Complete the missing ATM features using functions, lists, dictionaries, and while loops. Do NOT rewrite existing code. Only complete the required functions.

gistfile1.txt

#### ADVANCED ATM SIMULATOR ####
"""
FEATURES
1. Multiple users with unique account numbers and PINs
2. Pin verifications (3 trials before account lock)
3. Balance inquiry
4. Cash withdrawal with balance checks
5. Cash deposit
6. Fund transfer 
7. Transaction history
8. Change pin
9. Exit Safely
"""

# ================================
# STORE USERS IN A LIST OF DICTIONARIES
# ================================
users = [
    {"username": "John", "full_name": "John Doe", "account_number": "1234567890", "pin": "1234", "balance": 10000.0, "transaction_history": []},
    {"username": "Ayomide", "full_name": "Ayomide Smith", "account_number": "0987654321", "pin": "5678", "balance": 15000.0, "transaction_history": []},
    {"username": "Samuel", "full_name": "Samuel Johnson", "account_number": "1122334455", "pin": "4321", "balance": 20000.0, "transaction_history": []},
    {"username": "Bob", "full_name": "Bob Brown", "account_number": "5566778899", "pin": "8765", "balance": 5000.0, "transaction_history": []},
    {"username": "Charlie", "full_name": "Charlie Davis", "account_number": "6677889900", "pin": "2468", "balance": 8000.0, "transaction_history": []}
]

# ================================
# FUNCTIONS
# ================================

# Function to find a user by username
def find_user(username):
    for user in users:
        if user["username"].lower() == username.lower():
            return user
    return None

def login():
    entered_username = input("Enter your username: ")
    user_info = find_user(entered_username)
    if user_info is None:
        print("User not found!")
        return login()
    
    trials = 3
    while trials > 0:
        pin = input("Enter your pin: ")
        if pin == user_info["pin"]:
            print("Login Successful!\n")
            return user_info
        else:
            trials -= 1
            print("Incorrect Pin. Attempts left:", trials)
            
    print("Too many failed attempts. Account locked.")
    return login()

def check_balance(user_info):
    print(f"Current Balance: N{user_info['balance']}")

def deposit(user_info):
    amount = input("Enter amount to deposit: ")
    if amount.isdigit():
        amount = int(amount)
        if amount > 0:
            user_info["balance"] += amount
            user_info["transaction_history"].append(f"Deposited N{amount}")
            print("Deposit successful!")
        else:
            print("Amount must be greater than 0")
    else:
        print("Invalid amount")


# ================================
# 🧠 TASKS (COMPLETED)
# ================================

# TASK 1:
# Create a withdraw(user_info) function
def withdraw(user_info):
    amount = input("Enter amount to withdraw: ")
    if amount.isdigit():
        amount = int(amount)
        if amount > 0:
            if amount <= user_info["balance"]:
                user_info["balance"] -= amount
                user_info["transaction_history"].append(f"Withdrew N{amount}")
                print("Withdrawal successful!")
            else:
                print("Insufficient balance!")
        else:
            print("Amount must be greater than 0")
    else:
        print("Invalid amount")

# TASK 2:
# Create a transfer(user_info) function
def transfer(user_info):
    receiver_username = input("Enter receiver's username: ")
    
    # Prevent transferring to oneself
    if receiver_username.lower() == user_info["username"].lower():
        print("You cannot transfer money to your own account.")
        return

    receiver_info = find_user(receiver_username)
    if receiver_info is None:
        print("Receiver not found!")
        return
        
    amount = input("Enter amount to transfer: ")
    if amount.isdigit():
        amount = int(amount)
        if amount > 0:
            if amount <= user_info["balance"]:
                # Deduct from sender and add to receiver
                user_info["balance"] -= amount
                receiver_info["balance"] += amount
                
                # Update transaction history for both parties
                user_info["transaction_history"].append(f"Transferred N{amount} to {receiver_info['username']}")
                receiver_info["transaction_history"].append(f"Received N{amount} from {user_info['username']}")
                
                print("Transfer successful!")
            else:
                print("Insufficient balance!")
        else:
            print("Amount must be greater than 0")
    else:
        print("Invalid amount")

# TASK 3:
# Create a change_pin(user_info) function
def change_pin(user_info):
    new_pin = input("Enter new 4-digit PIN: ")
    if new_pin.isdigit() and len(new_pin) == 4:
        user_info["pin"] = new_pin
        print("PIN changed successfully!")
    else:
        print("Invalid PIN format. Please ensure it is exactly 4 digits.")

# TASK 4:
# Create a view_transaction_history(user_info) function
def view_transaction_history(user_info):
    history = user_info["transaction_history"]
    if not history:
        print("No transactions yet")
    else:
        print("\n--- Transaction History ---")
        for i, transaction in enumerate(history, 1):
            print(f"{i}. {transaction}")
        print("---------------------------")


# ================================
# MAIN PROGRAM
# ================================
def main():
    print("======== Welcome to Optimum Bank ATM ========")
    current_user = login()
    
    if current_user:
        while True:
            print("\n====== MAIN MENU ======")
            print("1. Check Balance")
            print("2. Deposit")
            print("3. Withdraw")
            print("4. Transfer")
            print("5. Change Pin")
            print("6. View Transaction History")
            print("7. Exit")
            
            choice = input("Select option (1-7): ")
            
            if choice == "1":
                check_balance(current_user)
            elif choice == "2":
                deposit(current_user)
            elif choice == "3":
                withdraw(current_user)
            elif choice == "4":
                transfer(current_user)
            elif choice == "5":
                change_pin(current_user)
            elif choice == "6":
                view_transaction_history(current_user)
            elif choice == "7":
                print("Thank you for using Optimum Bank ATM.")
                break
            else:
                print("Invalid option!")

main()