namespace Highscore;

/// <summary>
///     Processing of gamer scores to determine an overall highscore
/// </summary>
public static class HighscoreProcessing
{
    private const char Separator = ';';

    /// <summary>
    ///     Executes the <see cref="HighscoreProcessing"/> program.
    /// </summary>
    public static void Run()
    {
        var scores = LoadScoresFromFile("Data/scores.csv");
        var bestScores = FindBestScorePerUser(scores);
        SortGameScores(bestScores);
        WriteOutputFileAndPrint(bestScores, "Data/highscore.csv");
    }

    /// <summary>
    ///     Writes the provided <see cref="GameScore"/> instances to a file at the supplied path.
    ///     The CSV format is Score;Date;Player.
    /// </summary>
    /// <param name="highscore">Game scores to persist</param>
    /// <param name="filePath">Path to write to</param>
    public static void WriteOutputFileAndPrint(GameScore[] highscore, string filePath)
    {
        string[] lines = new string[highscore.Length + 1];
        lines[0] = "Score;Date;Player";
        for (int i = 0; i < highscore.Length; i++)
        {
            lines[i + 1] = $"{highscore[i].Score};{highscore[i].Date:dd.MM.yyyy};{highscore[i].Player.NickName} (#{highscore[i].Player.Id})";
        }
        File.WriteAllLines(filePath, lines);
    }

    /// <summary>
    ///     Loads the CSV file at the supplied path and attempts to parse its content to
    ///     create an array of <see cref="GameScore"/> instances utilizing <see cref="TryParseGameScore"/>.
    /// </summary>
    /// <param name="filePath">Path to read from</param>
    /// <returns>Array of parsed items; empty array if file does not exist or is empty</returns>
    public static GameScore[] LoadScoresFromFile(string filePath)
    {
        if (!Path.Exists(filePath))
        {
            return Array.Empty<GameScore>();
        }
        
        string[] loadedScores = File.ReadAllLines(filePath);
        if (loadedScores.Length <= 1)
        {
            return Array.Empty<GameScore>();
        }
        loadedScores = loadedScores[1..];
        GameScore?[] gameScores = new GameScore[loadedScores.Length];
        for (int i = 0; i < loadedScores.Length; i++)
        {
            if (TryParseGameScore(loadedScores[i], out GameScore? gameScore))
            {
                if(gameScore!.Player.Id < 0 || gameScore.Score < 0)
                {
                    gameScores[i] = null;
                    continue;
                }
                gameScores[i] = gameScore!;
            }
            else
            {
                gameScores[i] = null;
            }
        }

        return TrimArray(gameScores);
    }

    /// <summary>
    ///     Attempts to parse a CSV formatted string to a <see cref="GameScore"/> object.
    /// </summary>
    /// <param name="line">String to parse</param>
    /// <param name="gameScore">Successfully parsed object; null if parsing fails</param>
    /// <returns>True if parsed successfully; false otherwise</returns>
    public static bool TryParseGameScore(string line, out GameScore? gameScore)
    {
        gameScore = null;
        
        string[] parts = line.Split(Separator);
        if (parts.Length != 4)
        {
            return false;
        }

        if (!int.TryParse(parts[0], out int id) || !DateTime.TryParse(parts[2], out DateTime date) ||
            !int.TryParse(parts[3], out int score))
        {
            return false;
        }
        if(parts[1] == string.Empty || score < 0)
        {
            return false;
        }
        
        gameScore = new GameScore(new Player(id, parts[1]), score, date);
        return true;
    }

    /// <summary>
    ///     Based on the provided full set of game scores for each user the best score is determined.
    ///     If a user has two or more entries with the same score the oldest (earliest) entry is considered to
    ///     be the highest.
    /// </summary>
    /// <param name="allScores">Collection of all scores; may contain multiple entries for one user</param>
    /// <returns>An array containing the highest score of each user, based on passed scores</returns>
    public static GameScore[] FindBestScorePerUser(GameScore[] allScores)
    {
        GameScore[] sortedScored = allScores;
        SortGameScores(sortedScored);
        sortedScored = TrimScorePerUser(sortedScored);
        return sortedScored;
    }

    private static GameScore[] TrimScorePerUser(GameScore?[] scores)
    {
        for (int i = 0; i < scores.Length; i++)
        {
            for (int j = 0; j < scores.Length; j++)
            {
                if (scores[i]?.Player.Id == scores[j]?.Player.Id && i != j)
                {
                    if(scores[i] == null || scores[j] == null)
                    {
                        continue;
                    }
                    if (scores[i]!.Score < scores[j]!.Score || 
                        (scores[i]!.Score == scores[j]!.Score && scores[i]!.Date > scores[j]!.Date))
                    {
                        (scores[i], scores[j]) = (scores[j], scores[i]);
                    }
                    scores[j] = null;
                }
            }
        }

        return TrimArray(scores);
    }

    /// <summary>
    ///     Sorts the provided <see cref="GameScore"/> instances so that those with the
    ///     highest score (older date is preferred if score is equal) are ranked first.
    ///     Sorting happens in-place.
    /// </summary>
    /// <param name="scores">Scores to sort</param>
    public static void SortGameScores(GameScore[] scores)
    {
        for (int i = 0; i < scores.Length; i++)
        {
            for (int j = i + 1; j < scores.Length; j++)
            {
                if (scores[i].Score < scores[j].Score)
                {
                    (scores[i], scores[j]) = (scores[j], scores[i]);
                }
                else if (scores[i].Score == scores[j].Score && scores[i].Date > scores[j].Date)
                {
                    (scores[i], scores[j]) = (scores[j], scores[i]);
                }
            }
        }
    }

    /// <summary>
    ///     Trims empty (null) entries from the provided array.
    /// </summary>
    /// <param name="arrayToTrim">The array to process</param>
    /// <returns>A new array containing only the non-null entries from the passed array</returns>
    public static GameScore[] TrimArray(GameScore?[] arrayToTrim)
    {
        if (arrayToTrim.Length == 0)
        {
            return Array.Empty<GameScore>();
        }
        int index = 0;
        foreach (var VARIABLE in arrayToTrim)
        {
            if (VARIABLE != null)
            {
                index++;
            }
        }
        if (index == 0)
        {
            return Array.Empty<GameScore>();
        }
        
        var trimmedArray = new GameScore[index];
        index = 0;
        for (int i = 0; i < arrayToTrim.Length; i++)
        {
            if (arrayToTrim[i] != null)
            {
                trimmedArray[index++] = arrayToTrim[i]!;
            }
        }
        return trimmedArray;
    }
}