LehrerApp/LehrerApp.Desktop/ViewModels/MainWindowViewModel.cs

using Avalonia.Threading;
using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LehrerApp.Core.Services;
using LehrerApp.Desktop.Services;
using LehrerApp.Desktop.ViewModels.ClassTeacher;
using LehrerApp.Desktop.ViewModels.Exams;
using LehrerApp.Desktop.ViewModels.Groups;
using LehrerApp.Desktop.ViewModels.Planning;
using LehrerApp.Desktop.ViewModels.Settings;
using LehrerApp.Desktop.ViewModels.Students;
using LehrerApp.Desktop.ViewModels.Workload;
using Microsoft.Extensions.DependencyInjection;
using System.Collections.ObjectModel;

namespace LehrerApp.Desktop.ViewModels;

public partial class MainWindowViewModel : ObservableObject
{
    private readonly IServiceProvider _services;

    [ObservableProperty] private ObservableObject? _currentPage;
    [ObservableProperty] private NavItem _activeNavItem = NavItem.Dashboard;
    [ObservableProperty] private string _currentSchoolYear = "";
    [ObservableProperty] private bool _isCommandPaletteOpen;

    public SyncStatusViewModel SyncStatus { get; }
    public ObservableCollection<ToastItem> Toasts { get; }
    public AppLockViewModel AppLock { get; }
    public GlobalSearchViewModel CommandPalette { get; }

    public bool IsDashboardActive => ActiveNavItem == NavItem.Dashboard;
    public bool IsGroupsActive    => ActiveNavItem == NavItem.Groups;
    public bool IsStudentsActive  => ActiveNavItem == NavItem.Students;
    public bool IsExamsActive     => ActiveNavItem == NavItem.Exams;
    public bool IsPlannerActive   => ActiveNavItem == NavItem.Planner;
    public bool IsWorkloadActive  => ActiveNavItem == NavItem.Workload;
    public bool IsClassTeacherActive => ActiveNavItem == NavItem.ClassTeacher;
    public bool IsSettingsActive  => ActiveNavItem == NavItem.Settings;

    public MainWindowViewModel(IServiceProvider services,
        DashboardViewModel dashboard, SchoolYearService sy,
        SyncStatusViewModel syncStatus, NotificationService notifications, AppLockViewModel appLock,
        GlobalSearchViewModel commandPalette)
    {
        _services         = services;
        SyncStatus        = syncStatus;
        Toasts            = notifications.Toasts;
        AppLock           = appLock;
        CommandPalette    = commandPalette;
        CommandPalette.OnClose = CloseCommandPalette;
        CurrentSchoolYear = sy.CurrentSchoolYear();
        CurrentPage       = dashboard;
        AppLock.ApplyConfig();
        SyncStatus.DataChanged += OnSyncDataChanged;
    }

    [RelayCommand]
    private void OpenCommandPalette()
    {
        if (AppLock.IsLocked) return;
        CommandPalette.Reset();
        IsCommandPaletteOpen = true;
    }

    [RelayCommand]
    private void CloseCommandPalette() => IsCommandPaletteOpen = false;

    // EventApplier schreibt bei eingehenden Sync-Ereignissen absichtlich direkt auf die rohe
    // LiteDB-Collection, an jedem ViewModel vorbei (Ping-Pong-Vermeidung, siehe EventApplier-
    // Klassenkommentar) - ohne diesen Hook blieb die gerade sichtbare Seite bis zum nächsten
    // manuellen Neuladen (z.B. Tab-Wechsel) auf dem alten Stand (TODO 10.1.11). Lädt bewusst nur
    // die aktuell sichtbare Seite über ihren eigenen, längst vorhandenen Lade-Einstieg neu - keine
    // neue Lade-Logik, keine Navigation weg von einer offenen Detailansicht. SyncEngine.DataChanged
    // feuert aus dem Sync-Timer-Hintergrundthread - daher der Dispatcher-Sprung zurück auf den
    // UI-Thread (gleiches Muster wie NotificationService.Show).
    private void OnSyncDataChanged()
    {
        if (Dispatcher.UIThread.CheckAccess()) RefreshCurrentPage();
        else Dispatcher.UIThread.Post(RefreshCurrentPage);
    }

    private void RefreshCurrentPage()
    {
        switch (CurrentPage)
        {
            case DashboardViewModel vm: vm.RefreshCommand.Execute(null); break;
            case GroupListViewModel vm: vm.RefreshCommand.Execute(null); break;
            case StudentListViewModel vm: vm.LoadStudents(); break;
            case TimetableViewModel vm: vm.Load(); break;
            case WorkloadViewModel vm:
                vm.Tasks.Load(); vm.TimeTracking.Load(); vm.Evaluation.Load(); break;
            case ClassTeacherOverviewViewModel vm: vm.LoadCommand.Execute(null); break;
            case ExamsOverviewViewModel vm: vm.LoadCommand.Execute(null); break;
            case GroupDetailViewModel { Group: { } group } vm: vm.LoadGroup(group.Id); break;
            // Inline-Bearbeitung (IsEditing) nicht überschreiben - anders als die Gruppenansicht
            // laufen Namens-/Geschlechtsänderungen hier nicht über einen Dialog.
            case StudentDetailViewModel { Student: { } student, IsEditing: false } vm:
                vm.LoadStudent(student.Id); break;
        }
    }

