NadekoBot/NadekoBot/Commands/CopyCommand.cs

using System;
using System.Collections.Generic;
using System.Threading.Tasks;
using Discord.Commands;

namespace NadekoBot.Commands
{
    internal class CopyCommand : IDiscordCommand
    {
        private readonly HashSet<ulong> CopiedUsers = new HashSet<ulong>();

        public CopyCommand() 
        {
            NadekoBot.Client.MessageReceived += Client_MessageReceived;
        }

        private async void Client_MessageReceived(object sender, Discord.MessageEventArgs e)
        {
            try {
                if (string.IsNullOrWhiteSpace(e.Message.Text))
                    return;
                if (CopiedUsers.Contains(e.User.Id)) {
                    await e.Channel.SendMessage(e.Message.Text);
                }
            }
            catch { }
        }

        public Func<CommandEventArgs, Task> DoFunc() => async e =>
        {
            if (CopiedUsers.Contains(e.User.Id)) return;

            CopiedUsers.Add(e.User.Id);
            await e.Channel.SendMessage(" I'll start copying you now.");
        };

        public void Init(CommandGroupBuilder cgb)
        {
            cgb.CreateCommand("copyme")
                .Alias("cm")
                .Description("Nadeko starts copying everything you say. Disable with cs")
                .Parameter("silent")
                .Do(DoFunc());

            cgb.CreateCommand("cs")
                .Alias("copystop")
                .Description("Nadeko stops copying you")
                .Do(StopCopy());
        }

        private Func<CommandEventArgs, Task> StopCopy() => async e =>
        {
            if (!CopiedUsers.Contains(e.User.Id)) return;

            CopiedUsers.Remove(e.User.Id);
            await e.Channel.SendMessage(" I wont copy anymore.");
        };
    }
}