quiz_app.py

import json
import random
import time
from datetime import datetime, timedelta

# In-memory data storage
user_data = {}
questions_data = {
            "DBMS": {
                "Easy": [
                    {"question": "What does DBMS stand for?", "options": ["Database Management System", "Data Backup Management System", "Database Machine System", "Data Management System"], "answer": 1},
                    {"question": "Which of the following is a DBMS software?", "options": ["MySQL", "Word", "Excel", "PowerPoint"], "answer": 1},
                    {"question": "Which of the following is a data model used in DBMS?", "options": ["Hierarchical", "Network", "Relational", "All of the above"], "answer": 4},
                    {"question": "In DBMS, what is a primary key?", "options": ["A unique identifier for a record", "A key used for sorting", "A foreign key", "A key that is used for backup"], "answer": 1},
                    {"question": "Which of the following is a relational database management system?", "options": ["Oracle", "MS Access", "SQL Server", "All of the above"], "answer": 4},
                    {"question": "Which language is used to interact with a DBMS?", "options": ["SQL", "HTML", "C", "Python"], "answer": 1},
                    {"question": "What is normalization in DBMS?", "options": ["Process of converting data into a more useful format", "Process of organizing data", "Process of back up", "Process of reducing data size"], "answer": 2},
                    {"question": "What is the purpose of a foreign key in DBMS?", "options": ["To link two tables", "To encrypt data", "To create indexes", "To store a backup"], "answer": 1},
                    {"question": "Which of the following is not a part of DBMS?", "options": ["Database", "Query processor", "Printer", "Transaction manager"], "answer": 3},
                    {"question": "Which of the following is a component of a DBMS?", "options": ["DBMS engine", "Database schema", "Database manager", "All of the above"], "answer": 4}
                ],
                "Medium": [
                    {"question": "What is an index in DBMS?", "options": ["A special type of table", "A pointer to data", "A stored procedure", "None of the above"], "answer": 2},
                    {"question": "Which of the following ensures that no data is lost in a transaction?", "options": ["Atomicity", "Consistency", "Isolation", "Durability"], "answer": 1},
                    {"question": "Which is a type of SQL join?", "options": ["Inner join", "Outer join", "Cross join", "All of the above"], "answer": 4},
                    {"question": "What is denormalization?", "options": ["Splitting a table into smaller tables", "Combining tables to optimize performance", "Removing redundant data", "None of the above"], "answer": 2},
                    {"question": "Which of the following is true about a deadlock in DBMS?", "options": ["All processes can proceed after a deadlock", "Deadlock leads to blocking of processes", "It occurs due to excess resources", "It is a form of concurrency control"], "answer": 2},
                    {"question": "What is ACID in DBMS?", "options": ["Atomicity, Consistency, Isolation, Durability", "Access Control Identification", "Application Communication Interface Database", "Automatic Control Information Database"], "answer": 1},
                    {"question": "Which command is used to remove all rows from a table without deleting the table?", "options": ["DELETE", "REMOVE", "TRUNCATE", "DROP"], "answer": 3},
                    {"question": "In a relational database, a table is also known as:", "options": ["Relation", "Tuple", "Field", "Record"], "answer": 1},
                    {"question": "What does the term 'cascade' refer to in foreign key constraints?", "options": ["Automatically delete related rows", "Automatically update related rows", "Both 1 and 2", "None of the above"], "answer": 3},
                    {"question": "Which of the following is used to manage concurrency in DBMS?", "options": ["Locks", "Transactions", "Buffer management", "All of the above"], "answer": 4}
                ],
                "Hard": [
                    {"question": "What is the purpose of an ORM in DBMS?", "options": ["Object Relation Mapping", "Object Retrieval Mechanism", "Optimized Record Manager", "None of the above"], "answer": 1},
                    {"question": "What is a trigger in a database?", "options": ["A mechanism that automatically activates actions", "A mechanism to load data", "A data validation tool", "None of the above"], "answer": 1},
                    {"question": "Which of the following is an advantage of NoSQL over relational databases?", "options": ["Better support for complex queries", "Faster for large data", "Better for structured data", "All of the above"], "answer": 2},
                    {"question": "What is a stored procedure in DBMS?", "options": ["A set of SQL statements that can be stored and executed", "A backup utility", "A tool for data retrieval", "None of the above"], "answer": 1},
