Embedded images replaced with cid linked resources. (#313)

* Added logic to replace embedded images with linked resources

* Added alt text for images and replaced NewtonSoft with Text.Json

* Fix draft mime preparation

* Fix crashes for signatures without images.

---------

Co-authored-by: Burak Kaan Köse <bkaankose@outlook.com>

Wino.Core/Extensions/MimeExtensions.cs

@@ -1,9 +1,12 @@
-using System.IO;
+using System;
+using System.IO;
 using System.Text;
 using Google.Apis.Gmail.v1.Data;
+using HtmlAgilityPack;
 using MimeKit;
 using MimeKit.IO;
 using MimeKit.IO.Filters;
+using MimeKit.Utils;
 using Wino.Core.Domain;
 using Wino.Core.Domain.Entities;
 
@@ -48,5 +51,71 @@ namespace Wino.Core.Extensions
 
             return new AddressInformation() { Name = address.Name, Address = address.Address };
         }
+
+        /// <summary>
+        /// Sets html body replacing base64 images with cid linked resources.
+        /// Updates text body based on html.
+        /// </summary>
+        /// <param name="bodyBuilder">Body builder.</param>
+        /// <param name="htmlContent">Html content that can have embedded images.</param>
+        /// <returns>Body builder with set HtmlBody.</returns>
+        public static BodyBuilder SetHtmlBody(this BodyBuilder bodyBuilder, string htmlContent)
+        {
+            if (string.IsNullOrEmpty(htmlContent)) return bodyBuilder;
+
+            var doc = new HtmlDocument();
+            doc.LoadHtml(htmlContent);
+
+            var imgNodes = doc.DocumentNode.SelectNodes("//img");
+
+            if (imgNodes != null)
+            {
+                foreach (var node in imgNodes)
+                {
+                    var src = node.GetAttributeValue("src", string.Empty);
+
+                    if (string.IsNullOrEmpty(src)) continue;
+
+                    if (!src.StartsWith("data:image"))
+                    {
+                        continue;
+                    }
+
+                    var parts = src.Substring(11).Split([";base64,"], StringSplitOptions.None);
+
+                    string mimeType = parts[0];
+                    string base64Content = parts[1];
+
+                    var alt = node.GetAttributeValue("alt", $"Embedded_Image.{mimeType}");
+
+                    // Convert the base64 content to binary data
+                    byte[] imageData = Convert.FromBase64String(base64Content);
+
+                    // Create a new linked resource as MimePart
+                    var image = new MimePart("image", mimeType)
+                    {
+                        ContentId = MimeUtils.GenerateMessageId(),
+                        Content = new MimeContent(new MemoryStream(imageData)),
+                        ContentDisposition = new ContentDisposition(ContentDisposition.Inline),
+                        ContentDescription = alt.Replace(" ", "_"),
+                        FileName = alt,
+                        ContentTransferEncoding = ContentEncoding.Base64
+                    };
+
+                    bodyBuilder.LinkedResources.Add(image);
+
+                    node.SetAttributeValue("src", $"cid:{image.ContentId}");
+                }
+            }
+
+            bodyBuilder.HtmlBody = doc.DocumentNode.InnerHtml;
+
+            if (!string.IsNullOrEmpty(bodyBuilder.HtmlBody))
+            {
+                bodyBuilder.TextBody = HtmlAgilityPackExtensions.GetPreviewText(bodyBuilder.HtmlBody);
+            }
+
+            return bodyBuilder;
+        }
     }
 }