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player == null) return;

            CuiHelper.DestroyUi(player, PanelName);
            CuiHelper.DestroyUi(player, DimName);
            player.Kick(Msg("KickReason", player.UserIDString));
        }

        [ChatCommand("rules")]
        private void CmdRules(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermShow))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }
            ShowPanel(player);
        }

        [ConsoleCommand("rules.reset")]
        private void CcmdReset(ConsoleSystem.Arg arg)
        {
            var id = arg.GetString(0, string.Empty);
            if (string.IsNullOrEmpty(id))
            {
                arg.ReplyWith(Msg("ResetUsage"));
                return;
            }

            var player = arg.Player();
            if (player != null && !player.IsAdmin && !permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                arg.ReplyWith(Msg("NoPermission", player.UserIDString));
                return;
            }

            data.Accepted.Remove(id);
            SaveData();
            arg.ReplyWith(Msg("ResetDone", null, id));
        }
    }
}