use xml writer so strings are properly escaped (#4)

ErsatzTV.Core/Iptv/ChannelGuide.cs

@@ -2,6 +2,7 @@
 using System.IO;
 using System.Linq;
 using System.Text;
+using System.Xml;
 using ErsatzTV.Core.Domain;
 using static LanguageExt.Prelude;
 
@@ -23,19 +24,31 @@ namespace ErsatzTV.Core.Iptv
         public string ToXml()
         {
             var sb = new StringBuilder();
-            sb.AppendLine("<?xml version=\"1.0\"?>");
-            sb.AppendLine("<tv generator-info-name=\"ersatztv\">");
-
+            using var xml = XmlWriter.Create(sb);
+            xml.WriteStartDocument();
+            
+            xml.WriteStartElement("tv");
+            xml.WriteAttributeString("generator-info-name", "ersatztv");
+            
             foreach (Channel channel in _channels)
             {
-                sb.AppendLine($"<channel id=\"{channel.Number}\">");
-                sb.AppendLine($"<display-name lang=\"en\">{channel.Name}</display-name>");
-                sb.AppendLine(
+                xml.WriteStartElement("channel");
+                xml.WriteAttributeString("id", channel.Number.ToString());
+                
+                xml.WriteStartElement("display-name");
+                xml.WriteAttributeString("lang", "en");
+                xml.WriteString(channel.Name);
+                xml.WriteEndElement(); // display-name
+
+                xml.WriteStartElement("icon");
+                xml.WriteAttributeString(
+                    "src",
                     !string.IsNullOrWhiteSpace(channel.Logo)
-                        ? $"<icon src=\"{_scheme}://{_host}/iptv/images/{channel.Logo}\"/>"
-                        : $"<icon src=\"{_scheme}://{_host}/images/ersatztv-500.png\"/>");
+                        ? $"{_scheme}://{_host}/iptv/images/{channel.Logo}"
+                        : $"{_scheme}://{_host}/images/ersatztv-500.png");
+                xml.WriteEndElement(); // icon
 
-                sb.AppendLine("</channel>");
+                xml.WriteEndElement(); // channel
             }
 
             foreach (Channel channel in _channels)
@@ -50,35 +63,55 @@ namespace ErsatzTV.Core.Iptv
                             Title = Path.GetFileName(playoutItem.MediaItem.Path)
                         });
 
-                    sb.AppendLine(
-                        $"<programme start=\"{start}\" stop=\"{stop}\" channel=\"{channel.Number}\">");
-                    sb.AppendLine($"<title lang=\"en\">{metadata.Title}</title>");
-                    sb.AppendLine("<previously-shown/>");
-                    sb.AppendLine("<sub-title lang=\"en\"></sub-title>");
+                    xml.WriteStartElement("programme");
+                    xml.WriteAttributeString("start", start);
+                    xml.WriteAttributeString("stop", stop);
+                    xml.WriteAttributeString("channel", channel.Number.ToString());
+
+                    xml.WriteStartElement("title");
+                    xml.WriteAttributeString("lang", "en");
+                    xml.WriteString(metadata.Title);
+                    xml.WriteEndElement(); // title
+                    
+                    xml.WriteStartElement("previously-shown");
+                    xml.WriteEndElement(); // previously-shown
+
+                    xml.WriteStartElement("sub-title");
+                    xml.WriteAttributeString("lang", "en");
+                    xml.WriteEndElement(); // sub-title
 
                     int season = Optional(metadata.SeasonNumber).IfNone(0);
                     int episode = Optional(metadata.EpisodeNumber).IfNone(0);
                     if (season > 0 && episode > 0)
                     {
-                        sb.AppendLine($"<episode-num system=\"xmltv_ns\">{season - 1}.{episode - 1}.0/1</episode-num>");
+                        xml.WriteStartElement("episode-num");
+                        xml.WriteAttributeString("system", "xmltv_ns");
+                        xml.WriteString($"{season - 1}.{episode - 1}.0/1");
+                        xml.WriteEndElement(); // episode-num
                     }
 
                     // sb.AppendLine("<icon src=\"\"/>");
-                    sb.AppendLine($"<desc lang=\"en\">{metadata.Description}</desc>");
+                    xml.WriteStartElement("desc");
+                    xml.WriteAttributeString("lang", "en");
+                    xml.WriteString(metadata.Description);
+                    xml.WriteEndElement(); // desc
 
                     if (!string.IsNullOrWhiteSpace(metadata.ContentRating))
                     {
-                        sb.AppendLine("<rating system=\"MPAA\">");
-                        sb.AppendLine($"<value>{metadata.ContentRating}</value>");
-                        sb.AppendLine("</rating>");
+                        xml.WriteStartElement("rating");
+                        xml.WriteAttributeString("system", "MPAA");
+                        xml.WriteStartElement("value");
+                        xml.WriteString(metadata.ContentRating);
+                        xml.WriteEndElement(); // value
+                        xml.WriteEndElement(); // rating
                     }
 
-                    sb.AppendLine("</programme>");
+                    xml.WriteEndElement(); // programme
                 }
             }
 
-            sb.AppendLine("</tv>");
-
+            xml.WriteEndElement(); // tv
+            xml.WriteEndDocument();
 
             return sb.ToString();
         }