Add support for invoice attachments

Introduced the `InvoiceAttachment` entity and its relationship with `ZugferdInvoice` to manage extracted invoice attachments. Updated `AppDbContext` and added a migration to create the `InvoiceAttachments` table with cascading delete behavior and an index for optimized queries.

Enhanced the UI to display attachments in `Details.cshtml`, including file type icons, file size, and extraction date. Added a new `ViewAttachment` page to render or download attachments based on their type, with support for XML, plain text, images, and downloads.

Implemented `AttachmentViewerService` to determine viewer types and MIME types for attachments. Registered the service in the DI container. Updated `Upload.cshtml.cs` to save extracted attachments to the database.

Improved user experience with syntax highlighting for XML files and appropriate messages for unsupported file types.

DXApp.TemplateKitProject/Data/AppDbContext.cs

@@ -6,6 +6,7 @@ namespace DXApp.TemplateKitProject.Data;
 public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(options)
 {
     public DbSet<ZugferdInvoice> ZugferdInvoices { get; set; }
+    public DbSet<InvoiceAttachment> InvoiceAttachments { get; set; }
 
     protected override void OnModelCreating(ModelBuilder modelBuilder)
     {
@@ -27,6 +28,19 @@ public class AppDbContext(DbContextOptions<AppDbContext> options) : DbContext(op
 
             entity.Property(e => e.TaxAmount)
                 .HasColumnType("decimal(18,2)");
+
+            // Relationship: One-to-Many mit InvoiceAttachments
+            entity.HasMany(e => e.Attachments)
+                .WithOne(a => a.ZugferdInvoice)
+                .HasForeignKey(a => a.ZugferdInvoiceId)
+                .OnDelete(DeleteBehavior.Cascade);
+        });
+
+        modelBuilder.Entity<InvoiceAttachment>(entity =>
+        {
+            // Index für schnelleres Laden der Attachments einer Rechnung
+            entity.HasIndex(e => e.ZugferdInvoiceId)
+                .HasDatabaseName("IX_InvoiceAttachments_ZugferdInvoiceId");
         });
     }
 }

DXApp.TemplateKitProject/Migrations/20260602123528_AddInvoiceAttachments.Designer.cs

@@ -0,0 +1,141 @@
+// <auto-generated />
+using System;
+using DXApp.TemplateKitProject.Data;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.EntityFrameworkCore.Infrastructure;
+using Microsoft.EntityFrameworkCore.Metadata;
+using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Storage.ValueConversion;
+
+#nullable disable
+
+namespace DXApp.TemplateKitProject.Migrations
+{
+    [DbContext(typeof(AppDbContext))]
+    [Migration("20260602123528_AddInvoiceAttachments")]
+    partial class AddInvoiceAttachments
+    {
+        /// <inheritdoc />
+        protected override void BuildTargetModel(ModelBuilder modelBuilder)
+        {
+#pragma warning disable 612, 618
+            modelBuilder
+                .HasAnnotation("ProductVersion", "8.0.8")
+                .HasAnnotation("Relational:MaxIdentifierLength", 128);
+
+            SqlServerModelBuilderExtensions.UseIdentityColumns(modelBuilder);
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.InvoiceAttachment", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("int");
+
+                    SqlServerPropertyBuilderExtensions.UseIdentityColumn(b.Property<int>("Id"));
+
+                    b.Property<DateTime>("ExtractedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<long>("FileSizeBytes")
+                        .HasColumnType("bigint");
+
+                    b.Property<bool>("IsZugferdXml")
+                        .HasColumnType("bit");
+
+                    b.Property<string>("OriginalFileName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SavedFilePath")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<int>("ZugferdInvoiceId")
+                        .HasColumnType("int");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("ZugferdInvoiceId")
+                        .HasDatabaseName("IX_InvoiceAttachments_ZugferdInvoiceId");
+
+                    b.ToTable("InvoiceAttachments");
+                });
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.ZugferdInvoice", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("int");
+
+                    SqlServerPropertyBuilderExtensions.UseIdentityColumn(b.Property<int>("Id"));
+
+                    b.Property<string>("BuyerName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("CurrencyCode")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("GuidelineId")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("Iban")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<DateTime>("ImportedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<DateTime>("InvoiceDate")
+                        .HasColumnType("datetime2");
+
+                    b.Property<string>("InvoiceNumber")
+                        .HasColumnType("nvarchar(450)");
+
+                    b.Property<string>("RawXml")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("ResultFilePath")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SellerName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SellerTaxId")
+                        .HasColumnType("nvarchar(450)");
+
+                    b.Property<string>("SourceType")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<decimal>("TaxAmount")
+                        .HasColumnType("decimal(18,2)");
+
+                    b.Property<decimal>("TotalAmount")
+                        .HasColumnType("decimal(18,2)");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("ImportedAt")
+                        .HasDatabaseName("IX_ZugferdInvoices_ImportedAt");
+
+                    b.HasIndex("InvoiceNumber", "SellerTaxId")
+                        .HasDatabaseName("IX_ZugferdInvoices_InvoiceNumber_SellerTaxId");
+
+                    b.ToTable("ZugferdInvoices");
+                });
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.InvoiceAttachment", b =>
+                {
+                    b.HasOne("DXApp.TemplateKitProject.Models.ZugferdInvoice", "ZugferdInvoice")
+                        .WithMany("Attachments")
+                        .HasForeignKey("ZugferdInvoiceId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("ZugferdInvoice");
+                });
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.ZugferdInvoice", b =>
+                {
+                    b.Navigation("Attachments");
+                });
+#pragma warning restore 612, 618
+        }
+    }
+}

