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

namespace LehrerApp.Desktop.ViewModels.Groups;

// ── Schüler-Leistungsüberblick + Zielnoten-Rechner (Nutzer-Feedback) ─────────────
//
// Zeigt die Leistungen eines einzelnen Schülers in einem Kurs im Überblick — Klausuren,
// Mitarbeit- und sonstige Noten, die daraus berechnete Zeugnisnote sowie zwei Rechner
// ("Zielnote": was brauche ich noch? / "Was-wäre-wenn": wie wirkt sich eine zusätzliche
// Klausurnote aus?). Bewusst pro Kurs statt fächerübergreifend, da Gewichtungsschema und
// Notensystem am Kurs hängen. Zwei Modi über IsTeacherMode: im Bewertermodus zusätzlich
// Kursdurchschnitt je Klausur und Bearbeitbarkeit der Mitarbeit-/Sonstige-Noten; im
// Schülermodus ausschließlich die eigenen Werte, rein lesend — gedacht, um den Bildschirm im
// Gespräch umzudrehen. Exam-Noten bleiben bewusst nur lesbar: eine Korrektur läuft weiterhin
// über den bestehenden ExamGradingDialog, der die Punkte-Struktur konsistent hält — direktes
// Überschreiben von Exam.Grade hier könnte mit ExamResult.Points/TotalPoints auseinanderlaufen.
public partial class StudentPerformanceOverviewViewModel : ObservableObject
{
    private readonly IGradeRepository _grades;
    private readonly IExamRepository _exams;
    private readonly IExamResultRepository _results;
    private readonly IGroupMembershipRepository _memberships;
    private readonly IGradingSchemeRepository _schemes;
    private readonly GradingService _grading;

    private readonly Guid _groupId;
    private readonly Guid _studentId;
    private readonly GroupType _groupType;
    private readonly GradingSystem _gradingSystem;
    private readonly string _schoolYear;

    private GradingScheme _scheme = new();
    private double? _examsAverage;
    private double? _participationAverage;
    private double? _otherAverage;
    private List<(string Grade, double Weight)> _examGradesRaw = [];
    private List<(string Grade, double Weight)> _participationGradesRaw = [];
    private List<(string Grade, double Weight)> _otherGradesRaw = [];

    public string StudentName { get; }
    public string GroupLabel { get; }

    [ObservableProperty] private ParticipationPeriodOption _selectedPeriod;
    [ObservableProperty] private bool _isTeacherMode = true;
    [ObservableProperty] private string _schemeSummary = "";
    [ObservableProperty] private string? _examsAverageDisplay;
    [ObservableProperty] private string? _participationAverageDisplay;
    [ObservableProperty] private string? _otherAverageDisplay;
    [ObservableProperty] private string _currentReportGradeDisplay = "";

    [ObservableProperty] private string _targetGradeText = "";
    [ObservableProperty] private GradeBucketKind _targetBucket = GradeBucketKind.Exams;
    [ObservableProperty] private string _targetResultDisplay = "";

    [ObservableProperty] private string _whatIfExamGradeText = "";
    [ObservableProperty] private string _whatIfResultDisplay = "";

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

    public string[] TargetBucketOptions { get; } = ["Klausuren", "Mitarbeit", "Sonstige"];

    public string TargetBucketName
    {
        get => TargetBucket switch
        {
            GradeBucketKind.Participation => "Mitarbeit",
            GradeBucketKind.Other => "Sonstige",
            _ => "Klausuren",
        };
        set => TargetBucket = value switch
        {
            "Mitarbeit" => GradeBucketKind.Participation,
            "Sonstige" => GradeBucketKind.Other,
            _ => GradeBucketKind.Exams,
        };
    }

    public ObservableCollection<StudentExamRow> ExamRows { get; } = [];
    /// Eigener Verlauf (Nutzer-Feedback): dieselbe Balken-Sparkline wie die bestehende
    /// Notenentwicklung im Schülerdetail (2.5), hier nur auf die Klausuren dieses Kurses
    /// beschränkt statt aller Lerngruppen — passt zum Kursdurchschnitt-Vergleich je Klausur.
    public StudentGradeHistoryGroup ExamHistory { get; } = new("Klausurverlauf");
    public ObservableCollection<StudentSimpleGradeRow> ParticipationRows { get; } = [];
    public ObservableCollection<StudentSimpleGradeRow> OtherRows { get; } = [];

    public StudentPerformanceOverviewViewModel(IGradeRepository grades, IExamRepository exams,
        IExamResultRepository results, IGroupMembershipRepository memberships,
        IGradingSchemeRepository schemes, GradingService grading,
        Guid groupId, Guid studentId, GroupType groupType, GradingSystem gradingSystem,
        string studentName, string groupLabel, string schoolYear)
    {
        _grades = grades; _exams = exams; _results = results; _memberships = memberships;
        _schemes = schemes; _grading = grading;
        _groupId = groupId; _studentId = studentId; _groupType = groupType;
        _gradingSystem = gradingSystem; _schoolYear = schoolYear;
        StudentName = studentName; GroupLabel = groupLabel;

