OnTakeCurrencyItem

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

namespace Oxide.Plugins
{
    [Info("VendingCurrencyTax", "RustPluginGenerator", "1.0.0")]
    [Description("Logs scrap payments to vending machines and pays a configurable rebate to the buyer.")]
    public class VendingCurrencyTax : RustPlugin
    {
        private const string PermUse = "vendingcurrencytax.use";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Currency shortname to watch")]
            public string CurrencyShortname = "scrap";

            [JsonProperty("Rebate percentage of paid amount")]
            public int RebatePercent = 10;

            [JsonProperty("Log payments to server console")]
            public bool LogToConsole = 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>
            {
                ["Rebate"] = "You received {0} {1} back from your purchase.",
                ["ConsoleLog"] = "{0} paid {1} {2} to machine at {3}",
                ["NotAllowed"] = "This machine does not accept {0}."
            }, 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);
        }

        private object OnTakeCurrencyItem(VendingMachine vendingMachine, Item takenCurrencyItem)
        {
            if (vendingMachine == null || takenCurrencyItem == null || takenCurrencyItem.info == null)
                return null;

            if (takenCurrencyItem.info.shortname != config.CurrencyShortname)
                return null;

            BasePlayer buyer = takenCurrencyItem.GetOwnerPlayer();
            if (buyer == null || !buyer.IsConnected)
                return null;

            if (config.LogToConsole)
            {
                Puts(Msg("ConsoleLog", null, buyer.displayName, takenCurrencyItem.amount,
                    config.CurrencyShortname, vendingMachine.transform.position.ToString("F0")));
            }

            if (!permission.UserHasPermission(buyer.UserIDString, PermUse))
                return null;

            int rebate = takenCurrencyItem.amount * Mathf.Clamp(config.RebatePercent, 0, 100) / 100;
            if (rebate <= 0)
                return null;

            Item refund = ItemManager.CreateByName(config.CurrencyShortname, rebate, 0);
            if (refund == null)
                return null;

            if (!buyer.inventory.GiveItem(refund))
                refund.Drop(buyer.transform.position, Vector3.zero);

            buyer.ChatMessage(Msg("Rebate", buyer.UserIDString, rebate, config.CurrencyShortname));
            return null;
        }
    }
}