How to make a Rust chat titles and colors plugin (Oxide group tags)

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

namespace Oxide.Plugins
{
    [Info("Better Chat Titles", "RustPluginGenerator", "1.0.0")]
    [Description("Formats chat lines with an Oxide group tag and colors, keeping the player's avatar.")]
    public class BetterChatTitles : RustPlugin
    {
        private const string PermAdmin = "betterchattitles.admin";

        private PluginConfig config;

        private class GroupFormat
        {
            [JsonProperty("Priority")]
            public int Priority { get; set; }

            [JsonProperty("Tag")]
            public string Tag { get; set; }

            [JsonProperty("Name color")]
            public string NameColor { get; set; }

            [JsonProperty("Message color")]
            public string MessageColor { get; set; }
        }

        private class PluginConfig
        {
            [JsonProperty("Chat format")]
            public string Format { get; set; }

            [JsonProperty("Show admin marker")]
            public bool ShowAdminMarker { get; set; }

            [JsonProperty("Admin marker")]
            public string AdminMarker { get; set; }

            [JsonProperty("Default group")]
            public GroupFormat Default { get; set; }

            [JsonProperty("Groups")]
            public Dictionary<string, GroupFormat> Groups { get; set; }
        }

        protected override void LoadDefaultConfig()
        {
            config = new PluginConfig
            {
                Format = "{tag}{name}: {message}",
                ShowAdminMarker = true,
                AdminMarker = "[ADMIN] ",
                Default = new GroupFormat
                {
                    Priority = 0,
                    Tag = string.Empty,
                    NameColor = "#FFFFFF",
                    MessageColor = "#EEEEEE"
                },
                Groups = new Dictionary<string, GroupFormat>
                {
                    ["vip"] = new GroupFormat { Priority = 10, Tag = "[VIP] ", NameColor = "#FFD166", MessageColor = "#FFFFFF" },
                    ["moderator"] = new GroupFormat { Priority = 50, Tag = "[MOD] ", NameColor = "#66CCFF", MessageColor = "#E6F7FF" },
                    ["admin"] = new GroupFormat { Priority = 100, Tag = "[ADMIN] ", NameColor = "#FF6666", MessageColor = "#FFE6E6" }
                }
            };
        }

        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>
            {
                ["FormatInfo"] = "Your tag: '{0}' | name color: {1} | message color: {2}\nTemplate: {3}"
            }, 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 object OnPlayerChat(BasePlayer player, string message, ConVar.Chat.ChatChannel channel)
        {
            if (player == null || string.IsNullOrEmpty(message)) return null;
            if (channel != ConVar.Chat.ChatChannel.Global) return null;

            message = message.Trim();
            if (message.Length == 0) return null;

            var format = ResolveFormat(player);
            string tag = format.Tag ?? string.Empty;
            if (config.ShowAdminMarker && player.IsAdmin)
                tag = (config.AdminMarker ?? string.Empty) + tag;

            string line = (config.Format ?? "{tag}{name}: {message}")
                .Replace("{tag}", tag)
                .Replace("{name}", Colorize(player.displayName, format.NameColor))
                .Replace("{message}", Colorize(message, format.MessageColor));

            player.SendConsoleCommand("chat.add", 0, player.userID.Get(), line);
            return true;
        }

        private GroupFormat ResolveFormat(BasePlayer player)
        {
            GroupFormat best = null;
            var groups = permission.GetUserGroups(player.UserIDString);
            if (groups != null && config.Groups != null)
            {
                foreach (var group in groups)
                {
                    if (string.IsNullOrEmpty(group)) continue;
                    GroupFormat entry;
                    if (!config.Groups.TryGetValue(group, out entry) || entry == null) continue;
                    if (best == null || entry.Priority > best.Priority) best = entry;
                }
            }

            return best ?? config.Default ?? new GroupFormat
            {
                Priority = 0,
                Tag = string.Empty,
                NameColor = "#FFFFFF",
                MessageColor = "#EEEEEE"
            };
        }

        private static string Colorize(string text, string color)
        {
            if (string.IsNullOrEmpty(color)) return text;
            return string.Format("<color={0}>{1}</color>", color, text);
        }

        [ChatCommand("chatformat")]
        private void CmdChatFormat(BasePlayer player, string command, string[] args)
        {
            if (player == null) return;
            if (!permission.UserHasPermission(player.UserIDString, PermAdmin))
            {
                player.ChatMessage("You do not have permission to use this command.");
                return;
            }

            var format = ResolveFormat(player);
            player.ChatMessage(Msg("FormatInfo", player.UserIDString,
                format.Tag ?? string.Empty,
                format.NameColor ?? "none",
                format.MessageColor ?? "none",
                config.Format ?? "{tag}{name}: {message}"));
        }
    }
}