How to make a Rust vehicle limit plugin (per player, per type)

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

namespace Oxide.Plugins
{
    [Info("Vehicle Limits", "RustPluginGenerator", "1.0.0")]
    [Description("Caps how many vehicles each player can own per vehicle type, with permission-based extra slots.")]
    public class VehicleLimits : RustPlugin
    {
        private const string PermUse = "vehiclelimits.use";
        private const string PermAdmin = "vehiclelimits.admin";
        private const string PermExtra = "vehiclelimits.extra";

        private PluginConfig config;
        private readonly Dictionary<ulong, EntityRef> tracked = new Dictionary<ulong, EntityRef>();

        private class EntityRef
        {
            public ulong OwnerId;
            public string Key;
        }

        private class VehicleEntry
        {
            [JsonProperty("Readable name")]
            public string DisplayName { get; set; } = "Vehicle";

            [JsonProperty("Prefab short name contains")]
            public string Prefab { get; set; } = "";

            [JsonProperty("Base limit (0 = uncapped)")]
            public int Limit { get; set; } = 1;
        }

        private class PluginConfig
        {
            [JsonProperty("Extra slots per player with the extra permission")]
            public int ExtraPerPermission { get; set; } = 2;

            [JsonProperty("Kill over-limit vehicles on spawn")]
            public bool KillOverLimit { get; set; } = true;

            [JsonProperty("Notify owner when a spawn is blocked")]
            public bool NotifyOwner { get; set; } = true;

            [JsonProperty("Vehicles")]
            public List<VehicleEntry> Vehicles { get; set; } = new List<VehicleEntry>
            {
                new VehicleEntry { DisplayName = "Minicopter", Prefab = "minicopter.entity", Limit = 2 },
                new VehicleEntry { DisplayName = "Scrap Transport Helicopter", Prefab = "scraptransporthelicopter", Limit = 1 },
                new VehicleEntry { DisplayName = "Rowboat", Prefab = "rowboat", Limit = 3 },
                new VehicleEntry { DisplayName = "RHIB", Prefab = "rhib", Limit = 2 }
            };
        }

        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>
            {
                ["Blocked"] = "You already own {0} {1} (limit {2}). Destroy one before spawning another.",
                ["NoPermission"] = "You do not have permission to use this command.",
                ["ListHeader"] = "Your vehicles:",
                ["ListLine"] = "{0}: {1}/{2}",
                ["TargetHeader"] = "Vehicles owned by {0}:",
                ["TargetNotFound"] = "Player '{0}' not found.",
                ["RescanDone"] = "Rescan complete. Tracking {0} vehicles."
            }, 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);
            permission.RegisterPermission(PermAdmin, this);
            permission.RegisterPermission(PermExtra, this);
        }

        private void OnServerInitialized()
        {
            Rebuild();
        }

        private void Unload()
        {
            tracked.Clear();
        }

        private void Rebuild()
        {
            tracked.Clear();
            foreach (var networkable in BaseNetworkable.serverEntities)
            {
                var entity = networkable as BaseEntity;
                if (entity == null) continue;
                Track(entity, false);
            }
        }

        private VehicleEntry FindEntry(string shortName)
        {
            if (string.IsNullOrEmpty(shortName) || config?.Vehicles == null) return null;
            foreach (var entry in config.Vehicles)
            {
                if (entry == null || string.IsNullOrEmpty(entry.Prefab) || entry.Limit <= 0) continue;
                if (shortName.IndexOf(entry.Prefab, StringComparison.OrdinalIgnoreCase) >= 0)
                    return entry;
            }
            return null;
        }

        private int GetLimit(BasePlayer player, VehicleEntry entry)
        {
            int limit = entry.Limit;
            if (player != null && permission.UserHasPermission(player.UserIDString, PermExtra))
                limit += Math.Max(0, config.ExtraPerPermission);
            return limit;
        }

        private int Count(ulong ownerId, VehicleEntry entry)
        {
            int count = 0;
            foreach (var pair in tracked)
            {
                if (pair.Value.OwnerId == ownerId && pair.Value.Key == entry.Prefab)
                    count++;
            }
            return count;
        }

        private bool Track(BaseEntity entity, bool enforce)
        {
            if (entity == null || entity.IsDestroyed) return false;
            var entry = FindEntry(entity.ShortPrefabName);
            if (entry == null) return false;

            ulong entityId = entity.net.ID.Value;
            if (tracked.ContainsKey(entityId)) return false;

            ulong ownerId = entity.OwnerID;
            if (ownerId == 0) return false;

            BasePlayer owner = BasePlayer.FindByID(ownerId);
            if (owner != null && (owner.IsAdmin || owner.IsNpc)) return false;

            if (enforce)
            {
                int limit = GetLimit(owner, entry);
                int current = Count(ownerId, entry);
                if (current >= limit)
                {
                    if (config.KillOverLimit)
                    {
                        if (owner != null && owner.IsConnected && config.NotifyOwner)
                            owner.ChatMessage(Msg("Blocked", owner.UserIDString, current, entry.DisplayName, limit));
                        entity.Kill();
                    }
                    return false;
                }
            }

            tracked[entityId] = new EntityRef { OwnerId = ownerId, Key = entry.Prefab };
            return true;
        }

        private void OnEntitySpawned(BaseNetworkable entity)
        {
            Track(entity as BaseEntity, true);
        }

        private object OnEntityKill(BaseNetworkable entity)
        {
            if (entity != null && entity.net != null)
                tracked.Remove(entity.net.ID.Value);
            return null;
        }

        [ChatCommand("vlimit")]
        private void CmdVLimit(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)
            {
                if (!permission.UserHasPermission(player.UserIDString, PermAdmin))
                {
                    player.ChatMessage(Msg("NoPermission", player.UserIDString));
                    return;
                }
                string target = string.Join(" ", args);
                BasePlayer other = BasePlayer.FindAwakeOrSleeping(target);
                if (other == null)
                {
                    player.ChatMessage(Msg("TargetNotFound", player.UserIDString, target));
                    return;
                }
                player.ChatMessage(Msg("TargetHeader", player.UserIDString, other.displayName));
                PrintList(player, other);
                return;
            }

            player.ChatMessage(Msg("ListHeader", player.UserIDString));
            PrintList(player, player);
        }

        private void PrintList(BasePlayer to, BasePlayer target)
        {
            foreach (var entry in config.Vehicles)
            {
                if (entry == null || entry.Limit <= 0) continue;
                int count = Count(target.userID.Get(), entry);
                int limit = GetLimit(target, entry);
                to.ChatMessage(Msg("ListLine", to.UserIDString, entry.DisplayName, count, limit));
            }
        }

        [ConsoleCommand("vehiclelimits.rescan")]
        private void CcmdRescan(ConsoleSystem.Arg arg)
        {
            if (arg == null) return;
            var player = arg.Player();
            if (player != null && !permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                arg.ReplyWith(Msg("NoPermission", player.UserIDString));
                return;
            }
            Rebuild();
            arg.ReplyWith(Msg("RescanDone", player?.UserIDString, tracked.Count));
        }
    }
}