W Mart, a new retail chain, has announced a discount on the total sale amount, in a single transaction, using the following scheme. Table 1: Discount on Sale Amount Total Sale Amount Discount on this sale amount Less than $100 0% From $100 up to less than $500 10% for each dollar over $100 From $500 up to less than $1,000 $40 PLUS 20% of the total sale amount over $500 From $1,000 up to less than $2,000 $140 PLUS 30% of the total sale amount over $1,000 $2,000 and above $440 PLUS 40% of the total sale amount over $2,000 That is, if the total sale amount is $100 then the discount will be $0. However, if the total sale amount is $101 then the discount will be $0.10. If the total sale amount is $500 then the discount will be $40, but if the total sale amount is $501 then the discount will be $40.20. W Mart keeps track of a customer through a unique customer ID. W Mart gives one reward point for every $100 spent irrespective of the number of transactions. The points accumulate over the time for a customer for his/her purchases. Finally, for each 100 reward points it gives an additional discount of $10 on a purchase over $10 in a transaction. Write a Python program that first displays a main menu as follows and waits for a user to choose an option. A user needs to select an option from the main menuIf a user selects the option then the program takes input for a transaction. For a transaction, the program takes input on the customer ID and the total sale amount in the transaction. It then reads a text file called discount.txt that stores information on the discount on sales amount as shown in Table 1 above. The text file stores the information in a plain text format as follows. Less than $100 --> 0% From $100 up to less than $500 --> 10% From $500 up to less than $1,000 --> $40 PLUS 20% From $1,000 up to less than $2,000 --> $140 PLUS 30% $2,000 and above --> $440 PLUS 40% At the end of each transaction the following information is written (appended) out in a file called sales.txt. The same information is also displayed on screen. Customer ID: 1 Total sale amount: 110 Discount amount: 1 Discounted sale amount: 109 Reward point: 1 Additional discount: 0 Additional discounted sale amount: 109 Cumulative sale amount for the next reward point: 10 Final sale amount: 109 In order to compute the reward points of a customer your program will need to read the sales.txt file. A customer is identified by her/his unique Customer ID, and may appear multiple times in the sales.txt file. After displaying the transactional information the program will again display the main menu and wait for a user to choose an option. Now, if a user selects the option then the program should prompt the user to enter a customer ID for which the last transaction will be deleted from the sales.txt file. If the given Customer ID is found in the sales.txt file, the program should first collect and display the last transaction of the customer and then delete the information from the sales.txt file. Otherwise, the program should display a message reporting that "The customer does not exist in the database." The program will then display the main menu again and wait for a user to choose an option. Finally, the program should quit if a user chooses the option . Note that a user can choose any of the three options whenever the main menu is displayed and the program should respond accordingly. Use appropriate data structure in writing your code. All exceptions need to be handled. Invalid inputs need to be handled and the program should ask for a valid input again. Use functions to make your program well designed, instead of just using a single main function. For example, you could use a function to add a new transaction for a customer, a function to take inputs from a user, a function to compute the discount, a function to compute the reward points, a function to display the output on the screen, a function to delete the details of a customer, and so on. We expect you to use at least four (4) functions other than the main function.