How to make a Rust patrol helicopter event plugin (admin calls + timer)

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

namespace Oxide.Plugins
{
    [Info("Heli Event", "RustPluginGenerator", "1.0.0")]
    [Description("Spawns a patrol helicopter on command or timer and announces who destroyed it.")]
    public class HeliEvent : RustPlugin
    {
        private const string PermCall = "helievent.call";

        private class PluginConfig
        {
            [JsonProperty("Helicopter prefab")]
            public string Prefab = "assets/prefabs/npc/patrol helicopter/patrolhelicopter.prefab";

            [JsonProperty("Spawn height above ground")]
            public float SpawnHeight = 60f;

            [JsonProperty("Auto spawn enabled")]
            public bool AutoSpawnEnabled = false;

            [JsonProperty("Auto spawn interval minutes")]
            public float AutoSpawnMinutes = 120f;

            [JsonProperty("Broadcast spawn message")]
            public bool AnnounceSpawn = true;
        }

        private PluginConfig config;
        private Timer autoSpawnTimer;
        private readonly HashSet<ulong> trackedHelis = new HashSet<ulong>();

        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>
            {
                ["SpawnManual"] = "{0} called in a patrol helicopter. Watch the skies.",
                ["SpawnTimer"] = "A patrol helicopter has entered the area.",
                ["Denied"] = "You do not have permission to call a helicopter.",
                ["Blocked"] = "You cannot call a helicopter while building blocked.",
                ["Failed"] = "The helicopter could not be spawned. Check the plugin config.",
                ["DestroyedByPlayer"] = "The patrol helicopter was destroyed by {0}.",
                ["DestroyedUnknown"] = "The patrol helicopter was destroyed."
            }, 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(PermCall, this);
        }

        private void OnServerInitialized()
        {
            if (!config.AutoSpawnEnabled || config.AutoSpawnMinutes <= 0f) return;
            autoSpawnTimer = timer.Every(config.AutoSpawnMinutes * 60f, SpawnFromTimer);
        }

        private void Unload()
        {
            autoSpawnTimer?.Destroy();
            trackedHelis.Clear();
        }

        [ChatCommand("callheli")]
        private void CmdCallHeli(BasePlayer player, string command, string[] args)
        {
            if (player == null || !player.IsConnected) return;
            if (!permission.UserHasPermission(player.UserIDString, PermCall))
            {
                player.ChatMessage(Msg("Denied", player.UserIDString));
                return;
            }
            if (player.IsBuildingBlocked())
            {
                player.ChatMessage(Msg("Blocked", player.UserIDString));
                return;
            }

            var position = player.transform.position + Vector3.up * config.SpawnHeight;
            var heli = SpawnHeli(position);
            if (heli == null)
            {
                player.ChatMessage(Msg("Failed", player.UserIDString));
                return;
            }

            if (config.AnnounceSpawn)
                Server.Broadcast(Msg("SpawnManual", null, player.displayName));
        }

        private void SpawnFromTimer()
        {
            var position = new Vector3(0f, config.SpawnHeight, 0f);
            if (SpawnHeli(position) != null && config.AnnounceSpawn)
                Server.Broadcast(Msg("SpawnTimer"));
        }

        private BaseHelicopter SpawnHeli(Vector3 position)
        {
            var entity = GameManager.server.CreateEntity(config.Prefab, position, Quaternion.identity);
            var heli = entity as BaseHelicopter;
            if (heli == null)
            {
                if (entity != null) entity.Kill();
                return null;
            }

            heli.Spawn();
            trackedHelis.Add(heli.net.ID.Value);
            return heli;
        }

        private void OnEntityDeath(BaseCombatEntity entity, HitInfo info)
        {
            var heli = entity as BaseHelicopter;
            if (heli == null) return;
            if (!trackedHelis.Remove(heli.net.ID.Value)) return;

            var killer = info?.InitiatorPlayer;
            if (killer == null && info?.Initiator is BasePlayer)
                killer = info.Initiator as BasePlayer;

            if (killer != null)
                Server.Broadcast(Msg("DestroyedByPlayer", null, killer.displayName));
            else
                Server.Broadcast(Msg("DestroyedUnknown"));
        }
    }
}