feat: Langchain HN RAG demo

hn.py

@@ -0,0 +1,46 @@
+from datetime import datetime
+
+import dateutil.parser
+import httpx
+from pydantic import BaseModel, Field
+
+
+class Story(BaseModel):
+    """Model representing a Hacker News story."""
+
+    id: str
+    title: str = Field(description="Title of the story.")
+    url: str | None = Field(description="URL of the story.")
+
+    created_at: datetime
+
+
+class HackerNewsClient:
+    def __init__(self, client: httpx.Client | None = None):
+        base_url = "https://hn.algolia.com/api/v1"
+        if client:
+            client.base_url = base_url
+            self._client = client
+        else:
+            self._client = httpx.Client(base_url=base_url)
+
+    def get_top_stories(self, limit: int = 10) -> list[Story]:
+        resp = self._client.get(
+            "search",
+            params={"tags": "front_page", "hitsPerPage": limit, "page": 0},
+        )
+        resp.raise_for_status()
+        return [
+            Story(
+                id=hit["objectID"],
+                title=hit["title"],
+                url=hit.get("url"),
+                created_at=dateutil.parser.isoparse(hit["created_at"]),
+            )
+            for hit in resp.json().get("hits", [])
+        ]
+
+    def get_item(self, item_id):
+        resp = self._client.get(f"items/{item_id}")
+        resp.raise_for_status()
+        return resp.json()