def get_main_menu_choice():
    '''
    Get a valid main menu choice from the user.

    Returns
    -------
    choice : string
        The choice.

    '''
    choice = ''
    while not is_menu_choice_valid(choice):
        choice = input_menu_choice()
        if not is_menu_choice_valid(choice):
            print('Plese enter a valid command.')
    return choice

def input_menu_choice():
    '''
    Show the main menu, and ask the user for a choice.
    Might not be valid.

    Returns
    -------
    choice : TYPE
        DESCRIPTION.

    '''
    print()
    print('Menu')
    print('----')
    print(' S: sale')
    print(' R: return')
    print(' T: sTatus report')
    print(' Q: quit')
    choice = input('Command? ')
    choice = choice.strip().lower()
    return choice

def is_menu_choice_valid(choice):
    '''
    Check whether a string is a valid main menu command.

    Parameters
    ----------
    choice : string
        Command to check.

    Returns
    -------
    valid_choice : boolean
        True if valid.

    '''
    valid_choice = \
        choice == 's' \
        or choice == 'r' \
        or choice == 't' \
        or choice == 'q'
    return valid_choice

def ticket_sale():
    '''
    Ask the user how many tickets were sold.

    Returns
    -------
    tickets : int
        User response.

    '''
    tickets = get_tickets_amount('How many sold? ')
    return tickets
    
def ticket_return():
    '''
    Ask the user how many tickets were returned.

    Returns
    -------
    tickets : int
        User response.

    '''
    tickets = get_tickets_amount('How many returned? ')
    return tickets

def get_tickets_amount(prompt):
    '''
    Ask the user for a ticket amount.

    Parameters
    ----------
    prompt : string
        Question to ask.

    Returns
    -------
    amount : int
        Number of tickets.

    '''
    is_input_ok = False
    while not is_input_ok:
        # Start off assuming data is OK.
        is_input_ok = True
        # Get input from the user.
        user_input = input(prompt)
        # Is the input an integer?
        try:
            amount = int(user_input)
        except ValueError:
            print('Sorry, you must enter a number.')
            is_input_ok = False
        # Check the range.
        if is_input_ok:
            if amount < 1 or amount > 10:
                print('Sorry, please enter a number from 1 to 10.')
                is_input_ok = False
    return amount
    
def show_status_report(inventory, sold):
    '''
    Show a sales status report.

    Parameters
    ----------
    inventory : int
        Inventory.
    sold : int
        Sales.

    Returns
    -------
    None.

    '''
    print()
    print('Status report')
    print('------ ------')
    print('Ticket inventory:', inventory)
    print('Tickets sold:', sold)


# --------------- Main program -------------

# Initialize inventory and sales.
current_inv = 50
total_sold = 0

# Loop until the user quits.
command = ''
while command != 'q':
    command = get_main_menu_choice()
    if command == 's':
        # Sale.
        num_sold = get_tickets_amount('How many sold? ')
        # Check whether we have the inventory.
        if num_sold > current_inv:
            print("Sorry, we don't have that many tickets.")
        else:
            # Adjust inventory and sales.
            current_inv -= num_sold
            total_sold += num_sold
            print('Cha-ching!')
    elif command == 'r':
        # Return.
        num_returned = get_tickets_amount('How many returned? ')
        # Have we sold that many?
        if num_returned > total_sold:
            print("Sorry, we haven't sold that many tickets.")
        else:
            # Adjust inventory and sales.
            current_inv += num_returned
            total_sold -= num_returned
    elif command == 't':
        # Show the status report.
        show_status_report(current_inv, total_sold)
print()
print('OK, bye!')