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

namespace LehrerApp.Desktop.ViewModels.Groups;

// ── Ergebnisse der Verschieben-/Kopieren-Dialoge (4.2.4 / 4.1.4) ─────────────

public record MoveLessonTarget(DateOnly NewDate, bool ShiftFollowing);
public record CopyUnitTarget(Guid TargetGroupId, DateOnly AnchorDate);

// ── Tab-ViewModel: Unterrichtsplanung (4.1 Einheiten / 4.2 Einzelstunden) ────

public partial class PlanningTabViewModel : ObservableObject
{
    private readonly IUnitRepository _units;
    private readonly ILessonRepository _lessons;
    private readonly IGroupRepository _groups;
    private readonly ISubjectRepository _subjects;
    private readonly ICompetencyDomainRepository _competencyDomains;

    private Guid _groupId;

    public Guid GroupId => _groupId;
    public Guid? SubjectId { get; private set; }
    public int GradeLevel { get; private set; }
    public string SubjectName { get; private set; } = "";

    [ObservableProperty] private UnitSummary? _selectedUnit;
    [ObservableProperty] private LessonSummary? _selectedLesson;

    // Eigene Property statt "SelectedUnit.Title" im Binding-Pfad: SelectedUnit ist zwischen
    // Gruppenwechsel/Laden kurzzeitig null — ein verschachtelter Pfad würde dafür jedes Mal
    // einen Binding-Fehler loggen (siehe GroupDetailViewModel.IsDifferentiated für dasselbe Muster).
    public string SelectedUnitTitleSuffix => SelectedUnit is null ? "" : $" – {SelectedUnit.Title}";

    public ObservableCollection<UnitSummary> Units { get; } = [];
    public ObservableCollection<LessonSummary> Lessons { get; } = [];

    /// Aus den Material-/Kurzsymbol-Werten aller bereits vorhandenen Stunden-Phasen der Gruppe
    /// zusammengestellt (4.2.2 Autovervollständigung im Verlaufsplan-Editor). Alternative Abläufe
    /// kommen seit dem Katalog-Redesign nicht mehr aus der Stundenhistorie, sondern direkt aus
    /// IAlternativeLessonPathRepository (siehe LessonDialogViewModel).
    public List<string> KnownMaterials { get; private set; } = [];
    public List<string> KnownShorthands { get; private set; } = [];

    public Func<Guid, Task<bool>>? OnAddUnit { get; set; }
    public Func<Unit, Task<bool>>? OnEditUnit { get; set; }
    public Func<UnitSummary, Task<bool>>? OnConfirmDeleteUnit { get; set; }
    public Func<Unit, Task<CopyUnitTarget?>>? OnPickCopyTarget { get; set; }
    public Func<Guid, Guid, List<string>, List<string>, Task<bool>>? OnAddLesson { get; set; }
    public Func<Lesson, List<string>, List<string>, Task<bool>>? OnEditLesson { get; set; }
    public Func<LessonSummary, Task<bool>>? OnConfirmDeleteLesson { get; set; }
    public Func<Lesson, Task<MoveLessonTarget?>>? OnPickMoveTarget { get; set; }
    public Func<Lesson, Task>? OnShowLesson { get; set; }

    public PlanningTabViewModel(IUnitRepository units, ILessonRepository lessons,
        IGroupRepository groups, ISubjectRepository subjects,
        ICompetencyDomainRepository competencyDomains)
    {
        _units = units; _lessons = lessons; _groups = groups;
        _subjects = subjects; _competencyDomains = competencyDomains;
    }

    public void Initialize(Guid groupId)
    {
        _groupId = groupId;
        var group = _groups.GetById(groupId);
        SubjectId  = group?.SubjectId;
        GradeLevel = group?.GradeLevel ?? 0;
        SubjectName = SubjectId is Guid sid ? _subjects.GetById(sid)?.Name ?? "" : "";
        LoadUnits();
    }

    private void LoadUnits()
    {
        var selectedId = SelectedUnit?.Id;
        Units.Clear();

        var materials = new HashSet<string>();
        var shorthands = new HashSet<string>();

        foreach (var unit in _units.GetByGroup(_groupId))
        {
            var unitLessons = _lessons.GetByUnit(unit.Id);
            foreach (var l in unitLessons)
                foreach (var p in l.Phases)
                {
                    if (!string.IsNullOrWhiteSpace(p.Material)) materials.Add(p.Material);
                    if (!string.IsNullOrWhiteSpace(p.Shorthand)) shorthands.Add(p.Shorthand);
                }
            Units.Add(new UnitSummary(unit, unitLessons));
        }

        KnownMaterials  = materials.OrderBy(m => m, StringComparer.CurrentCultureIgnoreCase).ToList();
        KnownShorthands = shorthands.OrderBy(s => s, StringComparer.CurrentCultureIgnoreCase).ToList();

