Update app.py

app.py

@@ -481,9 +481,127 @@ with st.sidebar:
     st.divider()
     st.caption("Made with ❤️ for H2 Physics students | Powered by Groq AI")
 
+# 7 Main Chat Interface
+if "messages" not in st.session_state:
+    st.session_state.messages = [
+        {"role": "system", "content": SYSTEM_INSTRUCTIONS},
+        {"role": "assistant", "content": "**Hello JPJC Physics students! I'm Richard Feynman, ready to help you master H2 Physics!** ⚛️\n\nI can:\n- 📊 **Plot graphs** using Python (ask me to plot any physics equation!)\n- 🖼️ **Find diagrams** through web search  \n- 💬 **Explain concepts** with analogies\n- ❓ **Ask questions** to test your understanding\n\n**What would you like to learn today?**"}
+    ]
+
+# Title and mode indicator
+st.title("⚛️ H2 Physics Feynman Tutor")
+st.caption(f"**Topic:** {topic} | **Mode:** {'Text + Image' if visual_content else 'Text'} | **Powered by Groq AI**")
+
+# Display chat history
+for message in st.session_state.messages:
+    if message["role"] != "system":  # Don't show system messages
+        display_message(message["role"], message["content"], enable_voice)
+
+# Chat input - MUST BE HERE (not inside an if block)
+user_input = st.chat_input("Type your physics question here...")
+
+# Process user input
+if user_input or visual_content:
+    # Prepare user message
+    user_message = ""
+    if user_input:
+        user_message += user_input + " "
+    if visual_content:
+        user_message += "[I've uploaded an image related to physics. Please analyze it.] "
+    if topic != "General / Any":
+        user_message += f"(Focus on: {topic})"
+    
+    # Add user message to history
+    st.session_state.messages.append({"role": "user", "content": user_message})
+    
+    # Display user message
+    with st.chat_message("user"):
+        if user_input:
+            st.markdown(user_input)
+        if visual_content:
+            st.image(visual_content, caption="Uploaded Image", use_column_width=True)
+            st.caption("📸 Image attached for analysis")
+    
+    # Check for API key
+    if not api_key:
+        st.error(
+            "**❌ Groq API Key Required**\n\n"
+            "Please enter your Groq API Key in the sidebar to continue.\n\n"
+            "**How to get one (FREE):**\n"
+            "1. Go to [console.groq.com](https://console.groq.com)\n"
+            "2. Sign up (free, no credit card needed)\n"
+            "3. Navigate to API Keys\n"
+            "4. Create a new key\n"
+            "5. Copy and paste it in the sidebar\n\n"
+            "**Free Tier:** 10,000 requests/month\n"
+            "**Perfect for testing!** ⚡"
+        )
+        st.stop()
+    
+    # Prepare API call
+    try:
+        # Build conversation context
+        conversation_context = []
+        
+        # Add system message
+        conversation_context.append({"role": "system", "content": SYSTEM_INSTRUCTIONS})
+        
+        # Add recent conversation (last 8 messages for context)
+        recent_messages = st.session_state.messages[-8:]
+        for msg in recent_messages:
+            if msg["role"] != "system":  # Don't duplicate system message
+                conversation_context.append(msg)
+        
+        # Call Groq API
+        with st.spinner("Feynman is thinking... ⚛️"):
+            response_text = call_groq_api(api_key, conversation_context)
+        
+        # Handle response
+        if response_text:
+            # Check for error messages
+            if response_text.startswith("❌") or response_text.startswith("⚠️"):
+                st.error(response_text)
+                if "Invalid API Key" in response_text:
+                    st.info(
+                        "**Fix Invalid API Key:**\n"
+                        "1. Go to [console.groq.com](https://console.groq.com)\n"
+                        "2. Check your API keys\n"
+                        "3. Make sure you're using the correct key\n"
+                        "4. Keys start with: `gsk_`"
+                    )
+            else:
+                # Add assistant response to history
+                st.session_state.messages.append({"role": "assistant", "content": response_text})
+                
+                # Display response
+                display_message("assistant", response_text, enable_voice)
+                
+                # Show token estimate
+                estimated_tokens = len(response_text) // 4
+                st.caption(f"📝 Response length: ~{estimated_tokens} tokens | ⚡ Powered by Groq")
+        else:
+            st.error(
+                "**Failed to get response from Groq API.**\n\n"
+                "Possible reasons:\n"
+                "1. **Rate Limit** - Free tier has limits, wait a moment\n"
+                "2. **Service Down** - Groq might be experiencing issues\n"
+                "3. **Network Issue** - Check your connection\n\n"
+                "Try again in a moment."
+            )
+            
+    except Exception as e:
+        st.error(
+            f"**❌ Unexpected Error**\n\n"
+            f"```python\n{str(e)[:200]}\n```\n\n"
+            f"**Troubleshooting:**\n"
+            f"1. Refresh the page\n"
+            f"2. Check your API key\n"
+            f"3. Clear chat and try again\n"
+            f"4. Visit [status.groq.com](https://status.groq.com) for service status"
+        )
 
-# Footer - SUPER SIMPLE VERSION
+# Footer - SIMPLE VERSION
 st.divider()
 st.markdown("**H2 Physics Feynman Tutor** | Singapore H2 Physics (9478) Syllabus")
 st.markdown("Powered by [Groq AI](https://groq.com)")
-st.markdown("*Disclaimer: AI tutoring assistant. Verify with official syllabus.*")
+st.markdown("*Disclaimer: AI tutoring assistant. Always verify with official syllabus documents.*")