CanUserLogin

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

namespace Oxide.Plugins
{
    [Info("Login Name Filter", "RustPluginGenerator", "1.0.0")]
    [Description("Rejects connections whose display name contains blocked fragments, unless the IP is allowed")]
    public class LoginNameFilter : RustPlugin
    {
        private const string PermBypass = "loginnamefilter.bypass";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Blocked name fragments (lowercase)")]
            public List<string> BlockedFragments = new List<string> { "discord.gg", "server name" };

            [JsonProperty("Allowed IP addresses")]
            public List<string> AllowedIps = new List<string>();

            [JsonProperty("Rejection message")]
            public string Rejection = "Your name contains blocked text: {0}";
        }

        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>
            {
                ["Rejected"] = "You cannot join with this name."
            }, 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(PermBypass, this);
        }

        private object CanUserLogin(string playerName, string connectionId, string connectionIp)
        {
            if (string.IsNullOrEmpty(playerName)) return null;
            if (config.AllowedIps != null && connectionIp != null && config.AllowedIps.Contains(connectionIp)) return null;
            if (permission.UserHasPermission(connectionId, PermBypass)) return null;

            var name = playerName.ToLowerInvariant();
            foreach (var fragment in config.BlockedFragments)
            {
                if (string.IsNullOrEmpty(fragment)) continue;
                if (name.Contains(fragment.ToLowerInvariant()))
                {
                    return Msg("Rejected", connectionId) + " (" + fragment + ")";
                }
            }
            return null;
        }
    }
}