Documents: Replace Razor templates with iText

Elwig/Documents/Document.cs

@@ -1,19 +1,42 @@
-using System;
-using System.Threading.Tasks;
-using System.IO;
 using Elwig.Helpers;
-using System.Collections.Generic;
-using System.Linq;
 using Elwig.Helpers.Printing;
+using iText.IO.Font;
+using iText.Kernel.Font;
+using iText.Kernel.Pdf;
+using iText.Kernel.Pdf.Canvas;
+using iText.Kernel.Pdf.Event;
+using iText.Kernel.Pdf.Xobject;
+using iText.Kernel.Utils;
+using iText.Layout;
+using iText.Layout.Borders;
+using iText.Layout.Element;
+using iText.Layout.Properties;
 using MimeKit;
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
 using System.Threading;
+using System.Threading.Tasks;
 
 namespace Elwig.Documents {
-    public abstract partial class Document : IDisposable {
+    public class Document : IDisposable {
 
         public static string Name => "Dokument";
 
-        protected static readonly double GenerationProportion = 0.125;
+        public const float PtInMM = 2.8346456693f;
+        public const float BorderThickness = 0.5f;
+
+        protected PdfFont NF = null!;
+        protected PdfFont BF = null!;
+        protected PdfFont IF = null!;
+        protected PdfFont BI = null!;
+        protected PdfFont SF = null!;
+
+        //protected readonly PdfFont NF = PdfFontFactory.CreateFont(StandardFonts.TIMES_ROMAN);
+        //protected readonly PdfFont BF = PdfFontFactory.CreateFont(StandardFonts.TIMES_BOLD);
+        //protected readonly PdfFont IF = PdfFontFactory.CreateFont(StandardFonts.TIMES_ITALIC);
+        //protected readonly PdfFont BI = PdfFontFactory.CreateFont(StandardFonts.TIMES_BOLDITALIC);
 
         protected TempFile? _pdfFile = null;
         protected string? _pdfPath;
@@ -24,22 +47,18 @@ namespace Elwig.Documents {
         public bool ShowFoldMarks = App.Config.Debug;
         public bool IsDoublePaged = false;
         public bool IsPreview = false;
+        private iText.Layout.Document? _doc;
 
-        public string DocumentsPath;
         public int CurrentNextSeason;
         public string? DocumentId;
         public string Title;
         public string Author;
-        public string Header;
         public DateOnly Date;
 
         public Document(string title) {
-            var c = App.Client;
-            DocumentsPath = App.DocumentsPath;
             CurrentNextSeason = Utils.CurrentNextSeason;
             Title = title;
-            Author = c.NameFull;
-            Header = "";
+            Author = App.Client.NameFull;
             Date = DateOnly.FromDateTime(Utils.Today);
         }
 
@@ -58,99 +77,173 @@ namespace Elwig.Documents {
         }
 
         public static Document FromPdf(string path) {
-            return new PdfDocument(path);
+            return new RawPdfDocument(path);
         }
 
-        private async Task<string> Render() {
-            string name;
-            if (this is BusinessLetter) {
-                name = "BusinessLetter";
-            } else if (this is DeliveryNote) {
-                name = "DeliveryNote";
-            } else if (this is CreditNote) {
-                name = "CreditNote";
-            } else if (this is DeliveryJournal) {
-                name = "DeliveryJournal";
-            } else if (this is DeliveryDepreciationList) {
-                name = "DeliveryDepreciationList";
-            } else if (this is Letterhead) {
-                name = "Letterhead";
-            } else if (this is DeliveryConfirmation) {
-                name = "DeliveryConfirmation";
-            } else if (this is MemberDataSheet) {
-                name = "MemberDataSheet";
-            } else if (this is MemberList) {
-                name = "MemberList";
-            } else if (this is WineQualityStatistics) {
-                name = "WineQualityStatistics";
-            } else if (this is PaymentVariantSummary) {
-                name = "PaymentVariantSummary";
-            } else if (this is DeliveryAncmtList) {
-                name = "DeliveryAncmtList";
-            } else {
-                throw new InvalidOperationException("Invalid document object");
+        private class RawPdfDocument : Document {
+            public RawPdfDocument(string pdfPath) :
+                base(Path.GetFileNameWithoutExtension(pdfPath)) {
+                _pdfPath = pdfPath;
             }
-            return await Render(name);
         }
 