        SelectedUnit = Units.FirstOrDefault(u => u.Id == selectedId) ?? Units.FirstOrDefault();
    }

    partial void OnSelectedUnitChanged(UnitSummary? value)
    {
        LoadLessons();
        OnPropertyChanged(nameof(SelectedUnitTitleSuffix));
        EditUnitCommand.NotifyCanExecuteChanged();
        DeleteUnitCommand.NotifyCanExecuteChanged();
        CopyUnitCommand.NotifyCanExecuteChanged();
        AddLessonCommand.NotifyCanExecuteChanged();
    }

    private void LoadLessons()
    {
        var selectedId = SelectedLesson?.Id;
        Lessons.Clear();
        if (SelectedUnit is not null)
            foreach (var l in _lessons.GetByUnit(SelectedUnit.Id))
                Lessons.Add(new LessonSummary(l));
        SelectedLesson = Lessons.FirstOrDefault(l => l.Id == selectedId);
    }

    partial void OnSelectedLessonChanged(LessonSummary? value)
    {
        ShowLessonCommand.NotifyCanExecuteChanged();
        EditLessonCommand.NotifyCanExecuteChanged();
        DeleteLessonCommand.NotifyCanExecuteChanged();
        MoveLessonCommand.NotifyCanExecuteChanged();
        AdvanceLessonStatusCommand.NotifyCanExecuteChanged();
    }

    private bool HasSelectedUnit()   => SelectedUnit   is not null;
    private bool HasSelectedLesson() => SelectedLesson is not null;

    // ── Einheiten (4.1) ────────────────────────────────────────────────────────

    [RelayCommand]
    private async Task AddUnit()
    {
        if (OnAddUnit is null) return;
        if (await OnAddUnit(_groupId)) LoadUnits();
    }

    [RelayCommand(CanExecute = nameof(HasSelectedUnit))]
    private async Task EditUnit()
    {
        if (OnEditUnit is null || SelectedUnit is null) return;
        if (await OnEditUnit(SelectedUnit.Model)) LoadUnits();
    }

    [RelayCommand(CanExecute = nameof(HasSelectedUnit))]
    private async Task DeleteUnit()
    {
        if (OnConfirmDeleteUnit is null || SelectedUnit is null) return;
        var unit = SelectedUnit;
        if (!await OnConfirmDeleteUnit(unit)) return;
        foreach (var l in _lessons.GetByUnit(unit.Id)) _lessons.Delete(l.Id);
        _units.Delete(unit.Id);
        LoadUnits();
    }

    [RelayCommand(CanExecute = nameof(HasSelectedUnit))]
    private async Task CopyUnit()
    {
        if (OnPickCopyTarget is null || SelectedUnit is null) return;
        var unit = SelectedUnit.Model;
        var target = await OnPickCopyTarget(unit);
        if (target is null) return;
        CopyUnitAsTemplate(unit, _lessons.GetByUnit(unit.Id), target.TargetGroupId, target.AnchorDate);
        LoadUnits();
    }

    /// Kopiert eine Einheit inkl. Stunden in eine andere Gruppe (4.1.4). "Ohne Datumsbezug"
    /// bedeutet: die relativen Tages-Abstände der Stunden zueinander bleiben erhalten, werden
    /// aber auf das neu gewählte Startdatum re-verankert statt die alten Kalendertage zu übernehmen.
    /// Reflexion wird geleert, Status auf "Geplant" zurückgesetzt. GroupId wird auf jeder neuen
    /// Lesson explizit auf die Zielgruppe gesetzt (siehe docs/Datenmodell.md).
    private void CopyUnitAsTemplate(Unit source, List<Lesson> sourceLessons, Guid targetGroupId, DateOnly anchorDate)
    {
        var earliest = sourceLessons.Count > 0
            ? sourceLessons.Min(l => l.Date)
            : source.StartDate ?? anchorDate;

        var newUnit = new Unit
        {
            GroupId = targetGroupId,
            Title = source.Title,
            Competencies = [.. source.Competencies],
            Status = UnitStatus.Planned,
            Notes = source.Notes,
            StartDate = source.StartDate.HasValue
                ? anchorDate.AddDays(source.StartDate.Value.DayNumber - earliest.DayNumber) : null,
            EndDate = source.EndDate.HasValue
                ? anchorDate.AddDays(source.EndDate.Value.DayNumber - earliest.DayNumber) : null,
        };
        _units.Save(newUnit);

        foreach (var lesson in sourceLessons)
        {
            _lessons.Save(new Lesson
            {
                UnitId = newUnit.Id,
                GroupId = targetGroupId,
                Date = anchorDate.AddDays(lesson.Date.DayNumber - earliest.DayNumber),
                LessonNumber = lesson.LessonNumber,
                Topic = lesson.Topic,
                StartTime = lesson.StartTime,
                Phases = [.. lesson.Phases.Select(p => new LessonPhaseStep
                {
                    Name = p.Name,
                    DurationMinutes = p.DurationMinutes,
                    Activity = p.Activity,
                    Material = p.Material,
                    Shorthand = p.Shorthand,
                    AlternativePathId = p.AlternativePathId,
                })],
                Homework = lesson.Homework,
                Reflection = null,
                Status = LessonStatus.Planned,
            });
        }
    }

    // ── Einzelstunden (4.2) ───────────────────────────────────────────────────

    [RelayCommand(CanExecute = nameof(HasSelectedUnit))]
    private async Task AddLesson()
    {
        if (OnAddLesson is null || SelectedUnit is null) return;
        if (await OnAddLesson(SelectedUnit.Id, _groupId, KnownMaterials, KnownShorthands)) LoadUnits();
    }

    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
    private async Task EditLesson()
    {
        if (OnEditLesson is null || SelectedLesson is null) return;
        if (await OnEditLesson(SelectedLesson.Model, KnownMaterials, KnownShorthands)) LoadUnits();
    }

    /// Schreibgeschützte Anzeige des Verlaufsplans für den Einsatz im Unterricht (kein
    /// Bearbeitungsrisiko). Bewusst ohne Live-Anpassung (Verlängern/Verschieben während des
    /// Haltens) — das gehört zur zurückgestellten Live-Unterrichtsmodus-Ideensammlung (TODO.md).
    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
    private async Task ShowLesson()
    {
        if (OnShowLesson is null || SelectedLesson is null) return;
        await OnShowLesson(SelectedLesson.Model);
    }

