pragma solidity ^0.4.13;

library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
      return 0;
    }
    uint256 c = a * b;
    assert(c / a == b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return c;
  }

  /**
  * @dev Substracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

contract Ownable {
  address public owner;


  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  function Ownable() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

contract VestingFund is Ownable {
  using SafeMath for uint256;
  using SafeERC20 for ERC20Basic;

  event Released(uint256 amount);

  // beneficiary of tokens after they are released
  address public beneficiary;
  ERC20Basic public token;

  uint256 public quarters;
  uint256 public start;


  uint256 public released;

  /**
   * @dev Creates a vesting contract that vests its balance of any ERC20 token to the
   * _beneficiary, tokens are release in an incremental fashion after a quater has passed until _start + _quarters * 3 * months. 
   * By then all of the balance will have vested.
   * @param _beneficiary address of the beneficiary to whom vested tokens are transferred
   * @param _quarters number of quarters the vesting will last
   * @param _token ERC20 token which is being vested
   */
  function VestingFund(address _beneficiary, uint256 _start, uint256 _quarters, address _token) public {
    
    require(_beneficiary != address(0) && _token != address(0));
    require(_quarters > 0);

    beneficiary = _beneficiary;
    quarters = _quarters;
    start = _start;
    token = ERC20Basic(_token);
  }

  /**
   * @notice Transfers vested tokens to beneficiary.
   */
  function release() public {
    uint256 unreleased = releasableAmount();
    require(unreleased > 0);

    released = released.add(unreleased);
    token.safeTransfer(beneficiary, unreleased);

    Released(unreleased);
  }

  /**
   * @dev Calculates the amount that has already vested but hasn't been released yet.
   */
  function releasableAmount() public view returns(uint256) {
    return vestedAmount().sub(released);
  }

  /**
   * @dev Calculates the amount that has already vested.
   */
  function vestedAmount() public view returns(uint256) {
    uint256 currentBalance = token.balanceOf(this);
    uint256 totalBalance = currentBalance.add(released);

    if (now < start) {
      return 0;
    }

    uint256 dT = now.sub(start); // time passed since start
    uint256 dQuarters = dT.div(90 days); // quarters passed

    if (dQuarters >= quarters) {
      return totalBalance; // return everything if vesting period ended
    } else {
      return totalBalance.mul(dQuarters).div(quarters); // ammount = total * (quarters passed / total quarters)
    }
  }
}

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);
}

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);
}

library SafeERC20 {
  function safeTransfer(ERC20Basic token, address to, uint256 value) internal {
    assert(token.transfer(to, value));
  }

  function safeTransferFrom(ERC20 token, address from, address to, uint256 value) internal {
    assert(token.transferFrom(from, to, value));
  }

  function safeApprove(ERC20 token, address spender, uint256 value) internal {
    assert(token.approve(spender, value));
  }
}