We're going to build a BankAccount class where two instances of the class can transfer money to each other through a Transfer class.

You can't just transfer money to another account without the bank running checks first, and the Transfer class acts as a space to check the transaction between two instances of the BankAccount class. Transfer will do all of this, as well as check the validity of the accounts before the transaction occurs. Transfer should be able to reject a transaction if the accounts aren't valid or if the sender doesn't have the money.

A bank account:

• is associated with a user's name.
• is opened with a balance of exactly $1000.
• has a status, and can be open, closed, or zero. An account is initially always open.

Note: The name on the account should not be able to be changed, but we're going to ignore that for now.

1. Build a new class called BankAccount and instantiate a new account for a user named "Kiran".

   1. Confirm that Kiran's new account is of the type BankAccount.
   2. Confirm that the name on Kiran's account is "Kiran".
   3. Confirm that Kiran's account has a balance of $1000.
   4. Confirm that Kiran's account is open.
   5. Set Kiran's balance to $2000. Confirm his new account balance.

2. What other properties might a bank account need? Add three more properties to the BankAccount class.

3. Write a new method for the BankAccount class called deposit that adds money to the account.

4. Write a new method for the BankAccount class called check_balance that displays a message to the user indicating their balance.

5. Write a new method for the BankAccount class called is_valid that determines whether the account is valid (open and with funds) or not. The method returns true if the bank account is open. If the account is closed or zero, the method returns false.

   1. Instantiate a new account, and set its balance to 0.
   2. Check that the status of the account is zero.
   3. Check whether the account is valid.
   4. Instantiate another new account, and set its status to closed.
   5. Check whether the account is valid.

6. Write a new method for the BankAccount class called close_account that closes an account.

7. Make a new bank account for "Amanda".
8. Build a new class called Transfer that initializes with a sender, a recipient, and an amount. Then instantiate a new Transfer that sends $50 from Amanda to Kiran.
   1. Confirm that the transfer is of the type Transfer.
   2. Confirm that the transfer had a sender named Amanda, a recipient named Kiran, and an amount of $50.
9. Write a new method for the Transfer class called both_valid that confirms whether both accounts are valid.
   1. Confirm that the transfer from Amanda to Kiran is a valid transaction.
   2. Confirm that the both_valid method uses the is_valid method on each BankAccount.
10. Add a property to the Transfer class called status:
    • The status of a transfer is always initially pending.
    • A transfer's status is complete once it has occurred.
    • A transfer's status is rejected if the sender doesn't have sufficient funds. If this occurs, the sender gets the message: "Transaction rejected. Please check your account balance."
    • A transfer's status is reversed if money is returned from a recipient to a sender, but only for a transfer that was complete.
11. Write a new method for the Transfer class called execute_transaction that removes money from the sender's account, deposits that same amount of money into the recipient's account, and sets the status of the transfer to complete.
    1. Confirm that the status of the transfer is complete after the transaction has taken place, and that the account balances are what you would expect.

11. Use the Transfer class to send $4000 from Kiran to Amanda.
    1. Confirm that the transfer is rejected and display the message "Transaction rejected. Please check your account balance."
12. Write a new method for the Transfer class called reverse_transfer that reverses the transfer and sets the status to reversed.
    1. Confirm that a reversed transaction for $50 from Kiran back to Amanda has the status reversed and that the account balances are what you would expect.
    2. Confirm that a transfer can only be reversed if it had previously been completed.

13. Have you tried to change the name on an account? Do you find it a bit weird that we could just swap in a new name on an account? Explore and implement "getters" and "setters" in order to fix the value of a property. Then try to change the name on an account and see what happens.