app.py

from sentence_transformers import SentenceTransformer, CrossEncoder, util
import re
import pandas as pd
from newspaper import Article
import docx2txt
from io import StringIO
from PyPDF2 import PdfFileReader
import validators
import nltk
import warnings
import streamlit as st

nltk.download('punkt')

from nltk import sent_tokenize

warnings.filterwarnings("ignore")


def extract_text_from_url(url: str):
    '''Extract text from url'''

    article = Article(url)
    article.download()
    article.parse()

    # get text
    text = article.text

    # get article title
    title = article.title

    return title, text


def extract_text_from_file(file):
    '''Extract text from uploaded file'''

    # read text file
    if file.type == "text/plain":
        # To convert to a string based IO:
        stringio = StringIO(file.getvalue().decode("utf-8"))

        # To read file as string:
        file_text = stringio.read()

        return file_text, None

    # read pdf file
    elif file.type == "application/pdf":
        pdfReader = PdfFileReader(file)
        count = pdfReader.numPages
        all_text = ""
        pdf_title = pdfReader.getDocumentInfo().title

        for i in range(count):

            try:
                page = pdfReader.getPage(i)
                all_text += page.extractText()

            except:
                continue

        file_text = all_text

        return file_text, pdf_title

    # read docx file
    elif (
            file.type
            == "application/vnd.openxmlformats-officedocument.wordprocessingml.document"
    ):
        file_text = docx2txt.process(file)

        return file_text, None


def preprocess_plain_text(text, window_size=3):
    text = text.encode("ascii", "ignore").decode()  # unicode
    text = re.sub(r"https*\S+", " ", text)  # url
    text = re.sub(r"@\S+", " ", text)  # mentions
    text = re.sub(r"#\S+", " ", text)  # hastags
    text = re.sub(r"\s{2,}", " ", text)  # over spaces
    text = re.sub("[^.,!?%$A-Za-z0-9]+", " ", text)  # special characters except .,!?

    # break into lines and remove leading and trailing space on each
    lines = [line.strip() for line in text.splitlines()]

    # #break multi-headlines into a line each
    chunks = [phrase.strip() for line in lines for phrase in line.split("  ")]

    # # drop blank lines
    text = '\n'.join(chunk for chunk in chunks if chunk)

    ## We split this article into paragraphs and then every paragraph into sentences
    paragraphs = []
    for paragraph in text.replace('\n', ' ').split("\n\n"):
        if len(paragraph.strip()) > 0:
            paragraphs.append(sent_tokenize(paragraph.strip()))

    window_size = 3
    passages = []
    for paragraph in paragraphs:
        for start_idx in range(0, len(paragraph), window_size):
            end_idx = min(start_idx + window_size, len(paragraph))
            passages.append(" ".join(paragraph[start_idx:end_idx]))

    st.write(f"Sentences: {sum([len(p) for p in paragraphs])}")
    st.write(f"Passages: {len(passages)}")

    return passages


@st.experimental_memo(suppress_st_warning=True)
def bi_encode(bi_enc, passages):
    global bi_encoder
    # We use the Bi-Encoder to encode all passages, so that we can use it with sematic search
    bi_encoder = SentenceTransformer(bi_enc)

    # quantize the model
    # bi_encoder = quantize_dynamic(model, {Linear, Embedding})

    # Compute the embeddings using the multi-process pool
    with st.spinner('Encoding passages into a vector space...'):
        corpus_embeddings = bi_encoder.encode(passages, convert_to_tensor=True, show_progress_bar=True)

    st.success(f"Embeddings computed. Shape: {corpus_embeddings.shape}")

    return bi_encoder, corpus_embeddings


@st.experimental_singleton(suppress_st_warning=True)
def cross_encode():
    global cross_encoder
    # We use a cross-encoder, to re-rank the results list to improve the quality
    cross_encoder = CrossEncoder('cross-encoder/ms-marco-MiniLM-L-12-v2')
    return cross_encoder



