TokenVesting

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

/**
 * @title TokenVesting
 * @dev Manages the gradual release of tokens to beneficiaries (Team, Advisors, Investors).
 */
contract TokenVesting is Ownable, ReentrancyGuard {
    using SafeERC20 for IERC20;

    struct VestingSchedule {
        uint256 totalAmount;    // Total tokens assigned to this user
        uint256 amountReleased; // How many have been claimed so far
        uint256 startTime;      // When vesting starts
        uint256 cliffDuration;  // Delay before ANY tokens are released
        uint256 duration;       // Total duration of the vesting period
    }

    IERC20 public immutable token;
    
    // Maps User Address -> Vesting Schedule
    mapping(address => VestingSchedule) public schedules;
    
    // Total tokens required to back all schedules
    uint256 public totalTokensLocked;

    event ScheduleCreated(address indexed beneficiary, uint256 amount, uint256 start, uint256 cliff, uint256 duration);
    event TokensReleased(address indexed beneficiary, uint256 amount);

    constructor(address _token) Ownable(msg.sender) {
        token = IERC20(_token);
    }

    /**
     * @notice Create a vesting schedule for a beneficiary.
     * @dev The contract MUST hold enough tokens before calling this.
     * @param _beneficiary Who gets the tokens.
     * @param _amount Total tokens to vest.
     * @param _start Unix timestamp for start.
     * @param _cliffDuration Seconds before first release (