ragchain.py

"""
Main RAG chain based on langchain.
"""

from langchain.chains import LLMChain

from langchain.prompts import (
    SystemMessagePromptTemplate,
    HumanMessagePromptTemplate,
    ChatPromptTemplate,
    PromptTemplate,
)

from langchain.chains import ConversationalRetrievalChain
from langchain.chains.conversation.memory import (
    ConversationBufferWindowMemory,
)
from langchain.chains import StuffDocumentsChain


def get_cite_combine_docs_chain(llm):
    """Get doc chain which adds metadata to text chunks."""

    # Ref: https://github.com/langchain-ai/langchain/issues/7239
    # Function to format each document with an index, source, and content.
    def format_document(doc, index, prompt):
        """Format a document into a string based on a prompt template."""

        # Create a dictionary with document content and metadata.
        base_info = {
            "page_content": doc.page_content,
            "index": index,
            "source": doc.metadata["source"],
        }

        # Check if any metadata is missing.
        missing_metadata = set(prompt.input_variables).difference(base_info)
        if len(missing_metadata) > 0:
            raise ValueError(f"Missing metadata: {list(missing_metadata)}.")

        # Filter only necessary variables for the prompt.
        document_info = {k: base_info[k] for k in prompt.input_variables}
        return prompt.format(**document_info)

    # Custom chain class to handle document combination with source indices.
    class StuffDocumentsWithIndexChain(StuffDocumentsChain):
        """Custom chain class to handle document combination with source indices."""

        def _get_inputs(self, docs, **kwargs):
            """Overwrite _get_inputs to add metadata for text chunks."""

            # Format each document and combine them.
            doc_strings = [
                format_document(doc, i, self.document_prompt)
                for i, doc in enumerate(docs, 1)
            ]

            # Filter only relevant input variables for the LLM chain prompt.
            inputs = {
                k: v
                for k, v in kwargs.items()
                if k in self.llm_chain.prompt.input_variables
            }
            inputs[self.document_variable_name] = self.document_separator.join(
                doc_strings
            )
            return inputs

    # Main prompt for RAG chain with citation
    # Ref: https://huggingface.co./spaces/Ekimetrics/climate-question-answering/blob/main/climateqa/engine/prompts.py
    # Define a chat prompt with instructions for citing documents.
    combine_doc_prompt = PromptTemplate(
        input_variables=["context", "question"],
        template="""You are given a question and passages. Provide a clear and structured Helpful Answer based on the passages provided, 
        the context and the guidelines.
        
        Guidelines:
        - If the passages have useful facts or numbers, use them in your answer.
        - When you use information from a passage, mention where it came from by using format [[i]] at the end of the sentence. i stands for the paper index of the document.
        - Do not cite the passage in a style like 'passage i', always use format [[i]] where i stands for the passage index of the document.
        - Do not use the sentence such as 'Doc i says ...' or '... in Doc i' or 'Passage i ...'  to say where information came from.
        - If the same thing is said in more than one document, you can mention all of them like this: [[i]], [[j]], [[k]].
        - Do not just summarize each passage one by one. Group your summaries to highlight the key parts in the explanation.
        - If it makes sense, use bullet points and lists to make your answers easier to understand.
        - You do not need to use every passage. Only use the ones that help answer the question.
        - If the documents do not have the information needed to answer the question, just say you do not have enough information.
        - If the passage is the caption of a picture, you can still use it as part of your answer as any other document.

        -----------------------
        Passages:
        {context}
        -----------------------
        Question: {question}

        Helpful Answer with format citations:""",
    )

    # Initialize the custom chain with a specific document format.
    combine_docs_chain = StuffDocumentsWithIndexChain(
        llm_chain=LLMChain(
            llm=llm,
            prompt=combine_doc_prompt,
        ),
        document_prompt=PromptTemplate(
            input_variables=["index", "source", "page_content"],
            template="[[{index}]]\nsource: {source}:\n{page_content}",
        ),
        document_variable_name="context",
    )

    return combine_docs_chain


class RAGChain:
    """Main RAG chain."""

    def __init__(
        self, memory_key="chat_history", output_key="answer", return_messages=True
    ):
        self.memory_key = memory_key
        self.output_key = output_key
        self.return_messages = return_messages

    def create(self, retriever, llm, add_citation=False):
        """Create a rag chain instance."""

        # Memory is kept for later support of conversational chat
        memory = ConversationBufferWindowMemory(  # Or ConversationBufferMemory
            k=2,
            memory_key=self.memory_key,
            return_messages=self.return_messages,
            output_key=self.output_key,
        )

        # Ref: https://github.com/langchain-ai/langchain/issues/4608
        conversation_chain = ConversationalRetrievalChain.from_llm(
            llm=llm,
            retriever=retriever,
            memory=memory,
            return_source_documents=True,
            rephrase_question=False,  # disable rephrase, for test purpose
            get_chat_history=lambda x: x,
            # return_generated_question=True,  # for debug
            # combine_docs_chain_kwargs={"prompt": PROMPT},  # additional prompt control
            # condense_question_prompt=CONDENSE_QUESTION_PROMPT,  # additional prompt control
        )

        # Add citation, ATTENTION: experimental
        if add_citation:
            cite_combine_docs_chain = get_cite_combine_docs_chain(llm)
            conversation_chain.combine_docs_chain = cite_combine_docs_chain

        return conversation_chain