LehrerApp/LehrerApp.Desktop/ViewModels/DashboardViewModel.cs

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using LehrerApp.Core.Services;
using System.Collections.ObjectModel;
using System.Globalization;

namespace LehrerApp.Desktop.ViewModels;

public partial class DashboardViewModel : ObservableObject
{
    private static readonly CultureInfo De = new("de-DE");

    private readonly IGroupRepository _groups;
    private readonly ILessonRepository _lessons;
    private readonly IExamRepository _exams;
    private readonly IWorkTaskRepository _tasks;
    private readonly SchoolYearService _sy;

    [ObservableProperty] private string _greeting = "";
    [ObservableProperty] private string _currentDate = "";
    [ObservableProperty] private string _currentSchoolYear = "";
    [ObservableProperty] private DateOnly _calendarMonth = FirstOfMonth(DateTime.Today);

    public string CalendarMonthLabel => CalendarMonth.ToString("MMMM yyyy", De);

    public ObservableCollection<LessonItem> TodaysLessons { get; } = [];
    public ObservableCollection<TaskItem> OpenTasks { get; } = [];
    public ObservableCollection<GroupChip> CurrentGroups { get; } = [];
    public ObservableCollection<CalendarDayCell> CalendarDays { get; } = [];
    public static string[] CalendarWeekdayHeaders { get; } = ["Mo", "Di", "Mi", "Do", "Fr", "Sa", "So"];

    // Navigation-Callback – wird von App.axaml.cs verdrahtet
    public Action<Guid>? OnNavigateToGroup { get; set; }

    public DashboardViewModel(IGroupRepository groups, ILessonRepository lessons,
        IExamRepository exams, IWorkTaskRepository tasks, SchoolYearService sy)
    {
        _groups = groups; _lessons = lessons; _exams = exams; _tasks = tasks; _sy = sy;
        Load();
    }

    private static DateOnly FirstOfMonth(DateTime d) => new(d.Year, d.Month, 1);

    private void Load()
    {
        var now   = DateTime.Now;
        var today = DateOnly.FromDateTime(now);
        CurrentDate        = now.ToString("dddd, d. MMMM yyyy", De);
        CurrentSchoolYear  = _sy.CurrentSchoolYear();
        Greeting = now.Hour < 12 ? "Guten Morgen" : now.Hour < 18 ? "Guten Tag" : "Guten Abend";

        TodaysLessons.Clear();
        var groups = _groups.GetBySchoolYear(_sy.CurrentSchoolYear()).ToDictionary(g => g.Id);
        foreach (var l in groups.Keys.SelectMany(gid => _lessons.GetByGroupAndDate(gid, today))
                                     .OrderBy(l => l.LessonNumber))
        {
            if (groups.TryGetValue(l.GroupId, out var g))
                TodaysLessons.Add(new() { GroupName = g.Name, Topic = l.Topic });
        }

        OpenTasks.Clear();
        foreach (var t in _tasks.GetByStatus(WorkTaskStatus.Open)
                                .Concat(_tasks.GetByStatus(WorkTaskStatus.InProgress))
                                .OrderBy(t => t.DueDate ?? DateOnly.MaxValue).Take(5))
            OpenTasks.Add(new() { Title = t.Title,
                DueDate   = t.DueDate?.ToString("dd.MM.") ?? "",
                IsOverdue = t.DueDate.HasValue && t.DueDate < today });

        CurrentGroups.Clear();
        foreach (var g in groups.Values.OrderBy(g => g.Name))
            CurrentGroups.Add(new() { GroupId = g.Id, Name = g.Name, Subject = g.Subject ?? "" });

        CalendarMonth = FirstOfMonth(now);
        LoadCalendar();
    }

    private void LoadCalendar()
    {
        CalendarDays.Clear();
        var today = DateOnly.FromDateTime(DateTime.Today);

