Implement functionality to handle table header columns spans

- Add functionality to process column headers using an opt-in config TableHeaderColumnSpanHandling
- Add unit test
- Fixes GH-392

src/ReverseMarkdown.Test/ConverterTests.WhenTable_WithColSpan_TableHeaderColumnSpansHandling_ThenConvertToGFMTable.verified.md

@@ -0,0 +1,3 @@
+| col1 | col2 | col2 | col3 |
+| --- | --- | --- | --- |
+| data1 | data2.1 | data2.2 | data3 |

src/ReverseMarkdown.Test/ConverterTests.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Threading.Tasks;
+using ReverseMarkdown.Converters;
 using VerifyTests;
 using VerifyXunit;
 using Xunit;
@@ -1350,5 +1351,19 @@ public Task When_SuppressNewlineFlag_PrefixDiv_Should_Be_Empty()
                 SuppressDivNewlines = true
             });
         }
+
+        [Fact]
+        public Task WhenTable_WithColSpan_TableHeaderColumnSpansHandling_ThenConvertToGFMTable()
+        {
+            var html =
+                "<table><tr><th>col1</th><th colspan=\"2\">col2</th><th>col3</th></tr><tr><td>data1</td><td>data2.1</td><td>data2.2</td><td>data3</td></tr></table>";
+
+            var config = new Config
+            {
+                UnknownTags = Config.UnknownTagsOption.Bypass,
+                TableHeaderColumnSpanHandling = true
+            };
+            return CheckConversion(html, config);
+        }
     }
 }

src/ReverseMarkdown/Config.cs

@@ -1,7 +1,5 @@
 using System;
 using System.Linq;
-using System;
-using System.Linq;
 
 namespace ReverseMarkdown
 {
@@ -80,6 +78,11 @@ public enum TableWithoutHeaderRowHandlingOption
             EmptyRow
         }
 
+        /// <summary>
+        /// Set this flag to handle table header column with column spans
+        /// </summary>
+        public bool TableHeaderColumnSpanHandling { get; set; } = false;
+
 
         /// <summary>
         /// Determines whether url is allowed: WhitelistUriSchemes contains no elements or contains passed url.

src/ReverseMarkdown/Converters/Td.cs

@@ -1,5 +1,7 @@
 using HtmlAgilityPack;
 using System;
+using System.Linq;
+using System.Runtime.CompilerServices;
 using System.Text.RegularExpressions;
 
 namespace ReverseMarkdown.Converters
@@ -22,7 +24,8 @@ public override string Convert(HtmlNode node)
                 .Chomp()
                 .Replace(Environment.NewLine, "<br>");
 
-            return $" {content} |";
+            var colSpan = GetColSpan(node);
+            return string.Concat(Enumerable.Repeat($" {content} |", colSpan));
         }
 
         /// <summary>
@@ -55,5 +58,16 @@ public override string Convert(HtmlNode node)
             }
             return false;
         }
+
+        private int GetColSpan(HtmlNode node)
+        {
+            var colSpan = 1;
+
+            if (Converter.Config.TableHeaderColumnSpanHandling && node.Name == "th")
+            {
+                colSpan = node.GetAttributeValue("colspan", 1);
+            }
+            return colSpan;
+        }
     }
 }

src/ReverseMarkdown/Converters/Tr.cs

@@ -28,7 +28,7 @@ public override string Convert(HtmlNode node)
 
             if (IsTableHeaderRow(node) || UseFirstRowAsHeaderRow(node))
             {
-                underline = UnderlineFor(node, indent);
+                underline = UnderlineFor(node, indent, Converter.Config.TableHeaderColumnSpanHandling);
             }
 
             return $"{indent}|{content}{Environment.NewLine}{underline}";
@@ -58,35 +58,53 @@ private static bool IsTableHeaderRow(HtmlNode node)
             return node.ChildNodes.FindFirst("th") != null;
         }
 
-        private static string UnderlineFor(HtmlNode node, string indent)
+        private static string UnderlineFor(HtmlNode node, string indent, bool tableHeaderColumnSpanHandling)
         {
             var nodes = node.ChildNodes.Where(x => x.Name == "th" || x.Name == "td").ToList();
 
             var cols = new List<string>();
-            foreach (var styles in nodes.Select(nd => StringUtils.ParseStyle(nd.GetAttributeValue("style", ""))))
+            foreach (var nd in nodes)
             {
+                var colSpan = GetColSpan(nd, tableHeaderColumnSpanHandling);
+                var styles = StringUtils.ParseStyle(nd.GetAttributeValue("style", ""));
                 styles.TryGetValue("text-align", out var align);
 
+                string content;
                 switch (align?.Trim())
                 {
                     case "left":
-                        cols.Add(":---");
+                        content = ":---";
                         break;
                     case "right":
-                        cols.Add("---:");
+                        content ="---:";
                         break;
                     case "center":
-                        cols.Add(":---:");
+                        content = ":---:";
                         break;
                     default:
-                        cols.Add("---");
+                        content ="---";
                         break;
                 }
+
+                for (var i = 0; i < colSpan; i++) {
+                    cols.Add(content);
+                }
             }
 
             var colsAggregated = string.Join(" | ", cols);
 
             return $"{indent}| {colsAggregated} |{Environment.NewLine}";
         }
+
+        private static int GetColSpan(HtmlNode node, bool tableHeaderColumnSpanHandling)
+        {
+            var colSpan = 1;
+
+            if (tableHeaderColumnSpanHandling && node.Name == "th")
+            {
+                colSpan = node.GetAttributeValue("colspan", 1);
+            }
+            return colSpan;
+        }
     }
 }