feat: add external drawing boxes and paged callbacks

LehrerApp.Templating/Model.cs

@@ -2,7 +2,7 @@ using System.Text.Json.Serialization;
 
 namespace LehrerApp.Templating;
 
-public enum PlaceholderType { Text, Multiline, Date, Number, Image, Table, Chart }
+public enum PlaceholderType { Text, Multiline, Date, Number, Image, Table, Chart, Drawing }
 
 public abstract record PlaceholderValue(PlaceholderType Type);
 public sealed record TextValue(string Value) : PlaceholderValue(PlaceholderType.Text);
@@ -16,6 +16,67 @@ public sealed record TableValue(IReadOnlyList<string> Columns, IReadOnlyList<IRe
 public sealed record ChartPoint(string X, decimal Y);
 public sealed record ChartSeries(string Label, IReadOnlyList<ChartPoint> Points);
 public sealed record ChartValue(IReadOnlyList<ChartSeries> Series) : PlaceholderValue(PlaceholderType.Chart);
+public abstract record DrawingCommand;
+public sealed record DrawString(float X, float Y, string Text, float FontSize = 11,
+    string Color = "#000000", bool Bold = false, bool Italic = false, string FontFamily = "") : DrawingCommand;
+public enum DrawingTextAlignment { AlignLeft, AlignCenter, AlignRight }
+public sealed record DrawStringEx(float X, float Y, float Height, float Width, string Text,
+    DrawingTextAlignment Alignment = DrawingTextAlignment.AlignLeft, float FontSize = 11,
+    string FontFamily = "", string Color = "#000000", bool Bold = false, bool Italic = false)
+    : DrawingCommand;
+public sealed record MoveTo(float X, float Y) : DrawingCommand;
+public sealed record LineTo(float X, float Y, string Color = "#000000", float StrokeWidth = 1) : DrawingCommand;
+public sealed record DrawLine(float X1, float Y1, float X2, float Y2,
+    string Color = "#000000", float StrokeWidth = 1) : DrawingCommand;
+public sealed record DrawRectangle(float X, float Y, float Width, float Height,
+    string StrokeColor = "#000000", float StrokeWidth = 1, string FillColor = "none") : DrawingCommand;
+public sealed record DrawImage(float X, float Y, float Width, float Height, byte[] Data, string MimeType) : DrawingCommand;
+/// <summary>Declarative drawing supplied by an external data provider. Coordinates use the template layout unit; font sizes use points.</summary>
+public sealed record DrawingValue(IReadOnlyList<DrawingCommand> Commands, float ContentHeight)
+    : PlaceholderValue(PlaceholderType.Drawing);
+
+/// <summary>A recorded drawing surface handed to an in-process external renderer.</summary>
+public sealed class DrawingCanvas
+{
+    private readonly List<DrawingCommand> _commands = [];
+    public IReadOnlyList<DrawingCommand> Commands => _commands;
+    public void DrawString(float x, float y, string text, float fontSize = 11, string color = "#000000",
+        bool bold = false, bool italic = false, string fontFamily = "") =>
+        _commands.Add(new LehrerApp.Templating.DrawString(x, y, text, fontSize, color, bold, italic, fontFamily));
+    public void DrawStringEx(float x, float y, float height, float width, string text,
+        DrawingTextAlignment alignment = DrawingTextAlignment.AlignLeft, float fontSize = 11,
+        string fontFamily = "", string color = "#000000", bool bold = false, bool italic = false) =>
+        _commands.Add(new LehrerApp.Templating.DrawStringEx(x, y, height, width, text, alignment,
+            fontSize, fontFamily, color, bold, italic));
+    public void MoveTo(float x, float y) => _commands.Add(new LehrerApp.Templating.MoveTo(x, y));
+    public void LineTo(float x, float y, string color = "#000000", float strokeWidth = 1) =>
+        _commands.Add(new LehrerApp.Templating.LineTo(x, y, color, strokeWidth));
+    public void DrawLine(float x1, float y1, float x2, float y2, string color = "#000000", float strokeWidth = 1) =>
+        _commands.Add(new LehrerApp.Templating.DrawLine(x1, y1, x2, y2, color, strokeWidth));
+    public void DrawRectangle(float x, float y, float width, float height, string strokeColor = "#000000",
+        float strokeWidth = 1, string fillColor = "none") =>
+        _commands.Add(new LehrerApp.Templating.DrawRectangle(x, y, width, height, strokeColor, strokeWidth, fillColor));
+    public void DrawImage(float x, float y, float width, float height, byte[] data, string mimeType) =>
+        _commands.Add(new LehrerApp.Templating.DrawImage(x, y, width, height, data, mimeType));
+}
+
+public sealed class DrawingPageContext(float width, float height, int pageNumber, DrawingCanvas canvas, object? state)
+{
+    public float Width { get; } = width;
+    public float Height { get; } = height;
+    public int PageNumber { get; } = pageNumber;
+    public DrawingCanvas Canvas { get; } = canvas;
+    public object? State { get; set; } = state;
+}
+
+public delegate bool DrawingPageCallback(DrawingPageContext context);
+
+/// <summary>
+/// In-process callback drawing. The callback returns true when finished or false to request another box.
+/// State is carried across callbacks. It is recorded before QuestPDF performs layout and is never executed by a package.
+/// </summary>
+public sealed record PagedDrawingValue(DrawingPageCallback DrawPage, object? InitialState = null,
+    int MaxPages = 1_000) : PlaceholderValue(PlaceholderType.Drawing);
 
 public interface ITemplateDataProvider
 {
@@ -58,6 +119,12 @@ public sealed record TextBoxElement(int Line, float X, float Y, float Width, flo
 public sealed record FlowBoxElement(int Line, float X, float Y, float Width, float Height,
     string Content, string? Placeholder, string? Format, IReadOnlyDictionary<string, string> Attributes)
     : TemplateElement(Line, X, Y, Width, Height, Attributes);
+public sealed record DrawBoxElement(int Line, float X, float Y, float Width, float Height,
+    string Placeholder, IReadOnlyDictionary<string, string> Attributes)
+    : TemplateElement(Line, X, Y, Width, Height, Attributes);
+public sealed record FlowDrawBoxElement(int Line, float X, float Y, float Width, float Height,
+    string Placeholder, IReadOnlyDictionary<string, string> Attributes)
+    : TemplateElement(Line, X, Y, Width, Height, Attributes);
 public sealed record TableElement(int Line, float X, float Y, float Width, float Height,
     string Placeholder, IReadOnlyDictionary<string, string> Attributes)
     : TemplateElement(Line, X, Y, Width, Height, Attributes);