CanCombineDroppedItem

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

namespace Oxide.Plugins
{
    [Info("No Dropped Stack Merge", "RustPluginGenerator", "1.0.0")]
    [Description("Prevents selected players' dropped items from merging with other stacks on the ground")]
    public class NoDroppedStackMerge : RustPlugin
    {
        private const string PermKeep = "nodroppedstackmerge.keep";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Block merging for all players")]
            public bool BlockForEveryone { get; set; } = false;
        }

        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>
            {
                ["Status"] = "Dropped stack merging - everyone blocked: {0}. Permission '{1}' holders are always exempt from merging.",
                ["Granted"] = "You now keep your dropped stacks separate.",
                ["Revoked"] = "Your dropped stacks can merge again."
            }, 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(PermKeep, this);
        }

        private object CanCombineDroppedItem(DroppedItem droppedItem, DroppedItem di)
        {
            if (droppedItem == null || di == null) return null;
            if (droppedItem.item == null || di.item == null) return null;

            if (config.BlockForEveryone) return true;

            if (IsProtected(droppedItem.item) || IsProtected(di.item)) return true;

            return null;
        }

        private bool IsProtected(Item item)
        {
            var owner = item.GetOwnerPlayer();
            if (owner == null) return false;
            return permission.UserHasPermission(owner.UserIDString, PermKeep);
        }

        [ChatCommand("mergestatus")]
        private void CmdMergeStatus(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            SendReply(player, Msg("Status", player.UserIDString, config.BlockForEveryone, PermKeep));
        }

        [ChatCommand("mergetoggle")]
        private void CmdMergeToggle(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!player.IsAdmin) return;

            bool granted;
            if (permission.UserHasPermission(player.UserIDString, PermKeep))
            {
                permission.RevokeUserPermission(player.UserIDString, PermKeep);
                granted = false;
            }
            else
            {
                permission.GrantUserPermission(player.UserIDString, PermKeep, this);
                granted = true;
            }

            SendReply(player, Msg(granted ? "Granted" : "Revoked", player.UserIDString));
        }
    }
}