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.Groups;

// ── Notenübersicht der Gruppe (2.1) ──────────────────────────────────────────

public partial class GradeOverviewTabViewModel : ObservableObject
{
    private readonly IGradeRepository _grades;
    private readonly IExamRepository _exams;
    private readonly IExamResultRepository _results;
    private readonly IStudentRepository _students;
    private readonly IGroupMembershipRepository _memberships;
    private readonly GradingService _grading;

    private Guid _groupId;
    private GradingSystem _gradingSystem;
    private GroupType _groupType;
    private string _groupLabel = "";
    private string _schoolYear = "";
    private bool _sortByTotal;
    private bool _sortDescending;

    public Guid GroupId => _groupId;
    public GradingSystem GradingSystem => _gradingSystem;
    public GroupType GroupType => _groupType;
    public string GroupLabel => _groupLabel;
    public string SchoolYear => _schoolYear;

    [ObservableProperty] private ParticipationPeriodOption _selectedPeriod;
    [ObservableProperty] private bool _showAsPoints = true;
    [ObservableProperty] private GradeOverviewRow? _selectedRow;
    [ObservableProperty] private int _rebuildColumnsSignal;

    public bool CanTogglePointsView => _gradingSystem == GradingSystem.Points0To15;

    public List<ParticipationPeriodOption> PeriodOptions { get; } =
    [
        new(ParticipationPeriod.FullYear, "Gesamtes Schuljahr"),
        new(ParticipationPeriod.H1, "1. Halbjahr"),
        new(ParticipationPeriod.H2, "2. Halbjahr"),
    ];

    public ObservableCollection<GradeOverviewColumnDef> Columns { get; } = [];
    public ObservableCollection<GradeOverviewRow> Rows { get; } = [];

    public Func<GradeOverviewRow, Task>? OnManageStudentGrades { get; set; }
    public Func<Task>? OnCollectiveGrade { get; set; }
    public Func<Task>? OnReportGrades { get; set; }

    public GradeOverviewTabViewModel(IGradeRepository grades, IExamRepository exams,
        IExamResultRepository results, IStudentRepository students,
        IGroupMembershipRepository memberships, GradingService grading)
    {
        _grades = grades; _exams = exams; _results = results;
        _students = students; _memberships = memberships; _grading = grading;
        _selectedPeriod = PeriodOptions[0];
    }

    public void Initialize(Guid groupId, GradingSystem gradingSystem, GroupType groupType,
        string groupLabel, string schoolYear)
    {
        _groupId = groupId;
        _gradingSystem = gradingSystem;
        _groupType = groupType;
        _groupLabel = groupLabel;
        _schoolYear = schoolYear;
        ShowAsPoints = gradingSystem == GradingSystem.Points0To15;
        OnPropertyChanged(nameof(CanTogglePointsView));
        Recompute();
    }

    public void Refresh() => Recompute();

    partial void OnSelectedPeriodChanged(ParticipationPeriodOption value) => Recompute();
    partial void OnShowAsPointsChanged(bool value) => Recompute();

    [RelayCommand]
    private void SortByName()
    {
        if (!_sortByTotal) _sortDescending = !_sortDescending;
        else { _sortByTotal = false; _sortDescending = false; }
        ApplySort();
    }

    [RelayCommand]
    private void SortByTotal()
    {
        if (_sortByTotal) _sortDescending = !_sortDescending;
        else { _sortByTotal = true; _sortDescending = false; }
        ApplySort();
    }

    [RelayCommand]
    private async Task ManageStudentGrades()
    {
        if (SelectedRow is null || OnManageStudentGrades is null) return;
        await OnManageStudentGrades(SelectedRow);
        Recompute();
    }

    [RelayCommand]
    private async Task CollectiveGrade()
    {
        if (OnCollectiveGrade is null) return;
        await OnCollectiveGrade();
        Recompute();
    }

