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from langchain_openai import ChatOpenAI, OpenAIEmbeddings
from langchain_community.vectorstores import Chroma
from langchain.chains import RetrievalQA
from langchain_core.prompts import ChatPromptTemplate

# RAG pipeline
embeddings = OpenAIEmbeddings(model="text-embedding-3-small")
vectorstore = Chroma.from_documents(docs, embeddings)
retriever = vectorstore.as_retriever(search_kwargs={"k": 5})

prompt = ChatPromptTemplate.from_messages([
    ("system", "Answer using only the provided context.\nContext: {context}"),
    ("human", "{question}"),
])

chain = RetrievalQA.from_chain_type(
    llm=ChatOpenAI(model="gpt-4o"),
    retriever=retriever,
    chain_type_kwargs={"prompt": prompt},
)

answer = chain.invoke({"query": "What is the refund policy?"})