-        private async Task<string> Render(string name) {
-            return await Html.CompileRenderAsync(name, this); ;
+        public int Render(string path) {
+            using var writer = new PdfWriter(path);
+            return Render(writer);
+        }
+
+        private int Render(PdfWriter writer) {
+            NF = PdfFontFactory.CreateFont(@"C:\Windows\Fonts\times.ttf",    PdfEncodings.IDENTITY_H, PdfFontFactory.EmbeddingStrategy.PREFER_NOT_EMBEDDED);
+            BF = PdfFontFactory.CreateFont(@"C:\Windows\Fonts\timesbd.ttf",  PdfEncodings.IDENTITY_H, PdfFontFactory.EmbeddingStrategy.PREFER_NOT_EMBEDDED);
+            IF = PdfFontFactory.CreateFont(@"C:\Windows\Fonts\timesi.ttf",   PdfEncodings.IDENTITY_H, PdfFontFactory.EmbeddingStrategy.PREFER_NOT_EMBEDDED);
+            BI = PdfFontFactory.CreateFont(@"C:\Windows\Fonts\timesbi.ttf",  PdfEncodings.IDENTITY_H, PdfFontFactory.EmbeddingStrategy.PREFER_NOT_EMBEDDED);
+            SF = PdfFontFactory.CreateFont(@"C:\Windows\Fonts\seguisym.ttf", PdfEncodings.IDENTITY_H, PdfFontFactory.EmbeddingStrategy.PREFER_NOT_EMBEDDED);
+            NF.SetSubset(true);
+            BF.SetSubset(true);
+            IF.SetSubset(true);
+            BI.SetSubset(true);
+            SF.SetSubset(true);
+            writer.SetCompressionLevel(CompressionConstants.BEST_COMPRESSION);
+            writer.SetSmartMode(true);
+            using var pdf = new PdfDocument(writer);
+            pdf.GetDocumentInfo()
+                .SetTitle(Title)
+                .SetAuthor(Author)
+                .SetCreator($"Elwig {App.Version}");
+            var handler = new EventHandler(this);
+            pdf.AddEventHandler(PdfDocumentEvent.START_PAGE, handler);
+            pdf.AddEventHandler(PdfDocumentEvent.END_PAGE, handler);
+            pdf.AddEventHandler(PdfDocumentEvent.START_DOCUMENT_CLOSING, handler);
+            _doc = new iText.Layout.Document(pdf, iText.Kernel.Geom.PageSize.A4);
+            try {
+                _doc.SetFont(NF).SetFontSize(12);
+                RenderHeader(_doc, pdf);
+                RenderBody(_doc, pdf);
+                var pageNum = pdf.GetNumberOfPages();
+                return pageNum;
+            } finally {
+                _doc.Close();
+            }
+        }
+
+        protected virtual void RenderHeader(iText.Layout.Document doc, PdfDocument pdf) { }
+
+        protected virtual void RenderBody(iText.Layout.Document doc, PdfDocument pdf) { }
+
+        protected virtual Paragraph GetFooter() {
+            return new KernedParagraph(App.Client.NameFull, 10);
         }
 