    partial void OnActiveNavItemChanged(NavItem value)
    {
        OnPropertyChanged(nameof(IsDashboardActive));
        OnPropertyChanged(nameof(IsGroupsActive));
        OnPropertyChanged(nameof(IsStudentsActive));
        OnPropertyChanged(nameof(IsExamsActive));
        OnPropertyChanged(nameof(IsPlannerActive));
        OnPropertyChanged(nameof(IsWorkloadActive));
        OnPropertyChanged(nameof(IsClassTeacherActive));
        OnPropertyChanged(nameof(IsSettingsActive));
    }

    [RelayCommand]
    private void NavigateTo(NavItem item)
    {
        ActiveNavItem = item;
        CurrentPage = item switch
        {
            NavItem.Dashboard => GetDashboard(),
            NavItem.Groups    => _services.GetRequiredService<GroupListViewModel>(),
            NavItem.Students  => GetStudents(),
            NavItem.Exams     => GetExams(),
            NavItem.Planner   => GetTimetable(),
            NavItem.Workload  => GetWorkload(),
            NavItem.ClassTeacher => GetClassTeacherOverview(),
            NavItem.Settings  => _services.GetRequiredService<SettingsViewModel>(),
            _                 => CurrentPage,
        };
    }

    private DashboardViewModel GetDashboard()
    {
        var dashboard = _services.GetRequiredService<DashboardViewModel>();
        dashboard.RefreshCommand.Execute(null);
        return dashboard;
    }

    private StudentListViewModel GetStudents()
    {
        var students = _services.GetRequiredService<StudentListViewModel>();
        students.SelectedStudent = null;
        students.LoadStudents();
        return students;
    }

    private TimetableViewModel GetTimetable()
    {
        var timetable = _services.GetRequiredService<TimetableViewModel>();
        timetable.WeekOffset = 0;
        timetable.Load();
        timetable.ActiveTabIndex = 0;
        return timetable;
    }

    private WorkloadViewModel GetWorkload()
    {
        var workload = _services.GetRequiredService<WorkloadViewModel>();
        workload.Tasks.Load();
        workload.TimeTracking.Load();
        workload.Evaluation.Load();
        workload.ActiveTabIndex = 0;
        return workload;
    }

    private ExamsOverviewViewModel GetExams()
    {
        var exams = _services.GetRequiredService<ExamsOverviewViewModel>();
        exams.LoadCommand.Execute(null);
        return exams;
    }

    private ClassTeacherOverviewViewModel GetClassTeacherOverview()
    {
        var vm = _services.GetRequiredService<ClassTeacherOverviewViewModel>();
        vm.OnNavigateToSettings = () => { NavigateToSettings(SettingsTab.WebUntis); return Task.CompletedTask; };
        vm.OnNavigateToWorkload = () => { NavigateToWorkload(); return Task.CompletedTask; };
        vm.LoadCommand.Execute(null);
        return vm;
    }

    public void NavigateToGroupDetail(Guid groupId, int initialTab = 0)
    {
        ActiveNavItem     = NavItem.Groups;
        var vm            = _services.GetRequiredService<GroupDetailViewModel>();
        vm.ActiveTabIndex = initialTab;
        CurrentPage       = vm;          // View bindet zuerst → Callbacks werden registriert
        vm.LoadGroup(groupId);           // dann Daten laden
    }

    public void NavigateToSettings(SettingsTab initialTab = SettingsTab.Subjects)
    {
        ActiveNavItem     = NavItem.Settings;
        var vm            = _services.GetRequiredService<SettingsViewModel>();
        vm.ActiveTabIndex = (int)initialTab;
        CurrentPage       = vm;
    }

    public void NavigateToStudent(Guid studentId)
    {
        ActiveNavItem = NavItem.Students;
        var vm = _services.GetRequiredService<StudentDetailViewModel>();
        vm.OnReturnToStudentList = NavigateToStudents;
        vm.LoadStudent(studentId);
        CurrentPage = vm;
    }

    public void NavigateToStudents() => NavigateTo(NavItem.Students);

    /// Sprungziel aus dem Kurs-Dashboard ("Anstehende Aufgaben für diese Klasse") in den
    /// Aufgaben-Bereich — anders als NavigateToGroupDetail/NavigateToSettings kein Tab innerhalb
    /// einer Detailansicht, sondern ein eigener Top-Level-Bereich (NavItem.Workload).
    public void NavigateToWorkload() => NavigateTo(NavItem.Workload);
}

public enum NavItem { Dashboard, Groups, Students, Exams, Planner, Workload, ClassTeacher, Settings }

public partial class PlaceholderViewModel : ObservableObject
{
    [ObservableProperty] private string _title = "";
    [ObservableProperty] private string _icon = "";
}