19-Vault.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

/// user can deposit his money 
/// it wll mint some share
/// vault generate some yield
/// user can withdraw the shares with the increased amount 

contract Vault {
    IERC20 public immutable token;
    uint public totalSupply ;

    mapping(address => uint) public balanceOf ;

    constructor(address _token){
        token = IERC20(_token) ;

    }

    function mint(address _to ,uint shares) private {
        totalSupply += shares ;
        balanceOf[_to] += shares ;
    }

    function burn(address _from ,uint shares) private {
        totalSupply -= shares ;
        balanceOf[_from] -= shares ;
    }

    function deposit(uint _amount) external {

        uint shares;
        if(totalSupply==0){
            shares = _amount;
        }else{
            shares =(_amount*totalSupply) / token.balanceOf(address(this)) ;

        }

        mint(msg.sender,shares) ;
        token.transferFrom(msg.sender, address(this) , _amount) ;
    }


    
    function withdraw(uint _shares) external {

       uint amount = (_shares*token.balanceOf(address(this)))/ totalSupply ;
       burn(msg.sender,_shares) ;
       token.transfer(msg.sender, amount) ;
    }

}


interface IERC20 {
    function totalSupply() external view returns (uint);

    function balanceOf(address account) external view returns (uint);

    function transfer(address recipient, uint amount) external returns (bool);

    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint amount) external returns (bool);

    function transferFrom(
        address sender,
        address recipient,
        uint amount
    ) external returns (bool);

    event Transfer(address indexed from, address indexed to, uint amount);
    event Approval(address indexed owner, address indexed spender, uint amount);
}