         public async Task Generate(CancellationToken? cancelToken = null, IProgress<double>? progress = null) {
             if (_pdfFile != null)
                 return;
             progress?.Report(0.0);
-            if (this is PdfDocument) {
+            if (this is RawPdfDocument) {
                 // nothing to do
             } else if (this is MergedDocument m) {
+                using var tmpPdf = new TempFile("pdf");
                 var pdf = new TempFile("pdf");
-                var tmpHtmls = new List<TempFile>();
-                var tmpFiles = new List<string>();
                 try {
-                    var n = m.Documents.Count();
-                    int i = 0;
-                    foreach (var doc in m.Documents) {
-                        if (doc is PdfDocument) {
-                            tmpFiles.Add(doc.PdfPath!);
-                            continue;
-                        }
+                    var pageNums = new List<int>();
+
+                    using var writer = new PdfWriter(pdf.FilePath);
+                    using var mergedPdf = new PdfDocument(writer);
+                    var merger = new PdfMerger(mergedPdf);
+
+                    PdfPage? letterheadPage = null;
+                    int letterheadInsertIndex = 0;
+                    int letterheadDocIndex = 0;
+
+                    for (int i = 0; i < m.Documents.Count; i++) {
                         if (cancelToken?.IsCancellationRequested ?? false)
                             throw new OperationCanceledException("Dokumentenerzeugung abgebrochen!");
-                        var tmpHtml = new TempFile("html");
-                        await File.WriteAllTextAsync(tmpHtml.FilePath, await doc.Render(), Utils.UTF8);
-                        tmpHtmls.Add(tmpHtml);
-                        tmpFiles.Add((doc is Letterhead ? "#" : "") + tmpHtml.FilePath);
-                        i++;
-                        progress?.Report(GenerationProportion * 100 * i / n);
+                        var doc = m.Documents[i];
+                        int p0 = mergedPdf.GetNumberOfPages();
+
+                        if (letterheadPage != null && doc is Letterhead) {
+                            if (mergedPdf.GetNumberOfPages() <= letterheadInsertIndex) {
+                                mergedPdf.AddPage(letterheadPage);
+                                mergedPdf.AddNewPage();
+                            } else {
+                                mergedPdf.AddPage(letterheadInsertIndex + 1, letterheadPage);
+                                mergedPdf.AddNewPage(letterheadInsertIndex + 2);
+                            }
+
+                            pageNums[letterheadDocIndex] = 1;
+                            letterheadPage = null;
+                        }
+
+                        if (doc is RawPdfDocument) {
+                            if (IsDoublePaged && doc is Letterhead) {
+                                using var reader = new PdfReader(doc.PdfPath);
+                                using var src = new PdfDocument(reader);
+                                letterheadPage = src.GetPage(1).CopyTo(mergedPdf);
+                                letterheadInsertIndex = p0;
+                                letterheadDocIndex = i;
+                            } else {
+                                using var reader = new PdfReader(doc.PdfPath);
+                                using var src = new PdfDocument(reader);
+                                merger.Merge(src, 1, src.GetNumberOfPages());
+                            }
+                        } else {
+                            int pageNum = doc.Render(tmpPdf.FilePath);
