using CommunityToolkit.Mvvm.ComponentModel;
using LehrerApp.Core.Importing;
using LehrerApp.Core.Services;
using System.Collections.ObjectModel;

namespace LehrerApp.Desktop.ViewModels.Students;

public partial class StudentImportDialogViewModel : ObservableObject
{
    private readonly StudentImportService _service;
    private readonly StudentImportPreview _preview;

    [ObservableProperty] private bool _isBusy;
    [ObservableProperty] private string _error = "";

    public string FileName { get; }
    public string FormatName => _preview.FormatName;
    public int TotalStudents => _preview.Entries.Count;
    public int NewStudents => _preview.Entries.Count(entry =>
        entry.AutomaticResolution?.Kind == StudentImportResolutionKind.CreateNew);
    public int ExistingStudents => _preview.Entries.Count(entry =>
        entry.AutomaticResolution?.Kind == StudentImportResolutionKind.UseExisting);
    public int StudentsToSupplement => _preview.Entries.Count(entry => entry.FieldsToSupplement.Count > 0);
    public string Summary =>
        $"{TotalStudents} erkannt · {NewStudents} neu · {ExistingStudents} eindeutig vorhanden · "
        + $"{StudentsToSupplement} mit Ergänzungen";

    public string GroupSummary { get; }
    public ObservableCollection<StudentImportMessageItem> Messages { get; } = [];
    public ObservableCollection<StudentImportConflictItem> Conflicts { get; } = [];
    public bool HasMessages => Messages.Count > 0;
    public bool HasConflicts => Conflicts.Count > 0;
    public bool CanUseExistingForAll => Conflicts.Any(conflict => conflict.HasSingleExistingStudentOption);
    public bool IsReadyWithoutConflicts => !HasConflicts && _preview.CanApply;
    public bool HasBlockingErrors => !_preview.CanApply;
    public bool CanApply => _preview.CanApply && !IsBusy;
    public StudentImportApplyResult? Result { get; private set; }

    public StudentImportDialogViewModel(
        StudentImportService service,
        StudentImportPreview preview,
        string fileName)
    {
        _service = service;
        _preview = preview;
        FileName = fileName;

        foreach (var message in preview.Messages)
            Messages.Add(new StudentImportMessageItem(message));
        foreach (var conflict in preview.Conflicts)
            Conflicts.Add(new StudentImportConflictItem(conflict));

        var automaticGroups = preview.GroupAssignments.Count(group => group.AutomaticGroupId is not null);
        var unresolvedGroups = preview.GroupAssignments.Count(group => group.ConflictId is not null);
        var unassignedGroups = preview.GroupAssignments.Count - automaticGroups - unresolvedGroups;
        GroupSummary = preview.GroupAssignments.Count == 0
            ? "Die Datei enthält keine Klassenangabe."
            : $"Lerngruppen: {automaticGroups} automatisch · {unresolvedGroups} zu entscheiden"
              + (unassignedGroups > 0 ? $" · {unassignedGroups} nicht zugeordnet" : "");
    }

    partial void OnIsBusyChanged(bool value) => OnPropertyChanged(nameof(CanApply));

    public IReadOnlyList<ImportDecision> BuildDecisions() => Conflicts
        .Select(conflict => new ImportDecision(conflict.Id, conflict.SelectedOption.Id))
        .ToList()
        .AsReadOnly();

    /// <summary>
    /// Wählt für alle eindeutigen Schüler-Konflikte den jeweils vorhandenen Datensatz.
    /// Mehrdeutige Treffer und Lerngruppen-Konflikte bleiben unverändert.
    /// </summary>
    public void UseExistingForAll()
    {
        foreach (var conflict in Conflicts)
            conflict.TrySelectSingleExistingStudent();
    }

    public async Task<bool> TryApplyAsync()
    {
        Error = "";
        if (!_preview.CanApply)
        {
            Error = "Der Import enthält Fehler und kann nicht angewendet werden.";
            return false;
        }

        IsBusy = true;
        try
        {
            var decisions = BuildDecisions();
            Result = await Task.Run(async () =>
                await _service.ApplyAsync(_preview, decisions).ConfigureAwait(false));
            return true;
        }
        catch (InvalidOperationException ex)
        {
            Error = ex.Message;
            return false;
        }
        finally
        {
            IsBusy = false;
        }
    }
}

public sealed class StudentImportMessageItem
{
    public string Message { get; }
    public string SourceReference { get; }
    public string Display => SourceReference.Length == 0 ? Message : $"{SourceReference}: {Message}";
    public string Foreground { get; }

    public StudentImportMessageItem(ImportMessage message)
    {
        Message = message.Message;
        SourceReference = message.SourceReference ?? "";
        Foreground = message.Severity switch
        {
            ImportMessageSeverity.Error => "#C62828",
            ImportMessageSeverity.Warning => "#B06A00",
            _ => "#2563EB",
        };
    }
}

public partial class StudentImportConflictItem : ObservableObject
{
    private const string ExistingStudentOptionPrefix = "existing:";

    [ObservableProperty] private StudentImportConflictOptionItem _selectedOption;

    public string Id { get; }
    public string Title { get; }
    public string Description { get; }
    public string ImportedValue { get; }
    public string ExistingValue { get; }
    public string SourceReference { get; }
    public IReadOnlyList<StudentImportConflictOptionItem> Options { get; }
    public bool HasSingleExistingStudentOption => ExistingStudentOptions.Count == 1;

    private IReadOnlyList<StudentImportConflictOptionItem> ExistingStudentOptions => Options
        .Where(option => option.Id.StartsWith(ExistingStudentOptionPrefix, StringComparison.Ordinal))
        .ToList();

    public StudentImportConflictItem(ImportConflict conflict)
    {
        Id = conflict.Id;
        Title = conflict.Title;
        Description = conflict.Description;
        ImportedValue = conflict.ImportedValue;
        ExistingValue = conflict.ExistingValue ?? "";
        SourceReference = conflict.SourceReference ?? "";
        Options = conflict.Options
            .Select(option => new StudentImportConflictOptionItem(
                option.Id, option.Label, option.Description ?? ""))
            .ToList()
            .AsReadOnly();
        _selectedOption = Options.First(option => option.Id == conflict.DefaultOptionId);
    }

    public bool TrySelectSingleExistingStudent()
    {
        var options = ExistingStudentOptions;
        if (options.Count != 1) return false;
        SelectedOption = options[0];
        return true;
    }
}

public sealed record StudentImportConflictOptionItem(
    string Id,
    string Label,
    string Description);