                    {"question": "Which is the correct order of steps in query optimization?", "options": ["Parse, Plan, Execute", "Parse, Execute, Plan", "Execute, Plan, Parse", "None of the above"], "answer": 1},
                    {"question": "Which of the following isolation levels can cause non-repeatable reads?", "options": ["Read Uncommitted", "Repeatable Read", "Serializable", "Read Committed"], "answer": 4},
                    {"question": "What is the advantage of using sharding in a distributed database?", "options": ["Improves query speed", "Provides backup of data", "Splits data for better management", "Reduces number of tables"], "answer": 3},
                    {"question": "What does SQL injection refer to?", "options": ["Injecting a new SQL command to manipulate data", "A method of data encryption", "Injecting a stored procedure", "None of the above"], "answer": 1},
                    {"question": "What is the advantage of using multi-version concurrency control?", "options": ["Faster data retrieval", "More accurate results during transactions", "No deadlocks", "Improved query performance"], "answer": 2},
                    {"question": "Which of the following is the main disadvantage of the ACID properties in DBMS?", "options": ["Requires more resources", "Slows down the system", "Difficult to implement", "None of the above"], "answer": 2}
                ]
            },
            "Computer Networks": {
                "Easy": [
                    {"question": "What does the acronym HTTP stand for?", "options": ["HyperText Transfer Protocol", "Hyper Tool Transfer Protocol", "Hyper Transaction Transfer Protocol", "Hyper Tool Transmission Protocol"], "answer": 1},
                    {"question": "Which device connects multiple networks together?", "options": ["Router", "Switch", "Hub", "Repeater"], "answer": 1},
                    {"question": "Which layer of the OSI model is responsible for routing?", "options": ["Network Layer", "Data Link Layer", "Application Layer", "Physical Layer"], "answer": 1},
                    {"question": "Which of the following is an example of a physical layer device?", "options": ["Router", "Hub", "Switch", "Bridge"], "answer": 2},
                    {"question": "Which protocol is used for sending email?", "options": ["SMTP", "HTTP", "FTP", "IP"], "answer": 1},
                    {"question": "In TCP/IP, which layer corresponds to the transport layer?", "options": ["TCP", "IP", "HTTP", "ARP"], "answer": 1},
                    {"question": "Which type of IP address is used for private networks?", "options": ["Public IP", "Private IP", "Loopback IP", "Multicast IP"], "answer": 2},
                    {"question": "What is the purpose of DNS?", "options": ["Translate domain names to IP addresses", "Manage email", "Transmit data over the internet", "Establish connections between devices"], "answer": 1},
                    {"question": "What is the maximum length of an Ethernet cable?", "options": ["100 meters", "50 meters", "200 meters", "150 meters"], "answer": 1},
                    {"question": "What type of protocol is FTP?", "options": ["Application Layer", "Transport Layer", "Network Layer", "Data Link Layer"], "answer": 1}
                ],
                "Medium": [
                    {"question": "Which of the following protocols is connection-oriented?", "options": ["TCP", "UDP", "ICMP", "IP"], "answer": 1},
                    {"question": "Which protocol is used to obtain an IP address from a DHCP server?", "options": ["DHCP", "TCP", "UDP", "HTTP"], "answer": 1},
                    {"question": "In IP addressing, how many bits are used for an IPv6 address?", "options": ["32", "64", "128", "256"], "answer": 3},
                    {"question": "Which of the following is used for error detection in data transmission?", "options": ["Checksum", "Data Link Layer", "Routing", "ARP"], "answer": 1},
                    {"question": "What is the purpose of the ARP protocol?", "options": ["Resolve IP addresses to MAC addresses", "Maintain IP addresses", "Route packets between networks", "Encrypt data"], "answer": 1},
                    {"question": "What does a subnet mask do in a network?", "options": ["Defines the network and host portions of an IP address", "Encrypts data", "Allocates IP addresses", "None of the above"], "answer": 1},
                    {"question": "Which type of switch supports VLANs?", "options": ["Managed switch", "Unmanaged switch", "Hub", "Router"], "answer": 1},
                    {"question": "Which of the following is an example of a link-state routing protocol?", "options": ["OSPF", "RIP", "BGP", "EIGRP"], "answer": 1},
                    {"question": "What is the purpose of the ICMP protocol?", "options": ["Error reporting", "Data transmission", "Routing", "Address allocation"], "answer": 1},
                    {"question": "Which of the following is used for NAT?", "options": ["Router", "Switch", "Hub", "Bridge"], "answer": 1}