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

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

    public string ModeButtonLabel => IsTeacherMode ? "Modus: Bewerter" : "Modus: Schüler";

    partial void OnIsTeacherModeChanged(bool value) => OnPropertyChanged(nameof(ModeButtonLabel));

    [RelayCommand]
    private void ToggleMode() => IsTeacherMode = !IsTeacherMode;

    private GradingScheme ResolveScheme() =>
        _schemes.GetByGroup(_groupId)
        ?? _schemes.GetDefaultForType(_groupType)
        ?? new GradingScheme { ExamsPercent = 50, ParticipationPercent = 40, OtherPercent = 10 };

    private void Recompute()
    {
        _scheme = ResolveScheme();
        SchemeSummary = $"Klausuren {_scheme.ExamsPercent:0.#} % · Mitarbeit {_scheme.ParticipationPercent:0.#} % · " +
                         $"Sonstige {_scheme.OtherPercent:0.#} %";

        var (periodFrom, periodTo) = GroupMembershipService.SchoolYearPeriod(_schoolYear, SelectedPeriod.Period switch
        {
            ParticipationPeriod.H1 => SchoolYearPeriodKind.H1,
            ParticipationPeriod.H2 => SchoolYearPeriodKind.H2,
            _ => SchoolYearPeriodKind.FullYear,
        });
        var membership = _memberships.GetByGroup(_groupId).FirstOrDefault(m => m.StudentId == _studentId);

        // ── Klausuren ─────────────────────────────────────────────────────
        ExamRows.Clear();
        ExamHistory.Points.Clear();
        _examGradesRaw = [];
        int? previousNoteEquivalent = null;
        foreach (var exam in _exams.GetByGroup(_groupId)
                     .Where(e => e.Date >= periodFrom && e.Date <= periodTo)
                     .Where(e => membership is null || GroupMembershipService.IsActiveOn(membership, e.Date))
                     .Where(e => !e.Niveau.HasValue || membership?.Niveau == e.Niveau)
                     .OrderBy(e => e.Date))
        {
            var allResults = _results.GetByExam(exam.Id);
            var own = allResults.FirstOrDefault(r => r.StudentId == _studentId);
            string? ownGrade = own is { Absent: false, Grade: not null } ? own.Grade : null;
            if (ownGrade is not null) _examGradesRaw.Add((ownGrade, 1.0));

            var classGrades = allResults.Where(r => !r.Absent && r.Grade is not null)
                .Select(r => (r.Grade!, 1.0)).ToList();
            var classAverage = classGrades.Count > 0 ? _grading.WeightedAverage(classGrades) : (double?)null;

            ExamRows.Add(new StudentExamRow(exam.Title, exam.Date, ownGrade,
                classAverage.HasValue ? FormatGrade(classAverage.Value) : "–"));

            // Gleiche Balken-Sparkline wie die bestehende Notenentwicklung (2.5): Rohwert auf die
            // 1..6-Notenäquivalent-Achse abbilden, damit Grades1To6 und Points0To15 dieselbe
            // Balkenhöhen-Formel nutzen können.
            int? noteEquivalent = ownGrade is not null && int.TryParse(ownGrade, out var raw)
                ? (_gradingSystem == GradingSystem.Grades1To6 ? raw : int.Parse(PointsNoteMapping.PointsToNote(raw)))
                : null;
            var isFailing = noteEquivalent is >= 5;
            var isDrop = noteEquivalent.HasValue && previousNoteEquivalent.HasValue
                         && noteEquivalent.Value - previousNoteEquivalent.Value >= 1;
            var warnings = new List<string>();
            if (isDrop) warnings.Add("Abfall um ≥ 1 Note");
            if (isFailing) warnings.Add("Versetzungsgefährdung");
            ExamHistory.Points.Add(new GradeHistoryPoint(exam.Date, exam.Title, ownGrade ?? "–",
                noteEquivalent, warnings.Count > 0, string.Join(" · ", warnings)));
            if (noteEquivalent.HasValue) previousNoteEquivalent = noteEquivalent;
        }
        _examsAverage = _examGradesRaw.Count > 0 ? _grading.WeightedAverage(_examGradesRaw) : null;

        // ── Mitarbeit & Sonstige ──────────────────────────────────────────
        var allGrades = _grades.GetByStudentAndGroup(_studentId, _groupId)
            .Where(g => g.Date >= periodFrom && g.Date <= periodTo)
            .Where(g => membership is null || GroupMembershipService.IsActiveOn(membership, g.Date))
            .OrderBy(g => g.Date).ToList();

