pragma solidity 0.4.24;

/**
 * @title ERC20Basic
 * @dev see https://github.com/ethereum/EIPs/issues/179 */
contract ERC20Basic {
    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
}

/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20 */
contract ERC20 is ERC20Basic {
    function allowance(address owner, address spender) public view returns (uint256);
    function transferFrom(address from, address to, uint256 value) public returns (bool);
    function approve(address spender, uint256 value) public returns (bool);
    event Approval(
        address indexed owner,
        address indexed spender,
        uint256 value
    );
}

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure. */
library SafeERC20 {
    function safeTransfer(ERC20Basic token, address to, uint256 value) internal {
        require(token.transfer(to, value));
    }

    function safeTransferFrom(
        ERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        require(token.transferFrom(from, to, value));
    }

    function safeApprove(ERC20 token, address spender, uint256 value) internal {
        require(token.approve(spender, value));
    }
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control */
contract Ownable {
    address public owner;

    event OwnershipTransferred(
        address indexed previousOwner,
        address indexed newOwner
    );

    constructor() public {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner);
        _;
    }

    function transferOwnership(address newOwner) public onlyOwner {
        require(newOwner != address(0));
        emit OwnershipTransferred(owner, newOwner);
        owner = newOwner;
    }
}

/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error */
library SafeMath {

    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
        if (a == 0) {
            return 0;
        }
        c = a * b;
        assert(c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal pure returns (uint256) {

        return a / b;
    }

    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
        c = a + b;
        assert(c >= a);
        return c;
    }
}

/**
 * @title TokenVesting
 * @dev A token holder contract that can release its token balance gradually like a
 * typical vesting scheme, with a cliff and vesting period. Optionally revocable by the owner.*/
contract TokenVesting is Ownable {
    using SafeMath for uint256;
    using SafeERC20 for ERC20Basic;

    event Released(uint256 amount);
    event Revoked();

    address public beneficiary;

    uint256 public cliff;
    uint256 public start;
    uint256 public duration;

    bool public revocable;

    mapping (address => uint256) public released;
    mapping (address => bool) public revoked;

    constructor(
        address _beneficiary,
        uint256 _start,
        uint256 _cliff,
        uint256 _duration,
        bool _revocable
    )
    public {
        require(_beneficiary != address(0));
        require(_cliff <= _duration);
        beneficiary = _beneficiary;
        revocable = _revocable;
        duration = _duration;
        cliff = _start.add(_cliff);
        start = _start;
    }

    function release(ERC20Basic token) public {
        uint256 unreleased = releasableAmount(token);

        require(unreleased > 0);

        released[token] = released[token].add(unreleased);

        token.safeTransfer(beneficiary, unreleased);

        emit Released(unreleased);
    }

    function revoke(ERC20Basic token) public onlyOwner {
        require(revocable);
        require(!revoked[token]);

        uint256 balance = token.balanceOf(this);

        uint256 unreleased = releasableAmount(token);
        uint256 refund = balance.sub(unreleased);

        revoked[token] = true;

        token.safeTransfer(owner, refund);

        emit Revoked();
    }

    function releasableAmount(ERC20Basic token) public view returns (uint256) {
        return vestedAmount(token).sub(released[token]);
    }

    function vestedAmount(ERC20Basic token) public view returns (uint256) {
        uint256 currentBalance = token.balanceOf(this);
        uint256 totalBalance = currentBalance.add(released[token]);

        if (block.timestamp < cliff) {
            return 0;
        } else if (block.timestamp >= start.add(duration) || revoked[token]) {
            return totalBalance;
        } else {
            return totalBalance.mul(block.timestamp.sub(start)).div(duration);
        }
    }
}