app.py

from fastapi import FastAPI, UploadFile,File,HTTPException
from fastapi.responses import JSONResponse
from fastapi.middleware.cors import CORSMiddleware
from dotenv import load_dotenv
from langchain_community.document_loaders import PyMuPDFLoader, UnstructuredPDFLoader
from langchain_text_splitters import RecursiveCharacterTextSplitter
from langchain_huggingface import HuggingFaceEmbeddings
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.output_parsers import StrOutputParser
from langchain_groq import ChatGroq
from langchain_core.runnables import RunnablePassthrough
from pathlib import Path
import uvicorn
import shutil
import os
import hashlib
import fitz
import pytesseract
from PIL import Image
from langchain.schema import Document
from langchain_community.vectorstores import Chroma
from langchain_community.vectorstores.utils import filter_complex_metadata
import io
import chromadb

app = FastAPI()

app.add_middleware(
    CORSMiddleware,
    allow_origins=["*"],
    allow_credentials=True,
    allow_methods=["*"],
    allow_headers=["*"],
)

UPLOAD_DIR = "uploads"
os.makedirs(UPLOAD_DIR, exist_ok=True)

persist_directory = "/home/user/.cache/chroma_db"

load_dotenv()
os.environ["HF_TOKEN"] = os.getenv("HF_TOKEN")
os.environ["GROQ_API_KEY"] = os.getenv("GROQ_API_KEY")

llm = ChatGroq(model_name = "qwen-2.5-32b")
embeddings = HuggingFaceEmbeddings(model_name="sentence-transformers/all-MiniLM-L6-v2")

prompt = '''You are an AI assistant tasked with answering questions based on the given context.  
Follow these guidelines:  
- If the answer is **explicitly stated in the context**, provide a **concise and factual response**.  
- If the answer is **not in the context**, simply state: *"I don't know based on the provided context."*  
- If the question requires **logical reasoning** based on the context, summarize the necessary details before answering.  
- If the question is about **duration or summary**, calculate or extract the total duration and provide a brief overview. 
- If the question contains **end date** and is not found in the context, consider it as **Completion date**. 
<context>  
{context}  
</context>  
Question: {question}  
Answer:'''

parser = StrOutputParser()

def generate_file_id(file_path):   
    hasher = hashlib.md5()
    with open(file_path, "rb") as f:
        hasher.update(f.read())
    return hasher.hexdigest()

def delete_existing_embedding(file_id):
    if os.path.exists(persist_directory):
        client_settings = chromadb.config.Settings(allow_reset=True)
        vector_store = Chroma(persist_directory=persist_directory, embedding_function=embeddings,client_settings=client_settings)       
        vector_store.delete_collection()  # Drop all stored vectors

def tempUploadFile(filePath,file):
    with open(filePath,'wb') as buffer:
        shutil.copyfileobj(file.file, buffer)

def loadAndSplitDocuments(filePath):
    loader = UnstructuredPDFLoader(filePath)
    docs = loader.load()
    
    splitter = RecursiveCharacterTextSplitter(chunk_size=2000, chunk_overlap=500)
    final_chunks = splitter.split_documents(docs)
    return final_chunks

def loadAndSplitPdfFile(filePath):
    doc = fitz.open(filePath)
    documents = []

    for i, page in enumerate(doc):
        text = page.get_text("text")  # Extract text from page
        metadata = {"source": filePath, "page": i + 1}

        if text.strip():
            documents.append(Document(page_content=text, metadata=metadata))

        # Extract and process images with OCR
        images = page.get_images(full=True)
        for img_index, img in enumerate(images):
            xref = img[0]
            base_image = doc.extract_image(xref)
            image_bytes = base_image["image"]
            img = Image.open(io.BytesIO(image_bytes))

            # Perform OCR on the image
            ocr_text = pytesseract.image_to_string(img)
            if ocr_text.strip():
                img_metadata = metadata.copy()
                img_metadata["type"] = "image"
                img_metadata["image_index"] = img_index
                documents.append(Document(page_content=ocr_text, metadata=img_metadata))

    splitter = RecursiveCharacterTextSplitter(chunk_size=1500, chunk_overlap=500)
    final_chunks = splitter.split_documents(documents)
    return final_chunks

def prepare_retriever(filePath = "", load_from_chromadb = False):
    if load_from_chromadb:      
        vector_store = Chroma(persist_directory=persist_directory, embedding_function = embeddings)
        print("Total documents stored:", vector_store._collection.count())
        return vector_store.as_retriever(search_kwargs={"k": 10})    
    elif filePath:   
        doc_chunks = loadAndSplitPdfFile(filePath)        
        print(f"Loaded {len(doc_chunks)} documents from {filePath}") 
        for doc in doc_chunks:
            if hasattr(doc, "metadata") and isinstance(doc.metadata, dict):
                # Convert Path objects to strings
                doc.metadata = {
                    key: str(value) if isinstance(value, Path) else value
                    for key, value in doc.metadata.items()
                    if isinstance(value, (str, int, float, bool, Path))
                }

        client_settings = chromadb.config.Settings(
        allow_reset=True  
        )
        vector_store = Chroma.from_documents(documents= doc_chunks, persist_directory=persist_directory, embedding= embeddings)
        vector_store.persist()

def get_retriever_chain(retriever):    
    chat_prompt = ChatPromptTemplate.from_template(prompt)
    chain =({"context": retriever, "question": RunnablePassthrough()} | chat_prompt | llm | parser)
    return chain

@app.post("/UploadFileInStore")
def UploadFileInStore(file: UploadFile = File(...)):
    if not file.filename.endswith('.pdf'):
        raise HTTPException(status_code=400, detail="File must be a pdf file")
    
    filePath = Path(UPLOAD_DIR) / file.filename
    tempUploadFile(filePath,file)
    file_id = generate_file_id(filePath)
    
    delete_existing_embedding(file_id)
    prepare_retriever(filePath)
    
    if os.path.exists(filePath):  
        os.remove(filePath) 
    return JSONResponse({"message": "File uploaded successfully"})


@app.get("/QnAFromPdf")
async def QnAFromPdf(query: str):   
    retriever = prepare_retriever(load_from_chromadb=True) 
    chain = get_retriever_chain(retriever)
    response = chain.invoke(query)    
    return response

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)