// SPDX-License-Identifier: MIT
pragma solidity 0.8.12;

interface IERC20 {
    function balanceOf(address account) external view returns (uint256);
    function transfer(address to, uint256 amount) external returns (bool);
}

contract Vesting {
    IERC20 private _token = IERC20(0x173771c0fa751C56579536A85b2DACb562CDE80B);
    address private _deployer;
    uint256 private _creation;
    uint256 private _unlocked = 0;
    uint256 private _unlocks = 24;
    
    constructor() {
        _deployer = msg.sender;
        _creation = block.timestamp;
    }

    function unlock() external {
        // Only the contract deployer is authorized to unlock
        require(msg.sender == _deployer, 'not authorized');

        // Get the current token balance
        uint256 balance = _token.balanceOf(address(this));

        // The contract token balance needs to be positive
        require(balance > 0, 'empty balance');

        // Get the difference in seconds between current timestamp and creation time
        uint256 difference = block.timestamp - _creation;

        // Calculate months that have passed since creation (1 month = 60 seconds * 60 minutes * 24 hours * 30 days)
        uint256 months = difference / 60 / 60 / 24 / 30;

        // Cap months at max. number of unlocks (the vesting ends when months == _unlocks)
        if (months > _unlocks) months = _unlocks;

        // Calculate the initial amount of locked tokens
        // This is equal to the current token balance of the contract plus tokens that have been unlocked
        uint256 tokens = balance + _unlocked;

        // Calculate the max. unlockable amount based on the number of passed months
        // For example, if months = 6 and _unlocks = 24, this becomes initially locked tokens * 0.25
        uint256 unlockable = tokens * months / _unlocks;

        // Calculate the withdrawable amount, based on previously unlocked tokens
        uint256 withdrawable = unlockable - _unlocked;

        // Update the unlocked amount
        _unlocked += withdrawable;

        // Transfer the withdrawable amount
        _token.transfer(_deployer, withdrawable);
    }
}

{
  "compilationTarget": {
    "Vesting.sol": "Vesting"
  },
  "evmVersion": "london",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}