How to make a Rust NPC kill rewards plugin (economy payouts)

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

namespace Oxide.Plugins
{
    [Info("Npc Kill Rewards", "RustPluginGenerator", "1.0.0")]
    [Description("Pays a configurable reward when a player kills a configured NPC prefab.")]
    public class NpcKillRewards : RustPlugin
    {
        private const string PermReset = "npckillrewards.reset";
        private const string PermAdmin = "npckillrewards.admin";

        private PluginConfig config;
        private readonly Dictionary<ulong, double> lastPaid = new Dictionary<ulong, double>();

        [PluginReference] private Plugin Economics;

        private class PluginConfig
        {
            [JsonProperty("Cooldown seconds per player")]
            public double CooldownSeconds = 15.0;

            [JsonProperty("Use Economics deposit")]
            public bool UseEconomics = false;

            [JsonProperty("Rewards")]
            public Dictionary<string, RewardEntry> Rewards = new Dictionary<string, RewardEntry>
            {
                ["scientistnpc_roam"] = new RewardEntry { Shortname = "scrap", Amount = 10 },
                ["scientistnpc_peacekeeper"] = new RewardEntry { Shortname = "scrap", Amount = 12 },
                ["scientistnpc_heavy"] = new RewardEntry { Shortname = "scrap", Amount = 25 },
                ["boar"] = new RewardEntry { Shortname = "scrap", Amount = 2 },
                ["stag"] = new RewardEntry { Shortname = "scrap", Amount = 3 },
                ["bear"] = new RewardEntry { Shortname = "scrap", Amount = 6 },
                ["wolf"] = new RewardEntry { Shortname = "scrap", Amount = 5 },
                ["bradleyapc"] = new RewardEntry { Shortname = "scrap", Amount = 150 },
                ["patrolhelicopter"] = new RewardEntry { Shortname = "scrap", Amount = 200 }
            };
        }

        private class RewardEntry
        {
            [JsonProperty("Item shortname")]
            public string Shortname = "scrap";

            [JsonProperty("Amount")]
            public int Amount = 10;
        }

        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>
            {
                ["Reward"] = "+{1} {0} for killing {2}",
                ["Reset.Done"] = "Your kill cooldown has been cleared.",
                ["NoPermission"] = "You do not have permission to use this command.",
                ["Reloaded"] = "NpcKillRewards config reloaded."
            }, 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(PermReset, this);
            permission.RegisterPermission(PermAdmin, this);
        }

        private void OnEntityDeath(BaseCombatEntity entity, HitInfo info)
        {
            if (entity == null || info == null || entity.IsDestroyed) return;

            var player = info.InitiatorPlayer;
            if (player == null || player.IsNpc || player.IsDead()) return;

            string prefab = entity.ShortPrefabName;
            if (string.IsNullOrEmpty(prefab)) return;

            RewardEntry reward;
            if (!config.Rewards.TryGetValue(prefab, out reward) || reward == null) return;
            if (reward.Amount <= 0 || string.IsNullOrEmpty(reward.Shortname)) return;

            double now = Time.realtimeSinceStartup;
            double last;
            if (lastPaid.TryGetValue(player.userID, out last) && now - last < config.CooldownSeconds) return;

            if (!PayReward(player, reward)) return;

            lastPaid[player.userID] = now;

            string itemName = ItemManager.FindItemDefinition(reward.Shortname)?.displayName?.english ?? reward.Shortname;
            SendReply(player, Msg("Reward", player.UserIDString, itemName, reward.Amount, entity.ShortPrefabName));
        }

        private bool PayReward(BasePlayer player, RewardEntry reward)
        {
            if (config.UseEconomics && Economics != null)
            {
                object result = Economics.Call("Deposit", player.UserIDString, (double)reward.Amount);
                if (result != null) return true;
                PrintWarning("Economics deposit failed, falling back to item reward");
            }

            var item = ItemManager.CreateByName(reward.Shortname, reward.Amount, 0UL);
            if (item == null) return false;

            player.GiveItem(item);
            return true;
        }

        private void OnPlayerDisconnected(BasePlayer player, string reason)
        {
            if (player == null) return;
            lastPaid.Remove(player.userID);
        }

        [ChatCommand("npcreset")]
        private void CmdReset(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermReset))
            {
                player.ChatMessage(Msg("NoPermission", player.UserIDString));
                return;
            }

            lastPaid.Remove(player.userID);
            player.ChatMessage(Msg("Reset.Done", player.UserIDString));
        }

        [ConsoleCommand("npckillrewards.reload")]
        private void CcmdReload(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player != null && !permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                arg.ReplyWith(Msg("NoPermission", player.UserIDString));
                return;
            }

            LoadConfig();
            arg.ReplyWith(Msg("Reloaded", player?.UserIDString));
        }

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