OnCodeChange

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

namespace Oxide.Plugins
{
    [Info("Vehicle Code Validator", "RustPluginGenerator", "1.0.0")]
    [Description("Validates and restricts lock code changes on modular cars")]
    public class VehicleCodeValidator : RustPlugin
    {
        private const string PermBypass = "vehiclecodevalidator.bypass";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Required code length")]
            public int CodeLength = 4;

            [JsonProperty("Require building authorization")]
            public bool RequireAuth = 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>
            {
                ["InvalidLength"] = "A car lock code must be exactly {0} digits.",
                ["NotAuthorized"] = "You are not authorized to change the code on this vehicle."
            }, 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(PermBypass, this);
        }

        private object OnCodeChange(ModularCar carOccupant, BasePlayer player, string text)
        {
            if (carOccupant == null || player == null || text == null) return null;
            if (permission.UserHasPermission(player.UserIDString, PermBypass)) return null;

            if (text.Length != config.CodeLength || !int.TryParse(text, out _))
            {
                player.ChatMessage(Msg("InvalidLength", player.UserIDString, config.CodeLength));
                return true;
            }

            if (config.RequireAuth)
            {
                var privilege = carOccupant.GetBuildingPrivilege();
                bool authorized = (privilege != null && privilege.IsAuthed(player)) || carOccupant.OwnerID == player.userID;
                if (!authorized)
                {
                    player.ChatMessage(Msg("NotAuthorized", player.UserIDString));
                    return true;
                }
            }

            return null;
        }
    }
}