+                            if (IsDoublePaged && doc is Letterhead) {
+                                using var reader = new PdfReader(tmpPdf.FilePath);
+                                using var src = new PdfDocument(reader);
+                                letterheadPage = src.GetPage(1).CopyTo(mergedPdf);
+                                letterheadInsertIndex = p0;
+                                letterheadDocIndex = i;
+                            } else {
+                                using var reader = new PdfReader(tmpPdf.FilePath);
+                                using var src = new PdfDocument(reader);
+                                merger.Merge(src, 1, pageNum);
+                            }
+                        }
+
+                        int p1 = mergedPdf.GetNumberOfPages();
+                        pageNums.Add(p1 - p0);
+
+                        if (IsDoublePaged && doc is not Letterhead && mergedPdf.GetNumberOfPages() % 2 != 0) {
+                            if (letterheadPage != null) {
+                                mergedPdf.AddPage(letterheadPage);
+                                letterheadPage = null;
+                            } else {
+                                mergedPdf.AddNewPage();
+                            }
+                        }
+
+                        progress?.Report(100.0 * (i + 1) / (m.Documents.Count + 1));
                     }
-                    progress?.Report(GenerationProportion * 100);
-                    var pages = Pdf.Convert(tmpFiles, pdf.FilePath, IsDoublePaged, m.Documents, cancelToken, new Progress<double>(v => progress?.Report(GenerationProportion * 100 + v * (1 - GenerationProportion))));
-                    TotalPages = pages.Pages;
-                    _pdfFile = pdf;
+
+                    if (letterheadPage != null) {
+                        if (mergedPdf.GetNumberOfPages() <= letterheadInsertIndex) {
+                            mergedPdf.AddPage(letterheadPage.CopyTo(mergedPdf));
+                            mergedPdf.AddNewPage();
+                        } else {
+                            mergedPdf.AddPage(letterheadInsertIndex + 1, letterheadPage.CopyTo(mergedPdf));
+                            mergedPdf.AddNewPage(letterheadInsertIndex + 2);
+                        }
+
+                        pageNums[letterheadDocIndex] = 1;
+                    }
+
+                    TotalPages = pageNums.Sum();
                 } catch {
                     pdf.Dispose();
                     throw;
-                } finally {
-                    foreach (var tmp in tmpHtmls) {
-                        tmp.Dispose();
-                    }
                 }
+                _pdfFile = pdf;
             } else {
                 if (cancelToken?.IsCancellationRequested ?? false)
                     throw new OperationCanceledException("Dokumentenerzeugung abgebrochen!");
                 var pdf = new TempFile("pdf");
                 try {
-                    using var tmpHtml = new TempFile("html");
-                    await File.WriteAllTextAsync(tmpHtml.FilePath, await Render(), Utils.UTF8);
-                    progress?.Report(50.0);
-                    var pages = Pdf.Convert(tmpHtml.FilePath, pdf.FilePath, this);
-                    TotalPages = pages.Pages;
-                    _pdfFile = pdf;
+                    TotalPages = Render(pdf.FilePath);
                 } catch {
                     pdf.Dispose();
                     throw;
                 }
+                _pdfFile = pdf;
             }
             progress?.Report(100.0);
         }
@@ -180,14 +273,239 @@ namespace Elwig.Documents {
             };
         }
 