    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
    private async Task DeleteLesson()
    {
        if (OnConfirmDeleteLesson is null || SelectedLesson is null) return;
        var lesson = SelectedLesson;
        if (!await OnConfirmDeleteLesson(lesson)) return;
        _lessons.Delete(lesson.Id);
        LoadUnits();
    }

    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
    private async Task MoveLesson()
    {
        if (OnPickMoveTarget is null || SelectedLesson is null) return;
        var lesson = SelectedLesson.Model;
        var target = await OnPickMoveTarget(lesson);
        if (target is null) return;
        MoveLessonInternal(lesson, target.NewDate, target.ShiftFollowing);
        LoadUnits();
    }

    /// Verschiebt eine Stunde auf ein neues Datum (4.2.4). Ist "Nachrücken" aktiv, verschieben
    /// sich alle anderen noch geplanten Stunden derselben Einheit, die ursprünglich NACH der
    /// verschobenen Stunde lagen, um denselben Tages-Delta. Bereits durchgeführte Stunden werden
    /// nie angefasst — nur Date ändert sich, UnitId/GroupId bleiben unverändert.
    private void MoveLessonInternal(Lesson moved, DateOnly newDate, bool shiftFollowing)
    {
        var oldDate = moved.Date;
        var delta = newDate.DayNumber - oldDate.DayNumber;

        if (shiftFollowing && delta != 0)
        {
            foreach (var other in _lessons.GetByUnit(moved.UnitId))
            {
                if (other.Id == moved.Id) continue;
                if (other.Status != LessonStatus.Planned) continue;
                if (other.Date <= oldDate) continue;
                other.Date = other.Date.AddDays(delta);
                _lessons.Save(other);
            }
        }

        moved.Date = newDate;
        _lessons.Save(moved);
    }

    [RelayCommand(CanExecute = nameof(HasSelectedLesson))]
    private void AdvanceLessonStatus()
    {
        if (SelectedLesson is null || SelectedLesson.Model.Status != LessonStatus.Planned) return;
        var lesson = SelectedLesson.Model;
        lesson.Status = LessonStatus.Conducted;
        _lessons.Save(lesson);
        LoadUnits();
    }
}

// ── Anzeige-DTOs ──────────────────────────────────────────────────────────────

public class UnitSummary
{
    public Guid Id { get; }
    public Unit Model { get; }
    public string Title { get; }
    public string DateRangeDisplay { get; }
    public UnitStatus Status { get; }
    public string StatusLabel { get; }
    public string StatusColorHex { get; }
    public string CompetencyCountLabel { get; }
    public int ConductedCount { get; }
    public int TotalCount { get; }
    public double ProgressFraction { get; }
    public string ProgressText { get; }

    public UnitSummary(Unit u, List<Lesson> lessons)
    {
        Id = u.Id;
        Model = u;
        Title = u.Title;
        DateRangeDisplay = (u.StartDate, u.EndDate) switch
        {
            ({ } start, { } end) => $"{start:dd.MM.yyyy} – {end:dd.MM.yyyy}",
            ({ } start, null)    => $"ab {start:dd.MM.yyyy}",
            (null, { } end)      => $"bis {end:dd.MM.yyyy}",
            _                    => "–",
        };
        Status = u.Status;
        StatusLabel = u.Status switch
        {
            UnitStatus.Planned   => "Geplant",
            UnitStatus.Active    => "Laufend",
            UnitStatus.Completed => "Abgeschlossen",
            _ => "",
        };
        StatusColorHex = u.Status switch
        {
            UnitStatus.Planned   => "#9E9E9E",
            UnitStatus.Active    => "#FB8C00",
            UnitStatus.Completed => "#43A047",
            _ => "#9E9E9E",
        };
        CompetencyCountLabel = u.Competencies.Count == 0 ? "–" : $"{u.Competencies.Count} Kompetenz(en)";

        TotalCount     = lessons.Count;
        ConductedCount = lessons.Count(l => l.Status == LessonStatus.Conducted);
        ProgressFraction = TotalCount == 0 ? 0 : (double)ConductedCount / TotalCount;
        ProgressText = TotalCount == 0 ? "Keine Stunden" : $"{ConductedCount} / {TotalCount} Stunden gehalten";
    }
}

public class LessonSummary
{
    public Guid Id { get; }
    public Lesson Model { get; }
    public Guid UnitId { get; }
    public string DateDisplay { get; }
    public int? LessonNumber { get; }
    public string Topic { get; }
    public string StartTimeDisplay { get; }
    public LessonStatus Status { get; }
    public string StatusLabel { get; }
    public string StatusColorHex { get; }
    public string PhaseCountLabel { get; }
    public string TotalDurationLabel { get; }
    public string MaterialsDisplay { get; }
    public bool HasHomework { get; }

    public LessonSummary(Lesson l)
    {
        Id = l.Id;
        Model = l;
        UnitId = l.UnitId;
        DateDisplay = l.Date.ToString("dd.MM.yyyy");
        LessonNumber = l.LessonNumber;
        Topic = l.Topic;
        StartTimeDisplay = l.StartTime?.ToString("HH:mm") ?? "–";
        Status = l.Status;
        StatusLabel = l.Status == LessonStatus.Conducted ? "Durchgeführt" : "Geplant";
        StatusColorHex = l.Status == LessonStatus.Conducted ? "#43A047" : "#9E9E9E";
        PhaseCountLabel = l.Phases.Count == 0 ? "–" : $"{l.Phases.Count} Phasen";
        var totalMinutes = l.Phases.Sum(p => p.DurationMinutes);
        TotalDurationLabel = totalMinutes == 0 ? "–" : $"{totalMinutes} Min.";
        MaterialsDisplay = string.Join(", ", l.Phases
            .Select(p => p.Material)
            .Where(m => !string.IsNullOrWhiteSpace(m))
            .Distinct());
        HasHomework = !string.IsNullOrWhiteSpace(l.Homework);
    }
}

