import streamlit as st
from PyPDF2 import PdfReader
from langchain.text_splitter import CharacterTextSplitter
from langchain.embeddings.huggingface import HuggingFaceEmbeddings
from langchain.vectorstores import FAISS
from langchain.chains.question_answering import load_qa_chain
import os
from streamlit_chat import message
from langchain import HuggingFaceHub

def LLM_pdf(model_name = 'google/flan-t5-large'):
    # st.header("Ask your PDF 💬")
    
    # upload file
    pdf = st.file_uploader("Upload your PDF", type="pdf")
    print(pdf)
    # extract the text
    if pdf is not None:
      pdf_reader = PdfReader(pdf)
      text = ""
      for page in pdf_reader.pages:
        text += page.extract_text()
      print(pdf_reader)
        
      # split into chunks
      text_splitter = CharacterTextSplitter(
        separator="\n",
        chunk_size=1000,
        chunk_overlap=200,
        length_function=len
      )
      print(text_splitter)
      chunks = text_splitter.split_text(text)
      
      # create embeddings
      embeddings = HuggingFaceEmbeddings()
      knowledge_base = FAISS.from_texts(chunks, embeddings)
        
      if 'generated' not in st.session_state:
          st.session_state['generated'] = []
      if 'past' not in st.session_state:
          st.session_state['past'] = []
      
      # show user input
      user_question = st.text_input("Ask a question about your PDF:")
      if user_question:
        docs = knowledge_base.similarity_search(user_question)
        
        llm = HuggingFaceHub(repo_id=model_name, model_kwargs={"temperature":5,
                                                      "max_length":64})
        chain = load_qa_chain(llm, chain_type="stuff")
        response = chain.run(input_documents=docs,question=user_question)
           
        #st.write(response)
        st.session_state.past.append(user_question)
        st.session_state.generated.append(response)
          
      if st.session_state['generated']:
        for i in range(len(st.session_state['generated'])-1, -1, -1):
            message(st.session_state["generated"][i], key=str(i))
            message(st.session_state['past'][i], is_user=True, key=str(i) + '_user')