-        private class MergedDocument(IEnumerable<Document> docs) : Document("Mehrere Dokumente") {
-            public IEnumerable<Document> Documents = docs;
+        private class MergedDocument : Document {
+            public List<Document> Documents;
+
+            public MergedDocument(IEnumerable<Document> docs) :
+                base("Mehrere Dokumente") {
+                Documents = [.. docs];
+                IsDoublePaged = docs.Any(x => x.IsDoublePaged);
+            }
         }
 
-        private class PdfDocument : Document {
-            public PdfDocument(string pdfPath) :
-                base(Path.GetFileNameWithoutExtension(pdfPath)) {
-                _pdfPath = pdfPath;
+        protected static Cell NewCell(Paragraph? p = null, int rowspan = 1, int colspan = 1, bool overflow = false) {
+            var cell = new Cell(rowspan, colspan)
+                .SetBorder(Border.NO_BORDER)
+                .SetPaddingsMM(0.5f, 1, 0.5f, 1);
+            if (p != null) {
+                p.SetProperty(Property.NO_SOFT_WRAP_INLINE, true);
+                if (!overflow) p.SetProperty(Property.OVERFLOW_X, OverflowPropertyValue.HIDDEN);
+                cell.Add(p);
+            }
+            return cell;
+        }
+
+        protected Cell NewTh(string? text, float fontSize = 8, int rowspan = 1, int colspan = 1, bool left = false, bool rotated = false) {
+            var p = new KernedParagraph(text ?? "", fontSize);
+            if (rotated) p.SetRotationAngle(rotated ? 0.5 * Math.PI : 0);
+            var cell = NewCell(p, rowspan: rowspan, colspan: colspan)
+                .SetTextAlignment(left ? TextAlignment.LEFT : TextAlignment.CENTER)
+                .SetVerticalAlignment(VerticalAlignment.MIDDLE)
+                .SetFont(IF);
+            if (rotated || !left) cell.SetPadding(0);
+            return cell;
+        }
+
+        protected Cell NewTd(string? text = null, float fontSize = 10, int rowspan = 1, int colspan = 1, bool center = false, bool right = false, bool bold = false, bool italic = false, bool borderTop = false, bool overflow = false) {
+            return NewTd(new KernedParagraph(text ?? "", fontSize), rowspan: rowspan, colspan: colspan, center: center, right: right, bold: bold, italic: italic, borderTop: borderTop, overflow: overflow);
+        }
+
+        protected Cell NewTd(KernedParagraph p, int rowspan = 1, int colspan = 1, bool center = false, bool right = false, bool bold = false, bool italic = false, bool borderTop = false, bool overflow = false) {
+            return NewCell(p, rowspan: rowspan, colspan: colspan, overflow: overflow)
+                .SetTextAlignment(center ? TextAlignment.CENTER : right ? TextAlignment.RIGHT : TextAlignment.LEFT)
+                .SetVerticalAlignment(VerticalAlignment.MIDDLE)
+                .SetBorderTop(borderTop ? new SolidBorder(BorderThickness) : Border.NO_BORDER)
+                .SetFont(bold ? (italic ? BI : BF) : (italic ? IF : NF));
+        }
+
+        public static float[] ColsMM(params double[] widths) {
+            return [.. widths.Select(w => (float)w * PtInMM)];
+        }
+
+        public Text Normal(string? text, float? fontSize = null) {
+            var t = new Text(text ?? "").SetFont(NF);
+            if (fontSize != null) t.SetFontSize(fontSize.Value);
+            return t;
+        }
+
+        public Text Bold(string? text, float? fontSize = null) {
+            var t = new Text(text ?? "").SetFont(BF);
+            if (fontSize != null) t.SetFontSize(fontSize.Value);
+            return t;
+        }
+
+        public Text Italic(string? text, float? fontSize = null) {
+            var t = new Text(text ?? "").SetFont(IF);
+            if (fontSize != null) t.SetFontSize(fontSize.Value);
+            return t;
+        }
+
+        public Text BoldItalic(string? text, float? fontSize = null) {
+            var t = new Text(text ?? "").SetFont(BI);
+            if (fontSize != null) t.SetFontSize(fontSize.Value);
+            return t;
+        }
+
