Backend (Flask).py

from flask import Flask, request, jsonify, session, redirect, url_for
from flask_sqlalchemy import SQLAlchemy
from werkzeug.security import generate_password_hash, check_password_hash

app = Flask(__name__)
app.secret_key = 'your_secret_key'
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///tasks.db'
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    username = db.Column(db.String(50), unique=True, nullable=False)
    password = db.Column(db.String(100), nullable=False)

class Task(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    user_id = db.Column(db.Integer, db.ForeignKey('user.id'), nullable=False)
    title = db.Column(db.String(100), nullable=False)
    description = db.Column(db.Text)
    completed = db.Column(db.Boolean, default=False)

@app.route('/signup', methods=['POST'])
def signup():
    username = request.json.get('username')
    password = request.json.get('password')
    if not username or not password:
        return jsonify({'error': 'Missing username or password'}), 400
    if User.query.filter_by(username=username).first():
        return jsonify({'error': 'Username already exists'}), 400
    hashed_password = generate_password_hash(password)
    new_user = User(username=username, password=hashed_password)
    db.session.add(new_user)
    db.session.commit()
    return jsonify({'message': 'User created successfully'}), 201

@app.route('/login', methods=['POST'])
def login():
    username = request.json.get('username')
    password = request.json.get('password')
    user = User.query.filter_by(username=username).first()
    if not user or not check_password_hash(user.password, password):
        return jsonify({'error': 'Invalid username or password'}), 401
    session['user_id'] = user.id
    return jsonify({'message': 'Login successful'}), 200

@app.route('/logout', methods=['GET'])
def logout():
    session.pop('user_id', None)
    return jsonify({'message': 'Logout successful'}), 200

# Implement CRUD operations for tasks as per your requirement

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