    [RelayCommand]
    private async Task ReportGrades()
    {
        if (OnReportGrades is null) return;
        await OnReportGrades();
    }

    private void Recompute()
    {
        var period = SelectedPeriod.Period;
        var (periodFrom, periodTo) = GroupMembershipService.SchoolYearPeriod(_schoolYear, period switch
        {
            ParticipationPeriod.H1 => SchoolYearPeriodKind.H1,
            ParticipationPeriod.H2 => SchoolYearPeriodKind.H2,
            _ => SchoolYearPeriodKind.FullYear,
        });

        var students = _students.GetByGroup(_groupId);
        var membershipsByStudent = _memberships.GetByGroup(_groupId).ToDictionary(m => m.StudentId);

        var exams = _exams.GetByGroup(_groupId)
            .Where(e => e.Date >= periodFrom && e.Date <= periodTo)
            .OrderBy(e => e.Date)
            .ToList();
        var resultsByExam = exams.ToDictionary(e => e.Id, e => _results.GetByExam(e.Id).ToDictionary(r => r.StudentId));

        var otherGrades = _grades.GetByGroup(_groupId)
            .Where(g => g.Date >= periodFrom && g.Date <= periodTo)
            .ToList();
        var gradeColumnKeys = otherGrades
            .Select(g => (g.Category, Note: g.Note ?? "", g.Date))
            .Distinct()
            .OrderBy(k => k.Date)
            .ToList();

        Columns.Clear();
        foreach (var exam in exams)
            Columns.Add(new GradeOverviewColumnDef($"{exam.Date:dd.MM.} {exam.Title}"));
        foreach (var key in gradeColumnKeys)
        {
            var header = string.IsNullOrWhiteSpace(key.Note)
                ? $"{GradeCategoryDisplay.Label(key.Category)} {key.Date:dd.MM.}"
                : key.Note;
            Columns.Add(new GradeOverviewColumnDef(header));
        }

        Rows.Clear();
        foreach (var student in students)
        {
            membershipsByStudent.TryGetValue(student.Id, out var membership);
            if (membership is not null && !GroupMembershipService.Overlaps(membership, periodFrom, periodTo)) continue;

            var cells = new List<string>();
            var numeric = new List<(string Grade, double Weight)>();

            foreach (var exam in exams)
            {
                if (membership is not null && !GroupMembershipService.IsActiveOn(membership, exam.Date))
                { cells.Add(""); continue; }
                if (exam.Niveau.HasValue && membership?.Niveau != exam.Niveau) { cells.Add(""); continue; }
                resultsByExam[exam.Id].TryGetValue(student.Id, out var result);
                if (result is null) { cells.Add(""); continue; }
                if (result.Absent) { cells.Add("abwesend"); continue; }
                var display = FormatValue(result.Grade);
                cells.Add(display);
                if (result.Grade is not null) numeric.Add((result.Grade, 1.0));
            }

            foreach (var key in gradeColumnKeys)
            {
                if (membership is not null && !GroupMembershipService.IsActiveOn(membership, key.Date))
                { cells.Add(""); continue; }
                var grade = otherGrades.FirstOrDefault(g =>
                    g.StudentId == student.Id && g.Category == key.Category &&
                    (g.Note ?? "") == key.Note && g.Date == key.Date);
                if (grade is null) { cells.Add(""); continue; }
                cells.Add(FormatValue(grade.Value));
                numeric.Add((grade.Value, grade.Weight));
            }

            var total = numeric.Count == 0 ? (double?)null : _grading.WeightedAverage(numeric);
            var totalDisplay = total is null ? "–" : total.Value.ToString("0.00", CultureInfo.InvariantCulture);

            Rows.Add(new GradeOverviewRow(student.Id, student.FullName, cells, totalDisplay, total));
        }

        ApplySort();
        RebuildColumnsSignal++;
    }

    private string FormatValue(string? raw)
    {
        if (string.IsNullOrWhiteSpace(raw)) return "";
        if (!ShowAsPoints && _gradingSystem == GradingSystem.Points0To15 && int.TryParse(raw, out var points))
            return PointsNoteMapping.PointsToNote(points);
        return raw;
    }

    private void ApplySort()
    {
        var sorted = _sortByTotal
            ? Rows.OrderBy(r => r.TotalSortValue is null).ThenBy(r => r.TotalSortValue).ToList()
            : Rows.OrderBy(r => r.Name).ToList();
        if (_sortDescending) sorted.Reverse();
        for (var i = 0; i < sorted.Count; i++) Rows.Move(Rows.IndexOf(sorted[i]), i);
    }

}

public class GradeOverviewColumnDef(string header)
{
    public string Header { get; } = header;
}

public class GradeOverviewRow(Guid studentId, string name, List<string> cells, string totalDisplay, double? totalSortValue)
{
    public Guid StudentId { get; } = studentId;
    public string Name { get; } = name;
    public List<string> Cells { get; } = cells;
    public string TotalDisplay { get; } = totalDisplay;
    public double? TotalSortValue { get; } = totalSortValue;
}