// ── Status-Anzeige (Einheiten/Stunden, analog NiveauDisplay) ──────────────────

public static class UnitStatusDisplay
{
    public static string[] Options { get; } = ["Geplant", "Laufend", "Abgeschlossen"];

    public static string ToName(UnitStatus s) => s switch
    {
        UnitStatus.Active    => "Laufend",
        UnitStatus.Completed => "Abgeschlossen",
        _                    => "Geplant",
    };

    public static UnitStatus FromName(string? name) => name switch
    {
        "Laufend"       => UnitStatus.Active,
        "Abgeschlossen" => UnitStatus.Completed,
        _               => UnitStatus.Planned,
    };
}

public static class LessonStatusDisplay
{
    public static string[] Options { get; } = ["Geplant", "Durchgeführt"];

    public static string ToName(LessonStatus s) => s == LessonStatus.Conducted ? "Durchgeführt" : "Geplant";

    public static LessonStatus FromName(string? name) =>
        name == "Durchgeführt" ? LessonStatus.Conducted : LessonStatus.Planned;
}

// ── Dialog: Einheit anlegen / bearbeiten (4.1.2 / 4.1.3) ─────────────────────

public partial class UnitDialogViewModel : ObservableObject
{
    private readonly IUnitRepository _units;
    private readonly ICompetencyDomainRepository _competencyDomains;
    private readonly Guid _groupId;
    private readonly Guid? _subjectId;
    private readonly int _gradeLevel;
    private readonly Unit? _editingUnit;
    private readonly List<string> _competencyCodes;

    [ObservableProperty] private string _title = "";
    [ObservableProperty] private string _startDateText = "";
    [ObservableProperty] private string _endDateText = "";
    [ObservableProperty] private string _statusName = UnitStatusDisplay.Options[0];
    [ObservableProperty] private string _notes = "";
    [ObservableProperty] private bool _isCompetencyPanelOpen;
    [ObservableProperty] private string _titleError = "";
    [ObservableProperty] private string _startDateTextError = "";
    [ObservableProperty] private string _endDateTextError = "";

    public string[] StatusOptions => UnitStatusDisplay.Options;
    public ObservableCollection<CompetencyTagGroup> CompetencyTagGroups { get; } = [];
    public string CompetencySummary => _competencyCodes.Count == 0
        ? "Keine Kompetenzen" : $"{_competencyCodes.Count} Kompetenz(en)";

    /// Fach kommt von der Lerngruppe, nicht editierbar (jede Gruppe unterrichtet ein Fach).
    public string SubjectDisplay { get; }

    public Unit? Result { get; private set; }
    public string DialogTitle => _editingUnit is null ? "Neue Einheit anlegen" : "Einheit bearbeiten";
    public string SaveButtonText => _editingUnit is null ? "Anlegen" : "Speichern";

    public UnitDialogViewModel(IUnitRepository units, ICompetencyDomainRepository competencyDomains,
        Guid groupId, Guid? subjectId, int gradeLevel, string subjectName, Unit? editingUnit)
    {
        _units = units; _competencyDomains = competencyDomains;
        _groupId = groupId; _subjectId = subjectId; _gradeLevel = gradeLevel;
        _editingUnit = editingUnit;
        SubjectDisplay = string.IsNullOrWhiteSpace(subjectName)
            ? "Kein Fach hinterlegt (siehe Lerngruppe)" : $"Fach: {subjectName}";

        _competencyCodes = editingUnit is not null ? [.. editingUnit.Competencies] : [];
        BuildCompetencyTagGroups();

        if (editingUnit is not null)
        {
            Title = editingUnit.Title;
            StartDateText = editingUnit.StartDate?.ToString("dd.MM.yyyy") ?? "";
            EndDateText = editingUnit.EndDate?.ToString("dd.MM.yyyy") ?? "";
            StatusName = UnitStatusDisplay.ToName(editingUnit.Status);
            Notes = editingUnit.Notes ?? "";
        }
    }

    private void BuildCompetencyTagGroups()
    {
        CompetencyTagGroups.Clear();
        if (!_subjectId.HasValue) return;
        var selected = _competencyCodes.ToHashSet();
        foreach (var domain in _competencyDomains.GetBySubjectAndGrade(_subjectId.Value, _gradeLevel))
        {
            var group = new CompetencyTagGroup(domain.Name, domain.Code);
            foreach (var item in domain.Items.OrderBy(i => i.SortOrder))
            {
                var tag = new CompetencyTag(item.Code, item.Description, selected.Contains(item.Code));
                tag.OnChanged = OnCompetencyToggled;
                group.Items.Add(tag);
            }
            if (group.Items.Count > 0) CompetencyTagGroups.Add(group);
        }
    }

    private void OnCompetencyToggled(string code, bool selected)
    {
        if (selected) { if (!_competencyCodes.Contains(code)) _competencyCodes.Add(code); }
        else            _competencyCodes.Remove(code);
        OnPropertyChanged(nameof(CompetencySummary));
    }