                ],
                "Hard": [
                    {"question": "Which type of error does a cyclic redundancy check (CRC) detect?", "options": ["Bit errors", "Parity errors", "Routing errors", "Connection errors"], "answer": 1},
                    {"question": "Which protocol ensures secure communication over a network?", "options": ["SSL/TLS", "TCP", "UDP", "ARP"], "answer": 1},
                    {"question": "In IPv6, how many bytes does the address consist of?", "options": ["16 bytes", "32 bytes", "64 bytes", "128 bytes"], "answer": 1},
                    {"question": "What is the purpose of the BGP protocol?", "options": ["Inter-domain routing", "Intra-domain routing", "IP address allocation", "Error correction"], "answer": 1},
                    {"question": "What is the difference between a hub and a switch?", "options": ["Hub broadcasts data; switch routes data", "Hub routes data; switch broadcasts data", "Hub uses IP; switch uses MAC", "None of the above"], "answer": 1},
                    {"question": "Which of the following protocols uses port 443?", "options": ["HTTPS", "HTTP", "FTP", "SMTP"], "answer": 1},
                    {"question": "Which layer in the OSI model is responsible for flow control?", "options": ["Transport Layer", "Network Layer", "Data Link Layer", "Physical Layer"], "answer": 1},
                    {"question": "Which of the following techniques is used in congestion control?", "options": ["TCP slow start", "ICMP error messages", "IP fragmentation", "ARP"], "answer": 1},
                    {"question": "Which routing algorithm is used in the Internet's backbone?", "options": ["BGP", "RIP", "OSPF", "ICMP"], "answer": 1},
                    {"question": "What is the maximum size of a segment in TCP before it is fragmented?", "options": ["1460 bytes", "1500 bytes", "1024 bytes", "2048 bytes"], "answer": 1}
                ]
            },
            "Operating System": {
                "Easy": [
                    {"question": "What does the OSI model stand for?", "options": ["Open Systems Interconnection", "Operating System Integration", "Open System Interlink", "Operational System Infrastructure"], "answer": 1},
                    {"question": "Which of the following is an example of an operating system?", "options": ["Linux", "Python", "Chrome", "Java"], "answer": 1},
                    {"question": "Which component of an operating system manages memory?", "options": ["Memory Manager", "File Manager", "Processor Manager", "Device Manager"], "answer": 1},
                    {"question": "What does the kernel of an operating system do?", "options": ["Manages hardware resources", "Manages user interfaces", "Handles files", "Manages network protocols"], "answer": 1},
                    {"question": "Which type of operating system allows multiple users to work simultaneously?", "options": ["Multitasking", "Multiprocessing", "Multiuser", "Real-time"], "answer": 3},
                    {"question": "What is the purpose of a process scheduler?", "options": ["Allocate CPU time", "Manage system memory", "Manage file storage", "Track running processes"], "answer": 1},
                    {"question": "Which of the following is a popular open-source operating system?", "options": ["Linux", "Windows", "macOS", "Android"], "answer": 1},
                    {"question": "Which layer of the operating system interacts with hardware?", "options": ["Kernel", "Shell", "User interface", "File System"], "answer": 1},
                    {"question": "Which of the following is not an operating system?", "options": ["Windows", "Linux", "Android", "Python"], "answer": 4},
                    {"question": "What is the primary function of an operating system?", "options": ["Provide an interface for hardware", "Manage files and processes", "Provide networking capabilities", "All of the above"], "answer": 4}
                ],
                "Medium": [
                    {"question": "What is a system call in an operating system?", "options": ["A function for file operations", "A request from user-space to kernel-space", "A function for memory allocation", "A function for process management"], "answer": 2},
                    {"question": "Which of the following is the first part of the OS that loads when a computer starts?", "options": ["Bootloader", "Kernel", "Shell", "Process manager"], "answer": 1},
                    {"question": "Which process management concept refers to preventing one process from taking over the CPU indefinitely?", "options": ["Fair scheduling", "Multitasking", "Preemption", "Threading"], "answer": 3},
                    {"question": "Which of the following is a form of inter-process communication?", "options": ["Message passing", "Shared memory", "Pipes", "All of the above"], "answer": 4},
                    {"question": "What is a deadlock in an operating system?", "options": ["A state where no process can continue because it is waiting on another", "A situation where a process uses all CPU resources", "A form of memory leak", "An error in system calls"], "answer": 1},
