Discord.Net/src/Discord.Net.Commands/Map/CommandMap.cs

using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Linq;

namespace Discord.Commands
{
    internal class CommandMap
    {
        static readonly char[] _whitespaceChars = new char[] { ' ', '\r', '\n' };

        private readonly ConcurrentDictionary<string, CommandMapNode> _nodes;

        public CommandMap()
        {
            _nodes = new ConcurrentDictionary<string, CommandMapNode>();
        }

        public void AddCommand(Command command)
        {
            foreach (string text in command.Aliases)
            {
                int nextSpace = NextWhitespace(text);
                string name;

                if (nextSpace == -1)
                    name = command.Text;
                else
                    name = command.Text.Substring(0, nextSpace);

                lock (this)
                {
                    var nextNode = _nodes.GetOrAdd(name, x => new CommandMapNode(x));
                    nextNode.AddCommand(nextSpace == -1 ? "" : text, nextSpace + 1, command);
                }
            }
        }
        public void RemoveCommand(Command command)
        {
            string text = command.Text;
            int nextSpace = NextWhitespace(text);
            string name;

            if (nextSpace == -1)
                name = command.Text;
            else
                name = command.Text.Substring(0, nextSpace);

            lock (this)
            {
                CommandMapNode nextNode;
                if (_nodes.TryGetValue(name, out nextNode))
                {
                    nextNode.AddCommand(nextSpace == -1 ? "" : text, nextSpace + 1, command);
                    if (nextNode.IsEmpty)
                        _nodes.TryRemove(name, out nextNode);
                }
            }
        }

        public IEnumerable<Command> GetCommands(string text)
        {
            int nextSpace = NextWhitespace(text);
            string name;

            if (nextSpace == -1)
                name = text;
            else
                name = text.Substring(0, nextSpace);

            lock (this)
            {
                CommandMapNode nextNode;
                if (_nodes.TryGetValue(name, out nextNode))
                    return nextNode.GetCommands(text, nextSpace + 1);
                else
                    return Enumerable.Empty<Command>();
            }
        }

        private static int NextWhitespace(string text)
        {
            int lowest = int.MaxValue;
            for (int i = 0; i < _whitespaceChars.Length; i++)
            {
                int index = text.IndexOf(_whitespaceChars[i]);
                if (index != -1 && index < lowest)
                    lowest = index;
            }
            return (lowest != int.MaxValue) ? lowest : -1;
        }
    }
}