// ── Kategorie-Anzeige & Punkte/Noten-Umrechnung ──────────────────────────────

public static class GradeCategoryDisplay
{
    public static string Label(GradeCategory c) => c switch
    {
        GradeCategory.Oral          => "Mündlich",
        GradeCategory.Homework      => "Hausaufgaben",
        GradeCategory.Participation => "Mitarbeit",
        GradeCategory.Project       => "Projekt",
        GradeCategory.Other         => "Sonstiges",
        _                           => c.ToString(),
    };

    public static string[] Options { get; } = Enum.GetValues<GradeCategory>().Select(Label).ToArray();

    public static GradeCategory FromLabel(string? label) =>
        Enum.GetValues<GradeCategory>().FirstOrDefault(c => Label(c) == label, GradeCategory.Other);
}

public static class PointsNoteMapping
{
    // Grobe, standardübliche Punkte-Noten-Umrechnung (Oberstufe), nur für die Anzeige.
    public static string PointsToNote(int points) => points switch
    {
        >= 13 => "1",
        >= 10 => "2",
        >= 7  => "3",
        >= 4  => "4",
        >= 1  => "5",
        _     => "6",
    };
}

// ── Note hinzufügen/bearbeiten für einen Schüler (2.2.1, 2.2.2) ──────────────

public partial class StudentGradesDialogViewModel : ObservableObject
{
    private readonly IGradeRepository _grades;
    private readonly Guid _studentId;
    private readonly Guid _groupId;

    public string StudentName { get; }

    public ObservableCollection<GradeEditItem> Entries { get; } = [];

    public StudentGradesDialogViewModel(IGradeRepository grades, Guid studentId, Guid groupId, string studentName)
    {
        _grades = grades; _studentId = studentId; _groupId = groupId;
        StudentName = studentName;
        Load();
    }

    private void Load()
    {
        Entries.Clear();
        foreach (var g in _grades.GetByStudentAndGroup(_studentId, _groupId).OrderByDescending(g => g.Date))
            Entries.Add(new GradeEditItem(g) { OnSave = Save, OnDelete = Delete });
    }

    [RelayCommand]
    private void AddEntry()
    {
        var item = new GradeEditItem(new Grade
        {
            StudentId = _studentId,
            GroupId = _groupId,
            Category = GradeCategory.Other,
            Date = DateOnly.FromDateTime(DateTime.Today),
        })
        { OnSave = Save, OnDelete = Delete, IsNew = true };
        Entries.Insert(0, item);
    }

    private void Save(GradeEditItem item)
    {
        item.ValueError = ""; item.DateTextError = "";
        var valid = true;

        if (string.IsNullOrWhiteSpace(item.Value)) { item.ValueError = "Wert darf nicht leer sein."; valid = false; }
        if (!DateOnly.TryParseExact(item.DateText, "dd.MM.yyyy", null,
                System.Globalization.DateTimeStyles.None, out _))
        { item.DateTextError = "Format TT.MM.JJJJ."; valid = false; }

        if (!valid) return;

        var grade = item.ToModel();
        _grades.Save(grade);
        item.IsNew = false;
        item.MarkSaved(grade.CreatedAt);
    }

    private void Delete(GradeEditItem item)
    {
        if (!item.IsNew) _grades.Delete(item.Id);
        Entries.Remove(item);
    }
}

public partial class GradeEditItem : ObservableObject
{
    public Guid Id { get; }
    private readonly Guid _studentId;
    private readonly Guid _groupId;
    public bool IsNew { get; set; }

    [ObservableProperty] private GradeCategory _category;
    [ObservableProperty] private string _value;
    [ObservableProperty] private string _dateText;
    [ObservableProperty] private double _weight;
    [ObservableProperty] private string? _note;
    [ObservableProperty] private string _valueError = "";
    [ObservableProperty] private string _dateTextError = "";

    // Für die ComboBox: deutsche Anzeige statt des rohen Enum-Namens.
    public string CategoryName
    {
        get => GradeCategoryDisplay.Label(Category);
        set => Category = GradeCategoryDisplay.FromLabel(value);
    }

    public string CreatedAtDisplay { get; private set; }

    public Action<GradeEditItem>? OnSave { get; set; }
    public Action<GradeEditItem>? OnDelete { get; set; }

    public GradeEditItem(Grade g)
    {
        Id = g.Id;
        _studentId = g.StudentId;
        _groupId = g.GroupId;
        _category = g.Category;
        _value = g.Value;
        _dateText = g.Date.ToString("dd.MM.yyyy");
        _weight = g.Weight;
        _note = g.Note;
        CreatedAtDisplay = $"erfasst am {g.CreatedAt.ToLocalTime():dd.MM.yyyy HH:mm}";
    }

