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;

// ── Aggregation zur Mitarbeitsnote (3.2) ─────────────────────────────────────

public partial class ParticipationGradeDialogViewModel : ObservableObject
{
    private readonly IParticipationSessionRepository _sessions;
    private readonly IParticipationRepository _entries;
    private readonly IParticipationAspectRepository _aspects;
    private readonly IStudentRepository _students;
    private readonly IEnrollmentRepository _enrollments;
    private readonly IGradeRepository _grades;
    private readonly GradingService _grading;
    private readonly Guid _groupId;
    private readonly string _schoolYear;
    private readonly GradingSystem _gradingSystem;

    [ObservableProperty] private ParticipationPeriodOption _selectedPeriod;
    [ObservableProperty] private string _statusMessage = "";

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

    public ObservableCollection<ParticipationGradeRow> Rows { get; } = [];
    public ObservableCollection<AspectWeightItem> AspectWeights { get; } = [];

    public ParticipationGradeDialogViewModel(
        IParticipationSessionRepository sessions, IParticipationRepository entries,
        IParticipationAspectRepository aspects, IStudentRepository students,
        IEnrollmentRepository enrollments, IGradeRepository grades, GradingService grading,
        Guid groupId, string schoolYear, GradingSystem gradingSystem)
    {
        _sessions = sessions; _entries = entries; _aspects = aspects;
        _students = students; _enrollments = enrollments; _grades = grades;
        _grading = grading; _groupId = groupId; _schoolYear = schoolYear;
        _gradingSystem = gradingSystem;

        _selectedPeriod = PeriodOptions[0];
        LoadAspectWeights();
        Recompute();
    }

    // 3.2.1: Gewichtung je Aspekt konfigurierbar — direkt hier, da es noch keine eigene
    // Aspekt-Verwaltung (3.1) gibt. Änderungen fließen sofort in die Vorschau ein.
    private void LoadAspectWeights()
    {
        var defaults = _aspects.GetDefaults();
        var specific = _aspects.GetByGroup(_groupId);
        var all = defaults.Concat(specific).ToList();
        if (all.Count == 0) all = DefaultParticipationAspects.All.ToList();

        foreach (var a in all)
        {
            var item = new AspectWeightItem(a, _aspects);
            item.OnChanged = Recompute;
            AspectWeights.Add(item);
        }
    }

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

    private void Recompute()
    {
        Rows.Clear();
        StatusMessage = "";

        var aspectWeights = AspectWeights.ToDictionary(a => a.Key, a => a.Weight);

        var sessions = _sessions.GetByGroup(_groupId)
            .Where(s => InPeriod(s.Date, SelectedPeriod.Period))
            .OrderBy(s => s.Date)
            .ToList();

        var studentList = _students.GetByGroup(_groupId, _schoolYear);
        var enrollmentList = _enrollments.GetByGroupAndYear(_groupId, _schoolYear);

        foreach (var student in studentList.OrderBy(s => s.LastName).ThenBy(s => s.FirstName))
        {
            var enrollment = enrollmentList.FirstOrDefault(e => e.StudentId == student.Id);
            var relevantSessions = sessions
                .Where(s => enrollment is null || IsEnrolledAtDate(enrollment, s.Date))
                .ToList();

            var points = new List<(DateOnly Date, double Rating)>();
            foreach (var session in relevantSessions)
            {
                var entry = _entries.GetBySessionAndStudent(session.Id, student.Id);
                if (entry is null || entry.Ratings.Count == 0) continue;

                var weightSum = 0.0;
                var valueSum = 0.0;
                foreach (var r in entry.Ratings)
                {
                    var w = aspectWeights.TryGetValue(r.Key, out var aw) ? aw : 1.0;
                    if (w <= 0) continue;
                    valueSum += r.Value * w;
                    weightSum += w;
                }
                if (weightSum > 0) points.Add((session.Date, valueSum / weightSum));
            }

            Rows.Add(new ParticipationGradeRow(student.Id, student.FullName, points, _grading, _gradingSystem));
        }
    }