                    {"question": "Which of the following is a key feature of a real-time operating system?", "options": ["Predictable behavior", "File system support", "Multitasking", "Graphical interface"], "answer": 1},
                    {"question": "What is a file descriptor in an operating system?", "options": ["A number that uniquely identifies a file in memory", "A pointer to a file in the operating system", "A command to open files", "None of the above"], "answer": 1},
                    {"question": "Which of the following is an example of a time-sharing system?", "options": ["Windows", "Linux", "macOS", "All of the above"], "answer": 4},
                    {"question": "Which technique does an operating system use to manage multiple processes in memory?", "options": ["Paging", "Segmentation", "Swapping", "All of the above"], "answer": 4},
                    {"question": "What is virtual memory?", "options": ["A system that uses hardware to extend available memory", "A part of the disk used as RAM", "A memory management technique", "All of the above"], "answer": 4}
                ],
                "Hard": [
                {"question": "Which algorithm is used for process scheduling in operating systems?", "options": ["Round-robin", "Shortest Job First", "Priority Scheduling", "All of the above"], "answer": 4},
                {"question": "What is the purpose of a semaphore in an operating system?", "options": ["To prevent race conditions", "To manage memory allocation", "To schedule processes", "To allocate file resources"], "answer": 1},
                {"question": "Which is the primary difference between a process and a thread?", "options": ["Threads share memory; processes do not", "Threads are independent; processes are not", "Processes can be suspended; threads cannot", "None of the above"], "answer": 1},
                {"question": "What is a page fault?", "options": ["When the requested page is not found in memory", "When a process exceeds its memory limit", "When a process accesses invalid memory", "None of the above"], "answer": 1},
                {"question": "Which of the following is not a form of memory allocation?", "options": ["Contiguous allocation", "Paged allocation", "Linked allocation", "Circular allocation"], "answer": 4},
                {"question": "What is a critical section problem?", "options": ["The inability to access a file system", "The inability to allocate memory", "The problem of ensuring mutual exclusion in shared resources", "The problem of process starvation"], "answer": 3},
                {"question": "What is the difference between user mode and kernel mode in operating systems?", "options": ["User mode is where user applications run; kernel mode handles system operations", "Kernel mode is restricted to memory management", "User mode executes hardware instructions", "None of the above"], "answer": 1},
                {"question": "Which technique is used to prevent deadlock in an operating system?", "options": ["Banker's algorithm", "Preemptive scheduling", "Deadlock avoidance", "All of the above"], "answer": 4},
                {"question": "What is the role of the file system in an operating system?", "options": ["Manages data storage and retrieval", "Allocates system resources", "Coordinates process scheduling", "Provides networking capabilities"], "answer": 1},
                {"question": "Which of the following is a key aspect of multi-core operating systems?", "options": ["Concurrent execution of multiple processes", "Better power management", "Improved performance", "All of the above"], "answer": 4}
            ]
            },
            "Data Structures": {
                "Easy": [
                    {"question": "What is an array?", "options": ["A collection of elements of the same type", "A collection of different types of elements", "A dynamic data structure", "None of the above"], "answer": 1},
                    {"question": "Which of the following is a linear data structure?", "options": ["Array", "Tree", "Graph", "None of the above"], "answer": 1},
                    {"question": "What is the time complexity of accessing an element in an array?", "options": ["O(1)", "O(n)", "O(log n)", "O(n^2)"], "answer": 1},
                    {"question": "What is a linked list?", "options": ["A collection of nodes where each node points to the next node", "A dynamic array", "A binary tree structure", "None of the above"], "answer": 1},
                    {"question": "Which data structure is used to implement a queue?", "options": ["Linked list", "Array", "Stack", "All of the above"], "answer": 2},
                    {"question": "What does the term 'push' mean in the context of a stack?", "options": ["Insert an element at the end", "Remove an element from the end", "Insert an element at the top", "Remove an element from the top"], "answer": 3},
