Add RDKit reaction SVG rendering tab

app.py

@@ -10,6 +10,7 @@ import gradio as gr
 import plotly.graph_objects as go
 from fastapi import FastAPI, HTTPException, Query
 from fastapi.middleware.cors import CORSMiddleware
+from rdkit.Chem import Draw, rdChemReactions
 
 from nist_kinetics_api import (
     Category,
@@ -325,6 +326,43 @@ def _build_dataset_plot(detail: ReactionDetail) -> go.Figure | None:
     return fig
 
 
+def render_reaction_svg(reaction_text: str):
+    reaction_text = (reaction_text or "").strip()
+    if not reaction_text:
+        return gr.update(value=""), "⚠️ Enter a reaction SMILES/SMARTS string (e.g. CH4.O>>CO2)."
+    if ">>" not in reaction_text:
+        return gr.update(value=""), "⚠️ Reaction input must include '>>' separating reactants and products."
+
+    try:
+        reaction = rdChemReactions.ReactionFromSmarts(reaction_text, useSmiles=True)
+    except Exception as exc:  # pragma: no cover - RDKit parsing issues
+        return gr.update(value=""), f"🚨 Could not parse reaction: {exc}"
+
+    if reaction is None or (reaction.GetNumReactantTemplates() == 0 and reaction.GetNumProductTemplates() == 0):
+        return gr.update(value=""), "⚠️ RDKit returned an empty reaction."
+
+    try:
+        svg = Draw.ReactionToImage(reaction, subImgSize=(220, 220), useSVG=True)
+    except Exception as exc:  # pragma: no cover - RDKit drawing issues
+        return gr.update(value=""), f"🚨 Failed to render reaction: {exc}"
+
+    if isinstance(svg, tuple):  # Some RDKit versions return (svg, legend)
+        svg = svg[0]
+    if hasattr(svg, "data"):
+        svg = svg.data
+    if isinstance(svg, bytes):
+        svg = svg.decode("utf-8", errors="ignore")
+
+    if not isinstance(svg, str) or "<svg" not in svg:
+        svg = f"<pre>{svg}</pre>"
+
+    status = (
+        f"Rendered reaction with {reaction.GetNumReactantTemplates()} reactant templates "
+        f"and {reaction.GetNumProductTemplates()} product templates."
+    )
+    return svg, status
+
+
 def fetch_detail(selected_url: str, manual_url: str):
     detail_url = (manual_url or "").strip() or (selected_url or "").strip()
     if not detail_url:
@@ -517,6 +555,26 @@ def build_interface() -> gr.Blocks:
             outputs=[detail_markdown, dataset_table, reaction_plot],
         )
 
+        with gr.Tab("Reaction SVG"):
+            gr.Markdown(
+                "Render an RDKit reaction sketch from reaction SMILES/SMARTS. "
+                "Example: `CCO.O=C=O>>CC(=O)O` or `[CH3:1].[Cl:2][C@@H](F)[Br]>>[CH3:1][C@@H](F)[Cl]`."
+            )
+            reaction_input = gr.Textbox(
+                label="Reaction SMILES/SMARTS",
+                placeholder="Reactant1.Reactant2>>Product1.Product2",
+                lines=2,
+            )
+            render_button = gr.Button("Render Reaction", variant="secondary")
+            reaction_svg = gr.HTML()
+            render_status = gr.Markdown()
+
+            render_button.click(
+                fn=render_reaction_svg,
+                inputs=reaction_input,
+                outputs=[reaction_svg, render_status],
+            )
+
     return demo