app.py

import streamlit as st
import json

# Function to load user data from a file
@st.cache(allow_output_mutation=True)
def load_user_data():
    try:
        with open("user_data.json", "r") as file:
            data = json.load(file)
        return data
    except FileNotFoundError:
        return {}

# Function to save user data to a file
@st.cache(allow_output_mutation=True)
def save_user_data(data):
    with open("user_data.json", "w") as file:
        json.dump(data, file)

# Function to display a separator line
def display_separator():
    st.write('-' * 50)

# Function to display a welcome message
def display_welcome_message():
    st.write("Welcome to the ATM MACHINE")

# Function to display a message with a border
def display_message(message, emoji="🔔"):
    display_separator()
    st.write(f"{emoji} {message} {emoji}")
    display_separator()

# Function to display the user's balance
def display_balance(user_data):
    display_separator()
    st.write(f"💰 Current Balance: {user_data['amount']} RUPEES 💰")
    display_separator()

# Function to display the main menu options
def display_menu():
    st.write('\nSelect an option:')
    st.write('1. View Balance (B)')
    st.write('2. Withdraw Cash (W)')
    st.write('3. Deposit Cash (D)')
    st.write('4. Change PIN (P)')
    st.write('5. Quit (Q)')

# Function to handle balance inquiry
def view_balance(user_data):
    display_balance(user_data)

# Function to handle cash withdrawal
def withdraw_cash(user_data):
    amount_to_withdraw = st.number_input('Enter the amount to withdraw:', step=10, format='%d')
    if amount_to_withdraw % 10 != 0:
        display_message('💡 Amount must be in multiples of 10 💡', "💸")
    elif amount_to_withdraw > user_data['amount']:
        display_message('❌ Insufficient balance ❌', "💸")
    else:
        user_data['amount'] -= amount_to_withdraw
        save_user_data(user_data)
        display_balance(user_data)
        display_message(f'💸 Withdrawal successful: {amount_to_withdraw} RUPEES 💸', "💸")

# Function to handle cash deposit
def deposit_cash(user_data):
    amount_to_deposit = st.number_input('Enter the amount to deposit:', step=10, format='%d')
    if amount_to_deposit % 10 != 0:
        display_message('💡 Amount must be in multiples of 10 💡', "💸")
    else:
        user_data['amount'] += amount_to_deposit
        save_user_data(user_data)
        display_balance(user_data)
        display_message(f'💸 Deposit successful: {amount_to_deposit} RUPEES 💸', "💸")

# Function to handle PIN change
def change_pin(user_data):
    new_pin = st.text_input('Enter a new PIN:', type='password')
    confirm_pin = st.text_input('Confirm new PIN:', type='password')
    
    if new_pin == confirm_pin:
        user_data['pin'] = new_pin
        save_user_data(user_data)
        display_message('🎉 PIN successfully changed 🎉', "🎉")
    else:
        display_message('❌ PINs do not match. Please try again. ❌', "❌")

# Main Program
display_welcome_message()

# Input user name
name = st.text_input('Enter your name:').lower()
user_data = load_user_data()

if user_data and name in user_data:
    # Existing user
    pass
else:
    # New user; create an entry with default values
    user_data[name] = {'pin': '', 'amount': 0}
    save_user_data(user_data)
    display_message(f'Welcome, {name.capitalize()}! You are a new user.')

# If the user is new, prompt to create a new PIN
if not user_data[name]['pin']:
    new_pin = st.text_input('Create a new PIN:', type='password')
    user_data[name]['pin'] = new_pin
    save_user_data(user_data)
    display_message('PIN created successfully!')

# comparing pin
count = 0
while count < 3:
    display_separator()
    pin = st.text_input('Please enter your PIN:', type='password')
    
    if pin.isdigit() and pin == user_data[name]['pin']:
        break
    else:
        count += 1
        display_message('❌ Invalid PIN. Please try again. ❌', "❌")

# in case of a valid pin - continuing, or exiting
if count == 3:
    display_message('❌ 3 UNSUCCESSFUL PIN ATTEMPTS, EXITING. YOUR CARD HAS BEEN LOCKED ❌', "❌")
    st.stop()

display_message(f'🎉 LOGIN SUCCESSFUL, CONTINUE {name.capitalize()}! 🎉', "🎉")

# Main menu
while True:
    display_menu()
    response = st.selectbox('Select an option:', ['View Balance (B)', 'Withdraw Cash (W)', 'Deposit Cash (D)', 'Change PIN (P)', 'Quit (Q)'])

    if response == 'View Balance (B)':
        view_balance(user_data)

    elif response == 'Withdraw Cash (W)':
        withdraw_cash(user_data)

    elif response == 'Deposit Cash (D)':
        deposit_cash(user_data)

    elif response == 'Change PIN (P)':
        change_pin(user_data)

    elif response == 'Quit (Q)':
        save_user_data(user_data)
        display_message('Thank you for using our ATM. Have a great day!')
        st.stop()

    else:
        display_message('❌ Invalid response. Please try again. ❌', "❌")