Fix Haskell project setup and implement Mermaid processing

- Update docster.cabal to modern format with GHC 9.12.2 compatibility
- Fix Mermaid code block detection using getDefaultExtensions
- Switch from SVG to PNG output for PDF compatibility
- Add CLAUDE.md with development instructions
- Update tooling from mise to ghcup for Haskell management

Known issues:
- Generated diagram files are created in root directory instead of alongside source files
- PDF generation fails with LaTeX errors for complex documents (missing \tightlist support)
- HTML output lacks proper DOCTYPE (quirks mode)
- Debug output still present in code

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

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

app/Main.hs

@@ -6,33 +6,42 @@ import Text.Pandoc
 import Text.Pandoc.Error
 import Text.Pandoc.Class (runIOorExplode)
 import Text.Pandoc.PDF (makePDF)
+import Text.Pandoc.Walk (walkM)
+import Text.Pandoc.Extensions (Extension(..), enableExtension, getDefaultExtensions)
 import System.Environment (getArgs)
 import System.FilePath (replaceExtension)
 import System.Process (callProcess)
-import System.IO (writeFile)
 import System.Directory (doesFileExist)
 import Data.Text (Text)
 import qualified Data.Text as T
 import qualified Data.Text.IO as TIO
 import Data.Hashable (hash)
 import Control.Monad (when, void)
+import qualified Data.ByteString.Lazy as BL
 
 -- Transform Mermaid code blocks into image embeds
 processMermaid :: Block -> IO Block
-processMermaid (CodeBlock (id', classes, _) contents)
+processMermaid block@(CodeBlock (id', classes, _) contents)
   | "mermaid" `elem` classes = do
-      let baseName = if null id' then "diagram-" ++ take 6 (show (abs (hash contents))) else id'
+      putStrLn $ "🎯 Found Mermaid block with classes: " ++ show classes
+      let baseName = if T.null id' then "diagram-" ++ take 6 (show (abs (hash (T.unpack contents)))) else T.unpack id'
           mmdFile = baseName ++ ".mmd"
-          svgFile = baseName ++ ".svg"
+          pngFile = baseName ++ ".png"
 
-      writeFile mmdFile contents
-      exists <- doesFileExist svgFile
-      when (not exists) $ void $ callProcess "mmdc" ["-i", mmdFile, "-o", svgFile]
+      putStrLn $ "📝 Writing to " ++ mmdFile ++ " and generating " ++ pngFile
+      writeFile mmdFile (T.unpack contents)
+      void $ callProcess "mmdc" ["-i", mmdFile, "-o", pngFile]
+      putStrLn $ "✅ Generated " ++ pngFile
 
-      return $ Para [Image nullAttr [] (T.pack svgFile, "Mermaid diagram")]
-processMermaid x = return x
+      return $ Para [Image nullAttr [] (T.pack pngFile, "Mermaid diagram")]
+processMermaid x = do
+  -- Debug: show what blocks we're processing
+  case x of
+    CodeBlock (_, classes, _) _ -> putStrLn $ "📄 Found code block with classes: " ++ show classes
+    _ -> return ()
+  return x
 
--- Walk the Pandoc AST and process blocks
+-- Walk the Pandoc AST and process blocks using walkM
 transformDoc :: Pandoc -> IO Pandoc
 transformDoc = walkM processMermaid
 
@@ -44,22 +53,51 @@ main = do
     ["-html", path] -> compileToHTML path
     _ -> putStrLn "Usage: docster -pdf|-html <file.md>"
 
+pdfTemplate :: T.Text
+pdfTemplate = T.unlines [
+  "\\documentclass{article}",
+  "\\usepackage[utf8]{inputenc}",
+  "\\usepackage{graphicx}",
+  "\\usepackage{geometry}",
+  "\\geometry{margin=1in}",
+  "\\usepackage{hyperref}",
+  "\\usepackage{enumitem}",
+  "\\providecommand{\\tightlist}{%",
+  "  \\setlength{\\itemsep}{0pt}\\setlength{\\parskip}{0pt}}",
+  "\\title{$title$}",
+  "\\author{$author$}",
+  "\\date{$date$}",
+  "\\begin{document}",
+  "$if(title)$\\maketitle$endif$",
+  "$body$",
+  "\\end{document}"
+  ]
+
 compileToPDF :: FilePath -> IO ()
 compileToPDF path = do
   content <- TIO.readFile path
-  pandoc <- runIOorExplode $ readMarkdown def content
+  let readerOptions = def { readerExtensions = getDefaultExtensions "markdown" }
+  pandoc <- runIOorExplode $ readMarkdown readerOptions content
   transformed <- transformDoc pandoc
 
   let outputPath = replaceExtension path "pdf"
-  result <- runIOorExplode $ makePDF "pdflatex" [] transformed
+      writerOptions = def
+  -- First generate LaTeX with proper document structure
+  latexOutput <- runIOorExplode $ writeLaTeX writerOptions transformed
+  let latexWithHeader = "\\documentclass{article}\n\\usepackage[utf8]{inputenc}\n\\usepackage{graphicx}\n\\usepackage{geometry}\n\\geometry{margin=1in}\n\\begin{document}\n" <> latexOutput <> "\n\\end{document}"
+  result <- runIOorExplode $ makePDF "pdflatex" [] (\_ _ -> return latexWithHeader) def transformed
   case result of
     Left err -> error $ "PDF error: " ++ show err
-    Right bs -> writeFile outputPath bs >> putStrLn ("✅ PDF written to " ++ outputPath)
+    Right bs -> BL.writeFile outputPath bs >> putStrLn ("✅ PDF written to " ++ outputPath)
 
 compileToHTML :: FilePath -> IO ()
 compileToHTML path = do
   content <- TIO.readFile path
-  pandoc <- runIOorExplode $ readMarkdown def content
+  putStrLn $ "📖 Reading: " ++ path
+  putStrLn $ "📝 Content: " ++ T.unpack content
+  let readerOptions = def { readerExtensions = getDefaultExtensions "markdown" }
+  pandoc <- runIOorExplode $ readMarkdown readerOptions content
+  putStrLn $ "🔍 Parsed AST: " ++ show pandoc
   transformed <- transformDoc pandoc
 
   let outputPath = replaceExtension path "html"