OnCuiDraggableDrop

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

namespace Oxide.Plugins
{
    [Info("Cui Drag Loadout", "RustPluginGenerator", "1.0.0")]
    [Description("Opens a CUI grid of belt slots players can drag to reorder their belt items.")]
    public class CuiDragLoadout : RustPlugin
    {
        private const string PermUse = "cuidragloadout.use";
        private const string PanelName = "CuiDragLoadoutPanel";

        private PluginConfig config;

        public class PluginConfig
        {
            [JsonProperty("Require permission")]
            public bool RequirePermission = true;

            [JsonProperty("Grid columns")]
            public int Columns = 6;

            [JsonProperty("Cell width (fraction)")]
            public float CellWidth = 0.1f;
        }

        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>
            {
                ["NoPermission"] = "You do not have permission to use this.",
                ["Opened"] = "Drag slots to reorder your belt. Type /loadout.close to close.",
                ["Invalid"] = "That drop was not valid."
            }, 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(PermUse, this);
        }

        [ChatCommand("loadout")]
        private void CmdLoadout(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (config.RequirePermission && !permission.UserHasPermission(player.UserIDString, PermUse))
            {
                SendReply(player, Msg("NoPermission", player.UserIDString));
                return;
            }
            Draw(player);
            SendReply(player, Msg("Opened", player.UserIDString));
        }

        [ChatCommand("loadout.close")]
        private void CmdClose(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            CuiHelper.DestroyUi(player, PanelName);
        }

        private void Draw(BasePlayer player)
        {
            CuiHelper.DestroyUi(player, PanelName);

            var c = new CuiElementContainer();
            var panel = c.Add(new CuiPanel
            {
                Image = { Color = "0.08 0.08 0.08 0.9" },
                RectTransform = { AnchorMin = "0.3 0.4", AnchorMax = "0.7 0.6" },
                CursorEnabled = true
            }, "Overlay", PanelName);

            var belt = player.inventory?.containerBelt;
            int count = Mathf.Max(config.Columns, belt?.capacity ?? config.Columns);
            float startX = 0.02f;

            for (int i = 0; i < count; i++)
            {
                float x0 = startX + i * config.CellWidth;
                float x1 = x0 + config.CellWidth * 0.9f;
                string label = "empty";
                var item = belt?.GetSlot(i);
                if (item != null && item.info != null) label = item.info.displayName.english;

                var slotName = "CuiDragLoadout.slot" + i;
                c.Add(new CuiButton
                {
                    Button = { Command = "cuidragloadout.move " + i, Color = "0.2 0.2 0.2 1" },
                    RectTransform = { AnchorMin = x0 + " 0.2", AnchorMax = x1 + " 0.8" },
                    Text = { Text = label, FontSize = 12, Align = TextAnchor.MiddleCenter, Color = "0.9 0.9 0.9 1" }
                }, panel, slotName);
            }

            CuiHelper.AddUi(player, c);
        }

        [ConsoleCommand("cuidragloadout.move")]
        private void CcmdMove(ConsoleSystem.Arg arg)
        {
            var player = arg.Player();
            if (player == null) return;
            if (config.RequirePermission && !permission.UserHasPermission(player.UserIDString, PermUse)) return;

            int from = arg.GetInt(0, -1);
            int to = arg.GetInt(1, -1);
            if (from < 0 || to < 0 || from == to) return;

            SwapSlots(player, from, to);
        }

        private bool SwapSlots(BasePlayer player, int from, int to)
        {
            var belt = player.inventory?.containerBelt;
            if (belt == null) return false;
            if (from < 0 || to < 0 || from >= belt.capacity || to >= belt.capacity) return false;

            var source = belt.GetSlot(from);
            var target = belt.GetSlot(to);
            if (source == null && target == null) return false;

            if (source != null) source.MoveToContainer(belt, to);
            if (target != null) target.MoveToContainer(belt, from);
            belt.MarkDirty();

            NextTick(() => { if (player != null && player.IsConnected) Draw(player); });
            return true;
        }

        // Drag-and-drop hook: reorder belt items when a draggable is dropped on a slot.
        // Returns null to keep default CUI behavior.
        private object OnCuiDraggableDrop(BasePlayer player, string dragId, string dropId, Vector2 position, Vector2 delta)
        {
            if (player == null || string.IsNullOrEmpty(dragId) || string.IsNullOrEmpty(dropId)) return null;
            if (config.RequirePermission && !permission.UserHasPermission(player.UserIDString, PermUse)) return null;

            const string prefix = "CuiDragLoadout.slot";
            if (!dragId.StartsWith(prefix) || !dropId.StartsWith(prefix)) return null;
            if (!int.TryParse(dragId.Substring(prefix.Length), out int from)) return null;
            if (!int.TryParse(dropId.Substring(prefix.Length), out int to)) return null;
            if (from == to) return null;

            if (!SwapSlots(player, from, to)) return null;
            return true;
        }

        private void Unload()
        {
            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player != null) CuiHelper.DestroyUi(player, PanelName);
            }
        }
    }
}