ImServerGui.cs

using System.Collections.Generic;
using System.Linq;
using Exiled.API.Features;
using Exiled.API.Features.Core.UserSettings;
using Exiled.Events.EventArgs.Player;
using ImServerGUI.Components;

namespace ImServerGUI
{
    public abstract class ImServerGui
    {
        private readonly Dictionary<int, SettingBase> _registeredDefinitions = new();
        private readonly List<SettingBase> _registeredSettings = new();

        public abstract string GuiId { get; set; }

        protected Player Player { get; set; } = null;

        public void RegisterGui()
        {
            SubscribeEvents();
        }
        
        public void UnregisterGui()
        {   
            UnsubscribeEvents();
            SettingBase.Unregister(settings: _registeredSettings);
            _registeredDefinitions.Clear();
            _registeredSettings.Clear();

            foreach (Player player in Player.List)
                player.GetServerGui()?.GuiProperties.GuiElements.Clear();
        }

        private void SubscribeEvents()
        {
            Exiled.Events.Handlers.Player.Verified += OnPlayerVerified;
        }
        
        private void UnsubscribeEvents()
        {
            Exiled.Events.Handlers.Player.Verified -= OnPlayerVerified;
        }

        private void OnPlayerVerified(VerifiedEventArgs ev)
        {
            if (ev.Player == null)
                return;
            
            Player = ev.Player;
            
            if (Player.GetServerGui() == null)
                Player.AddServerGui();

            var guiElements = Player.GetServerGui().GuiProperties.GuiElements;
            
            if (guiElements == null)
            {
                Log.Error("GuiElements not be found.");
                return;
            }
            
            Log.Debug("Target successfully processed.");
            
            guiElements.Clear();
            Gui(Player);
            RegisterDefinitions(guiElements);
            SettingBase.SendToPlayer(Player, guiElements);
        }

        protected abstract void Gui(Player player);
        
        protected void AddGuiElement(SettingBase setting) => Player.GetServerGui().GuiProperties.GuiElements.Add(setting);

        private void RegisterDefinitions(IEnumerable<SettingBase> settings)
        {
            List<SettingBase> settingsToRegister = new();

            foreach (SettingBase setting in settings.Where(setting => setting?.OnChanged != null))
            {
                if (_registeredDefinitions.TryGetValue(setting.Id, out SettingBase registeredSetting))
                {
                    registeredSetting.OnChanged = setting.OnChanged;
                    continue;
                }

                _registeredDefinitions[setting.Id] = setting;
                settingsToRegister.Add(setting);
            }

            if (settingsToRegister.Count == 0)
                return;

            _registeredSettings.AddRange(SettingBase.Register(settingsToRegister, _ => false));
        }
    }
}