Improve reaction SVG extraction and rendering from NIST data

app.py

@@ -333,15 +333,21 @@ def _render_smiles_to_svg(smiles_text: str) -> str | None:
         return None
 
     try:
+        # Try parsing as SMILES reaction first
         reaction = rdChemReactions.ReactionFromSmarts(smiles_text, useSmiles=True)
     except Exception:
-        return None
+        try:
+            # Fall back to SMARTS parsing
+            reaction = rdChemReactions.ReactionFromSmarts(smiles_text, useSmiles=False)
+        except Exception:
+            return None
 
     if reaction is None or (reaction.GetNumReactantTemplates() == 0 and reaction.GetNumProductTemplates() == 0):
         return None
 
     try:
-        svg = Draw.ReactionToImage(reaction, subImgSize=(220, 220), useSVG=True)
+        # Generate SVG with better sizing
+        svg = Draw.ReactionToImage(reaction, subImgSize=(250, 200), useSVG=True)
     except Exception:
         return None
 
@@ -394,16 +400,32 @@ def fetch_detail(selected_url: str, manual_url: str):
     # Try to render the reaction title as SVG
     reaction_svg = ""
     if detail.title:
-        # Extract SMILES-like patterns from title (heuristic)
         title = detail.title.strip()
-        # Look for patterns like "A + B → C" or "A >> B"
+        smiles_attempt = None
+        
+        # Try different reaction format conversions
         if " → " in title:
+            # Format: "A + B → C"
             parts = title.split(" → ")
             if len(parts) == 2:
-                smiles_attempt = parts[0].replace(" + ", ".") + ">>" + parts[1].replace(" + ", ".")
-                svg = _render_smiles_to_svg(smiles_attempt)
-                if svg:
-                    reaction_svg = svg
+                reactants = parts[0].replace(" + ", ".").strip()
+                products = parts[1].replace(" + ", ".").strip()
+                smiles_attempt = f"{reactants}>>{products}"
+        elif " → " in title and " ↔ " in title:
+            # Reversible reaction
+            smiles_attempt = title.replace(" ↔ ", ">>").replace(" + ", ".")
+        elif "->" in title:
+            # Alternative arrow format
+            parts = title.split("->")
+            if len(parts) == 2:
+                reactants = parts[0].replace(" + ", ".").strip()
+                products = parts[1].replace(" + ", ".").strip()
+                smiles_attempt = f"{reactants}>>{products}"
+        
+        if smiles_attempt:
+            svg = _render_smiles_to_svg(smiles_attempt)
+            if svg:
+                reaction_svg = svg
     
     return markdown, table, plot_fig, reaction_svg