Refactor respond function to include system message in model input and improve clarity

app.py

@@ -1,6 +1,7 @@
+from re import S
 import gradio as gr
 from langchain.chat_models import init_chat_model
-from langchain_core.messages import HumanMessage, AIMessage
+from langchain_core.messages import HumanMessage, AIMessage, SystemMessage
 
 model = init_chat_model("gemini-2.0-flash", model_provider="google_genai")
 
@@ -17,6 +18,8 @@ def respond(
     Respond to user input using the model.
     """
     history_langchain_format = []
+
+    # Add the dialog history to the history
     for msg in dialog_history:
         if msg['role'] == "user":
             history_langchain_format.append(
@@ -24,9 +27,11 @@ def respond(
         elif msg['role'] == "assistant":
             history_langchain_format.append(AIMessage(content=msg['content']))
 
-    history_langchain_format.append(HumanMessage(content=user_input))
-
-    response = model.invoke(history_langchain_format)
+    # Combine the system message, history, and user input into a single list
+    model_input = [SystemMessage(content=system_message)] + \
+        history_langchain_format + [HumanMessage(content=user_input)]
+    
+    response = model.invoke(model_input)
     return response.content