Scoreboard

using System;
using System.Collections.Generic;
using System.Linq;
using Wintellect.PowerCollections;

class Scoreboard
{
    private static Dictionary<string, string> usernameByPassword = new Dictionary<string, string>();

    private static Dictionary<string, string> gameByPassword = new Dictionary<string, string>();

    private static Dictionary<string, OrderedBag<User>> gameByScoreAndUsername =
        new Dictionary<string, OrderedBag<User>>();

    private static OrderedSet<string> gameNames = new OrderedSet<string>();

    static void Main()
    {
        string currentLine = null;

        while (currentLine != "End")
        {
            currentLine = Console.ReadLine();

            if (string.IsNullOrEmpty(currentLine))
            {
                continue;
            }

            var commandsArr = currentLine.Split(' ');
            var command = commandsArr[0];

            switch (command)
            {
                case "RegisterUser":
                    var regUsername = commandsArr[1];
                    var regPasss = commandsArr[2];
                    RegisterUser(regUsername, regPasss);
                    break;
                case "RegisterGame":
                    var regGameName = commandsArr[1];
                    var gamePasss = commandsArr[2];
                    RegisterGame(regGameName, gamePasss);
                    break;
                case "AddScore":
                    var regUser = commandsArr[1];
                    var regPassord = commandsArr[2];
                    var gameName = commandsArr[3];
                    var gamePassword = commandsArr[4];
                    int score = int.Parse(commandsArr[5]);
                    AddScore(regUser, regPassord, gameName, gamePassword, score);
                    break;
                case "ShowScoreboard":
                    var game = commandsArr[1];
                    ShowScoreboard(game);
                    break;
                case "ListGamesByPrefix":
                    var namePrefix = commandsArr[1];
                    ListGamesByPrefix(namePrefix);
                    break;
                case "DeleteGame":
                    var deleteGameName = commandsArr[1];
                    var deleteGamePass = commandsArr[2];
                    DeleteGame(deleteGameName, deleteGamePass);
                    break;
            }
        }
    }
    private static void ListGamesByPrefix(string namePrefix)
    {
        var prefixRange = gameNames.Range(namePrefix, true, namePrefix + "z", false)
            .Where(g => g.StartsWith(namePrefix)).Take(10);

        if (prefixRange.Any())
        {
            Console.WriteLine(string.Join(", ", prefixRange));
            return;
        }

        Console.WriteLine("No matches");
    }
    private static void DeleteGame(string gameNameForDelete, string gamePassForDelete)
    {
        if (!gameByPassword.ContainsKey(gameNameForDelete) ||
            gameByPassword[gameNameForDelete] != gamePassForDelete)
        {
            Console.WriteLine("Cannot delete game");
            return;
        }
        gameByPassword.Remove(gameNameForDelete);

        if (gameByScoreAndUsername.ContainsKey(gameNameForDelete))
        {
            gameByScoreAndUsername.Remove(gameNameForDelete);
        }
        gameNames.Remove(gameNameForDelete);

        Console.WriteLine("Game deleted");
    }

    private static void ShowScoreboard(string game)
    {
        if (!gameByScoreAndUsername.ContainsKey(game))
        {
            Console.WriteLine("Game not found");
            return;
        }
        if (gameByScoreAndUsername[game].Count == 0)
        {
            Console.WriteLine("No score");
            return;
        }

        var users = gameByScoreAndUsername[game].Take(10);
        var count = 1;
        foreach (var u in users)
        {
            Console.WriteLine("#{0} {1} {2}", count, u.Username, u.Score);
            count++;
        }
    }

    private static void AddScore(string regUser, string regPassord, string gameName, string gamePassword, int score)
    {
        if (!usernameByPassword.ContainsKey(regUser) ||
            usernameByPassword[regUser] != regPassord)
        {
            Console.WriteLine("Cannot add score");
            return;
        }
        if (!gameByPassword.ContainsKey(gameName) ||
            gameByPassword[gameName] != gamePassword)
        {
            Console.WriteLine("Cannot add score");
            return;
        }

        if (!gameByScoreAndUsername.ContainsKey(gameName))
        {
            gameByScoreAndUsername.Add(gameName, new OrderedBag<User>());
        }
        var user = new User()
        {
            Username = regUser,
            Score = score
        };
        gameByScoreAndUsername[gameName].Add(user);

        Console.WriteLine("Score added");
    }

    private static void RegisterUser(string regUsername, string regPasss)
    {
        if (usernameByPassword.ContainsKey(regUsername))
        {
            Console.WriteLine("Duplicated user");
            return;
        }
        usernameByPassword.Add(regUsername, regPasss);
        Console.WriteLine("User registered");
    }

    private static void RegisterGame(string regGameName, string gamePasss)
    {
        if (gameByPassword.ContainsKey(regGameName))
        {
            Console.WriteLine("Duplicated game");
            return;
        }
        gameByPassword.Add(regGameName, gamePasss);
        gameByScoreAndUsername.Add(regGameName, new OrderedBag<User>());
        gameNames.Add(regGameName);

        Console.WriteLine("Game registered");
    }
}

public class User : IComparable<User>
{
    public string Username { get; set; }
    public int Score { get; set; }

    public int CompareTo(User other)
    {
        var compareTo = this.Score.CompareTo(other.Score)*(-1);
        if (compareTo == 0)
        {
            compareTo = this.Username.CompareTo(other.Username);
        }

        return compareTo;
    }
}