    [RelayCommand] private void ToggleCompetencyPanel() => IsCompetencyPanelOpen = !IsCompetencyPanelOpen;

    [RelayCommand]
    private void Save()
    {
        TitleError = ""; StartDateTextError = ""; EndDateTextError = "";
        var valid = true;

        if (string.IsNullOrWhiteSpace(Title)) { TitleError = "Titel erforderlich."; valid = false; }

        DateOnly? startDate = null;
        if (!string.IsNullOrWhiteSpace(StartDateText))
        {
            if (!DateOnly.TryParseExact(StartDateText, "dd.MM.yyyy", null, DateTimeStyles.None, out var s))
            { StartDateTextError = "Format TT.MM.JJJJ."; valid = false; }
            else startDate = s;
        }

        DateOnly? endDate = null;
        if (!string.IsNullOrWhiteSpace(EndDateText))
        {
            if (!DateOnly.TryParseExact(EndDateText, "dd.MM.yyyy", null, DateTimeStyles.None, out var e))
            { EndDateTextError = "Format TT.MM.JJJJ."; valid = false; }
            else endDate = e;
        }

        if (valid && startDate is not null && endDate is not null && endDate < startDate)
        { EndDateTextError = "Ende darf nicht vor dem Start liegen."; valid = false; }

        if (!valid) return;

        Result = _editingUnit ?? new Unit { GroupId = _groupId };
        Result.Title = Title.Trim();
        Result.StartDate = startDate;
        Result.EndDate = endDate;
        Result.Status = UnitStatusDisplay.FromName(StatusName);
        Result.Notes = string.IsNullOrWhiteSpace(Notes) ? null : Notes.Trim();
        Result.Competencies = _competencyCodes;
        _units.Save(Result);
    }
}

// ── Dialog: Stunde anlegen / bearbeiten (4.2.2) — tabellarischer Verlaufsplan ────

public partial class LessonDialogViewModel : ObservableObject
{
    private readonly ILessonRepository _lessons;
    private readonly IAlternativeLessonPathRepository _alternativePaths;
    private readonly Guid _unitId;
    private readonly Guid _groupId;
    private readonly Lesson? _editingLesson;

    [ObservableProperty] private string _dateText = DateOnly.FromDateTime(DateTime.Today).ToString("dd.MM.yyyy");
    [ObservableProperty] private int? _lessonNumber;
    [ObservableProperty] private string _topic = "";
    [ObservableProperty] private string _startTimeText = "";
    [ObservableProperty] private string _homework = "";
    [ObservableProperty] private string _reflection = "";
    [ObservableProperty] private string _statusName = LessonStatusDisplay.Options[0];
    [ObservableProperty] private string _dateTextError = "";
    [ObservableProperty] private string _topicError = "";
    [ObservableProperty] private string _startTimeTextError = "";
    [ObservableProperty] private string _totalDurationDisplay = "0 Minuten gesamt";

    public string[] StatusOptions => LessonStatusDisplay.Options;
    public string[] MaterialSuggestions { get; }
    public string[] ShorthandSuggestions { get; }
    public ObservableCollection<PhaseStepEditItem> Phases { get; } = [];

    /// Vom Code-Behind gesetzt (Fenster als Owner für den Zuweisen-Dialog): fragt nach dem
    /// alternativen Ablauf, dem eine Phase zugeordnet werden soll (Auswahl oder Neuanlage
    /// per Combobox-Dialog). null zurückgegeben = abgebrochen.
    public Func<Guid?, Task<AlternativeLessonPath?>>? OnPickAlternativePath { get; set; }

    public Lesson? Result { get; private set; }
    public string DialogTitle => _editingLesson is null ? "Neue Stunde anlegen" : "Stunde bearbeiten";
    public string SaveButtonText => _editingLesson is null ? "Anlegen" : "Speichern";

    public LessonDialogViewModel(ILessonRepository lessons, IShorthandCodeRepository shorthandCodes,
        IAlternativeLessonPathRepository alternativePaths, Guid unitId, Guid groupId,
        List<string> materialSuggestions, List<string> shorthandHistorySuggestions, Lesson? editingLesson)
    {
        _lessons = lessons; _alternativePaths = alternativePaths;
        _unitId = unitId; _groupId = groupId; _editingLesson = editingLesson;
        MaterialSuggestions = [.. materialSuggestions];

        // Vorschläge kommen sowohl aus dem gepflegten Kürzel-Katalog (Einstellungen) als auch aus
        // bereits in anderen Stunden dieser Gruppe frei getippten Kurzsymbolen — ein Kurzsymbol
        // muss nicht vorab im Katalog stehen, um beim nächsten Mal wieder vorgeschlagen zu werden.
        var codes = shorthandCodes.GetAll();
        var catalogCodes = (codes.Count > 0 ? codes : DefaultShorthandCodes.All).Select(c => c.Code);
        ShorthandSuggestions = catalogCodes.Concat(shorthandHistorySuggestions)
            .Where(s => !string.IsNullOrWhiteSpace(s))
            .Distinct(StringComparer.OrdinalIgnoreCase)
            .OrderBy(s => s, StringComparer.CurrentCultureIgnoreCase)
            .ToArray();

        if (editingLesson is not null)
        {
            DateText      = editingLesson.Date.ToString("dd.MM.yyyy");
            LessonNumber  = editingLesson.LessonNumber;
            Topic         = editingLesson.Topic;
            StartTimeText = editingLesson.StartTime?.ToString("HH:mm") ?? "";
            Homework      = editingLesson.Homework ?? "";
            Reflection    = editingLesson.Reflection ?? "";
            StatusName    = LessonStatusDisplay.ToName(editingLesson.Status);
            foreach (var p in editingLesson.Phases) AddPhaseInternal(p);
        }
        RecomputeTimes();
    }