        // Rasterstart: Montag der Woche, die den 1. des Monats enthält – 6 Wochen (42 Tage) Raster.
        var firstOfMonth = CalendarMonth;
        var mondayOffset = ((int)firstOfMonth.DayOfWeek + 6) % 7; // Montag=0 ... Sonntag=6
        var gridStart    = firstOfMonth.AddDays(-mondayOffset);
        var gridEnd      = gridStart.AddDays(41);

        var groups = _groups.GetBySchoolYear(_sy.CurrentSchoolYear());
        var byDay  = new Dictionary<DateOnly, DayAgg>();

        DayAgg Agg(DateOnly d)
        {
            if (!byDay.TryGetValue(d, out var agg)) byDay[d] = agg = new DayAgg();
            return agg;
        }

        foreach (var g in groups)
        {
            foreach (var lesson in _lessons.GetByGroupAndRange(g.Id, gridStart, gridEnd))
            {
                var agg = Agg(lesson.Date);
                agg.HasLesson = true;
                if (g.IsOwnClass) agg.IsOwnClassDay = true;
                agg.Details.Add($"Unterricht: {g.Name}" +
                    (string.IsNullOrWhiteSpace(lesson.Topic) ? "" : $" – {lesson.Topic}"));
            }

            foreach (var exam in _exams.GetByGroup(g.Id).Where(e => e.Date >= gridStart && e.Date <= gridEnd))
            {
                var agg = Agg(exam.Date);
                agg.HasExam = true;
                if (g.IsOwnClass) agg.IsOwnClassDay = true;
                agg.Details.Add($"Klausur: {exam.Title} ({g.Name})");
            }
        }

        for (var i = 0; i < 42; i++)
        {
            var date = gridStart.AddDays(i);
            byDay.TryGetValue(date, out var agg);
            CalendarDays.Add(new CalendarDayCell(date, date.Month == firstOfMonth.Month, date == today,
                agg?.HasLesson ?? false, agg?.HasExam ?? false, agg?.IsOwnClassDay ?? false,
                agg?.Details ?? []));
        }
    }

    [RelayCommand]
    private void PrevMonth()
    {
        CalendarMonth = CalendarMonth.AddMonths(-1);
        OnPropertyChanged(nameof(CalendarMonthLabel));
        LoadCalendar();
    }

    [RelayCommand]
    private void NextMonth()
    {
        CalendarMonth = CalendarMonth.AddMonths(1);
        OnPropertyChanged(nameof(CalendarMonthLabel));
        LoadCalendar();
    }

    [RelayCommand]
    private void CalendarToday()
    {
        CalendarMonth = FirstOfMonth(DateTime.Today);
        OnPropertyChanged(nameof(CalendarMonthLabel));
        LoadCalendar();
    }

    [RelayCommand] private void OpenGroup(GroupChip? c) { if (c is not null) OnNavigateToGroup?.Invoke(c.GroupId); }
    [RelayCommand] private void Refresh() => Load();

    private class DayAgg
    {
        public bool HasLesson;
        public bool HasExam;
        public bool IsOwnClassDay;
        public List<string> Details { get; } = [];
    }
}

public class LessonItem { public string GroupName { get; set; } = ""; public string Topic { get; set; } = ""; }
public class TaskItem   { public string Title { get; set; } = ""; public string DueDate { get; set; } = ""; public bool IsOverdue { get; set; } }
public class GroupChip  { public Guid GroupId { get; set; } public string Name { get; set; } = ""; public string Subject { get; set; } = ""; }

public class CalendarDayCell
{
    public int DayNumber { get; }
    public bool IsCurrentMonth { get; }
    public bool IsToday { get; }
    public bool HasLesson { get; }
    public bool HasExam { get; }
    public bool IsOwnClassDay { get; }
    public string Tooltip { get; }

    internal CalendarDayCell(DateOnly date, bool isCurrentMonth, bool isToday,
        bool hasLesson, bool hasExam, bool isOwnClassDay, List<string> details)
    {
        DayNumber      = date.Day;
        IsCurrentMonth = isCurrentMonth;
        IsToday        = isToday;
        HasLesson      = hasLesson;
        HasExam        = hasExam;
        IsOwnClassDay  = isOwnClassDay;
        Tooltip        = details.Count == 0 ? date.ToString("dd.MM.yyyy") : string.Join("\n", details);
    }
}