source: binary-improvements/7dtd-server-fixes/src/PersistentData/Players.cs@ 158

using System;
using System.Collections.Generic;
using System.Runtime.Serialization;
using System.Text.RegularExpressions;

namespace AllocsFixes.PersistentData
{
        [Serializable]
        public class Players
        {
                private Dictionary<string, Player> players = new Dictionary<string, Player> ();

                public Player this [string steamId] {
                        get {
                                if (players.ContainsKey (steamId))
                                        return players [steamId];
                                else {
                                        if (steamId != null && steamId.Length == 17) {
                                                Log.Out ("Created new player entry for ID: " + steamId);
                                                Player p = new Player (steamId);
                                                players.Add (steamId, p);
                                                return p;
                                        }
                                        return null;
                                }
                        }
                }

                public List<string> SteamIDs {
                        get { return new List<string> (players.Keys); }
                }

                public int Count {
                        get { return players.Count; }
                }

                public Player GetPlayerByClientId (int _clientid)
                {
                        foreach (Player p in players.Values) {
                                if (p.ClientInfo.clientId == _clientid) {
                                        return p;
                                }
                        }
                        return null;
                }

                public string GetSteamID (string _nameOrId, bool _ignoreColorCodes)
                {
                        if (_nameOrId == null || _nameOrId.Length == 0)
                                return null;

                        long tempLong;
                        if (_nameOrId.Length == 17 && long.TryParse (_nameOrId, out tempLong)) {
                                return _nameOrId;
                        } else {
                                int entityId = -1;
                                if (int.TryParse (_nameOrId, out entityId)) {
                                        foreach (KeyValuePair<string, Player> kvp in players) {
                                                if (kvp.Value.IsOnline && kvp.Value.EntityID == entityId) {
                                                        return kvp.Key;
                                                }
                                        }
                                }

                                _nameOrId = _nameOrId.ToLower ();
                                foreach (KeyValuePair<string, Player> kvp in players) {
                                        string name = kvp.Value.Name.ToLower ();
                                        if (_ignoreColorCodes) {
                                                name = Regex.Replace (name, "\\[[0-9a-fA-F]{6}\\]", "");
                                        }
                                        if (kvp.Value.IsOnline && name.Equals (_nameOrId)) {
                                                return kvp.Key;
                                        }
                                }
                        }
                        return null;
                }
        }
}