How to make a Rust locked crate event plugin (timed monument drops)

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

namespace Oxide.Plugins
{
    [Info("Locked Crate Event", "RustPluginGenerator", "1.0.0")]
    [Description("Spawns a hackable locked crate at a random monument on a repeating timer and announces it.")]
    public class LockedCrateEvent : RustPlugin
    {
        private const string PermManage = "lockedcrateevent.manage";
        private const string DefaultPrefab = "assets/prefabs/misc/hackablelockedcrate/codelockedhackablecrate.prefab";

        private PluginConfig config;
        private Timer eventTimer;
        private BaseEntity currentCrate;
        private ulong currentCrateId;
        private int nextDropAt;

        private class PluginConfig
        {
            [JsonProperty("Interval minutes")]
            public int IntervalMinutes { get; set; } = 60;

            [JsonProperty("Crate prefab")]
            public string CratePrefab { get; set; } = DefaultPrefab;

            [JsonProperty("Height above monument")]
            public float HeightAboveMonument { get; set; } = 1.5f;

            [JsonProperty("Kill previous crate on spawn")]
            public bool KillPreviousOnStart { get; set; } = true;

            [JsonProperty("Announce message")]
            public string AnnounceMessage { get; set; } = "A hackable crate has dropped at {0}. Next event in {1} minutes.";

            [JsonProperty("Monuments")]
            public List<MonumentPoint> Monuments { get; set; } = new List<MonumentPoint>
            {
                new MonumentPoint { Name = "Launch Site", X = 0f, Y = 0f, Z = 0f },
                new MonumentPoint { Name = "Airfield", X = 0f, Y = 0f, Z = 0f },
                new MonumentPoint { Name = "Water Treatment", X = 0f, Y = 0f, Z = 0f }
            };
        }

        private class MonumentPoint
        {
            public string Name { get; set; }
            public float X { get; set; }
            public float Y { get; set; }
            public float Z { get; set; }
        }

        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>
            {
                ["Announce"] = "A hackable crate has dropped at {0}. Next event in {1} minutes.",
                ["Hacking"] = "Someone is hacking the event crate. Find it!",
                ["NoCrate"] = "There is no active event crate.",
                ["Status"] = "Event crate: {0}. Seconds until next drop: {1}.",
                ["Spawned"] = "Event crate spawned at {0}.",
                ["NoMonuments"] = "No valid monument coordinates are configured."
            }, 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(PermManage, this);
        }

        private void OnServerInitialized()
        {
            var valid = GetValidMonuments();
            if (valid.Count == 0)
            {
                PrintWarning("No monuments with non-zero coordinates configured. Event disabled until the config is fixed.");
                return;
            }

            SpawnEventCrate();
            StartTimer();
        }

        private void StartTimer()
        {
            if (eventTimer != null) eventTimer.Destroy();
            int minutes = Mathf.Max(1, config.IntervalMinutes);
            nextDropAt = Facepunch.Math.Epoch.Current + minutes * 60;
            eventTimer = timer.Every(minutes * 60f, () =>
            {
                SpawnEventCrate();
                nextDropAt = Facepunch.Math.Epoch.Current + minutes * 60;
            });
        }

        private List<MonumentPoint> GetValidMonuments()
        {
            var result = new List<MonumentPoint>();
            if (config.Monuments == null) return result;
            foreach (var m in config.Monuments)
            {
                if (m == null || string.IsNullOrEmpty(m.Name)) continue;
                if (m.X == 0f && m.Y == 0f && m.Z == 0f) continue;
                result.Add(m);
            }
            return result;
        }

        private void SpawnEventCrate()
        {
            var valid = GetValidMonuments();
            if (valid.Count == 0)
            {
                PrintWarning(lang.GetMessage("NoMonuments", this));
                return;
            }

            if (config.KillPreviousOnStart) DespawnCurrent();

            var monument = valid[UnityEngine.Random.Range(0, valid.Count)];
            var position = new Vector3(monument.X, monument.Y + config.HeightAboveMonument, monument.Z);
            string prefab = string.IsNullOrEmpty(config.CratePrefab) ? DefaultPrefab : config.CratePrefab;

            var entity = GameManager.server.CreateEntity(prefab, position, Quaternion.identity);
            if (entity == null)
            {
                PrintWarning("Could not create crate prefab: " + prefab);
                return;
            }

            entity.Spawn();
            currentCrate = entity;
            currentCrateId = entity.net != null ? entity.net.ID.Value : 0UL;

            int minutes = Mathf.Max(1, config.IntervalMinutes);
            string text = string.Format(string.IsNullOrEmpty(config.AnnounceMessage) ? lang.GetMessage("Announce", this) : config.AnnounceMessage, monument.Name, minutes);
            Server.Broadcast(text);
        }

        private void DespawnCurrent()
        {
            if (currentCrate != null && !currentCrate.IsDestroyed)
            {
                currentCrate.Kill();
            }
            currentCrate = null;
            currentCrateId = 0UL;
        }

        private void OnCrateHack(HackableLockedCrate crate)
        {
            if (crate == null || crate.net == null) return;
            if (currentCrateId == 0UL || crate.net.ID.Value != currentCrateId) return;
            Server.Broadcast(lang.GetMessage("Hacking", this));
        }

        private void OnEntityKill(BaseNetworkable entity)
        {
            if (entity == null || entity.net == null) return;
            if (currentCrateId != 0UL && entity.net.ID.Value == currentCrateId)
            {
                currentCrate = null;
                currentCrateId = 0UL;
            }
        }

        private void OnServerShutdown()
        {
            DespawnCurrent();
        }

        [ChatCommand("lockedcrate")]
        private void CmdLockedCrate(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermManage))
            {
                SendReply(player, "You do not have permission to use this command.");
                return;
            }
            if (args == null || args.Length == 0 || args[0].ToLower() != "start")
            {
                SendReply(player, "Usage: /lockedcrate start");
                return;
            }
            SpawnEventCrate();
            SendReply(player, "Event crate spawned.");
        }

        [ConsoleCommand("lockedcrateevent.status")]
        private void CcmdStatus(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player != null && !permission.UserHasPermission(player.UserIDString, PermManage))
            {
                SendReply(player, "You do not have permission to use this command.");
                return;
            }

            string location = "none";
            if (currentCrate != null && !currentCrate.IsDestroyed)
            {
                var p = currentCrate.transform.position;
                location = string.Format("{0:F0},{1:F0},{2:F0}", p.x, p.y, p.z);
            }
            int remaining = Mathf.Max(0, nextDropAt - Facepunch.Math.Epoch.Current);
            arg.ReplyWith(string.Format(lang.GetMessage("Status", this), location, remaining));
        }

        private void Unload()
        {
            if (eventTimer != null)
            {
                eventTimer.Destroy();
                eventTimer = null;
            }
            DespawnCurrent();
        }
    }
}