SimpleBankWithCDGToken.sol

SimpleBankWithCDGToken.sol

// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a, "SafeMath: subtraction overflow");
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, "SafeMath: division by zero");
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0, "SafeMath: modulo by zero");
        return a % b;
    }
}

interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);

    function mint(address to, uint256 amount) external;
}

contract SimpleBank { // CamelCase
    using SafeMath for uint256;
    mapping (address => uint256) private balances;

    address[] accounts;
    
    // Interest rate
    uint256 rate = 3;

    IERC20 cdgToken;
     // Constructor, can receive one or many variables here; only one allowed
    constructor(address tokenAddress) public {
        cdgToken = IERC20(tokenAddress);
    }

    /// @notice Deposit ether into bank
    /// @return The balance of the user after the deposit is made
    function deposit(uint256 depositAmount) public returns (uint256) {
        // Record account in array for looping
        if (0 == balances[msg.sender]) {
            accounts.push(msg.sender);
        }

        balances[msg.sender] = balances[msg.sender].add(depositAmount);
        cdgToken.transferFrom(msg.sender,address(this),depositAmount);

        return balances[msg.sender];
    }

    /// @notice Withdraw ether from bank
    /// @dev This does not return any excess ether sent to it
    /// @param withdrawAmount amount you want to withdraw
    /// @return remainingBal The balance remaining for the user
    function withdraw(uint256 withdrawAmount) public returns (uint256 remainingBal) {
        require(balances[msg.sender] >= withdrawAmount); // 1. check condition
        balances[msg.sender] = balances[msg.sender].sub(withdrawAmount); // 2. data layer
        cdgToken.transfer(msg.sender,withdrawAmount); // 3. money layer
        return balances[msg.sender];
    }

    /// @notice Get balance
    /// @return The balance of the user
    // 'constant' prevents function from editing state variables;
    // allows function to run locally/off blockchain
    function mybalance() public view returns (uint256) {
        return balances[msg.sender];
    }

    // Fallback function - Called if other functions don't match call or
    // sent ether without data
    // Typically, called when invalid data is sent
    // Added so ether sent to this contract is reverted if the contract fails
    // otherwise, the sender's money is transferred to contract
    fallback () external {
        revert(); // throw reverts state to before call
    }
    
    function calculateInterest(address user, uint256 _rate) private  returns(uint256) {
        uint256 interest = balances[user].mul(_rate).div(100);
        cdgToken.mint(address(this),interest);
        return interest;
    }
    
    function increaseYear() public {
        for(uint256 i = 0; i < accounts.length; i++) {
            address account = accounts[i];
            uint256 interest = calculateInterest(account, rate);
            balances[account] = balances[account].add(interest);
        }
    }
    
    function systemBalance() public view returns(uint256) {
        // return address(this).balance; // check ETH (native)
        cdgToken.balanceOf(address(this)); // check cdgToken balance of the bank
    }
}
// ** END EXAMPLE **