qa/utils.py

from langchain.text_splitter import RecursiveCharacterTextSplitter
from langchain.vectorstores.faiss import FAISS
from langchain import OpenAI
from langchain.chains.qa_with_sources import load_qa_with_sources_chain
from langchain.embeddings.openai import OpenAIEmbeddings
from langchain.llms import OpenAI
from langchain.chat_models import ChatOpenAI
from langchain.docstore.document import Document
from langchain.vectorstores import FAISS, VectorStore
import docx2txt
from typing import List, Dict, Any, Union, Text, Tuple, Iterable
import re
from io import BytesIO
import streamlit as st
from .prompts import STUFF_PROMPT
from pypdf import PdfReader
from langchain.memory import ConversationBufferWindowMemory

class PDFFile:
    """A PDF file class for typing purposes."""
    @classmethod
    def is_pdf(file:Any) -> bool:
        return file.name.endswith(".pdf")
    
class DocxFile:
    """A Docx file class for typing purposes."""
    @classmethod
    def is_docx(file:Any) -> bool:
        return file.name.endswith(".docx")
    
class TxtFile:
    """A Txt file class for typing purposes."""
    @classmethod
    def is_txt(file:Any) -> bool:
        return file.name.endswith(".txt")
    
class CodeFile:
    """A scripting-file class for typing purposes."""
    @classmethod
    def is_code(file:Any) -> bool:
        return file.name.split(".")[1] in [".py", ".json", ".html", ".css", ".md"]


class HashDocument(Document):
    """A document that uses the page content as the hash."""
    def __hash__(self):
        content = self.page_content + "".join(self.metadata[k] for k in self.metadata.keys())
        return hash(content)


@st.cache_data
def parse_docx(file: BytesIO) -> str:
    text = docx2txt.process(file)
    # Remove multiple newlines
    text = re.sub(r"\n\s*\n", "\n\n", text)
    return text


@st.cache_data
def parse_pdf(file: BytesIO) -> List[str]:
    pdf = PdfReader(file)
    output = []
    for page in pdf.pages:
        text = page.extract_text()
        # Merge hyphenated words
        text = re.sub(r"(\w+)-\n(\w+)", r"\1\2", text)
        # Fix newlines in the middle of sentences
        text = re.sub(r"(?<!\n\s)\n(?!\s\n)", " ", text.strip())
        # Remove multiple newlines
        text = re.sub(r"\n\s*\n", "\n\n", text)

        output.append(text)
    return output


@st.cache_data
def parse_txt(file: BytesIO) -> str:
    text = file.read().decode("utf-8")
    # Remove multiple newlines
    text = re.sub(r"\n\s*\n", "\n\n", text)
    return text

@st.cache_data
def get_text_splitter(
    chunk_size:int=500, 
    chunk_overlap:int=50, 
    separators:Iterable[Text]= ["\n\n", "\n", ".", "!", "?", ",", " ", ""])->RecursiveCharacterTextSplitter:
    """Returns a text splitter instance with the given parameters. Cached for performance."""
    # text splitter to split the text into chunks
    text_splitter = RecursiveCharacterTextSplitter(
            chunk_size=chunk_size,  # a limited chunk size ensures smaller chunks and more precise answers
            separators=separators,  # a list of separators to split the text on
            chunk_overlap=chunk_overlap,  # minimal overlap to capture sematic overlap across chunks
        )
    return text_splitter

@st.cache_data
def text_to_docs(text: Union[Text, Tuple[Text]]) -> List[Document]:
    """
    Converts a string or frozenset of strings to a list of Documents
    with metadata.
    """
    # sanity check on the input provided
    if not isinstance(text, (str, tuple)):
        raise ValueError("Text must be either a string or a list of strings. Got: {type(text)}")
    elif isinstance(text, str):
        # Take a single string as one page - make it a tuple so that is hashable
        text = (text, )
    if isinstance(text, tuple):
        # map each page into a document instance
        page_docs = [HashDocument(page_content=page) for page in text]
        # Add page numbers as metadata
        for i, doc in enumerate(page_docs):
            doc.metadata["page"] = i + 1
        # Split pages into chunks
        doc_chunks = []
        # Get the text splitter
        text_splitter = get_text_splitter()

        for doc in page_docs:
            # this splits the page into chunks
            chunks = text_splitter.split_text(doc.page_content)
            for i, chunk in enumerate(chunks):
                # Create a new document for each individual chunk
                doc = HashDocument(
                    page_content=chunk, metadata={"page": doc.metadata["page"], "chunk": i}
                )
                # Add sources to metadata for retrieval later on
                doc.metadata["source"] = f"{doc.metadata['page']}-{doc.metadata['chunk']}"
                doc_chunks.append(doc)
        
        return doc_chunks
    

@st.cache_data
def embed_docs(_docs: Tuple[Document]) -> VectorStore:
    """Embeds a list of Documents and returns a FAISS index"""
    # Embed the chunks
    embeddings = OpenAIEmbeddings(openai_api_key=st.session_state.get("OPENAI_API_KEY"))
    index = FAISS.from_documents(list(_docs), embeddings)

    return index


@st.cache_data
def search_docs(_index: VectorStore, query: str, k:int=5) -> List[Document]:
    """Searches a FAISS index for similar chunks to the query
    and returns a list of Documents."""

    # Search for similar chunks
    docs = _index.similarity_search(query, k=k)
    return docs


@st.cache_data
def get_answer(_docs: List[Document], query: str) -> Dict[str, Any]:
    """Gets an answer to a question from a list of Documents."""
    memory = ConversationBufferWindowMemory(k=5, input_key="question")  # only considering the last 5 messages
    
    # Create the chain to be used in this specific setting
    chain = load_qa_with_sources_chain(
        ChatOpenAI(temperature=0, openai_api_key=st.session_state.get("OPENAI_API_KEY"), model="gpt-4", streaming=True), 
        chain_type="stuff",
        prompt=STUFF_PROMPT,
        # memory=memory NOTE: As of Aug 2023, memory is not supported in the QA chain - uncomment this line when it is supported
        )
    # also returnig the text of the source used to form the answer
    answer = chain(
        {"input_documents": _docs, "question": query}
    )
    return answer


@st.cache_data
def get_sources(answer: Dict[str, Any], docs: List[Document]) -> List[Document]:
    """Gets the source documents for an answer."""

    # Get sources for the answer
    source_keys = [s for s in answer["output_text"].split("SOURCES: ")[-1].split(", ")]

    source_docs = []
    for doc in docs:
        if doc.metadata["source"] in source_keys:
            source_docs.append(doc)

    return source_docs

def wrap_text_in_html(text: str) -> str:
    """Wraps each text block separated by newlines in <p> tags"""
    if isinstance(text, list):
        # Add horizontal rules between pages
        text = "\n<hr/>\n".join(text)
    return "".join([f"<p>{line}</p>" for line in text.split("\n")])