CanVendingAcceptItem

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

namespace Oxide.Plugins
{
    [Info("VendingItemWhitelist", "RustPluginGenerator", "1.0.0")]
    [Description("Restricts which items can be placed into vending machines and warns the player on rejection.")]
    public class VendingItemWhitelist : RustPlugin
    {
        private const string PermBypass = "vendingitemwhitelist.bypass";

        private PluginConfig config;
        private readonly Dictionary<ulong, float> lastWarn = new Dictionary<ulong, float>();

        private class PluginConfig
        {
            [JsonProperty("Allowed shortnames")]
            public List<string> Allowed = new List<string> { "scrap", "wood", "stone", "metal.fragments", "lowgradefuel", "cloth" };

            [JsonProperty("Max amount per move")]
            public int MaxAmount = 1000;

            [JsonProperty("Warn cooldown seconds")]
            public float WarnCooldown = 3f;
        }

        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>
            {
                ["NotAllowed"] = "This vending machine does not accept {0}.",
                ["TooMany"] = "You can only move {0} of {1} at a time."
            }, 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 CanVendingAcceptItem(VendingMachine vendingMachine, Item item, int targetSlot, BasePlayer player)
        {
            if (vendingMachine == null || item == null || item.info == null) return null;
            if (player == null || player.IsNpc) return null;
            if (permission.UserHasPermission(player.UserIDString, PermBypass)) return null;

            string shortname = item.info.shortname;
            if (!config.Allowed.Contains(shortname))
            {
                Warn(player, Msg("NotAllowed", player.UserIDString, item.info.displayName.english));
                return false;
            }

            if (item.amount > config.MaxAmount)
            {
                Warn(player, Msg("TooMany", player.UserIDString, config.MaxAmount, item.info.displayName.english));
                return false;
            }

            return null;
        }

        private void Warn(BasePlayer player, string message)
        {
            float now = UnityEngine.Time.realtimeSinceStartup;
            float last;
            if (lastWarn.TryGetValue(player.userID, out last) && now - last < config.WarnCooldown) return;
            lastWarn[player.userID] = now;
            player.ChatMessage(message);
        }

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