feat(history): Implement get_messages_by_window in HistoryManager

backend/src/ea_chatbot/history/manager.py

@@ -185,4 +185,28 @@ class HistoryManager:
             # Pre-load plots for each message
             for m in messages:
                 _ = m.plots
-            return messages
+            return messages
+
+    def get_messages_by_window(self, conversation_id: str, window_size: int = 10) -> List[Message]:
+        """
+        Get the last N messages for a conversation, ordered by creation time (ascending).
+        """
+        with self.get_session() as session:
+            # 1. Get the last N messages in descending order
+            stmt = (
+                select(Message)
+                .where(Message.conversation_id == conversation_id)
+                .order_by(Message.created_at.desc())
+                .limit(window_size)
+            )
+            result = session.execute(stmt)
+            messages = list(result.scalars().all())
+            
+            # 2. Reverse to get ascending chronological order
+            messages.reverse()
+            
+            # Pre-load plots if needed (though graph usually only needs text)
+            for m in messages:
+                _ = m.plots
+                
+            return messages

backend/tests/test_history_window.py

@@ -0,0 +1,44 @@
+import pytest
+from ea_chatbot.history.manager import HistoryManager
+from ea_chatbot.history.models import Base
+from sqlalchemy import create_engine
+
+@pytest.fixture
+def history_manager():
+    # Use in-memory SQLite for testing
+    # Note: HistoryManager creates its own engine if we pass a URL,
+    # but we need to ensure the schema is created on the underlying DB.
+    hm = HistoryManager("sqlite:///:memory:")
+    # Get the engine from the manager's sessionmaker
+    engine = hm.engine
+    Base.metadata.create_all(engine)
+    return hm
+
+def test_get_messages_by_window(history_manager):
+    """
+    Test that get_messages_by_window returns the last N messages
+    in chronological order.
+    """
+    # 1. Setup a user and conversation
+    user = history_manager.create_user("test@test.com", "password", "Test User")
+    conv = history_manager.create_conversation(user.id, "nj", "Test Conv")
+    
+    # 2. Add 15 messages
+    for i in range(15):
+        history_manager.add_message(conv.id, "user" if i % 2 == 0 else "assistant", f"Message {i}")
+        
+    # 3. Fetch last 10 messages
+    messages = history_manager.get_messages_by_window(conv.id, window_size=10)
+    
+    # 4. Assertions
+    assert len(messages) == 10
+    # The first message in the list should be "Message 5" (15 - 10 = 5)
+    assert messages[0].content == "Message 5"
+    # The last message should be "Message 14"
+    assert messages[-1].content == "Message 14"
+    # Ensure they are in ascending order of creation (or at least order of content here)
+    for i in range(9):
+        # Extract number from "Message X"
+        current_val = int(messages[i].content.split(" ")[1])
+        next_val = int(messages[i+1].content.split(" ")[1])
+        assert current_val < next_val