DXApp.TemplateKitProject/Migrations/20260602123528_AddInvoiceAttachments.cs

@@ -0,0 +1,51 @@
+using System;
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace DXApp.TemplateKitProject.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddInvoiceAttachments : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.CreateTable(
+                name: "InvoiceAttachments",
+                columns: table => new
+                {
+                    Id = table.Column<int>(type: "int", nullable: false)
+                        .Annotation("SqlServer:Identity", "1, 1"),
+                    ZugferdInvoiceId = table.Column<int>(type: "int", nullable: false),
+                    OriginalFileName = table.Column<string>(type: "nvarchar(max)", nullable: true),
+                    SavedFilePath = table.Column<string>(type: "nvarchar(max)", nullable: true),
+                    FileSizeBytes = table.Column<long>(type: "bigint", nullable: false),
+                    IsZugferdXml = table.Column<bool>(type: "bit", nullable: false),
+                    ExtractedAt = table.Column<DateTime>(type: "datetime2", nullable: false)
+                },
+                constraints: table =>
+                {
+                    table.PrimaryKey("PK_InvoiceAttachments", x => x.Id);
+                    table.ForeignKey(
+                        name: "FK_InvoiceAttachments_ZugferdInvoices_ZugferdInvoiceId",
+                        column: x => x.ZugferdInvoiceId,
+                        principalTable: "ZugferdInvoices",
+                        principalColumn: "Id",
+                        onDelete: ReferentialAction.Cascade);
+                });
+
+            migrationBuilder.CreateIndex(
+                name: "IX_InvoiceAttachments_ZugferdInvoiceId",
+                table: "InvoiceAttachments",
+                column: "ZugferdInvoiceId");
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropTable(
+                name: "InvoiceAttachments");
+        }
+    }
+}

DXApp.TemplateKitProject/Migrations/AppDbContextModelSnapshot.cs

@@ -22,6 +22,40 @@ namespace DXApp.TemplateKitProject.Migrations
 
             SqlServerModelBuilderExtensions.UseIdentityColumns(modelBuilder);
 
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.InvoiceAttachment", b =>
+                {
+                    b.Property<int>("Id")
+                        .ValueGeneratedOnAdd()
+                        .HasColumnType("int");
+
+                    SqlServerPropertyBuilderExtensions.UseIdentityColumn(b.Property<int>("Id"));
+
+                    b.Property<DateTime>("ExtractedAt")
+                        .HasColumnType("datetime2");
+
+                    b.Property<long>("FileSizeBytes")
+                        .HasColumnType("bigint");
+
+                    b.Property<bool>("IsZugferdXml")
+                        .HasColumnType("bit");
+
+                    b.Property<string>("OriginalFileName")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<string>("SavedFilePath")
+                        .HasColumnType("nvarchar(max)");
+
+                    b.Property<int>("ZugferdInvoiceId")
+                        .HasColumnType("int");
+
+                    b.HasKey("Id");
+
+                    b.HasIndex("ZugferdInvoiceId")
+                        .HasDatabaseName("IX_InvoiceAttachments_ZugferdInvoiceId");
+
+                    b.ToTable("InvoiceAttachments");
+                });
+
             modelBuilder.Entity("DXApp.TemplateKitProject.Models.ZugferdInvoice", b =>
                 {
                     b.Property<int>("Id")
@@ -82,6 +116,22 @@ namespace DXApp.TemplateKitProject.Migrations
 
                     b.ToTable("ZugferdInvoices");
                 });
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.InvoiceAttachment", b =>
+                {
+                    b.HasOne("DXApp.TemplateKitProject.Models.ZugferdInvoice", "ZugferdInvoice")
+                        .WithMany("Attachments")
+                        .HasForeignKey("ZugferdInvoiceId")
+                        .OnDelete(DeleteBehavior.Cascade)
+                        .IsRequired();
+
+                    b.Navigation("ZugferdInvoice");
+                });
+
+            modelBuilder.Entity("DXApp.TemplateKitProject.Models.ZugferdInvoice", b =>
+                {
+                    b.Navigation("Attachments");
+                });
 #pragma warning restore 612, 618
         }
     }