        ParticipationRows.Clear();
        _participationGradesRaw = [];
        foreach (var g in allGrades.Where(g => g.Category == GradeCategory.Participation))
        {
            _participationGradesRaw.Add((g.Value, g.Weight));
            ParticipationRows.Add(new StudentSimpleGradeRow(g, SaveGrade));
        }
        _participationAverage = _participationGradesRaw.Count > 0 ? _grading.WeightedAverage(_participationGradesRaw) : null;

        OtherRows.Clear();
        _otherGradesRaw = [];
        foreach (var g in allGrades.Where(g => g.Category != GradeCategory.Participation))
        {
            _otherGradesRaw.Add((g.Value, g.Weight));
            OtherRows.Add(new StudentSimpleGradeRow(g, SaveGrade));
        }
        _otherAverage = _otherGradesRaw.Count > 0 ? _grading.WeightedAverage(_otherGradesRaw) : null;

        ExamsAverageDisplay = _examsAverage.HasValue ? FormatGrade(_examsAverage.Value) : null;
        ParticipationAverageDisplay = _participationAverage.HasValue ? FormatGrade(_participationAverage.Value) : null;
        OtherAverageDisplay = _otherAverage.HasValue ? FormatGrade(_otherAverage.Value) : null;

        var reportGrade = _grading.CalculateReportGrade(_examGradesRaw, _participationGradesRaw, _otherGradesRaw,
            _scheme, _gradingSystem, RoundingRule.Commercial);
        CurrentReportGradeDisplay = reportGrade is null
            ? "Noch nicht berechenbar — keine Werte im gewählten Zeitraum."
            : $"Note {reportGrade}";

        RecomputeTarget();
        RecomputeWhatIf();
    }

    private void SaveGrade(Grade grade)
    {
        _grades.Save(grade);
        Recompute();
    }

    partial void OnTargetGradeTextChanged(string value) => RecomputeTarget();
    partial void OnTargetBucketChanged(GradeBucketKind value)
    {
        OnPropertyChanged(nameof(TargetBucketName));
        RecomputeTarget();
    }

    private void RecomputeTarget()
    {
        if (!TryParseGrade(TargetGradeText, out var target))
        {
            TargetResultDisplay = "";
            return;
        }

        var result = ReportGradeTargetCalculator.SolveRequiredAverage(target, TargetBucket,
            _examsAverage, _participationAverage, _otherAverage, _scheme, _gradingSystem);

        TargetResultDisplay = result switch
        {
            null => $"{TargetBucketName} fließt laut Gewichtungsschema nicht in die Zeugnisnote ein.",
            { IsAchievable: true } r => $"Nötiger Schnitt in {TargetBucketName}: {FormatGrade(r.RequiredAverage)}",
            { IsAchievable: false } r =>
                $"Mit den übrigen Bereichen rechnerisch nicht mehr erreichbar (bräuchte {FormatGrade(r.RequiredAverage)}).",
        };
    }

    partial void OnWhatIfExamGradeTextChanged(string value) => RecomputeWhatIf();

    private void RecomputeWhatIf()
    {
        if (string.IsNullOrWhiteSpace(WhatIfExamGradeText))
        {
            WhatIfResultDisplay = "";
            return;
        }

        var hypothetical = new List<(string Grade, double Weight)>(_examGradesRaw) { (WhatIfExamGradeText.Trim(), 1.0) };
        var result = _grading.CalculateReportGrade(hypothetical, _participationGradesRaw, _otherGradesRaw,
            _scheme, _gradingSystem, RoundingRule.Commercial);
        WhatIfResultDisplay = result is null
            ? "Ungültige Note."
            : $"Zeugnisnote mit dieser zusätzlichen Klausurnote: {result}";
    }

    private static bool TryParseGrade(string text, out double value) =>
        double.TryParse(text.Trim().Replace(',', '.'), NumberStyles.Float, CultureInfo.InvariantCulture, out value);

    private static string FormatGrade(double value) => value.ToString("0.0", CultureInfo.InvariantCulture);
}

public class StudentExamRow(string title, DateOnly date, string? ownGrade, string classAverageDisplay)
{
    public string Title { get; } = title;
    public string DateDisplay { get; } = date.ToString("dd.MM.yyyy");
    public string OwnGradeDisplay { get; } = ownGrade ?? "–";
    public string ClassAverageDisplay { get; } = classAverageDisplay;
}

public partial class StudentSimpleGradeRow : ObservableObject
{
    private readonly Grade _grade;
    private readonly Action<Grade> _save;

    public string CategoryLabel { get; }
    public string DateDisplay { get; }
    [ObservableProperty] private string _value;

    public StudentSimpleGradeRow(Grade grade, Action<Grade> save)
    {
        _grade = grade;
        _save = save;
        CategoryLabel = GradeCategoryDisplay.Label(grade.Category);
        DateDisplay = grade.Date.ToString("dd.MM.yyyy");
        _value = grade.Value;
    }

    [RelayCommand]
    private void Save()
    {
        _grade.Value = Value.Trim();
        _save(_grade);
    }
}