OnServerMessage

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

namespace Oxide.Plugins
{
    [Info("Server Message Filter", "RustPluginGenerator", "1.0.0")]
    [Description("Suppresses configured automatic server chat broadcasts such as save warnings.")]
    public class ServerMessageFilter : RustPlugin
    {
        private const string PermAdmin = "servermessagefilter.admin";

        private PluginConfig config;

        private class PluginConfig
        {
            [JsonProperty("Filtering enabled")]
            public bool Enabled = true;

            [JsonProperty("Blocked keywords (case insensitive)")]
            public List<string> BlockedKeywords = new List<string>
            {
                "Saving",
                "Restarting",
                "Server is shutting down"
            };
        }

        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>
            {
                ["FilterOn"] = "Server message filtering is now enabled.",
                ["FilterOff"] = "Server message filtering is now disabled.",
                ["NoPermission"] = "You do not have permission to use this command."
            }, this);
        }

        private void Init()
        {
            permission.RegisterPermission(PermAdmin, this);
        }

        [ChatCommand("smsg")]
        private void CmdServerMessage(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                SendReply(player, Msg("NoPermission", player.UserIDString));
                return;
            }

            config.Enabled = !config.Enabled;
            SaveConfig();
            SendReply(player, Msg(config.Enabled ? "FilterOn" : "FilterOff", player.UserIDString));
        }

        private object OnServerMessage(string message, string username, string color, ulong userid)
        {
            if (!config.Enabled || string.IsNullOrEmpty(message)) return null;

            foreach (string keyword in config.BlockedKeywords)
            {
                if (string.IsNullOrEmpty(keyword)) continue;
                if (message.IndexOf(keyword, StringComparison.OrdinalIgnoreCase) >= 0)
                    return false;
            }

            return null;
        }

        private string Msg(string key, string userId = null) => lang.GetMessage(key, this, userId);
    }
}