How to make a Rust tool cupboard auth limit plugin (with VIP tiers)

using System;
using System.Collections.Generic;
using Newtonsoft.Json;
using Oxide.Core;

namespace Oxide.Plugins
{
    [Info("Cupboard Auth Limit", "RustPluginGenerator", "1.0.0")]
    [Description("Caps the number of players authorized on tool cupboards and vehicle privileges, with a VIP tier.")]
    public class CupboardAuthLimit : RustPlugin
    {
        private const string PermVip = "cupboardauthlimit.vip";
        private const string PermUse = "cupboardauthlimit.use";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Base auth limit")]
            public int BaseLimit { get; set; } = 4;

            [JsonProperty("VIP auth limit")]
            public int VipLimit { get; set; } = 8;

            [JsonProperty("Vehicle privilege limit")]
            public int VehicleLimit { get; set; } = 2;

            [JsonProperty("Bypass for admins")]
            public bool AdminBypass { 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>
            {
                ["LimitReached"] = "This tool cupboard is full ({0} authorized players maximum).",
                ["VehicleLimitReached"] = "This vehicle lock is full ({0} authorized players maximum).",
                ["Status"] = "Base limit: {0} | VIP limit: {1} | Your limit: {2} | Admin bypass: {3}",
                ["NoPermission"] = "You do not have permission to use this command.",
                ["Usage"] = "Usage: /cbauthlimit status"
            }, this);
        }

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

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

        private int GetLimit(BasePlayer player)
        {
            if (permission.UserHasPermission(player.UserIDString, PermVip))
                return config.VipLimit;
            return config.BaseLimit;
        }

        private int CountAuth(BuildingPrivlidge priv, BasePlayer player)
        {
            int count = 0;
            foreach (var entry in priv.authorizedPlayers)
            {
                if (player != null && entry == player.userID.Get())
                    continue; // re-authorizing an existing member is fine
                count++;
            }
            return count;
        }

        private int CountAuth(VehiclePrivilege priv, BasePlayer player)
        {
            int count = 0;
            foreach (var entry in priv.authorizedPlayers)
            {
                if (player != null && entry == player.userID.Get())
                    continue;
                count++;
            }
            return count;
        }

        private object OnCupboardAuthorize(BuildingPrivlidge buildingPrivlidge, BasePlayer player)
        {
            if (buildingPrivlidge == null || player == null || player.IsNpc) return null;
            if (config.AdminBypass && player.IsAdmin) return null;

            int limit = GetLimit(player);
            if (limit <= 0) return null;

            int current = CountAuth(buildingPrivlidge, player);
            if (current >= limit)
            {
                player.ChatMessage(Msg("LimitReached", player.UserIDString, limit));
                return false;
            }
            return null;
        }

        private object OnCupboardAuthorize(VehiclePrivilege vehiclePrivilege, BasePlayer player)
        {
            if (vehiclePrivilege == null || player == null || player.IsNpc) return null;
            if (config.AdminBypass && player.IsAdmin) return null;
            if (config.VehicleLimit <= 0) return null;

            int current = CountAuth(vehiclePrivilege, player);
            if (current >= config.VehicleLimit)
            {
                player.ChatMessage(Msg("VehicleLimitReached", player.UserIDString, config.VehicleLimit));
                return false;
            }
            return null;
        }

        [ChatCommand("cbauthlimit")]
        private void CmdAuthLimit(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermUse))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }
            if (args == null || args.Length == 0 || args[0].ToLowerInvariant() != "status")
            {
                player.ChatMessage(Msg("Usage", player.UserIDString));
                return;
            }

            player.ChatMessage(Msg("Status", player.UserIDString,
                config.BaseLimit, config.VipLimit, GetLimit(player), config.AdminBypass));
        }

        private void Unload()
        {
            config = null;
        }
    }
}