using LehrerApp.Core.Models;

namespace LehrerApp.Core.Services;

public class GradingService
{
    /// <summary>
    /// Berechnet die Note aus Punkten anhand des Notenschlüssels der Klausur.
    /// </summary>
    public string CalculateGrade(double achieved, double maximum, List<GradingKeyEntry> key)
    {
        if (maximum <= 0) return "-";
        var percent = achieved / maximum * 100.0;

        return key
            .OrderByDescending(k => k.MinPercent)
            .FirstOrDefault(k => percent >= k.MinPercent)
            ?.Grade ?? key.OrderBy(k => k.MinPercent).First().Grade;
    }

    /// <summary>
    /// Standardnotenschlüssel 1–6 nach NRW-Schema (anpassbar).
    /// </summary>
    public static List<GradingKeyEntry> DefaultKey1To6() =>
    [
        new() { Grade = "1", MinPercent = 87.5 },
        new() { Grade = "2", MinPercent = 75.0 },
        new() { Grade = "3", MinPercent = 62.5 },
        new() { Grade = "4", MinPercent = 50.0 },
        new() { Grade = "5", MinPercent = 25.0 },
        new() { Grade = "6", MinPercent = 0.0  },
    ];

    /// <summary>
    /// Standardnotenschlüssel 0–15 Punkte (Oberstufe).
    /// </summary>
    public static List<GradingKeyEntry> DefaultKey0To15() =>
    [
        new() { Grade = "15", MinPercent = 95.0 },
        new() { Grade = "14", MinPercent = 90.0 },
        new() { Grade = "13", MinPercent = 85.0 },
        new() { Grade = "12", MinPercent = 80.0 },
        new() { Grade = "11", MinPercent = 75.0 },
        new() { Grade = "10", MinPercent = 70.0 },
        new() { Grade = "9",  MinPercent = 65.0 },
        new() { Grade = "8",  MinPercent = 60.0 },
        new() { Grade = "7",  MinPercent = 55.0 },
        new() { Grade = "6",  MinPercent = 50.0 },
        new() { Grade = "5",  MinPercent = 45.0 },
        new() { Grade = "4",  MinPercent = 40.0 },
        new() { Grade = "3",  MinPercent = 33.0 },
        new() { Grade = "2",  MinPercent = 27.0 },
        new() { Grade = "1",  MinPercent = 20.0 },
        new() { Grade = "0",  MinPercent = 0.0  },
    ];

    /// <summary>
    /// Berechnet den Notendurchschnitt aus einer Liste von Notenwerten (1-6 System).
    /// </summary>
    public double AverageGrade1To6(List<string> grades)
    {
        var numeric = grades
            .Select(g => int.TryParse(g, out var n) ? (int?)n : null)
            .Where(n => n.HasValue)
            .Select(n => n!.Value)
            .ToList();

        return numeric.Count == 0 ? 0 : numeric.Average();
    }

    /// <summary>
    /// Berechnet den Notendurchschnitt aus gewichteten Noten.
    /// </summary>
    public double WeightedAverage(List<(string Grade, double Weight)> grades)
    {
        var numeric = grades
            .Select(g => (
                Value: int.TryParse(g.Grade, out var n) ? (int?)n : null,
                g.Weight))
            .Where(g => g.Value.HasValue)
            .ToList();

        if (numeric.Count == 0) return 0;

        var totalWeight = numeric.Sum(g => g.Weight);
        var weightedSum = numeric.Sum(g => g.Value!.Value * g.Weight);

        return totalWeight == 0 ? 0 : weightedSum / totalWeight;
    }
}