Add drag-and-drop support for PDF field repositioning

Introduced drag-and-drop functionality for fields in the PDF editor:
- Added `SenderPdfFieldMoveRequest` record to encapsulate field movement data.
- Enhanced `SenderPdfImageEditor.razor` with drag-and-drop event handlers (`OnFieldDragStart`, `OnPageDropAsync`) and updated field structure.
- Updated `SenderEditorPage.razor` to handle field movement via the `OnMoveFieldAsync` method.
- Improved CSS styles for draggable fields and added a delete button with hover effects.
- Added `getDropCoordsOnPage` function in `envelope-editor.js` to calculate normalized drop coordinates.

These changes improve the user experience by enabling intuitive field placement and management in the PDF editor.

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Components/PdfEditor/SenderPdfFieldMoveRequest.cs

@@ -0,0 +1,7 @@
+namespace EnvelopeGenerator.Server.Client.Components.PdfEditor;
+
+public sealed record SenderPdfFieldMoveRequest(
+    int Index,
+    int Page,
+    double XPt,
+    double YPt);

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Components/PdfEditor/SenderPdfImageEditor.razor

@@ -2,6 +2,7 @@
 @using EnvelopeGenerator.Application.Common.Dto
 @using Microsoft.Extensions.Localization
 @inject IStringLocalizer<Resource> UiLocalizer
+@inject IJSRuntime JSRuntime
 
 <div class="pdf-editor-wrapper sender-image-editor sender-editor-pdf-viewer"
      style="cursor: @(IsPlacementMode ? "crosshair" : "default");"
@@ -33,7 +34,13 @@
                       data-editor-page="@pageNumber"
                      data-page-width-pt="@widthPt"
                      data-page-height-pt="@heightPt">
-                    <div class="sender-image-editor__page-canvas">
+                    <div class="sender-image-editor__page-canvas"
+                         data-editor-page-canvas="@pageNumber"
+                         ondragover="event.preventDefault(); if (event.dataTransfer) event.dataTransfer.dropEffect = 'move';"
+                         ondragenter="event.preventDefault();"
+                         @ondrop:preventDefault="true"
+                         @ondrop:stopPropagation="true"
+                         @ondrop="args => OnPageDropAsync(args, pageNumber, widthPt, heightPt)">
                         @if (!string.IsNullOrWhiteSpace(pagePreview?.ImageDataUrl))
                         {
                             <img class="sender-image-editor__page-image"
@@ -48,14 +55,25 @@
 
                         @foreach (var field in Fields.Where(f => f.Page == pageNumber))
                         {
-                            <button type="button"
-                                    class="sender-image-editor__field"
-                                    style="@GetFieldStyle(field, widthPt, heightPt)"
-                                    title="@field.ReceiverName"
-                                    @onclick:stopPropagation="true"
-                                    @onclick="() => RemoveField.InvokeAsync(field.Index)">
-                                @field.ReceiverName
-                            </button>
+                            <div class="sender-image-editor__field"
+                                 style="@GetFieldStyle(field, widthPt, heightPt)"
+                                 title="@field.ReceiverName"
+                                 draggable="true"
+                                 @onmousedown="() => OnFieldDragStart(field.Index)"
+                                 ondragstart="event.dataTransfer.setData('text/plain', 'field'); event.dataTransfer.effectAllowed = 'move';"
+                                 @onclick:stopPropagation="true">
+                                <span class="sender-image-editor__field-label">@field.ReceiverName</span>
+                                <button type="button"
+                                        class="sender-image-editor__field-remove"
+                                        title='@L("Delete", "Löschen")'
+                                        draggable="false"
+                                        @onclick:stopPropagation="true"
+                                        @onclick="() => RemoveField.InvokeAsync(field.Index)">
+                                    <svg xmlns="http://www.w3.org/2000/svg" width="12" height="12" viewBox="0 0 16 16" fill="none" aria-hidden="true">
+                                        <path d="M4 4L12 12M12 4L4 12" stroke="currentColor" stroke-width="2" stroke-linecap="round" />
+                                    </svg>
+                                </button>
+                            </div>
                         }
                     </div>
                 </div>
@@ -86,6 +104,11 @@
     [Parameter]
     public EventCallback<int> RemoveField { get; set; }
 
+    [Parameter]
+    public EventCallback<SenderPdfFieldMoveRequest> MoveField { get; set; }
+
+    private int? _draggedFieldIndex;
+
     private static string GetFieldStyle(SenderPdfFieldOverlay field, double pageWidthPt, double pageHeightPt)
     {
         var leftPercent = (field.XPt / pageWidthPt) * 100.0;
@@ -108,6 +131,40 @@
             await EditorClick.InvokeAsync(args);
     }
 
