using System;

public class Program

{

    static double eloWeight = 400; // if the difference in elo equals the eloWeight, the better player is expected to win with a perfect score

    static double defaultKfactor = 25; // default kfactor for players who played at least X amount of matches

    static double defaultKfactorForAbsoluteNewPlayer = 50; // the default max value of kfactor where 0 matches played = abosulte value

    static double defaultKfactorForProPlayer = 15; // the default value for a pro player

    static double defaultKfactorEloRequiredForProPlayer = 2000; // the expected elo to be recoqnized as a pro player

    static double defaultKfactorNrMatches = 30; // amount of matches a players needs to play to reach the default kfactor

    static double defaultKfactorMinScoreResult = 0.1;

    static double negative1 = -1;

    public static void Main()

    {

        Console.WriteLine("Elo calculation");

        Console.WriteLine("");

        //MatchPlayed(1500, 1500, 7, 3, 0, 0); // First match between 2 players

        //MatchPlayed(1800, 1500, 10, 0, 30, 0); // Experienced high player vs new player

        //MatchPlayed(1800, 1500, 10, 0, 30, 30); // Experienced high player vs experienced avarage player

        //MatchPlayed(2050, 1500, 10, 0, 30, 30); // Pro player vs experienced avarage player

        MatchPlayed(1870, 1500, 4, 6, 30, 30); // Doubles match

        //MatchPlayed(2000, 1800, 7, 3, 50, 35);

    }

    public static void MatchPlayed(double eloPlayer1, double eloPlayer2, double scorePlayer1, double scorePlayer2, double matchesPlayedPlayer1, double matchesPlayedPlayer2)

    {

        Console.WriteLine("EloPlayer1: " + eloPlayer1);

        Console.WriteLine("EloPlayer2: " + eloPlayer2);

        Console.WriteLine("Match result: " + scorePlayer1 + " - " + scorePlayer2);

        CalculateElo(eloPlayer1, eloPlayer2, scorePlayer1, scorePlayer2, matchesPlayedPlayer1, matchesPlayedPlayer2);

    }

    public static void CalculateElo(double eloPlayer1, double eloPlayer2, double scorePlayer1, double scorePlayer2, double matchesPlayedPlayer1, double matchesPlayedPlayer2)

    {

        double winningScore = scorePlayer1 > scorePlayer2 ? scorePlayer1 : scorePlayer2; // Getting the winning score

        double losingScore = scorePlayer1 < scorePlayer2 ? scorePlayer1 : scorePlayer2; // Getting the losing score

        double winningScoreResult = winningScore / (winningScore + losingScore); // Calculating the winning score result

        // Assiging score result to player 1 and 2

        double scoreResultPlayer1 = scorePlayer1 == winningScore ? winningScoreResult : (1-winningScoreResult);

        double scoreResultPlayer2 = scorePlayer2 == winningScore ? winningScoreResult : (1-winningScoreResult);

        Console.WriteLine("Result player1: " + scoreResultPlayer1);

        Console.WriteLine("Result player2: " + scoreResultPlayer2);

        // Calculating expected score results

        double expectedScorePlayer1 = 1 / (1 + (Math.Pow(10, (eloPlayer2 - eloPlayer1) / eloWeight)));

        double expectedScorePlayer2 = 1 / (1 + (Math.Pow(10, (eloPlayer1 - eloPlayer2) / eloWeight)));

        Console.WriteLine("Expected result player1: " + expectedScorePlayer1);

        Console.WriteLine("Expected result player2: " + expectedScorePlayer2);

        // Calculating kFactor for players

        double kFactorPlayer1 = GetKfactor(eloPlayer1, expectedScorePlayer1, scoreResultPlayer1, expectedScorePlayer2, matchesPlayedPlayer1);

        double kFactorPlayer2 = GetKfactor(eloPlayer2, expectedScorePlayer2, scoreResultPlayer2, expectedScorePlayer1, matchesPlayedPlayer2);

        Console.WriteLine("kfactor player1: " + kFactorPlayer1);

        Console.WriteLine("kfactor player2: " + kFactorPlayer2);

        // Calculating new elo for players

        double newEloPlayer1 = eloPlayer1 + (kFactorPlayer1 * ( scoreResultPlayer1 - expectedScorePlayer1 ) );

        double newEloPlayer2 = eloPlayer2 + (kFactorPlayer2 * ( scoreResultPlayer2 - expectedScorePlayer2 ) );

        // Elo cannot drop below 0

        newEloPlayer1 = newEloPlayer1 >= 0 ? newEloPlayer1 : 0;

        newEloPlayer1 = newEloPlayer2 >= 0 ? newEloPlayer1 : 0;

        Console.WriteLine("New elo player1: " + newEloPlayer1);

        Console.WriteLine("New elo player2: " + newEloPlayer2);

    }

    public static double GetKfactor(double playerElo, double playerExpectedScore, double playerScoreResult, double opponentExpectedScore, double matchesPlayed)

    {

        double kfactor = 0;

        // Determine kfactor based on nr of matches played

        if (matchesPlayed == 0)

        {

            // absolute new player

            kfactor = defaultKfactorForAbsoluteNewPlayer;

        }

        else if (matchesPlayed < defaultKfactorNrMatches)

        {

            // substract kfactor based on amount of matches played

            double defaultKfactorDifference = defaultKfactorForAbsoluteNewPlayer - defaultKfactor;

            kfactor = defaultKfactorForAbsoluteNewPlayer - (defaultKfactorDifference * (1 / defaultKfactorNrMatches * matchesPlayed));

        }

        else if (matchesPlayed >= defaultKfactorNrMatches && playerElo >= defaultKfactorEloRequiredForProPlayer)

        {

            kfactor = defaultKfactorForProPlayer;

        }

        else

        {

            kfactor = defaultKfactor;

        }

        // kfactor bonus variant

        // kfactor bonus can be at maximum 10

        // kfactor bonus percentage is based on 

        double kfactorBonusPercentage = (1 - (1 / playerExpectedScore * playerScoreResult));

        kfactorBonusPercentage = kfactorBonusPercentage >= 0 ? kfactorBonusPercentage : kfactorBonusPercentage * negative1; // Set positive percentage if needed

        kfactorBonusPercentage = kfactorBonusPercentage > 1 ? 1 : kfactorBonusPercentage; // limit to max percentage

        // Add kfactor bonus variant

        kfactor += 10 * kfactorBonusPercentage;

        // another kfactor bonus variant

        // kfactor bonus is essentially unlimited

        // kfactor bonus is calculated based on expected score vs resulted score multiplied by 10

        // for instance

        // player expected to win with a score of 0.2

        // player won with a score of 0.6

        // player performed 3x better then expected

        // kfactor bonus = 30 (3x10)

        return kfactor;

    }

}