                    {"question": "Which of the following is an example of a non-linear data structure?", "options": ["Array", "Stack", "Queue", "Tree"], "answer": 4},
                    {"question": "What is the time complexity of inserting an element at the beginning of a linked list?", "options": ["O(1)", "O(n)", "O(log n)", "O(n^2)"], "answer": 1},
                    {"question": "Which of the following data structures can be used to implement recursion?", "options": ["Stack", "Queue", "Array", "Linked list"], "answer": 1},
                    {"question": "Which of the following operations is not possible with a stack?", "options": ["Push", "Pop", "Peek", "Insert at any position"], "answer": 4}
                ],
                "Medium": [
                    {"question": "What is a hash table?", "options": ["A data structure that stores data in key-value pairs", "A type of array", "A tree structure", "A list of nodes"], "answer": 1},
                    {"question": "Which of the following is true about a binary search tree?", "options": ["Left child is less than parent", "Right child is less than parent", "Both left and right children are greater than parent", "None of the above"], "answer": 1},
                    {"question": "What is the worst-case time complexity of a quicksort algorithm?", "options": ["O(n^2)", "O(n log n)", "O(log n)", "O(n)"], "answer": 1},
                    {"question": "What is the space complexity of a recursive function using a stack?", "options": ["O(n)", "O(1)", "O(log n)", "O(n^2)"], "answer": 1},
                    {"question": "In a binary tree, what is the minimum number of nodes required to have a height of 3?", "options": ["7", "3", "5", "9"], "answer": 1},
                    {"question": "What is the primary advantage of a doubly linked list over a singly linked list?", "options": ["Can be traversed in both directions", "Requires less memory", "Supports faster deletion", "None of the above"], "answer": 1},
                    {"question": "Which of the following sorting algorithms has a best case time complexity of O(n)?", "options": ["Insertion sort", "Merge sort", "Quick sort", "Heap sort"], "answer": 1},
                    {"question": "Which of the following is the correct implementation of a breadth-first search (BFS)?", "options": ["Using a queue", "Using a stack", "Using recursion", "Using an array"], "answer": 1},
                    {"question": "What does the term 'collision' mean in a hash table?", "options": ["Two keys mapping to the same index", "A node having more than one child", "A node having no children", "None of the above"], "answer": 1},
                    {"question": "What is the worst-case time complexity of searching in a balanced binary search tree?", "options": ["O(log n)", "O(n)", "O(1)", "O(n^2)"], "answer": 1}
                ],
                "Hard": [
                    {"question": "What is the time complexity of the Floyd-Warshall algorithm?", "options": ["O(n^3)", "O(n^2)", "O(n log n)", "O(n)"], "answer": 1},
                    {"question": "Which of the following is the correct way to implement a priority queue?", "options": ["Using a heap", "Using an array", "Using a linked list", "Using a stack"], "answer": 1},
                    {"question": "What is the difference between a min-heap and a max-heap?", "options": ["Min-heap: Root is the smallest element; Max-heap: Root is the largest element", "Min-heap: Root is the largest element; Max-heap: Root is the smallest element", "Both heaps are identical", "None of the above"], "answer": 1},
                    {"question": "What is the time complexity of finding the shortest path using Dijkstra’s algorithm with a priority queue?", "options": ["O(E log V)", "O(V log E)", "O(V^2)", "O(E + V)"], "answer": 1},
                    {"question": "What is the main disadvantage of the quicksort algorithm?", "options": ["Worst-case time complexity of O(n^2)", "Not stable", "Needs additional memory", "None of the above"], "answer": 1},
                    {"question": "Which of the following data structures is most appropriate for implementing an LRU cache?", "options": ["Hash map and doubly linked list", "Stack", "Queue", "Array"], "answer": 1},
                    {"question": "What is the time complexity of performing a binary search on a sorted array?", "options": ["O(log n)", "O(n)", "O(n log n)", "O(1)"], "answer": 1},
                    {"question": "Which of the following graph traversal algorithms can be implemented recursively?", "options": ["DFS", "BFS", "Dijkstra", "Prim's"], "answer": 1},
                    {"question": "What is the space complexity of the merge sort algorithm?", "options": ["O(n)", "O(1)", "O(log n)", "O(n^2)"], "answer": 1},
                    {"question": "Which of the following sorting algorithms has the worst-case time complexity of O(n^2)?", "options": ["Bubble sort", "Quick sort", "Merge sort", "Heap sort"], "answer": 1}
                ]
            }
        }
daily_challenge_data = {"last_challenge_date": None, "questions": []}
leaderboard_data = []