    [RelayCommand]
    private void AddPhase()
    {
        AddPhaseInternal(null);
        RecomputeTimes();
    }

    private void AddPhaseInternal(LessonPhaseStep? source)
    {
        var item = new PhaseStepEditItem
        {
            Name = source?.Name ?? "",
            DurationMinutes = source?.DurationMinutes ?? 5,
            Activity = source?.Activity ?? "",
            Material = source?.Material ?? "",
            Shorthand = source?.Shorthand ?? "",
        };
        item.OnChanged  = RecomputeTimes;
        item.OnRemove   = RemovePhase;
        item.OnMoveUp   = MovePhaseUp;
        item.OnMoveDown = MovePhaseDown;
        item.OnAssignAlternativePath = AssignAlternativePath;
        if (source?.AlternativePathId is Guid pathId)
            item.SetAlternativePath(_alternativePaths.GetById(pathId));
        Phases.Add(item);
    }

    private async Task AssignAlternativePath(PhaseStepEditItem item)
    {
        if (OnPickAlternativePath is null) { item.SetAlternativePath(null); return; }
        var picked = await OnPickAlternativePath(item.AlternativePathId);
        item.SetAlternativePath(picked);
    }

    private void RemovePhase(PhaseStepEditItem item) { Phases.Remove(item); RecomputeTimes(); }

    private void MovePhaseUp(PhaseStepEditItem item)
    {
        var idx = Phases.IndexOf(item);
        if (idx > 0) Phases.Move(idx, idx - 1);
        RecomputeTimes();
    }

    private void MovePhaseDown(PhaseStepEditItem item)
    {
        var idx = Phases.IndexOf(item);
        if (idx >= 0 && idx < Phases.Count - 1) Phases.Move(idx, idx + 1);
        RecomputeTimes();
    }

    partial void OnStartTimeTextChanged(string value) => RecomputeTimes();

    /// Dauer ist die primäre Eingabe je Phase; die Uhrzeit wird daraus nur zur Anzeige
    /// abgeleitet — kumulativ ab "Beginn", sofern gesetzt (sonst bleibt sie leer).
    private void RecomputeTimes()
    {
        var total = Phases.Sum(p => p.DurationMinutes);
        TotalDurationDisplay = $"{total} Minuten gesamt";

        TimeOnly? cursor = null;
        if (!string.IsNullOrWhiteSpace(StartTimeText) &&
            TimeOnly.TryParseExact(StartTimeText, "HH:mm", null, DateTimeStyles.None, out var start))
            cursor = start;

        foreach (var p in Phases)
        {
            p.ComputedTimeDisplay = cursor is { } c ? $"ab {c:HH:mm}" : "";
            if (cursor is { } cc) cursor = cc.AddMinutes(p.DurationMinutes);
        }
    }

    [RelayCommand]
    private void Save()
    {
        DateTextError = ""; TopicError = ""; StartTimeTextError = "";
        var valid = true;

        if (string.IsNullOrWhiteSpace(Topic)) { TopicError = "Thema erforderlich."; valid = false; }

        DateOnly date = default;
        if (!DateOnly.TryParseExact(DateText, "dd.MM.yyyy", null, DateTimeStyles.None, out date))
        { DateTextError = "Format TT.MM.JJJJ."; valid = false; }

        TimeOnly? startTime = null;
        if (!string.IsNullOrWhiteSpace(StartTimeText))
        {
            if (!TimeOnly.TryParseExact(StartTimeText, "HH:mm", null, DateTimeStyles.None, out var t))
            { StartTimeTextError = "Format HH:MM."; valid = false; }
            else startTime = t;
        }

        if (!valid) return;

        Result = _editingLesson ?? new Lesson { UnitId = _unitId, GroupId = _groupId };
        Result.UnitId       = _unitId;
        Result.GroupId      = _groupId;
        Result.Date         = date;
        Result.LessonNumber = LessonNumber;
        Result.Topic        = Topic.Trim();
        Result.StartTime    = startTime;
        Result.Phases       = Phases.Select(p => p.ToModel()).ToList();
        Result.Homework     = string.IsNullOrWhiteSpace(Homework) ? null : Homework.Trim();
        Result.Reflection   = string.IsNullOrWhiteSpace(Reflection) ? null : Reflection.Trim();
        Result.Status       = LessonStatusDisplay.FromName(StatusName);
        _lessons.Save(Result);
    }
}

// ── Zeile im Verlaufsplan-Editor (4.2.2) ──────────────────────────────────────

public partial class PhaseStepEditItem : ObservableObject
{
    private static readonly string[] AlternativePathPalette =
        ["#7F77DD", "#1D9E75", "#D85A30", "#D4537E", "#378ADD", "#639922", "#EF9F27"];

    [ObservableProperty] private string _name = "";
    [ObservableProperty] private int _durationMinutes = 5;
    [ObservableProperty] private string _activity = "";
    [ObservableProperty] private string _material = "";
    [ObservableProperty] private string _shorthand = "";
    [ObservableProperty] private string _computedTimeDisplay = "";

