VestedWithdrawals.sol

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppellin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";


contract ERC721VestedWithdrawals is Ownable, ReentrancyGuard, ERC721 {

    uint256 public constant VEST_CADENCE = 90 days;
    uint256 public constant VEST_PERIODS = 4;

    uint256 public mintCompletionTime;
    uint256 public totalMintFunds;
    uint256 public amountWithdrawn;

    /// @dev this hook should be called when the last NFT has been minted or
    /// a sale is deemed as completed.
    function _onMintCompletion() private {
        mintCompletionTime = block.timestamp;
        totalMintFunds = address(this).balance;
    }

    function vestedWithdraw() external onlyOwner nonReentrant {
        require(mintCompletionTime != 0 && totalMintFunds != 0, "Sale not over");

        uint256 withdrawableAmount;
        uint256 vestedPeriods = (block.timestamp - mintCompletionTime) / VEST_CADENCE;
        if (vestedPeriods >= VEST_PERIODS) {
            withdrawableAmount = address(this).balance;
        } else {
            uint256 vestedAmount = (totalMintFunds * vestedPeriods) / VEST_PERIODS;
            withdrawableAmount = vestedAmount - amountWithdrawn;
        }

        if (withdrawableAmount > 0) {
            amountWithdrawn = vestedAmount;
            (bool success, ) = msg.sender.call{value: withdrawableAmount}("");
            require(success, "Withdrawal failed.");
        }
    }
}