# User management functions
def register_user():
    global user_data
    username = input("Enter a new username: ").strip()
    if username in user_data:
        print("Username already exists. Please try logging in.")
        return
    password = input("Enter a password: ").strip()
    user_data[username] = {"password": password, "scores": [], "achievements": [], "hints_used": 0}
    print("Registration successful! You can now log in.")

def login_user():
    global user_data
    username = input("Enter your username: ").strip()
    if username not in user_data:
        print("Username not found. Please register first.")
        return None
    password = input("Enter your password: ").strip()
    if user_data[username]["password"] == password:
        print(f"Welcome back, {username}!")
        return username
    else:
        print("Incorrect password.")
        return None

# Hint system
def use_hint(question):
    correct_option = question["answer"]
    incorrect_options = [i for i in range(1, 5) if i != correct_option]
    hint_options = [correct_option, random.choice(incorrect_options)]
    random.shuffle(hint_options)
    print("\n50/50 Hint Used!")
    for opt in hint_options:
        print(f"{opt}. {question['options'][opt - 1]}")

# Review incorrect answers
def review_incorrect_answers(incorrect_answers):
    print("\nReview Incorrect Answers:")
    for q in incorrect_answers:
        print(f"Question: {q['question']}")
        print(f"Your answer: {q['your_answer']} - Correct answer: {q['correct_answer']}")

# Daily Challenge
def generate_daily_challenge():
    global daily_challenge_data, questions_data
    today = datetime.now().strftime("%Y-%m-%d")

    if daily_challenge_data["last_challenge_date"] == today:
        return daily_challenge_data["questions"]

    daily_questions = []
    for category, difficulties in questions_data.items():
        for difficulty, questions in difficulties.items():
            daily_questions.extend(random.sample(questions, min(2, len(questions))))

    daily_challenge_data = {"last_challenge_date": today, "questions": daily_questions}
    return daily_questions

# Save achievements
def save_achievement(username, achievement):
    global user_data
    if achievement not in user_data[username]["achievements"]:
        user_data[username]["achievements"].append(achievement)

# Update leaderboard
def update_leaderboard(username, score):
    global leaderboard_data
    leaderboard_data.append({"username": username, "score": score})
    leaderboard_data = sorted(leaderboard_data, key=lambda x: x["score"], reverse=True)[:10]

