OnCargoShipSpawnCrate

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

namespace Oxide.Plugins
{
    [Info("Cargo Ship Custom Loot", "RustPluginGenerator", "1.0.0")]
    [Description("Replaces the vanilla cargo ship crate spawn with a configurable crate set.")]
    public class CargoShipCustomLoot : RustPlugin
    {
        private class PluginConfig
        {
            [JsonProperty("Crate prefabs (path, amount)")]
            public List<CrateEntry> Crates = new List<CrateEntry>
            {
                new CrateEntry { Prefab = "assets/prefabs/misc/crate_grey.prefab", Amount = 1 },
                new CrateEntry { Prefab = "assets/prefabs/misc/crate_blue.prefab", Amount = 1 },
                new CrateEntry { Prefab = "assets/prefabs/misc/crate_green.prefab", Amount = 2 }
            };

            [JsonProperty("Delay before crates spawn (seconds)")]
            public float SpawnDelay = 1f;

            [JsonProperty("Offset between crates (meters)")]
            public float Offset = 1.5f;
        }

        public class CrateEntry
        {
            [JsonProperty("Prefab path")]
            public string Prefab;

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

        private PluginConfig config;
        private readonly HashSet<ulong> handledShips = new HashSet<ulong>();
        private Timer spawnTimer;

        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);

        private object OnCargoShipSpawnCrate(CargoShip cargoShip)
        {
            if (cargoShip == null || cargoShip.IsDestroyed) return null;
            if (handledShips.Contains(cargoShip.net.ID.Value)) return null;

            handledShips.Add(cargoShip.net.ID.Value);
            Vector3 origin = cargoShip.transform.position;

            spawnTimer = timer.Once(config.SpawnDelay, () =>
            {
                if (cargoShip == null || cargoShip.IsDestroyed) return;
                int index = 0;
                foreach (CrateEntry entry in config.Crates)
                {
                    if (entry == null || string.IsNullOrEmpty(entry.Prefab)) continue;
                    int count = Mathf.Max(1, entry.Amount);
                    for (int i = 0; i < count; i++)
                    {
                        Vector3 pos = origin + new Vector3(0f, 1f, index * config.Offset);
                        BaseEntity crate = GameManager.server.CreateEntity(entry.Prefab, pos, Quaternion.identity);
                        if (crate == null) continue;
                        crate.Spawn();
                        index++;
                    }
                }
            });

            return true;
        }

        private void OnEntityKill(BaseNetworkable entity)
        {
            CargoShip ship = entity as CargoShip;
            if (ship != null) handledShips.Remove(ship.net.ID.Value);
        }

        private void Unload()
        {
            spawnTimer?.Destroy();
            spawnTimer = null;
            handledShips.Clear();
        }
    }
}