    public void MarkSaved(DateTime createdAt) => CreatedAtDisplay = $"erfasst am {createdAt.ToLocalTime():dd.MM.yyyy HH:mm}";

    public Grade ToModel() => new()
    {
        Id = Id,
        StudentId = _studentId,
        GroupId = _groupId,
        Category = Category,
        Value = Value.Trim(),
        Date = DateOnly.ParseExact(DateText, "dd.MM.yyyy"),
        Weight = Weight,
        Note = string.IsNullOrWhiteSpace(Note) ? null : Note.Trim(),
    };

    [RelayCommand]
    private void Save() => OnSave?.Invoke(this);

    [RelayCommand]
    private void Delete() => OnDelete?.Invoke(this);
}

// ── Sammelerfassung für die ganze Gruppe (2.2.3) ─────────────────────────────

public partial class CollectiveGradeDialogViewModel : ObservableObject
{
    private readonly IGradeRepository _grades;
    private readonly IGroupMembershipRepository _memberships;
    private readonly List<Student> _students;
    private readonly Guid _groupId;

    [ObservableProperty] private GradeCategory _category = GradeCategory.Other;
    [ObservableProperty] private string _dateText = DateOnly.FromDateTime(DateTime.Today).ToString("dd.MM.yyyy");
    [ObservableProperty] private double _weight = 1.0;
    [ObservableProperty] private string? _note;
    [ObservableProperty] private string _statusMessage = "";
    [ObservableProperty] private string _dateTextError = "";

    // Für die ComboBox: deutsche Anzeige statt des rohen Enum-Namens.
    public string CategoryName
    {
        get => GradeCategoryDisplay.Label(Category);
        set => Category = GradeCategoryDisplay.FromLabel(value);
    }

    public ObservableCollection<CollectiveGradeStudentRow> Rows { get; } = [];

    public CollectiveGradeDialogViewModel(IGradeRepository grades, IStudentRepository students,
        IGroupMembershipRepository memberships, Guid groupId)
    {
        _grades = grades; _memberships = memberships; _groupId = groupId;
        _students = students.GetByGroup(groupId).OrderBy(s => s.LastName).ThenBy(s => s.FirstName).ToList();
        RebuildRows(DateOnly.FromDateTime(DateTime.Today));
    }

    partial void OnDateTextChanged(string value)
    {
        if (DateOnly.TryParseExact(value, "dd.MM.yyyy", null,
                System.Globalization.DateTimeStyles.None, out var date))
            RebuildRows(date);
    }

    private void RebuildRows(DateOnly date)
    {
        var previousValues = Rows.ToDictionary(r => r.StudentId, r => r.Value);
        var membershipByStudent = _memberships.GetByGroup(_groupId).ToDictionary(m => m.StudentId);
        Rows.Clear();
        foreach (var student in _students)
        {
            if (membershipByStudent.TryGetValue(student.Id, out var membership)
                && !GroupMembershipService.IsActiveOn(membership, date))
                continue;
            Rows.Add(new CollectiveGradeStudentRow(student.Id, student.FullName)
            {
                Value = previousValues.GetValueOrDefault(student.Id, ""),
            });
        }
    }

    [RelayCommand]
    private void SaveAll()
    {
        if (!DateOnly.TryParseExact(DateText, "dd.MM.yyyy", null,
                System.Globalization.DateTimeStyles.None, out var date))
        { DateTextError = "Format TT.MM.JJJJ."; return; }
        DateTextError = "";

        var count = 0;
        foreach (var row in Rows)
        {
            if (string.IsNullOrWhiteSpace(row.Value)) continue;
            _grades.Save(new Grade
            {
                StudentId = row.StudentId,
                GroupId = _groupId,
                Category = Category,
                Value = row.Value.Trim(),
                Date = date,
                Weight = Weight,
                Note = string.IsNullOrWhiteSpace(Note) ? null : Note.Trim(),
            });
            count++;
        }
        StatusMessage = count == 0
            ? "Keine Werte eingegeben."
            : $"{count} Note(n) gespeichert.";
    }
}

public partial class CollectiveGradeStudentRow(Guid studentId, string name) : ObservableObject
{
    public Guid StudentId { get; } = studentId;
    public string Name { get; } = name;
    [ObservableProperty] private string _value = "";
}