    /// Checkbox-Zustand im Editor: unchecked→checked öffnet den Zuweisen-Dialog
    /// (<see cref="OnAssignAlternativePath"/>); checked→unchecked entfernt die Zuordnung.
    /// Änderungen, die von <see cref="SetAlternativePath"/> selbst kommen, lösen das nicht erneut aus.
    [ObservableProperty] private bool _hasAlternativePath;
    [ObservableProperty] private string _alternativePathName = "";
    [ObservableProperty] private string _alternativePathColorHex = "#9E9E9E";

    private bool _suppressAlternativePathToggle;

    public Guid? AlternativePathId { get; private set; }

    public Action? OnChanged { get; set; }
    public Action<PhaseStepEditItem>? OnRemove   { get; set; }
    public Action<PhaseStepEditItem>? OnMoveUp   { get; set; }
    public Action<PhaseStepEditItem>? OnMoveDown { get; set; }
    public Func<PhaseStepEditItem, Task>? OnAssignAlternativePath { get; set; }

    partial void OnDurationMinutesChanged(int value) => OnChanged?.Invoke();

    partial void OnHasAlternativePathChanged(bool value)
    {
        if (_suppressAlternativePathToggle) return;
        if (value) _ = OnAssignAlternativePath?.Invoke(this);
        else SetAlternativePath(null);
    }

    /// Wird sowohl beim Laden einer bestehenden Zuordnung als auch nach dem Zuweisen-Dialog
    /// aufgerufen (auch mit null bei Abbruch/Entfernen) — setzt Id/Anzeigename/Farbe konsistent
    /// und unterdrückt dabei das erneute Öffnen des Dialogs über <see cref="OnHasAlternativePathChanged"/>.
    public void SetAlternativePath(AlternativeLessonPath? path)
    {
        _suppressAlternativePathToggle = true;
        AlternativePathId = path?.Id;
        AlternativePathName = path?.Name ?? "";
        AlternativePathColorHex = path is null ? "#9E9E9E" : ColorFor(path.Name);
        HasAlternativePath = path is not null;
        _suppressAlternativePathToggle = false;
        OnChanged?.Invoke();
    }

    private static string ColorFor(string name)
    {
        var hash = 0;
        foreach (var c in name) hash = hash * 31 + c;
        return AlternativePathPalette[Math.Abs(hash) % AlternativePathPalette.Length];
    }

    [RelayCommand] private void Remove()   => OnRemove?.Invoke(this);
    [RelayCommand] private void MoveUp()   => OnMoveUp?.Invoke(this);
    [RelayCommand] private void MoveDown() => OnMoveDown?.Invoke(this);

    public LessonPhaseStep ToModel() => new()
    {
        Name = Name.Trim(),
        DurationMinutes = DurationMinutes,
        Activity = Activity.Trim(),
        Material = Material.Trim(),
        Shorthand = Shorthand.Trim(),
        AlternativePathId = AlternativePathId,
    };
}

// ── Dialog: Alternativen Ablauf zuweisen/anlegen (4.2.2 Nachtrag) ────────────

public partial class AlternativePathDialogViewModel : ObservableObject
{
    private readonly IAlternativeLessonPathRepository _repo;

    [ObservableProperty] private AlternativeLessonPath? _selectedPath;
    [ObservableProperty] private string _newName = "";
    [ObservableProperty] private string _newDescription = "";
    [ObservableProperty] private string _newNameError = "";
    [ObservableProperty] private string _selectionError = "";

    public ObservableCollection<AlternativeLessonPath> Available { get; } = [];
    public AlternativeLessonPath? Result { get; private set; }

    public AlternativePathDialogViewModel(IAlternativeLessonPathRepository repo, Guid? currentId)
    {
        _repo = repo;
        foreach (var p in repo.GetAll()) Available.Add(p);
        if (currentId is Guid id) SelectedPath = Available.FirstOrDefault(p => p.Id == id);
    }

    [RelayCommand]
    private void CreateNew()
    {
        NewNameError = "";
        if (string.IsNullOrWhiteSpace(NewName)) { NewNameError = "Name erforderlich."; return; }

        var entry = new AlternativeLessonPath
        {
            Name = NewName.Trim(),
            Description = string.IsNullOrWhiteSpace(NewDescription) ? null : NewDescription.Trim(),
        };
        try { _repo.Save(entry); }
        catch (InvalidOperationException ex) { NewNameError = ex.Message; return; }
        catch (ArgumentException ex) { NewNameError = ex.Message; return; }

        Available.Add(entry);
        SelectedPath = entry;
        NewName = ""; NewDescription = "";
    }

    [RelayCommand]
    private void Confirm()
    {
        SelectionError = "";
        if (SelectedPath is null) { SelectionError = "Bitte einen Ablauf auswählen oder neu anlegen."; return; }
        Result = SelectedPath;
    }
}

// ── Dialog: Stunde verschieben (4.2.4) ────────────────────────────────────────

public partial class MoveLessonDialogViewModel : ObservableObject
{
    [ObservableProperty] private string _newDateText;
    [ObservableProperty] private bool _shiftFollowingPlanned = true;
    [ObservableProperty] private string _newDateTextError = "";

    public string CurrentDateDisplay { get; }
    public MoveLessonTarget? Result { get; private set; }

    public MoveLessonDialogViewModel(DateOnly currentDate)
    {
        CurrentDateDisplay = currentDate.ToString("dd.MM.yyyy");
        _newDateText = currentDate.ToString("dd.MM.yyyy");
    }

