Ethereum Solidity File

eth-bank.sol

pragma solidity >=0.4.22 <0.6.0;

/**
 * Interface for bank contract
 * Topics: How to use and implement an interface, syntax
 **/
interface Bank_Interface {
    
    /**
     * Deposit value into the bank
     * @param amount added to balance of bank contract
     **/
     function deposit(uint amount) external;
     
     /**
      * Withdraw value from the bank. Contract must have sufficient funds.
      * @param amount amount subtracted from bank contract. Can not be 0
      * @return true if the bank contract has sufficient value, and false otherwise
      **/
     function withdraw(uint amount) external returns (bool);
     
     /**
      * Return the current balance from the bank contract
      * @return uint value of bank contract
      **/
     function getBalance() external returns (uint);
}

/**
 * Bank contract
 * Topics: constructors, getters and setters, debugging, addresses
 **/
contract Bank is Bank_Interface {
    uint private balance;
    address private owner;
    
    constructor (uint amount) public {
        balance = amount;
        owner = msg.sender;
    }
    
    function deposit(uint amount) public {
        balance += amount;
    }
    
    function withdraw(uint amount) public returns (bool) { //this method is used to try debugging
        if (amount != 0 && balance >= amount) {
            balance -= amount;
            return true;
        } else {
            return false;
        }
    }
    
    function getBalance() public returns (uint) {
        return balance;
    }
}

/**
 * Vault verifies that only the owner can access the bank
 * Topics: understanding how contracts can be implemented like classes, understanding how to control access in solidity
 **/
contract Vault {
    address public bank_owner;
    Bank private bank;
    
    constructor () public {
        bank_owner = msg.sender;
        bank = new Bank(0);
    }
    
    function validateDeposit(uint amount) public {
        require(msg.sender == bank_owner);
        bank.deposit(amount);
    }  

    function validateWithdraw(uint amount) public returns (bool) {
        require(msg.sender == bank_owner);
        return bank.withdraw(amount);
    }  
    
    function validateGetBalance() public returns (uint) {
        require(msg.sender == bank_owner);
        return bank.getBalance();
    }
}