app.py

from flask import Flask, render_template, request, redirect, url_for, flash, session
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.secret_key = 'your_secret_key'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///users.db'
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = False

db = SQLAlchemy(app)

# User model
class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(80), unique=True, nullable=False)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password = db.Column(db.String(120), nullable=False)

# Initialize database
with app.app_context():
    db.create_all()

@app.route('/')
def home():
    return render_template('home.html')

@app.route('/login', methods=['GET', 'POST'])
def login():
    if request.method == 'POST':
        username = request.form['username']
        password = request.form['password']
        user = User.query.filter_by(username=username, password=password).first()
        if user:
            flash('Login successful!', 'success')
            session['username'] = user.username
            return redirect(url_for('home'))
        else:
            flash('Invalid username or password', 'danger')
    return render_template('login.html')

@app.route('/register', methods=['GET', 'POST'])
def register():
    if request.method == 'POST':
        username = request.form['username']
        email = request.form['email']
        password = request.form['password']
        existing_user = User.query.filter_by(username=username).first()
        if existing_user:
            flash('Username already exists', 'danger')
        else:
            new_user = User(username=username, email=email, password=password)
            db.session.add(new_user)
            db.session.commit()
            flash('Registration successful!', 'success')
            return redirect(url_for('login'))
    return render_template('register.html')

if __name__ == '__main__':
    app.run(debug=True)