+    private void OnFieldDragStart(int fieldIndex)
+    {
+        _draggedFieldIndex = fieldIndex;
+    }
+
+    private async Task OnPageDropAsync(DragEventArgs args, int pageNumber, double pageWidthPt, double pageHeightPt)
+    {
+        if (_draggedFieldIndex is null || !MoveField.HasDelegate)
+            return;
+
+        var coords = await JSRuntime.InvokeAsync<DropCoords?>(
+            "envelopeEditor.getDropCoordsOnPage",
+            "sender-editor-pdf-viewer",
+            pageNumber,
+            args.ClientX,
+            args.ClientY);
+
+        if (coords is null)
+            return;
+
+        const double sigWidthPt = 1.77 * 72;
+        const double sigHeightPt = 1.96 * 72;
+
+        var xPt = coords.NormX * pageWidthPt;
+        var yPt = coords.NormY * pageHeightPt;
+        xPt = Math.Max(0, Math.Min(xPt, pageWidthPt - sigWidthPt));
+        yPt = Math.Max(0, Math.Min(yPt, pageHeightPt - sigHeightPt));
+
+        await MoveField.InvokeAsync(new SenderPdfFieldMoveRequest(_draggedFieldIndex.Value, pageNumber, xPt, yPt));
+        _draggedFieldIndex = null;
+    }
+
+    private sealed record DropCoords(double NormX, double NormY);
+
     private string L(string key, string fallback)
     {
         var value = UiLocalizer[key];

EnvelopeGenerator.Server/EnvelopeGenerator.Server.Client/Pages/SenderEditorPage.razor

@@ -5,6 +5,7 @@
 @using EnvelopeGenerator.Application.Common.Dto
 @using EnvelopeGenerator.Application.Envelopes.Commands
 @using EnvelopeGenerator.Application.Resources
+@using EnvelopeGenerator.Server.Client.Components.PdfEditor
 @using EnvelopeGenerator.Server.Client.Services
 @using Microsoft.AspNetCore.WebUtilities
 @using Microsoft.AspNetCore.Components.Forms
@@ -336,6 +337,7 @@
                                   PdfDataUrl="@PdfDataUrl"
                                   Fields="@FieldOverlays"
                                   EditorClick="OnPdfAreaClickAsync"
+                                  MoveField="OnMoveFieldAsync"
                                   RemoveField="OnRemoveFieldByIndexAsync" />
         }
     </div>
@@ -806,6 +808,22 @@
         await Task.CompletedTask;
     }
 
+    async Task OnMoveFieldAsync(SenderPdfFieldMoveRequest request)
+    {
+        if (request.Index < 0 || request.Index >= _signatureFields.Count)
+            return;
+
+        var field = _signatureFields[request.Index];
+        _signatureFields[request.Index] = field with
+        {
+            XPt = request.XPt,
+            YPt = request.YPt,
+            Page = request.Page
+        };
+
+        await Task.CompletedTask;
+    }
+
     // ── Clear all fields ──
     async Task ClearAllFieldsAsync()
     {

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/css/envelope-viewer.css

@@ -134,13 +134,47 @@
     padding: 0.2rem 0.3rem;
     text-align: left;
     line-height: 1.1;
-    cursor: pointer;
+    cursor: grab;
     display: flex;
     align-items: flex-start;
-    justify-content: flex-start;
+    justify-content: space-between;
+    gap: 0.35rem;
     overflow: hidden;
 }
 
+.sender-image-editor__field:active {
+    cursor: grabbing;
+}
+
+.sender-image-editor__field-label {
+    min-width: 0;
+    overflow: hidden;
+    text-overflow: ellipsis;
+    white-space: nowrap;
+}
+
+.sender-image-editor__field-remove {
+    border: none;
+    background: rgba(15, 23, 42, 0.78);
+    color: #ffffff;
+    width: 1.1rem;
+    height: 1.1rem;
+    min-width: 1.1rem;
+    border-radius: 999px;
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 0;
+    cursor: pointer;
+    line-height: 1;
+    margin-left: auto;
+    flex-shrink: 0;
+}
+
+.sender-image-editor__field-remove:hover {
+    background: rgba(220, 38, 38, 0.9);
+}
+
 .sender-image-editor__field:hover {
     filter: brightness(0.96);
 }

EnvelopeGenerator.Server/EnvelopeGenerator.Server/wwwroot/js/envelope-editor.js

@@ -92,5 +92,31 @@ window.envelopeEditor = {
             normY:     normY,
             pageIndex: targetIndex
         };
+    },
+
+    getDropCoordsOnPage: function (viewerCssClass, pageNumber, clientX, clientY) {
+        const viewer = document.querySelector('.' + viewerCssClass);
+        if (!viewer) {
+            console.warn('[envelopeEditor] viewer not found for class:', viewerCssClass);
+            return null;
+        }
+
+        const page = viewer.querySelector('[data-editor-page="' + pageNumber + '"]');
+        if (!page) {
+            console.warn('[envelopeEditor] page not found:', pageNumber);
+            return null;
+        }
+
+        const rect = page.getBoundingClientRect();
+        const clampedX = Math.max(rect.left, Math.min(clientX, rect.right));
+        const clampedY = Math.max(rect.top, Math.min(clientY, rect.bottom));
+
+        const normX = (clampedX - rect.left) / rect.width;
+        const normY = (clampedY - rect.top) / rect.height;
+
+        return {
+            normX: normX,
+            normY: normY
+        };
     }
 };