Create langraph_rag_backend

src/langraph_rag_backend

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+from __future__ import annotations
+
+import os
+import sqlite3
+import tempfile
+from typing import Annotated, Any, Dict, List, Optional, TypedDict
+
+from dotenv import load_dotenv
+from langchain.text_splitter import RecursiveCharacterTextSplitter
+from langchain_community.document_loaders import PyPDFLoader
+from langchain_community.embeddings import HuggingFaceEmbeddings
+from langchain_community.tools import DuckDuckGoSearchRun
+from langchain_community.vectorstores import FAISS
+from langchain_core.messages import BaseMessage, SystemMessage
+from langchain_core.tools import tool
+from langchain_openai import ChatOpenAI
+from langgraph.checkpoint.sqlite import SqliteSaver
+from langgraph.graph import START, StateGraph
+from langgraph.graph.message import add_messages
+from langgraph.prebuilt import ToolNode, tools_condition
+import requests
+
+load_dotenv()
+
+# -------------------
+# 1. LLM + embeddings
+# -------------------
+llm = ChatOpenAI(
+    model="openai/gpt-oss-120b:free",
+    base_url="https://openrouter.ai/api/v1",
+    api_key=os.getenv("OPENROUTER_API_KEY"),
+    extra_body={"reasoning": {"enabled": True}}
+)
+
+embeddings = HuggingFaceEmbeddings(
+    model_name="sentence-transformers/all-MiniLM-L6-v2",
+    model_kwargs={"device": "cpu"},
+    encode_kwargs={"normalize_embeddings": True}
+)
+
+# -------------------
+# 2. Multi-PDF Store (per thread)
+# -------------------
+# Changed from _THREAD_RETRIEVERS to _THREAD_STORES to keep access to .add_documents()
+_THREAD_STORES: Dict[str, FAISS] = {}
+_THREAD_METADATA: Dict[str, List[dict]] = {}
+
+
+def ingest_pdf(file_bytes: bytes, thread_id: str, filename: Optional[str] = None) -> dict:
+    """
+    Adds a PDF to the existing FAISS index for a thread, or creates a new one.
+    """
+    if not file_bytes:
+        raise ValueError("No bytes received for ingestion.")
+
+    with tempfile.NamedTemporaryFile(delete=False, suffix=".pdf") as temp_file:
+        temp_file.write(file_bytes)
+        temp_path = temp_file.name
+
+    try:
+        loader = PyPDFLoader(temp_path)
+        docs = loader.load()
+
+        splitter = RecursiveCharacterTextSplitter(
+            chunk_size=500, chunk_overlap=100, separators=["\n\n", "\n", " ", ""]
+        )
+        chunks = splitter.split_documents(docs)
+
+        thread_key = str(thread_id)
+        
+        # --- Multi-PDF Logic ---
+        if thread_key in _THREAD_STORES:
+            # Add to existing vector store
+            _THREAD_STORES[thread_key].add_documents(chunks)
+        else:
+            # Create new vector store
+            _THREAD_STORES[thread_key] = FAISS.from_documents(chunks, embeddings)
+
+        # Track metadata as a list of files
+        file_info = {
+            "filename": filename or os.path.basename(temp_path),
+            "documents": len(docs),
+            "chunks": len(chunks),
+        }
+        
+        if thread_key not in _THREAD_METADATA:
+            _THREAD_METADATA[thread_key] = []
+        _THREAD_METADATA[thread_key].append(file_info)
+
+        return file_info
+    finally:
+        try:
+            os.remove(temp_path)
+        except OSError:
+            pass
+
+
+# -------------------
+# 3. Tools
+# -------------------
+search_tool = DuckDuckGoSearchRun(region="us-en")
+
+@tool
+def calculator(first_num: float, second_num: float, operation: str) -> dict:
+    """Perform basic arithmetic: add, sub, mul, div."""
+    # ... (same as your previous logic)
+    ops = {"add": first_num + second_num, "sub": first_num - second_num, 
+           "mul": first_num * second_num, "div": first_num / second_num if second_num != 0 else "Error"}
+    return {"result": ops.get(operation, "Unsupported")}
+
+@tool
+def get_stock_price(symbol: str) -> dict:
+    """Fetch latest stock price for a symbol."""
+    url = f"https://www.alphavantage.co/query?function=GLOBAL_QUOTE&symbol={symbol}&apikey=C9PE94QUEW9VWGFM"
+    return requests.get(url).json()
+
+@tool
+def rag_tool(query: str, thread_id: Optional[str] = None) -> dict:
+    """
+    Retrieve information from ALL uploaded PDFs for this chat thread.
+    """
+    thread_key = str(thread_id)
+    vector_store = _THREAD_STORES.get(thread_key)
+    
+    if vector_store is None:
+        return {
+            "error": "No documents indexed for this chat. Please upload one or more PDFs.",
+            "query": query,
+        }
+
+    # Search across all documents in the store
+    docs = vector_store.similarity_search(query, k=4)
+    
+    return {
+        "query": query,
+        "context": [doc.page_content for doc in docs],
+        "sources": [doc.metadata for doc in docs],
+        "uploaded_files": [f["filename"] for f in _THREAD_METADATA.get(thread_key, [])]
+    }
+
+tools = [search_tool, get_stock_price, calculator, rag_tool]
+llm_with_tools = llm.bind_tools(tools)
+
+# -------------------
+# 4. State & Nodes (Same as previous)
+# -------------------
+class ChatState(TypedDict):
+    messages: Annotated[list[BaseMessage], add_messages]
+
+def chat_node(state: ChatState, config=None):
+    thread_id = config.get("configurable", {}).get("thread_id") if config else None
+    
+    system_message = SystemMessage(
+        content=(
+            "You are a helpful assistant. You have access to multiple PDFs uploaded by the user. "
+            f"To search them, use `rag_tool` with thread_id `{thread_id}`. "
+            "You can synthesize info from multiple documents if needed."
+        )
+    )
+    return {"messages": [llm_with_tools.invoke([system_message, *state["messages"]], config=config)]}
+
+# -------------------
+# 5. Graph Setup
+# -------------------
+tool_node = ToolNode(tools)
+conn = sqlite3.connect(database="chatbot.db", check_same_thread=False)
+checkpointer = SqliteSaver(conn=conn)
+
+builder = StateGraph(ChatState)
+builder.add_node("chat_node", chat_node)
+builder.add_node("tools", tool_node)
+builder.add_edge(START, "chat_node")
+builder.add_conditional_edges("chat_node", tools_condition)
+builder.add_edge("tools", "chat_node")
+
+chatbot = builder.compile(checkpointer=checkpointer)
+
+# -------------------
+# 6. Helpers
+# -------------------
+def get_all_uploaded_files(thread_id: str) -> List[dict]:
+    """Returns a list of all files uploaded to this thread."""
+    return _THREAD_METADATA.get(str(thread_id), [])