Fix round-tripping of web-snippet

- Ensure that content of web-snippet is refreshed

Author: flcdrg

src/MarkdownSnippets/Processing/MarkdownProcessor.cs

@@ -230,6 +230,20 @@ void AppendWebSnippet(string url, string snippetKey)
                 continue;
             }
 
+            if (SnippetKey.ExtractStartCommentWebSnippet(line, out url, out snippetKey))
+            {
+                AppendWebSnippet(url, snippetKey);
+
+                index++;
+
+                lines.RemoveUntil(
+                    index,
+                    "<!-- endSnippet -->",
+                    relativePath,
+                    line);
+                continue;
+            }
+
             if (line.Current.TrimStart() == "<!-- toc -->")
             {
                 tocLine = line;
@@ -302,34 +316,46 @@ void ProcessWebSnippetLine(Action<string> appendLine, List<MissingSnippet> missi
     {
         appendLine($"<!-- web-snippet: {url}#{snippetKey} -->");
         // Download file content
-        var (success, content) = Downloader.DownloadContent(url).GetAwaiter().GetResult();
-        if (!success || string.IsNullOrWhiteSpace(content))
+        try
         {
-            var missing = new MissingSnippet($"{url}#{snippetKey}", line.LineNumber, line.Path);
-            missings.Add(missing);
-            appendLine("```");
-            appendLine($"** Could not fetch or parse web-snippet '{url}#{snippetKey}' **");
-            appendLine("```");
+            var (success, content) = Downloader.DownloadContent(url).GetAwaiter().GetResult();
+            if (!success || string.IsNullOrWhiteSpace(content))
+            {
+                var missing = new MissingSnippet($"{url}#{snippetKey}", line.LineNumber, line.Path);
+                missings.Add(missing);
+                appendLine("```");
+                appendLine($"** Could not fetch or parse web-snippet '{url}#{snippetKey}' **");
+                appendLine("```");
+                appendLine("<!-- endSnippet -->");
+                return;
+            }
+            // Extract snippets from content
+            using var reader = new StringReader(content);
+            var snippets = FileSnippetExtractor.Read(reader, url);
+            var found = snippets.FirstOrDefault(_ => _.Key == snippetKey);
+            if (found == null)
+            {
+                var missing = new MissingSnippet($"{url}#{snippetKey}", line.LineNumber, line.Path);
+                missings.Add(missing);
+                appendLine("```");
+                appendLine($"** Could not find snippet '{snippetKey}' in '{url}' **");
+                appendLine("```");
+                appendLine("<!-- endSnippet -->");
+                return;
+            }
+            appendSnippets(snippetKey, [found], appendLine);
             appendLine("<!-- endSnippet -->");
-            return;
+            used.Add(found);
         }
-        // Extract snippets from content
-        using var reader = new StringReader(content);
-        var snippets = FileSnippetExtractor.Read(reader, url);
-        var found = snippets.FirstOrDefault(_ => _.Key == snippetKey);
-        if (found == null)
+        catch
         {
             var missing = new MissingSnippet($"{url}#{snippetKey}", line.LineNumber, line.Path);
             missings.Add(missing);
             appendLine("```");
-            appendLine($"** Could not find snippet '{snippetKey}' in '{url}' **");
+            appendLine($"** Could not fetch or parse web-snippet '{url}#{snippetKey}' **");
             appendLine("```");
             appendLine("<!-- endSnippet -->");
-            return;
         }
-        appendSnippets(snippetKey, [found], appendLine);
-        appendLine("<!-- endSnippet -->");
-        used.Add(found);
     }
 
     bool TryGetSnippets(

src/MarkdownSnippets/Processing/SnippetKey.cs

@@ -16,6 +16,32 @@ public static bool ExtractStartCommentSnippet(Line line, [NotNullWhen(true)] out
         return true;
     }
 
+    public static bool ExtractStartCommentWebSnippet(Line line, [NotNullWhen(true)] out string? url, [NotNullWhen(true)] out string? snippetKey)
+    {
+        var lineCurrent = line.Current.TrimStart();
+        if (!IsStartCommentWebSnippetLine(lineCurrent))
+        {
+            url = null;
+            snippetKey = null;
+            return false;
+        }
+
+        var substring = lineCurrent[18..]; // after "<!-- web-snippet: "
+        var indexOf = substring.IndexOf("-->");
+        var value = substring[..indexOf].Trim();
+
+        var hashIndex = value.LastIndexOf('#');
+        if (hashIndex < 0 || hashIndex == value.Length - 1)
+        {
+            url = null;
+            snippetKey = null;
+            return false;
+        }
+        url = value[..hashIndex];
+        snippetKey = value[(hashIndex + 1)..];
+        return true;
+    }
+
     public static bool ExtractSnippet(Line line, [NotNullWhen(true)] out string? key)
     {
         var lineCurrent = line.Current.TrimStart();
@@ -65,4 +91,7 @@ public static bool IsStartCommentSnippetLine(string line) =>
 
     public static bool IsWebSnippetLine(string line) =>
         line.StartsWith("web-snippet:", StringComparison.OrdinalIgnoreCase);
+
+    public static bool IsStartCommentWebSnippetLine(string line) =>
+        line.StartsWith("<!-- web-snippet:", StringComparison.OrdinalIgnoreCase);
 }

src/Tests/MarkdownProcessor/MarkdownProcessorTests.WithCommentWebSnippetUpdate.verified.txt

@@ -0,0 +1,22 @@
+{
+  UsedSnippets: [
+    {
+      Key: snipPet,
+      Language: txt,
+      Value: Some code,
+      Error: ,
+      FileLocation: https://raw.githubusercontent.com/SimonCropp/MarkdownSnippets/main/src/Tests/DirectorySnippetExtractor/Case/code1.txt(1-3),
+      IsInError: false
+    }
+  ],
+  result:
+before
+
+<!-- web-snippet: https://raw.githubusercontent.com/SimonCropp/MarkdownSnippets/main/src/Tests/DirectorySnippetExtractor/Case/code1.txt#snipPet -->
+```txt
+Some code
+```
+<!-- endSnippet -->
+
+after
+}

src/Tests/MarkdownProcessor/MarkdownProcessorTests.cs

@@ -792,6 +792,28 @@ public Task WithIndentedMultiLineSnippet()
             ]);
     }
 
+    [Fact]
+    public Task WithCommentWebSnippetUpdate()
+    {
+        var content = """
+
+                      before
+
+                      <!-- web-snippet: https://raw.githubusercontent.com/SimonCropp/MarkdownSnippets/main/src/Tests/DirectorySnippetExtractor/Case/code1.txt#snipPet -->
+                      OLD CONTENT
+                      THAT SHOULD BE
+                      REPLACED
+                      <!-- endSnippet -->
+
+                      after
+
+                      """;
+
+        return SnippetVerifier.Verify(
+            DocumentConvention.InPlaceOverwrite,
+            content);
+    }
+
     static Snippet SnippetBuild(string language, string key) =>
         Snippet.Build(
             language: language,