    // 3.2.4: Übernahme als Grade (Category = Participation). Eine bereits übernommene
    // Note für denselben Zeitraum wird aktualisiert statt dupliziert (erkannt am Note-Tag).
    [RelayCommand]
    private void Apply()
    {
        var noteTag = $"Mitarbeit {SelectedPeriod.Label} {_schoolYear}";
        var applied = 0;
        foreach (var row in Rows)
        {
            if (row.Grade is null) continue;

            var grade = _grades.GetByStudentAndGroup(row.StudentId, _groupId)
                .FirstOrDefault(g => g.Category == GradeCategory.Participation && g.Note == noteTag)
                ?? new Grade
                {
                    StudentId = row.StudentId,
                    GroupId = _groupId,
                    SchoolYear = _schoolYear,
                    Category = GradeCategory.Participation,
                    Note = noteTag,
                };
            grade.Value = row.Grade;
            grade.Date = DateOnly.FromDateTime(DateTime.Today);
            _grades.Save(grade);
            applied++;
        }
        StatusMessage = applied == 0
            ? "Keine Schüler mit Bewertungen im gewählten Zeitraum."
            : $"{applied} Mitarbeitsnote(n) übernommen.";
    }

    private static bool InPeriod(DateOnly date, ParticipationPeriod period) => period switch
    {
        ParticipationPeriod.H1 => date.Month >= 8 || date.Month <= 1,
        ParticipationPeriod.H2 => date.Month >= 2 && date.Month <= 7,
        _                      => true,
    };

    private static bool IsEnrolledAtDate(Enrollment e, DateOnly date) => e.Period switch
    {
        EnrollmentPeriod.H1Only => date.Month >= 8 || date.Month <= 1,
        EnrollmentPeriod.H2Only => date.Month >= 2 && date.Month <= 7,
        EnrollmentPeriod.Custom => (e.JoinedAt is null || date >= e.JoinedAt.Value)
                                 && (e.LeftAt  is null || date <= e.LeftAt.Value),
        _                       => true,
    };
}

// ── Gewichtung eines Aspekts (3.2.1) ─────────────────────────────────────────

public partial class AspectWeightItem : ObservableObject
{
    private readonly ParticipationAspect _aspect;
    private readonly IParticipationAspectRepository _repo;

    public string Key => _aspect.Key;
    public string Label => _aspect.Label;

    [ObservableProperty] private double _weight;

    public Action? OnChanged { get; set; }

    public AspectWeightItem(ParticipationAspect aspect, IParticipationAspectRepository repo)
    {
        _aspect = aspect;
        _repo = repo;
        _weight = aspect.Weight;
    }

    partial void OnWeightChanged(double value)
    {
        _aspect.Weight = value;
        _repo.Save(_aspect);
        OnChanged?.Invoke();
    }
}

public enum ParticipationPeriod { FullYear, H1, H2 }

public class ParticipationPeriodOption(ParticipationPeriod period, string label)
{
    public ParticipationPeriod Period { get; } = period;
    public string Label { get; } = label;
    public override string ToString() => Label;
}

// ── Zeile: berechnete Mitarbeitsnote pro Schüler ─────────────────────────────

public class ParticipationGradeRow
{
    public Guid StudentId { get; }
    public string Name { get; }
    public string AverageDisplay { get; }
    public string? Grade { get; }
    public string GradeDisplay { get; }
    public string TrendSymbol { get; }
    public int SessionCount { get; }

    public ParticipationGradeRow(Guid studentId, string name, List<(DateOnly Date, double Rating)> points,
        GradingService grading, GradingSystem system)
    {
        StudentId = studentId;
        Name = name;
        SessionCount = points.Count;

        if (points.Count == 0)
        {
            // 3.2.3: nicht bewertet ≠ schlecht bewertet — kein Grade-Wert, klar erkennbar.
            AverageDisplay = "–";
            Grade = null;
            GradeDisplay = "nicht bewertet";
            TrendSymbol = "";
            return;
        }

        var average = points.Average(p => p.Rating);
        AverageDisplay = average.ToString("0.00", CultureInfo.InvariantCulture);
        Grade = grading.ParticipationGrade(average, system);
        GradeDisplay = Grade;
        TrendSymbol = ComputeTrend(points);
    }

    // 3.2.5: einfache Trendanzeige — Vergleich erste vs. zweite Hälfte der Sitzungen.
    private static string ComputeTrend(List<(DateOnly Date, double Rating)> points)
    {
        if (points.Count < 2) return "";
        var mid = points.Count / 2;
        var first = points.Take(mid).Average(p => p.Rating);
        var second = points.Skip(mid).Average(p => p.Rating);
        var diff = second - first;
        if (diff >= 0.4) return "↑";
        if (diff <= -0.4) return "↓";
        return "→";
    }
}