OnBuildingMerge

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

namespace Oxide.Plugins
{
    [Info("BuildingMergeAlert", "RustPluginGenerator", "1.0.0")]
    [Description("Notifies admins when two building structures on the server merge.")]
    public class BuildingMergeAlert : RustPlugin
    {
        private const string PermAdmin = "buildingmergealert.admin";

        private PluginConfig config;

        public class PluginConfig
        {
            [JsonProperty("Notify in chat")]
            public bool NotifyChat { get; set; } = true;

            [JsonProperty("Notify in console")]
            public bool NotifyConsole { get; set; } = true;
        }

        protected override void LoadDefaultConfig() => config = new PluginConfig();

        protected override void LoadConfig()
        {
            base.LoadConfig();
            try
            {
                config = Config.ReadObject<PluginConfig>();
                if (config == null) throw new System.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>
            {
                ["MergeAlert"] = "Buildings merged: {0} ({1} blocks, owner {2}) absorbed {3} ({4} blocks, owner {5})."
            }, 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(PermAdmin, this);
        }

        private void OnBuildingMerge(ServerBuildingManager serverBuildingManager,
            BuildingManager.Building building1, BuildingManager.Building building2)
        {
            if (building1 == null || building2 == null) return;

            int blocks1 = building1.buildingBlocks != null ? building1.buildingBlocks.Count : 0;
            int blocks2 = building2.buildingBlocks != null ? building2.buildingBlocks.Count : 0;

            string name1 = OwnerName(building1);
            string name2 = OwnerName(building2);

            foreach (var player in BasePlayer.activePlayerList)
            {
                if (player == null || !player.IsConnected) continue;
                if (!permission.UserHasPermission(player.UserIDString, PermAdmin)) continue;

                if (config.NotifyChat)
                {
                    player.ChatMessage(Msg("MergeAlert", player.UserIDString,
                        building1.ID, blocks1, name1, building2.ID, blocks2, name2));
                }
                if (config.NotifyConsole)
                {
                    player.SendConsoleCommand("echo", Msg("MergeAlert", player.UserIDString,
                        building1.ID, blocks1, name1, building2.ID, blocks2, name2));
                }
            }
        }

        private string OwnerName(BuildingManager.Building building)
        {
            if (building.buildingBlocks == null) return "none";
            foreach (var block in building.buildingBlocks)
            {
                if (block == null) continue;
                ulong ownerId = block.OwnerID;
                if (ownerId == 0) continue;
                var player = BasePlayer.FindByID(ownerId);
                if (player != null) return player.displayName;
                return ownerId.ToString();
            }
            return "none";
        }
    }
}