From 31224f02cb3ae2ad2fe23637c02c7f01d5371c41 Mon Sep 17 00:00:00 2001
From: wiz78 <wiz78>
Date: Tue, 19 Mar 2019 14:54:11 +0100
Subject: [PATCH] Make it possible to provide custom XMP metadata

The PdfMetadata class is now inheritable. PdfDocument has a new delegate that can be used to provide a different implementation of that class that creates custom metadata.

e.g.:

	class XMPMetadata : PdfMetadata
	{
		private readonly XmpCore	xmp;

		public XMPMetadata( PdfDocument document, XmpCore xmpCore ) : base( document )
		{
			xmp = xmpCore;

			SetupStream();
		}

		protected override byte[] GenerateXmp()
		{
			return xmp?.SerializeToRDF();
		}
	}
---
 src/PdfSharp/Pdf/PdfDocument.cs | 12 +++++++++++-
 src/PdfSharp/Pdf/PdfMetadata.cs | 12 ++++++------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/src/PdfSharp/Pdf/PdfDocument.cs b/src/PdfSharp/Pdf/PdfDocument.cs
index fe1b9af5..eb801d36 100644
--- a/src/PdfSharp/Pdf/PdfDocument.cs
+++ b/src/PdfSharp/Pdf/PdfDocument.cs
@@ -491,7 +491,10 @@ internal override void PrepareForSave()
             
             // @PDF/UA
             // Create PdfMetadata now to include the final document information in XMP generation.
-            Catalog.Elements.SetReference(PdfCatalog.Keys.Metadata, new PdfMetadata(this));
+			if( MetadataProvider != null )
+	            Catalog.Elements.SetReference(PdfCatalog.Keys.Metadata, MetadataProvider(this));
+			else
+	            Catalog.Elements.SetReference(PdfCatalog.Keys.Metadata, new PdfMetadata(this));
         }
 
         /// <summary>
@@ -808,6 +811,13 @@ internal PdfCatalog Catalog
         }
         PdfCatalog _catalog;  // never changes if once created
 
+		public delegate PdfMetadata PdfMetadataProvider(PdfDocument document);
+
+		/// <summary>
+		/// Gets or sets the delegate that will return the PdfMetadata object to use when saving the document
+		/// </summary>
+		public PdfMetadataProvider MetadataProvider { get; set; }
+
         /// <summary>
         /// Gets the PdfInternals object of this document, that grants access to some internal structures
         /// which are not part of the public interface of PdfDocument.
diff --git a/src/PdfSharp/Pdf/PdfMetadata.cs b/src/PdfSharp/Pdf/PdfMetadata.cs
index 6b4eafa9..29ef55cd 100644
--- a/src/PdfSharp/Pdf/PdfMetadata.cs
+++ b/src/PdfSharp/Pdf/PdfMetadata.cs
@@ -35,7 +35,7 @@ namespace PdfSharp.Pdf
     /// <summary>
     /// Represents an XML Metadata stream.
     /// </summary>
-    public sealed class PdfMetadata : PdfDictionary
+    public class PdfMetadata : PdfDictionary
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="PdfMetadata"/> class.
@@ -60,15 +60,15 @@ public PdfMetadata(PdfDocument document)
             SetupStream();
         }
 
-        void SetupStream()
+        protected void SetupStream()
         {
             var stream = GenerateXmp();
             
-            byte[] bytes = PdfEncoders.RawEncoding.GetBytes(stream);
-            CreateStream(bytes);
+			if(stream != null)
+	            CreateStream(stream);
         }
 
-        string GenerateXmp()
+        protected virtual byte[] GenerateXmp()
         {
             var instanceId = Guid.NewGuid().ToString();
             var documentId = Guid.NewGuid().ToString();
@@ -123,7 +123,7 @@ string GenerateXmp()
             "    </x:xmpmeta>\n" +
             "<?xpacket end=\"r\"?>\n";
 
-            return str;
+            return PdfEncoders.RawEncoding.GetBytes(str);
         }
 
         /// <summary>