app.py

import zipfile
import os
import pandas as pd
import numpy as np
import ast
import gradio as gr
import faiss

from sentence_transformers import SentenceTransformer
from transformers import pipeline

"""
Legal Assistant Chatbot using LexGLUE dataset and GPT-2
Includes session memory for last 5 Q&A and sample questions for user guidance.
"""

zip_path = "lexglue-legal-nlp-benchmark-dataset.zip"
extract_dir = "lexglue_data"

if not os.path.exists(extract_dir):
    with zipfile.ZipFile(zip_path, 'r') as zip_ref:
        zip_ref.extractall(extract_dir)

df = pd.read_csv(os.path.join(extract_dir, "case_hold_test.csv"))
df = df[['context', 'endings', 'label']]
df['endings'] = df['endings'].apply(ast.literal_eval)

corpus = []
for idx, row in df.iterrows():
    context = row['context']
    for ending in row['endings']:
        corpus.append(f"{context.strip()} {ending.strip()}")

embedder = SentenceTransformer('all-MiniLM-L6-v2')
corpus_embeddings = embedder.encode(corpus, show_progress_bar=True)

dimension = corpus_embeddings.shape[1]
index = faiss.IndexFlatL2(dimension)
index.add(np.array(corpus_embeddings))

generator = pipeline("text-generation", model="gpt2")

history = []

def legal_assistant_query(query):
    query_embedding = embedder.encode([query])
    D, I = index.search(np.array(query_embedding), k=5)

    retrieved_docs = [corpus[i] for i in I[0]]
    context_combined = "\n\n".join(retrieved_docs[:3])
    context_combined = context_combined[:1024]

    prompt = f"Given the following legal references, answer the question:\n\n{context_combined}\n\nQuestion: {query}\nAnswer:"
    result = generator(prompt, max_new_tokens=200, do_sample=True)[0]['generated_text']
    answer = result.split("Answer:")[-1].strip()

    history.append((query, answer))
    if len(history) > 5:
        history.pop(0)

    formatted_history = "\n\n".join([f"Q: {q}\nA: {a}" for q, a in history])
    return f"{answer}\n\n---\nRecent Q&A:\n{formatted_history}"

sample_questions = [
    "What rights does a person have under the Fourth Amendment?",
    "Explain due process in simple terms.",
    "What is double jeopardy?",
    "Can the police search your car without a warrant?",
    "What is considered a fair trial?"
]

iface = gr.Interface(
    fn=legal_assistant_query,
    inputs=gr.Textbox(lines=2, placeholder="Ask a legal question...", label="Your Question"),
    outputs=gr.Textbox(label="Legal Response with History"),
    title="🧑‍⚖️ Legal Assistant Chatbot",
    description="Ask any legal question and get context-based case.\n\n💡 Sample Questions:\n- " + "\n- ".join(sample_questions)
)

iface.launch()