Fix <figcaption> Conversion

No longer discard parsed child elements when adding figure number reference.
Change FigureCaptionExpression from inheriting PhrasingElementExpression to BlockElementExpression to support more complex <figcaption> contents.
<figcaption> can only be the first or last element of <figure>. Do not set keepnext if <figcaption> is last.

Author: Tranquilite0

src/Html2OpenXml/Expressions/FigureCaptionExpression.cs

@@ -1,4 +1,4 @@
-/* Copyright (C) Olivier Nizet https://github.com/onizet/html2openxml - All Rights Reserved
+/* Copyright (C) Olivier Nizet https://github.com/onizet/html2openxml - All Rights Reserved
  * 
  * This source is subject to the Microsoft Permissive License.
  * Please see the License.txt file for more information.
@@ -12,6 +12,7 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using AngleSharp.Dom;
 using AngleSharp.Html.Dom;
 using DocumentFormat.OpenXml;
 using DocumentFormat.OpenXml.Wordprocessing;
@@ -21,40 +22,81 @@ namespace HtmlToOpenXml.Expressions;
 /// <summary>
 /// Process the parsing of a <c>figcaption</c> element, which is used to describe an image.
 /// </summary>
-sealed class FigureCaptionExpression(IHtmlElement node) : PhrasingElementExpression(node)
+sealed class FigureCaptionExpression(IHtmlElement node) : BlockElementExpression(node)
 {
 
     /// <inheritdoc/>
     public override IEnumerable<OpenXmlElement> Interpret (ParsingContext context)
     {
         ComposeStyles(context);
-        var childElements = Interpret(context.CreateChild(this), node.ChildNodes);
-        if (!childElements.Any())
-            return [];
-
-        var p = new Paragraph (
+        var childElements = Interpret(context.CreateChild(this), node.ChildNodes);
+
+        var figNumRef = new List<OpenXmlElement>()
+        {
             new Run(
                 new Text("Figure ") { Space = SpaceProcessingModeValues.Preserve }
             ),
             new SimpleField(
                 new Run(
                     new Text(AddFigureCaption(context).ToString(CultureInfo.InvariantCulture)))
-            ) { Instruction = " SEQ Figure \\* ARABIC " }
-        ) {
-            ParagraphProperties = new ParagraphProperties {
-                ParagraphStyleId = context.DocumentStyle.GetParagraphStyle(context.DocumentStyle.DefaultStyles.CaptionStyle),
-                KeepNext = new KeepNext()
-            }
-        };
+            )
+            { Instruction = " SEQ Figure \\* ARABIC " }
+        };
+
 
-        if (childElements.First() is Run run) // any caption?
-        {
-            Text? t = run.GetFirstChild<Text>();
-            if (t != null)
-                t.Text = " " + t.InnerText; // append a space after the numero of the picture
+        if (!childElements.Any())
+        {
+            return
+                [new Paragraph(figNumRef)
+                {
+                    ParagraphProperties = new ParagraphProperties
+                    {
+                        ParagraphStyleId = context.DocumentStyle.GetParagraphStyle(context.DocumentStyle.DefaultStyles.CaptionStyle),
+                        KeepNext = DetermineKeepNext(node),
+                    }
+                }];
         }
-
-        return [p];
+
+        //Add the figure number references to the start of the first paragraph.
+        if(childElements.FirstOrDefault() is Paragraph p)
+        {
+            figNumRef.Add(new Run(
+                new Text(" ") { Space = SpaceProcessingModeValues.Preserve }
+            ));
+
+            figNumRef.Reverse();
+            foreach (var element in figNumRef)
+            {
+                p.InsertAt(element, 0);
+            }
+        }
+        else
+        {
+            //The first child of the figure caption is a table or something. Just prepend a new paragraph with the figure number reference.
+            childElements = 
+                [
+                    new Paragraph(figNumRef)
+                    {
+                        ParagraphProperties = new ParagraphProperties{ }
+                    },
+                    ..childElements
+                ];
+        }
+
+        foreach (var paragraph in childElements.OfType<Paragraph>())
+        {
+            paragraph.ParagraphProperties ??= new ParagraphProperties();
+            paragraph.ParagraphProperties.ParagraphStyleId ??= context.DocumentStyle.GetParagraphStyle(context.DocumentStyle.DefaultStyles.CaptionStyle);
+            //Keep caption paragraphs together.
+            paragraph.ParagraphProperties.KeepNext = new KeepNext();
+        }
+
+        if(childElements.OfType<Paragraph>().LastOrDefault() is Paragraph lastPara)
+        {
+            lastPara.ParagraphProperties!.KeepNext = DetermineKeepNext(node);
+        }
+
+        return childElements;
     }
 
     /// <summary>
@@ -78,4 +120,19 @@ private static int AddFigureCaption(ParsingContext context)
         context.Properties("figCaptionRef", figCaptionRef);
         return figCaptionRef.Value;
     }
-}
+
+    /// <summary>
+    /// Determines whether the KeepNext property should apply this this caption.
+    /// </summary>
+    /// <param name="node"></param>
+    /// <returns>A new <see cref="KeepNext"/> or null./></returns>
+    private static KeepNext? DetermineKeepNext(IHtmlElement node)
+    {
+        // A caption at the end of a figure will have no next sibling.
+        if(node.NextElementSibling is null)
+        {
+            return null;
+        }
+        return new();
+    }
+}