BasicBank.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.16;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";

/*
  建立一個 Bank 銀行
  在 web3 世界人人都可以當銀行家！我們想開張一間去中心化金融中心，簡易小而美的銀行

  使用者可以將我們發行的 Staking Token (ERC20代幣)存入銀行
  使用者執行定存，會開始計算 Reward 利息回饋
  使用者解除定存（withdraw），獲得 Reward 利息回饋

  Deposit 定存：實作 deposit function，可以將 Staking Token 存入 Bank 合約
  Withdraw 解除定存並提款，實作 withdraw function
  TimeLock 固定鎖倉期
*/
contract BasicBank {
    IERC20 public stakingToken;
    uint256 public totalSupply;
    mapping(address => uint256) public balanceOf;
    uint256 public withdrawDeadline = 10 seconds;
    uint256 public rewardRate = 1;
    mapping (address => uint256) public rewardOf;

    struct Deposit {
        uint256 amount;
        uint256 startTime;
        uint256 endTime;
    }

    mapping (address => Deposit[]) public depositOf;

    constructor(IERC20 _stakingToken) {
        stakingToken = _stakingToken;
    }

    function deposit(uint256 _amount) public {
        stakingToken.transferFrom(msg.sender, address(this), _amount);
        totalSupply =  totalSupply + _amount;
        balanceOf[msg.sender] = balanceOf[msg.sender] + _amount;
        depositOf[msg.sender].push(Deposit({
            amount: _amount,
            startTime: block.timestamp,
            endTime: (block.timestamp + withdrawDeadline)
        }));
    }

    function withdraw(uint256 _index) public {
        require(balanceOf[msg.sender] > 0, "You have no balance to withdraw");
        Deposit[] storage deposits = depositOf[msg.sender];
        require(block.timestamp > deposits[_index].endTime, "End time does not reach");
        uint256 amount = deposits[_index].amount;

        rewardOf[msg.sender] = rewardOf[msg.sender] + getReward(_index);
        stakingToken.transfer(msg.sender, amount);
        totalSupply = totalSupply - amount;
        balanceOf[msg.sender] = balanceOf[msg.sender] - amount;

        deposits[_index] = deposits[deposits.length - 1];
        deposits.pop();
    }

    function getReward(uint256 _index) public view returns(uint256) {
        uint256 start = depositOf[msg.sender][_index].startTime;
        uint256 amount = depositOf[msg.sender][_index].amount;

        return (block.timestamp - start) * rewardRate * amount;
    }

    function getAllReward() public view returns (uint256) {
        uint256 N = depositOf[msg.sender].length;
        uint256 allRewards;

        for (uint256 i = 0; i < N; i++) {
            allRewards += getReward(i);
        }

        return allRewards;
    }
}