Initial

LehrerApp.Core/Services/GradingService.cs

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+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;
+    }
+}

LehrerApp.Core/Services/SchoolYearService.cs

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+namespace LehrerApp.Core.Services;
+
+public class SchoolYearService
+{
+    /// <summary>
+    /// Gibt das aktuelle Schuljahr zurück, z.B. "2024/25".
+    /// Schuljahr beginnt am 1. August.
+    /// </summary>
+    public string CurrentSchoolYear()
+    {
+        var now = DateTime.Today;
+        var startYear = now.Month >= 8 ? now.Year : now.Year - 1;
+        return FormatSchoolYear(startYear);
+    }
+
+    public string FormatSchoolYear(int startYear) =>
+        $"{startYear}/{(startYear + 1) % 100:D2}";
+
+    /// <summary>
+    /// Gibt den Beginn des Schuljahres zurück (1. August).
+    /// </summary>
+    public DateOnly SchoolYearStart(string schoolYear)
+    {
+        var year = int.Parse(schoolYear.Split('/')[0]);
+        return new DateOnly(year, 8, 1);
+    }
+
+    /// <summary>
+    /// Gibt das Ende des Schuljahres zurück (31. Juli des Folgejahres).
+    /// </summary>
+    public DateOnly SchoolYearEnd(string schoolYear)
+    {
+        var year = int.Parse(schoolYear.Split('/')[0]) + 1;
+        return new DateOnly(year, 7, 31);
+    }
+
+    /// <summary>
+    /// Gibt die letzten N Schuljahre zurück (für Dropdowns).
+    /// </summary>
+    public List<string> RecentSchoolYears(int count = 5)
+    {
+        var now = DateTime.Today;
+        var currentStart = now.Month >= 8 ? now.Year : now.Year - 1;
+        return Enumerable.Range(0, count)
+            .Select(i => FormatSchoolYear(currentStart - i))
+            .ToList();
+    }
+}