DXApp.TemplateKitProject/Models/InvoiceAttachment.cs

@@ -0,0 +1,18 @@
+namespace DXApp.TemplateKitProject.Models;
+
+/// <summary>
+/// Extrahierte Anhänge einer ZUGFeRD-Rechnung (gespeichert in DB)
+/// </summary>
+public class InvoiceAttachment
+{
+    public int Id { get; set; }
+    public int ZugferdInvoiceId { get; set; }
+    public string OriginalFileName { get; set; } = string.Empty;
+    public string SavedFilePath { get; set; } = string.Empty;
+    public long FileSizeBytes { get; set; }
+    public bool IsZugferdXml { get; set; }
+    public DateTime ExtractedAt { get; set; }
+
+    // Navigation Property
+    public ZugferdInvoice? ZugferdInvoice { get; set; }
+}

DXApp.TemplateKitProject/Models/ZugferdInvoice.cs

@@ -17,5 +17,8 @@
         public string SourceType { get; set; } = string.Empty;      // "Upload" oder "Email"
         public string ResultFilePath { get; set; } = string.Empty;  // Pfad der Result-PDF
         public string GuidelineId { get; set; } = string.Empty;     // ZUGFeRD Guideline-ID aus XMP
+
+        // Navigation Property
+        public List<InvoiceAttachment> Attachments { get; set; } = [];
     }
 }

DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml

@@ -2,6 +2,13 @@
 @model DXApp.TemplateKitProject.Pages.Invoices.DetailsModel
 @{
     ViewData["Title"] = "Rechnungsdetails";
+
+    string FormatFileSize(long bytes)
+    {
+        if (bytes < 1024) return $"{bytes} Bytes";
+        if (bytes < 1024 * 1024) return $"{bytes / 1024.0:N2} KB";
+        return $"{bytes / (1024.0 * 1024.0):N2} MB";
+    }
 }
 
 <h2>📄 Rechnungsdetails</h2>
@@ -11,7 +18,7 @@
 {
     <button class="btn btn-primary mb-3 ms-2"
             onclick="openPdfViewer(@Model.Invoice.Id)">
-        📄 PDF anzeigen
+        📄 Ergebnis anzeigen
     </button>
 }
 
@@ -50,6 +57,51 @@ else
         </tr>
     </table>
 
+    @* Anhänge-Sektion *@
+    @if (Model.Invoice.Attachments.Any())
+    {
+        <h4 class="mt-4">📎 Anhänge (@Model.Invoice.Attachments.Count)</h4>
+        <div class="list-group">
+            @foreach (var attachment in Model.Invoice.Attachments)
+            {
+                var icon = attachment.IsZugferdXml ? "📋" : "📄";
+                var extension = System.IO.Path.GetExtension(attachment.OriginalFileName).ToLowerInvariant();
+                icon = extension switch
+                {
+                    ".xml" => "📋",
+                    ".pdf" => "📄",
+                    ".jpg" or ".jpeg" or ".png" or ".gif" => "🖼️",
+                    ".txt" => "📝",
+                    _ => "📎"
+                };
+
+                <a href="/Invoices/ViewAttachment?filePath=@Uri.EscapeDataString(attachment.SavedFilePath)" 
+                   class="list-group-item list-group-item-action d-flex justify-content-between align-items-center"
+                   target="_blank">
+                    <div>
+                        <span class="me-2">@icon</span>
+                        <strong>@attachment.OriginalFileName</strong>
+                        @if (attachment.IsZugferdXml)
+                        {
+                            <span class="badge bg-success ms-2">ZUGFeRD-XML</span>
+                        }
+                        <br />
+                        <small class="text-muted">
+                            Größe: @FormatFileSize(attachment.FileSizeBytes) · 
+                            Extrahiert: @attachment.ExtractedAt.ToString("dd.MM.yyyy HH:mm")
+                        </small>
+                    </div>
+                    <span class="badge bg-primary">Öffnen</span>
+                </a>
+            }
+        </div>
+    }
+    else
+    {
+        <h4 class="mt-4">📎 Anhänge</h4>
+        <div class="alert alert-info">Keine Anhänge extrahiert.</div>
+    }
+
 @(Html.DevExtreme().Popup()
     .ID("pdf-viewer-popup")
     .Title("PDF Viewer")

