StringSpam??

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;

namespace TestConsole
{
    class Program
    {
        static void Main()
        {
            Func<string, bool> sameLettersRule = s =>
            {
                if (s.Length < 3)
                    return false;
                return s.Select(c => char.ToLower(c))
                                         .GroupBy(c => c)
                                         .Select(a => ((double)a.Count() / s.Length) * 100)
                                         .Max() >= 50;
            };

            Func<string, bool> upperCaseLettersRule = s =>
                {
                    if (s.Length < 3)
                        return false;
                    return ((double)s.Count(c =>
                        char.IsUpper(c)) / s.Length * 100 >= 50);
                };

            string dataTest = string.Empty;

            SpamTest spamTest = new SpamTest(dataTest);
            spamTest.ApplyRule(sameLettersRule, "50% of the string must not be the same letter");
            spamTest.ApplyRule(upperCaseLettersRule, "Hop lige ned fra caps");

            User user = new User() { Id = 1, Name="Henrik" };
            spamTest.AddUser(user, user.DisplayTextForUser);

            while (true)
            {
                spamTest.AppendData(user, Console.ReadLine());
            }
        }
    }

    class User
    {
        public int Id { get; set; }
        public string Name { get; set; }

        public void DisplayTextForUser(string text)
        {
            Console.WriteLine(text);
        }
    }

    class SpamTest
    {
        private readonly StringBuilder dataTest;
        private readonly Dictionary<Func<string, bool>, string> contentControllers;
        private readonly Dictionary<User, Action<string>> userOutputWriters;
        private readonly Stopwatch stopWatch;
        private int appendedLineCounter = default(int);
        private const long SPAM_PROTECT_DELAY = 10000;

        public SpamTest(string dataTest)
        {
            this.dataTest = new StringBuilder(dataTest);
            contentControllers = new Dictionary<Func<string, bool>, string>();
            userOutputWriters = new Dictionary<User, Action<string>>();
            stopWatch = new Stopwatch();
        }

        public void AddUser(User user, Action<string> userOutputWriter)
        {
            userOutputWriters.Add(user, userOutputWriter);
        }

        public void AppendData(User sender, string someData)
        {
            Action<string> userOutputWriter;
            if (!userOutputWriters.TryGetValue(sender, out userOutputWriter))
                throw new Exception("User not found");

            if (string.IsNullOrEmpty(someData))
                return;
            if (DoesntHaveIllegalContent(someData, userOutputWriter))
                if (TryAppendData(someData, userOutputWriter))
                    Console.WriteLine("Data written to string");
        }

        private bool TryAppendData(string data, Action<string> writer)
        {
            if (stopWatch.ElapsedMilliseconds >= SPAM_PROTECT_DELAY)
            {
                stopWatch.Stop();
                stopWatch.Reset();
                appendedLineCounter = 0;
            }

            else if (stopWatch.ElapsedMilliseconds < SPAM_PROTECT_DELAY && appendedLineCounter >= 5)
            {
                writer("Stop spamming!");
                return false;
            }

            dataTest.AppendLine(data);
            stopWatch.Start();
            appendedLineCounter++;
            return true;
        }

        private bool DoesntHaveIllegalContent(string someData, Action<string> writer)
        {
            var errors = contentControllers.Where(kvp => kvp.Key(someData)).Select(e => e.Value);
            if (errors.Count() < 1)
                return true;

            foreach (var error in errors)
                writer(error);
            return false;
        }

        public void ApplyRule(Func<string, bool> func, string errorMessage)
        {
            contentControllers.Add(func, errorMessage);
        }
    }
}