# Main quiz function
def play_quiz(username, questions, timed=False):
    score = 0
    incorrect_answers = []
    hints_used = 0
    total_questions = len(questions)

    if total_questions < 10:
        print(f"\nOnly {total_questions} questions available for this category and difficulty. Proceeding with all available questions.")
        num_questions = total_questions
    else:
        num_questions = 10

    selected_questions = random.sample(questions, num_questions)

    for idx, q in enumerate(selected_questions, start=1):
        print(f"\nQuestion {idx}: {q['question']}")
        for i, option in enumerate(q["options"], start=1):
            print(f"{i}. {option}")

        if timed:
            print("\nYou have 10 seconds to answer this question.")
            start_time = time.time()

        while True:
            try:
                user_choice = input("Enter your choice (or 'h' for hint): ").strip()
                if user_choice.lower() == 'h':
                    if hints_used < 2:
                        use_hint(q)
                        hints_used += 1
                    else:
                        print("You have used all your hints.")
                    continue
                user_choice = int(user_choice)
                if user_choice in [1, 2, 3, 4]:
                    if user_choice == q["answer"]:
                        print("Correct!")
                        score += 1
                    else:
                        print("Wrong!")
                        incorrect_answers.append({
                            "question": q["question"],
                            "your_answer": user_choice,
                            "correct_answer": q["answer"]
                        })
                    break
                else:
                    print("Invalid input. Please select a valid option.")
            except ValueError:
                print("Invalid input. Please select a valid option.")

            if timed and time.time() - start_time > 10:
                print("Time's up! Moving to the next question.")
                break

    print(f"\nQuiz finished! Your score: {score}/{num_questions}")
    if score == num_questions:
        save_achievement(username, "Perfect Score!")
        print("You’re on fire! Perfect score! 🔥🔥🔥")
    if hints_used > 0:
        save_achievement(username, "Hint Master!")
    review_incorrect_answers(incorrect_answers)
    update_leaderboard(username, score)

# Display leaderboard
def display_leaderboard():
    global leaderboard_data
    print("\nLeaderboard:")
    for idx, entry in enumerate(leaderboard_data, start=1):
        print(f"{idx}. {entry['username']} - {entry['score']} points")

# Introduction
def intro():
    global leaderboard_data
    print("\n🎉 Welcome to QuizQuest! 🧠✨")
    print("Where questions are tough, but you're tougher! 💪\n")
    print("Think you've got what it takes to outsmart the quiz and claim the crown? 👑")
    if leaderboard_data:
        top_player = leaderboard_data[0]['username']
        top_score = leaderboard_data[0]['score']
        print(f"🥇 Top Spot: {top_player} with {top_score} points!")
    else:
        print("🤷‍♂️ No one at the top yet. Will you be the first?\n")

# Main menu
def main_menu():
    intro()
    username = None

    while True:
        print("\nMain Menu:")
        print("1. Register")
        print("2. Login")
        print("3. Play Quiz")
        print("4. Daily Challenge")
        print("5. Leaderboard")
        print("6. Exit")
        choice = input("Enter your choice: ").strip()

        if choice == "1":
            register_user()
        elif choice == "2":
            username = login_user()
        elif choice == "3":
            if not username:
                print("Please log in to play the quiz.")
                continue
            category_choice = input("\nChoose category (1. DBMS, 2. Computer Networks, 3. Operating System, 4. Data Structures): ").strip()
            if category_choice == '1':
                category = 'DBMS'
            elif category_choice == '2':
                category = 'Computer Networks'
            elif category_choice == '3':
                category = 'Operating System'
            elif category_choice == '4':
                category = 'Data Structures'
            else:
                print("Invalid category choice.")
                continue
            difficulty_choice = input("\nChoose difficulty (1. Easy, 2. Medium, 3. Hard): ").strip()
            if difficulty_choice == '1':
                difficulty = 'Easy'
            elif difficulty_choice == '2':
                difficulty = 'Medium'
            elif difficulty_choice == '3':
                difficulty = 'Hard'
            else:
                print("Invalid difficulty choice.")
                continue

            selected_questions = questions_data[category][difficulty][:10]
            play_quiz(username, selected_questions)
        elif choice == "4":
            if not username:
                print("Please log in to play the daily challenge.")
                continue
            daily_questions = generate_daily_challenge()
            print("\nToday's Daily Challenge:")
            play_quiz(username, daily_questions, timed=True)
        elif choice == "5":
            display_leaderboard()
        elif choice == "6":
            print("Exiting the Quiz App. See you next time!")
            break
        else:
            print("Invalid choice. Please try again.")

if __name__ == "__main__":
    main_menu()