+        private class EventHandler : AbstractPdfDocumentEventHandler {
+
+            private const float _fontSize = 10;
+            private const float _placeholderWidth = 50 * PtInMM;
+
+            private readonly Document _doc;
+            private readonly List<PdfFormXObject> _pageNumPlaceholders;
+
+
+            public int NumberOfPages { get; private set; }
+
+            public EventHandler(Document doc) {
+                _doc = doc;
+                _pageNumPlaceholders = [];
+            }
+
+            protected override void OnAcceptedEvent(AbstractPdfDocumentEvent evt) {
+                if (evt.GetType() == PdfDocumentEvent.START_PAGE) {
+                    OnPageStart((PdfDocumentEvent)evt);
+                } else if (evt.GetType() == PdfDocumentEvent.END_PAGE) {
+                    OnPageEnd((PdfDocumentEvent)evt);
+                } else if (evt.GetType() == PdfDocumentEvent.START_DOCUMENT_CLOSING) {
+                    OnDocumentClose((PdfDocumentEvent)evt);
+                }
+            }
+
+            private void OnPageStart(PdfDocumentEvent evt) {
+                var pdf = evt.GetDocument();
+                var page = evt.GetPage();
+                var pageNum = pdf.GetPageNumber(page);
+
+                if (pageNum == 1) {
+                    // first page
+                    if (_doc is BusinessDocument) {
+                        _doc._doc?.SetMarginsMM(90, 20, 35, 25);
+                    } else {
+                        _doc._doc?.SetMarginsMM(20, 20, 35, 25);
+                    }
+                } else if (_doc.IsDoublePaged && (pageNum % 2) == 0) {
+                    // left page (= swapped)
+                    _doc._doc?.SetMarginsMM(20, 25, 25, 20);
+                } else {
+                    // right page
+                    _doc._doc?.SetMarginsMM(20, 20, 25, 25);
+                }
+            }
+
+            private void OnPageEnd(PdfDocumentEvent evt) {
+                var pdf = evt.GetDocument();
+                var page = evt.GetPage();
+                var pageNum = pdf.GetPageNumber(page);
+
+                var pageSize = page.GetPageSize();
+                float leftX1 = pageSize.GetLeft() + 25 * PtInMM;
+                float leftX2 = pageSize.GetLeft() + 20 * PtInMM;
+                float rightX1 = pageSize.GetRight() - 20 * PtInMM;
+                float rightX2 = pageSize.GetRight() - 25 * PtInMM;
+                float footerY = pageSize.GetBottom() + 25 * PtInMM;
+                float y1 = footerY + _fontSize;
+                float y2 = footerY - _fontSize;
+
+                var pdfCanvas = new PdfCanvas(page.NewContentStreamAfter(), page.GetResources(), pdf);
+                using var canvas = new Canvas(pdfCanvas, pageSize);
+
+                var placeholder = new PdfFormXObject(new iText.Kernel.Geom.Rectangle(0, 0, _placeholderWidth, _fontSize));
+                _pageNumPlaceholders.Add(placeholder);
+
+                var c = App.Client;
+                var dateP = new KernedParagraph($"{_doc.Date:dddd, d. MMMM yyyy}", _fontSize).SetFont(_doc.NF);
+                var centerP = new KernedParagraph(_doc.DocumentId ?? "", _fontSize).SetFont(_doc.IF);
+                var pageNumP = new KernedParagraph(_fontSize).Add(new Image(placeholder)).SetFont(_doc.NF);
+
+                if (pageNum == 1) {
+                    // first page
+                    canvas.ShowTextAligned(dateP, leftX1, y1, TextAlignment.LEFT, VerticalAlignment.BOTTOM);
+                    canvas.ShowTextAligned(centerP, (leftX1 + rightX1) / 2, y1, TextAlignment.CENTER, VerticalAlignment.BOTTOM);
+                    canvas.ShowTextAligned(pageNumP, rightX1, y1, TextAlignment.RIGHT, VerticalAlignment.BOTTOM);
+
+                    var footer = _doc.GetFooter();
+                    using var footerCanvas = new Canvas(page, pageSize);
+                    footerCanvas.Add(new Table(1).AddCell(new Cell().Add(footer).SetBorder(Border.NO_BORDER).SetPaddingsMM(1, 0, 0, 0))
+                        .SetFixedPositionMM(25, 0, 165).SetHeightMM(25)
