LehrerApp/LehrerApp.Desktop/ViewModels/Settings/SettingsViewModel.JsonImportExport.cs

using CommunityToolkit.Mvvm.ComponentModel;
using CommunityToolkit.Mvvm.Input;
using LehrerApp.Core.Interfaces;
using LehrerApp.Core.Models;
using LehrerApp.Core.Services;
using LehrerApp.Data;
using LehrerApp.Desktop.Services;
using LehrerApp.Desktop.ViewModels.Planning;
using LehrerApp.Sync;
using LehrerApp.Sync.Crypto;
using System.Collections.ObjectModel;
using System.Globalization;
using System.Security.Cryptography;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace LehrerApp.Desktop.ViewModels.Settings;

public partial class SettingsViewModel
{
    // ── JSON Import / Export ──────────────────────────────────────────────────

    public CompetencyCatalogImportPreview? PrepareCatalogImport(string json)
    {
        if (CatalogSubject is null)
        {
            CatalogValidation = "Bitte zuerst ein Fach auswählen.";
            return null;
        }
        try
        {
            CatalogValidation = "";
            return _catalogImport.Analyze(
                json, CatalogSubject.Id, CatalogSubject.Name, CatalogGradeLevel);
        }
        catch (InvalidDataException ex)
        {
            CatalogValidation = ex.Message;
            return null;
        }
    }

    public void ApplyCatalogImport(CompetencyCatalogImportPreview preview,
        CompetencyCatalogImportMode mode, IReadOnlySet<string> useImportedConflicts)
    {
        _catalogImport.Apply(preview, mode, useImportedConflicts);
        LoadCatalog();
        CatalogValidation = mode == CompetencyCatalogImportMode.Merge
            ? "Kompetenzkatalog wurde sicher zusammengeführt."
            : "Kompetenzkatalog wurde vollständig ersetzt.";
    }

    public string ExportCatalog()
        => SerializeCatalog(CatalogGradeLevel);

    public CompetencyCatalogImportPreview? PrepareCatalogCopy(int targetGradeLevel)
    {
        if (CatalogSubject is null)
        {
            CatalogValidation = "Bitte zuerst ein Fach auswählen.";
            return null;
        }
        if (Domains.Count == 0)
        {
            CatalogValidation = "Der ausgewählte Katalog enthält keine Bereiche.";
            return null;
        }
        if (targetGradeLevel is < 1 or > 13 || targetGradeLevel == CatalogGradeLevel)
        {
            CatalogValidation = "Bitte eine andere Zielklassenstufe zwischen 1 und 13 auswählen.";
            return null;
        }

        CatalogValidation = "";
        return _catalogImport.Analyze(SerializeCatalog(targetGradeLevel), CatalogSubject.Id,
            CatalogSubject.Name, targetGradeLevel);
    }

    public void SetCatalogCopyStatus(int targetGradeLevel) =>
        CatalogValidation = $"Kompetenzkatalog wurde in Klassenstufe {targetGradeLevel} kopiert.";

    private string SerializeCatalog(int gradeLevel)
    {
        var dto = new CatalogDto
        {
            Subject    = CatalogSubject?.Name ?? "",
            GradeLevel = gradeLevel,
            Domains    = Domains.Select(d => new DomainDto
            {
                Name         = d.Name,
                Code         = d.Code,
                Competencies = d.Items.Select(i => new CompetencyDto
                {
                    Code        = i.Code,
                    Description = i.Description,
                }).ToList(),
            }).ToList(),
        };
        return JsonSerializer.Serialize(dto, new JsonSerializerOptions { WriteIndented = true });
    }
}

// ── JSON DTOs ─────────────────────────────────────────────────────────────────

internal class CatalogDto
{
    [JsonPropertyName("subject")]    public string?          Subject    { get; set; }
    [JsonPropertyName("gradeLevel")] public int              GradeLevel { get; set; }
    [JsonPropertyName("domains")]    public List<DomainDto>? Domains    { get; set; }
}

internal class DomainDto
{
    [JsonPropertyName("name")]          public string?               Name         { get; set; }
    [JsonPropertyName("code")]          public string?               Code         { get; set; }
    [JsonPropertyName("competencies")]  public List<CompetencyDto>?  Competencies { get; set; }
}

internal class CompetencyDto
{
    [JsonPropertyName("code")]        public string? Code        { get; set; }
    [JsonPropertyName("description")] public string? Description { get; set; }
}