def display_as_table(model, top_k=2, score='score'):
    # Display the df with text and scores as a table
    df = pd.DataFrame([(hit[score], passages[hit['corpus_id']]) for hit in model[0:top_k]], columns=['Score', 'Text'])
    df['Score'] = round(df['Score'], 2)

    return df


# Streamlit App

st.title("Search with Retrieve & Rerank")
window_size = 3

bi_encoder_type="multi-qa-mpnet-base-dot-v1"
# This function will search all wikipedia articles for passages that answer the query
def search_func(query, top_k=2):
    global bi_encoder, cross_encoder

    st.subheader(f"Search Query: {query}")

    if url_text:

        st.write(f"Document Header: {title}")

    elif pdf_title:

        st.write(f"Document Header: {pdf_title}")

    # Encode the query using the bi-encoder and find potentially relevant passages
    question_embedding = bi_encoder.encode(query, convert_to_tensor=True)
    question_embedding = question_embedding.cpu()
    hits = util.semantic_search(question_embedding, corpus_embeddings, top_k=top_k, score_function=util.dot_score)
    hits = hits[0]  # Get the hits for the first query

    # Now, score all retrieved passages with the cross_encoder
    cross_inp = [[query, passages[hit['corpus_id']]] for hit in hits]
    cross_scores = cross_encoder.predict(cross_inp)

    # Sort results by the cross-encoder scores
    for idx in range(len(cross_scores)):
        hits[idx]['cross-score'] = cross_scores[idx]

    # Output of top-3 hits from bi-encoder
    st.markdown("\n-------------------------\n")
    st.subheader(f"Top-{top_k} Bi-Encoder Retrieval hits")
    hits = sorted(hits, key=lambda x: x['score'], reverse=True)

    cross_df = display_as_table(hits, top_k)
    st.write(cross_df.to_html(index=False), unsafe_allow_html=True)

    # Output of top-3 hits from re-ranker
    st.markdown("\n-------------------------\n")
    st.subheader(f"Top-{top_k} Cross-Encoder Re-ranker hits")
    hits = sorted(hits, key=lambda x: x['cross-score'], reverse=True)

    rerank_df = display_as_table(hits, top_k, 'cross-score')
    st.write(rerank_df.to_html(index=False), unsafe_allow_html=True)


def clear_text():
    st.session_state["text_url"] = ""
    st.session_state["text_input"] = ""


def clear_search_text():
    st.session_state["text_input"] = ""


url_text = st.text_input("Please Enter a url here",
                         value="https://en.wikipedia.org/wiki/Virat_Kohli",
                         key='text_url', on_change=clear_search_text)

st.markdown(
    "<h3 style='text-align: center; color: red;'>OR</h3>",
    unsafe_allow_html=True,
)

upload_doc = st.file_uploader("Upload a .txt, .pdf, .docx file", key="upload")

search_query = st.text_input("Please Enter your search query here",
                             value="Who is Virat Kohli?", key="text_input")

if validators.url(url_text):
    # if input is URL
    title, text = extract_text_from_url(url_text)
    passages = preprocess_plain_text(text, window_size=3)

elif upload_doc:

    text, pdf_title = extract_text_from_file(upload_doc)
    passages = preprocess_plain_text(text, window_size=3)

col1, col2 = st.columns(2)

with col1:
    search = st.button("Search", key='search_but', help='Click to Search!!')

with col2:
    clear = st.button("Clear Text Input", on_click=clear_text, key='clear',
                      help='Click to clear the URL input and search query')

if search:
    if bi_encoder_type:
        with st.spinner(
                text=f"Loading {bi_encoder_type} bi-encoder and embedding document into vector space. This might take a few seconds depending on the length of your document..."
        ):
            bi_encoder, corpus_embeddings = bi_encode(bi_encoder_type, passages)
            cross_encoder = cross_encode()

        with st.spinner(
                text="Embedding completed, searching for relevant text for given query and hits..."):
            search_func(search_query, top_k=2)

st.markdown("""
            """)