def get_valid_input():
    global failed_attempts

    while True:
        user_input = input("Enter stock quantity: ").strip()

        if user_input.lower() == "quit":
            return "quit"

        if not user_input.isdigit():
            print("Error: Invalid input. Please enter a non-negative integer.\n")
            failed_attempts += 1
            continue

        quantity = int(user_input)

        if quantity < 0:
            print("Error: Negative numbers are not allowed.\n")
            failed_attempts += 1
            continue

        return quantity


def process_delivery(current_total, new_value):
    return current_total + new_value


def calculate_tax(amount):
    return amount * 0.10


def generate_report(total_units, failed_attempts):
    print("\n--- Audit Report ---")
    print(f"Total Units Processed: {total_units}")
    print(f"Failed/Rejected Entries: {failed_attempts}")


def load_inventory():
    try:
        with open("inventory.txt", "r") as inventory_file:
            inventory = int(inventory_file.readline().strip())
            history_line = inventory_file.readline().strip()
            history = [] if not history_line else [int(value) for value in history_line.split(",")]
            return inventory, history
    except FileNotFoundError:
        return 0, []


def save_inventory(inventory, transaction_history):
    with open("inventory.txt", "w") as inventory_file:
        inventory_file.write(f"{inventory}\n")
        inventory_file.write(",".join(str(quantity) for quantity in transaction_history))
        inventory_file.write("\n")


inventory, transaction_history = load_inventory()
total_units = 0
failed_attempts = 0

print("=== Stock Auditor ===")
print("Type 'quit' to exit.\n")

while True:
    quantity = get_valid_input()

    if quantity == "quit":
        save_inventory(inventory, transaction_history)
        break

    tax = calculate_tax(quantity)

    transaction_history.append(quantity)
    inventory = process_delivery(inventory, quantity)
    total_units = process_delivery(total_units, quantity)

    print(f"Stock added. Current inventory: {inventory}")
    print(f"Tax on this delivery: ${tax:.2f}\n")

    if inventory > 500:
        print(f"ALERT: Overstock detected! Inventory ({inventory}) exceeds 500 units.")
        break

generate_report(total_units, failed_attempts)