Code Editor for app.py

import streamlit as st
from sqlalchemy import create_engine, Column, Integer, String
from sqlalchemy.orm import Session, DeclarativeBase
from passlib.hash import pbkdf2_sha256

# Database setup
class Base(DeclarativeBase):
    pass

class User(Base):
    __tablename__ = 'users'
    
    id = Column(Integer, primary_key=True)
    username = Column(String(50), unique=True, nullable=False)
    password = Column(String(256), nullable=False)

# Create engine and tables
engine = create_engine('sqlite:///users.db')
Base.metadata.create_all(engine)

def create_user(username, password):
    with Session(engine) as session:
        # Check if user already exists
        if session.query(User).filter(User.username == username).first():
            return False
        
        # Hash password and create new user
        hashed_password = pbkdf2_sha256.hash(password)
        new_user = User(username=username, password=hashed_password)
        session.add(new_user)
        session.commit()
        return True

def verify_user(username, password):
    with Session(engine) as session:
        user = session.query(User).filter(User.username == username).first()
        if user and pbkdf2_sha256.verify(password, user.password):
            return True
    return False

# Initialize session state
if 'logged_in' not in st.session_state:
    st.session_state.logged_in = False

def login():
    st.session_state.logged_in = True

def logout():
    st.session_state.logged_in = False

st.title('Login System')

if not st.session_state.logged_in:
    tab1, tab2 = st.tabs(['Login', 'Register'])
    
    with tab1:
        st.subheader('Login')
        login_username = st.text_input('Username', key='login_username')
        login_password = st.text_input('Password', type='password', key='login_password')
        
        if st.button('Login'):
            if verify_user(login_username, login_password):
                login()
                st.success('Logged in successfully!')
                st.rerun()
            else:
                st.error('Invalid username or password')
    
    with tab2:
        st.subheader('Register')
        reg_username = st.text_input('Username', key='reg_username')
        reg_password = st.text_input('Password', type='password', key='reg_password')
        reg_password_confirm = st.text_input('Confirm Password', type='password')
        
        if st.button('Register'):
            if not reg_username or not reg_password:
                st.error('Please fill in all fields')
            elif reg_password != reg_password_confirm:
                st.error('Passwords do not match')
            else:
                if create_user(reg_username, reg_password):
                    st.success('Registration successful! You can now login.')
                else:
                    st.error('Username already exists')

else:
    st.write(f'Welcome! You are logged in.')
    if st.button('Logout'):
        logout()
        st.rerun()