+                        .SetFont(_doc.NF).SetFontSize(10)
+                        .SetTextAlignment(TextAlignment.CENTER)
+                        .SetBorder(Border.NO_BORDER)
+                        .SetBorderTop(new SolidBorder(BorderThickness)));
+                } else if (_doc.IsDoublePaged && (pageNum % 2 == 0)) {
+                    // left page (= swapped)
+                    canvas.ShowTextAligned(pageNumP, leftX2, y2, TextAlignment.LEFT, VerticalAlignment.TOP);
+                    canvas.ShowTextAligned(centerP, (leftX2 + rightX2) / 2, y2, TextAlignment.CENTER, VerticalAlignment.TOP);
+                    canvas.ShowTextAligned(dateP, rightX2, y2, TextAlignment.RIGHT, VerticalAlignment.TOP);
+                } else {
+                    // right page
+                    canvas.ShowTextAligned(dateP, leftX1, y2, TextAlignment.LEFT, VerticalAlignment.TOP);
+                    canvas.ShowTextAligned(centerP, (leftX1 + rightX1) / 2, y2, TextAlignment.CENTER, VerticalAlignment.TOP);
+                    canvas.ShowTextAligned(pageNumP, rightX1, y2, TextAlignment.RIGHT, VerticalAlignment.TOP);
+                }
+
+                if (_doc.ShowFoldMarks) {
+                    var m1 = pageSize.GetTop() - 105 * PtInMM;
+                    var m2 = pageSize.GetTop() - 148.5 * PtInMM;
+                    var m3 = pageSize.GetTop() - 210 * PtInMM;
+                    pdfCanvas.SetLineWidth(BorderThickness);
+
+                    pdfCanvas.MoveTo(0, m1);
+                    pdfCanvas.LineTo(10 * PtInMM, m1);
+                    pdfCanvas.MoveTo(pageSize.GetRight(), m1);
+                    pdfCanvas.LineTo(pageSize.GetRight() - 10 * PtInMM, m1);
+
+                    pdfCanvas.MoveTo(0, m2);
+                    pdfCanvas.LineTo(7 * PtInMM, m2);
+                    pdfCanvas.MoveTo(pageSize.GetRight(), m2);
+                    pdfCanvas.LineTo(pageSize.GetRight() - 7 * PtInMM, m2);
+
+                    pdfCanvas.MoveTo(0, m3);
+                    pdfCanvas.LineTo(10 * PtInMM, m3);
+                    pdfCanvas.MoveTo(pageSize.GetRight(), m3);
+                    pdfCanvas.LineTo(pageSize.GetRight() - 10 * PtInMM, m3);
+
+                    pdfCanvas.ClosePathStroke();
+                }
+
+                if (NumberOfPages > 0) {
+                    // FillPlaceholders() was already called
+                    FillPlaceholder(pdf, pageNum);
+                }
+            }
+
+            private void OnDocumentClose(PdfDocumentEvent evt) {
+                var pdf = evt.GetDocument();
+                var page = evt.GetPage();
+                var pageNum = pdf.GetPageNumber(page);
+
+                // ...
+
+                FillPlaceholders(pdf);
+            }
+
+            private void FillPlaceholders(PdfDocument pdf) {
+                NumberOfPages = pdf.GetNumberOfPages();
+                for (int i = 0; i < _pageNumPlaceholders.Count; i++)
+                    FillPlaceholder(pdf, i + 1);
+            }
+
+            private void FillPlaceholder(PdfDocument pdf, int pageNum) {
+                var placeholder = _pageNumPlaceholders[pageNum - 1];
+                using var canvas = new Canvas(placeholder, pdf);
+                if (_doc.IsDoublePaged && (pageNum % 2 == 0)) {
+                    // left page (= swapped)
+                    var p = new KernedParagraph(_fontSize).SetFont(_doc.NF);
+                    if (_doc.IsPreview) p.Add(_doc.Bold("(vorläufig) "));
+                    p.Add(_doc.Normal($"Seite {pageNum:N0} von {NumberOfPages:N0} "));
+                    canvas.ShowTextAligned(p, 0, 0, TextAlignment.LEFT);
+                } else {
+                    // right page
+                    var p = new KernedParagraph(_fontSize).SetFont(_doc.NF)
+                        .Add(_doc.Normal($"Seite {pageNum:N0} von {NumberOfPages:N0}"));
+                    if (_doc.IsPreview) p.Add(_doc.Bold(" (vorläufig)"));
+                    canvas.ShowTextAligned(p, _placeholderWidth, 0, TextAlignment.RIGHT);
+                }
             }
         }
     }