DXApp.TemplateKitProject/Pages/Invoices/Details.cshtml.cs

@@ -12,7 +12,9 @@ public class DetailsModel(AppDbContext db) : PageModel
 
     public async Task<IActionResult> OnGetAsync(int id)
     {
-        Invoice = await db.ZugferdInvoices.FirstOrDefaultAsync(i => i.Id == id);
+        Invoice = await db.ZugferdInvoices
+            .Include(i => i.Attachments)
+            .FirstOrDefaultAsync(i => i.Id == id);
 
         if (Invoice is null)
             return NotFound();

DXApp.TemplateKitProject/Pages/Invoices/Upload.cshtml.cs

@@ -75,6 +75,29 @@ public class UploadModel(
                         ImportedInvoice.ResultFilePath = ResultFilePath;
                         await db.SaveChangesAsync();
                     }
+
+                    // 4. Attachments in DB speichern
+                    if (Result.HasAttachments)
+                    {
+                        foreach (var attachment in Result.Attachments)
+                        {
+                            var invoiceAttachment = new InvoiceAttachment
+                            {
+                                ZugferdInvoiceId = ImportedInvoice.Id,
+                                OriginalFileName = attachment.OriginalFileName,
+                                SavedFilePath = attachment.SavedFilePath,
+                                FileSizeBytes = attachment.FileSizeBytes,
+                                IsZugferdXml = attachment.IsZugferdXml,
+                                ExtractedAt = DateTime.UtcNow
+                            };
+                            db.InvoiceAttachments.Add(invoiceAttachment);
+                        }
+                        await db.SaveChangesAsync();
+
+                        logger.LogInformation(
+                            "Rechnung '{InvoiceNumber}': {Count} Anhang/Anhänge in DB gespeichert.",
+                            ImportedInvoice.InvoiceNumber, Result.Attachments.Count);
+                    }
                 }
             }
         }

DXApp.TemplateKitProject/Pages/Invoices/ViewAttachment.cshtml

@@ -0,0 +1,88 @@
+@page
+@using DXApp.TemplateKitProject.Services
+@model DXApp.TemplateKitProject.Pages.Invoices.ViewAttachmentModel
+@{
+    ViewData["Title"] = $"Attachment: {Model.FileName}";
+}
+
+<h2>?? Attachment: @Model.FileName</h2>
+
+<div class="mb-3">
+    <a href="/Invoices/Details" class="btn btn-secondary">? Zurück</a>
+    <a href="?handler=Download&filePath=@Request.Query["filePath"]" 
+       class="btn btn-primary">
+        ?? Download
+    </a>
+</div>
+
+@switch (Model.ViewerType)
+{
+    case AttachmentViewerType.Pdf:
+        <div class="alert alert-info">
+            PDF-Dateien können Sie über die Result-PDF-Funktion anzeigen.
+        </div>
+        break;
+
+    case AttachmentViewerType.Xml:
+        <div class="card">
+            <div class="card-header bg-primary text-white">
+                <strong>XML-Inhalt</strong> (ZUGFeRD/Factur-X)
+            </div>
+            <div class="card-body p-0">
+                <textarea id="xml-viewer" style="display:none;">@Model.TextContent</textarea>
+                <div id="xml-rendered"></div>
+            </div>
+        </div>
+
+        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.16/codemirror.min.css">
+        <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.16/theme/monokai.min.css">
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.16/codemirror.min.js"></script>
+        <script src="https://cdnjs.cloudflare.com/ajax/libs/codemirror/5.65.16/mode/xml/xml.min.js"></script>
+        <script>
+            var editor = CodeMirror(document.getElementById('xml-rendered'), {
+                value: document.getElementById('xml-viewer').value,
+                mode: 'xml',
+                lineNumbers: true,
+                readOnly: true,
+                theme: 'monokai',
+                lineWrapping: true
+            });
+        </script>
+        break;
+
+    case AttachmentViewerType.Text:
+        <div class="card">
+            <div class="card-header bg-secondary text-white">
+                <strong>Text-Inhalt</strong>
+            </div>
+            <div class="card-body">
+                <pre style="background-color: #f5f5f5; padding: 15px; border-radius: 5px; max-height: 600px; overflow: auto;">@Model.TextContent</pre>
+            </div>
+        </div>
+        break;
+
+    case AttachmentViewerType.Image:
+        <div class="card">
+            <div class="card-body text-center">
+                <img src="?handler=Download&filePath=@Request.Query["filePath"]" 
+                     alt="@Model.FileName" 
+                     class="img-fluid" 
+                     style="max-height: 800px;">
+            </div>
+        </div>
+        break;
+
+    case AttachmentViewerType.Word:
+        <div class="alert alert-warning">
+            <strong>Word-Dokumente können nicht direkt angezeigt werden.</strong>
+            <p>Bitte laden Sie die Datei herunter oder implementieren Sie eine Konvertierung zu PDF.</p>
+        </div>
+        break;
+
+    default:
+        <div class="alert alert-warning">
+            <strong>Dieser Dateityp kann nicht angezeigt werden.</strong>
+            <p>Bitte laden Sie die Datei herunter.</p>
+        </div>
+        break;
+}