    [RelayCommand]
    private void Save()
    {
        NewDateTextError = "";
        if (!DateOnly.TryParseExact(NewDateText, "dd.MM.yyyy", null, DateTimeStyles.None, out var date))
        {
            NewDateTextError = "Format TT.MM.JJJJ.";
            return;
        }
        Result = new MoveLessonTarget(date, ShiftFollowingPlanned);
    }
}

// ── Dialog: Einheit als Vorlage in andere Gruppe kopieren (4.1.4) ────────────

public partial class CopyUnitDialogViewModel : ObservableObject
{
    [ObservableProperty] private LearningGroup? _selectedGroup;
    [ObservableProperty] private string _newStartDateText = DateOnly.FromDateTime(DateTime.Today).ToString("dd.MM.yyyy");
    [ObservableProperty] private string _selectedGroupError = "";
    [ObservableProperty] private string _newStartDateTextError = "";

    public ObservableCollection<LearningGroup> AvailableGroups { get; } = [];
    public CopyUnitTarget? Result { get; private set; }

    public CopyUnitDialogViewModel(IGroupRepository groups, Guid excludeGroupId)
    {
        foreach (var g in groups.GetAll().Where(g => g.Id != excludeGroupId).OrderBy(g => g.Name))
            AvailableGroups.Add(g);
    }

    [RelayCommand]
    private void Save()
    {
        SelectedGroupError = ""; NewStartDateTextError = "";
        var valid = true;

        if (SelectedGroup is null) { SelectedGroupError = "Zielgruppe auswählen."; valid = false; }

        DateOnly anchor = default;
        if (!DateOnly.TryParseExact(NewStartDateText, "dd.MM.yyyy", null, DateTimeStyles.None, out anchor))
        { NewStartDateTextError = "Format TT.MM.JJJJ."; valid = false; }

        if (!valid) return;

        Result = new CopyUnitTarget(SelectedGroup!.Id, anchor);
    }
}

// ── Verlaufsplan-Ansicht (schreibgeschützt, für den Unterrichtseinsatz) ──────

/// Eine Phasen-Zeile in der schreibgeschützten Ansicht — reine Anzeige, keine Bearbeitung.
public record PhaseViewItem(string Name, int DurationMinutes, string TimeDisplay,
    string Activity, string Material, string Shorthand);

/// Eine Gruppe von Phasen mit demselben <see cref="LessonPhaseStep.AlternativePathId"/>
/// ("Hauptweg" bei null). Jede Gruppe bekommt ihre eigene kumulierte Zeitberechnung ab
/// Lesson.StartTime — eine Alternative zeigt also "so würde die Uhr laufen, wenn man diesen Weg
/// von Stundenbeginn an nimmt", nicht ab einer gemeinsamen Verzweigungsstelle im Hauptweg.
public record PhaseGroupViewItem(string Label, bool IsMainPath, string? Description, List<PhaseViewItem> Phases);

public class LessonViewerViewModel
{
    private const string MainPathLabel = "Hauptweg";

    public string DateDisplay { get; }
    public string Topic { get; }
    public string StatusLabel { get; }
    public string StartTimeDisplay { get; }
    public string? Homework { get; }
    public string? Reflection { get; }
    public List<PhaseGroupViewItem> PhaseGroups { get; }
    public bool HasAlternatives { get; }

    public LessonViewerViewModel(Lesson lesson, IAlternativeLessonPathRepository alternativePaths)
    {
        DateDisplay = lesson.Date.ToString("dd.MM.yyyy");
        Topic = lesson.Topic;
        StatusLabel = LessonStatusDisplay.ToName(lesson.Status);
        StartTimeDisplay = lesson.StartTime?.ToString("HH:mm") ?? "–";
        Homework = lesson.Homework;
        Reflection = lesson.Reflection;

        var order = new List<string>();
        var descriptions = new Dictionary<string, string?>();
        var byLabel = new Dictionary<string, List<LessonPhaseStep>>();
        foreach (var p in lesson.Phases)
        {
            string label; string? description = null;
            if (p.AlternativePathId is Guid pathId)
            {
                var path = alternativePaths.GetById(pathId);
                label = path?.Name ?? "Unbekannter Ablauf";
                description = path?.Description;
            }
            else label = MainPathLabel;

            if (!byLabel.TryGetValue(label, out var list))
            {
                list = [];
                byLabel[label] = list;
                descriptions[label] = description;
                order.Add(label);
            }
            list.Add(p);
        }

        // Hauptweg immer zuerst, unabhängig davon, in welcher Reihenfolge Phasen angelegt wurden.
        var orderedLabels = order.OrderBy(l => l == MainPathLabel ? 0 : 1).ToList();
        PhaseGroups = orderedLabels
            .Select(label => new PhaseGroupViewItem(
                label, label == MainPathLabel, descriptions[label], BuildPhaseViewItems(byLabel[label], lesson.StartTime)))
            .ToList();
        HasAlternatives = PhaseGroups.Count > 1;
    }

    private static List<PhaseViewItem> BuildPhaseViewItems(List<LessonPhaseStep> steps, TimeOnly? startTime)
    {
        var cursor = startTime;
        var items = new List<PhaseViewItem>();
        foreach (var p in steps)
        {
            var timeDisplay = cursor is { } c ? $"ab {c:HH:mm}" : "";
            items.Add(new PhaseViewItem(p.Name, p.DurationMinutes, timeDisplay, p.Activity, p.Material, p.Shorthand));
            if (cursor is { } cc) cursor = cc.AddMinutes(p.DurationMinutes);
        }
        return items;
    }
}