Fix broken diagram links by implementing format-aware image paths

Problem: HTML output contained broken image links because all formats
used the same full path (e.g., living-documentation/diagram-536389.png).
This worked for PDFs but failed for HTML since both files are in the
same directory and need relative paths.

Solution:
- Add output format detection with isHTMLOutput function
- Update processMermaidBlock to take OutputPath parameter
- Generate context-appropriate paths:
  * HTML: relative path (diagram-536389.png)
  * PDF: full path (living-documentation/diagram-536389.png)
- Update transformDocument and compilation functions to pass output path

Both HTML and PDF generation now work correctly with proper image embedding.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Main.hs

@@ -9,7 +9,7 @@ import Text.Pandoc.PDF (makePDF)
 import Text.Pandoc.Walk (walkM)
 import Text.Pandoc.Extensions (getDefaultExtensions)
 import System.Environment (getArgs)
-import System.FilePath (replaceExtension, takeDirectory, (</>))
+import System.FilePath (replaceExtension, takeDirectory, takeFileName, takeExtension, (</>))
 import System.Process (callProcess)
 import System.Directory (removeFile)
 import Data.Text (Text)
@@ -52,13 +52,17 @@ generateDiagramId explicitId contents
   | otherwise = DiagramId explicitId
 
 -- | Transform Mermaid code blocks into image embeds with resource cleanup
-processMermaidBlock :: SourceDir -> Block -> IO Block
-processMermaidBlock (SourceDir sourceDir) (CodeBlock (id', classes, _) contents)
+processMermaidBlock :: SourceDir -> OutputPath -> Block -> IO Block
+processMermaidBlock (SourceDir sourceDir) (OutputPath outputPath) (CodeBlock (id', classes, _) contents)
   | "mermaid" `elem` classes = do
       let DiagramId diagId = generateDiagramId id' contents
           diagIdStr = T.unpack diagId
           mmdFile = sourceDir </> diagIdStr <> ".mmd"
           pngFile = sourceDir </> diagIdStr <> ".png"
+          -- Determine the correct image path based on output format
+          imagePath = if isHTMLOutput outputPath 
+                      then takeFileName pngFile  -- Just filename for HTML
+                      else pngFile               -- Full path for PDF/LaTeX
 
       -- Use bracket to ensure cleanup of temporary mermaid file
       bracket
@@ -67,12 +71,16 @@ processMermaidBlock (SourceDir sourceDir) (CodeBlock (id', classes, _) contents)
         (\_ -> do
           void $ callProcess mermaidCommand ["-i", mmdFile, "-o", pngFile]
           putStrLn $ successEmoji <> " Generated " <> pngFile
-          return $ Para [Image nullAttr [] (T.pack pngFile, "Mermaid diagram")])
-processMermaidBlock _ block = return block
+          return $ Para [Image nullAttr [] (T.pack imagePath, "Mermaid diagram")])
+processMermaidBlock _ _ block = return block
+
+-- | Check if output is HTML format based on file extension
+isHTMLOutput :: FilePath -> Bool
+isHTMLOutput path = takeExtension path == ".html"
 
 -- | Walk the Pandoc AST and process blocks using walkM
-transformDocument :: SourceDir -> Pandoc -> IO Pandoc
-transformDocument sourceDir = walkM (processMermaidBlock sourceDir)
+transformDocument :: SourceDir -> OutputPath -> Pandoc -> IO Pandoc
+transformDocument sourceDir outputPath = walkM (processMermaidBlock sourceDir outputPath)
 
 -- | LaTeX template with comprehensive package support
 latexTemplate :: Text -> Text
@@ -154,12 +162,12 @@ compileToPDF path = do
 
 -- | Safe PDF compilation with proper error handling
 compileToPDFSafe :: SourceDir -> OutputPath -> OutputPath -> IO (Either DocsterError ())
-compileToPDFSafe sourceDir (OutputPath inputPath) (OutputPath outputPath) = do
+compileToPDFSafe sourceDir (OutputPath inputPath) outputPath@(OutputPath outputPathStr) = do
   content <- TIO.readFile inputPath
   let readerOptions = def { readerExtensions = getDefaultExtensions "markdown" }
   
   pandoc <- runIOorExplode $ readMarkdown readerOptions content
-  transformed <- transformDocument sourceDir pandoc
+  transformed <- transformDocument sourceDir outputPath pandoc
   
   -- Generate LaTeX with proper template
   latexOutput <- runIOorExplode $ writeLaTeX def transformed
@@ -169,8 +177,8 @@ compileToPDFSafe sourceDir (OutputPath inputPath) (OutputPath outputPath) = do
   case result of
     Left err -> return $ Left $ PDFGenerationError $ T.pack $ show err
     Right bs -> do
-      BL.writeFile outputPath bs
-      putStrLn $ successEmoji <> " PDF written to " <> outputPath
+      BL.writeFile outputPathStr bs
+      putStrLn $ successEmoji <> " PDF written to " <> outputPathStr
       return $ Right ()
 
 -- | Compile markdown to HTML
@@ -186,20 +194,20 @@ compileToHTML path = do
 
 -- | Safe HTML compilation with proper error handling
 compileToHTMLSafe :: SourceDir -> OutputPath -> OutputPath -> IO (Either DocsterError ())
-compileToHTMLSafe sourceDir (OutputPath inputPath) (OutputPath outputPath) = do
+compileToHTMLSafe sourceDir (OutputPath inputPath) outputPath@(OutputPath outputPathStr) = do
   content <- TIO.readFile inputPath
   let readerOptions = def { readerExtensions = getDefaultExtensions "markdown" }
   
   pandoc <- runIOorExplode $ readMarkdown readerOptions content
-  transformed <- transformDocument sourceDir pandoc
+  transformed <- transformDocument sourceDir outputPath pandoc
   
   html <- runIOorExplode $ writeHtml5String def transformed
-  TIO.writeFile outputPath html
-  putStrLn $ successEmoji <> " HTML written to " <> outputPath
+  TIO.writeFile outputPathStr html
+  putStrLn $ successEmoji <> " HTML written to " <> outputPathStr
   
   -- Open the generated HTML file in browser
-  putStrLn $ "🌐 Opening " <> outputPath <> " in browser for error checking..."
-  void $ callProcess "open" [outputPath]
+  putStrLn $ "🌐 Opening " <> outputPathStr <> " in browser for error checking..."
+  void $ callProcess "open" [outputPathStr]
   
   return $ Right ()