DXApp.TemplateKitProject/Pages/Invoices/ViewAttachment.cshtml.cs

@@ -0,0 +1,42 @@
+using DXApp.TemplateKitProject.Services;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using System.Text;
+
+namespace DXApp.TemplateKitProject.Pages.Invoices;
+
+public class ViewAttachmentModel(AttachmentViewerService viewerService) : PageModel
+{
+    public string FileName { get; private set; } = string.Empty;
+    public AttachmentViewerType ViewerType { get; private set; }
+    public string? TextContent { get; private set; }
+
+    public IActionResult OnGet(string filePath)
+    {
+        if (string.IsNullOrEmpty(filePath) || !System.IO.File.Exists(filePath))
+            return NotFound();
+
+        FileName = Path.GetFileName(filePath);
+        ViewerType = viewerService.DetermineViewerType(FileName);
+
+        // Für Text/XML: Inhalt laden
+        if (ViewerType == AttachmentViewerType.Xml || ViewerType == AttachmentViewerType.Text)
+        {
+            TextContent = System.IO.File.ReadAllText(filePath, Encoding.UTF8);
+        }
+
+        return Page();
+    }
+
+    public IActionResult OnGetDownload(string filePath)
+    {
+        if (string.IsNullOrEmpty(filePath) || !System.IO.File.Exists(filePath))
+            return NotFound();
+
+        var fileName = Path.GetFileName(filePath);
+        var mimeType = viewerService.GetMimeType(fileName);
+        var bytes = System.IO.File.ReadAllBytes(filePath);
+
+        return File(bytes, mimeType, fileName);
+    }
+}

DXApp.TemplateKitProject/Program.cs

@@ -18,6 +18,7 @@ builder.Services.AddScoped<PdfResultPackageService>();
 builder.Services.AddScoped<ZugferdExtractorService>();
 builder.Services.AddScoped<ZugferdParserService>();
 builder.Services.AddScoped<ZugferdImportService>();
+builder.Services.AddScoped<AttachmentViewerService>();
 
 var app = builder.Build();
 

DXApp.TemplateKitProject/Services/AttachmentViewerService.cs

@@ -0,0 +1,49 @@
+using DXApp.TemplateKitProject.Models;
+
+namespace DXApp.TemplateKitProject.Services;
+
+public class AttachmentViewerService
+{
+    public AttachmentViewerType DetermineViewerType(string fileName)
+    {
+        var extension = Path.GetExtension(fileName).ToLowerInvariant();
+
+        return extension switch
+        {
+            ".pdf" => AttachmentViewerType.Pdf,
+            ".xml" => AttachmentViewerType.Xml,
+            ".txt" => AttachmentViewerType.Text,
+            ".jpg" or ".jpeg" or ".png" or ".gif" => AttachmentViewerType.Image,
+            ".docx" or ".doc" => AttachmentViewerType.Word,
+            _ => AttachmentViewerType.Download
+        };
+    }
+
+    public string GetMimeType(string fileName)
+    {
+        var extension = Path.GetExtension(fileName).ToLowerInvariant();
+
+        return extension switch
+        {
+            ".pdf" => "application/pdf",
+            ".xml" => "application/xml",
+            ".txt" => "text/plain",
+            ".jpg" or ".jpeg" => "image/jpeg",
+            ".png" => "image/png",
+            ".gif" => "image/gif",
+            ".docx" => "application/vnd.openxmlformats-officedocument.wordprocessingml.document",
+            ".doc" => "application/msword",
+            _ => "application/octet-stream"
+        };
+    }
+}
+
+public enum AttachmentViewerType
+{
+    Pdf,        // PDF.js Viewer
+    Xml,        // Syntax-highlighted XML
+    Text,       // Plain Text
+    Image,      // <img> Tag
+    Word,       // Konvertierung zu PDF (optional)
+    Download    // Nur Download-Button
+}