contract VestedToken is StandardToken, LimitedTransferToken {

  uint256 MAX_GRANTS_PER_ADDRESS = 20;

  struct TokenGrant {
    address granter;     
    uint256 value;       
    uint64 cliff;
    uint64 vesting;
    uint64 start;        
    bool revokable;
    bool burnsOnRevoke;  
  }

  mapping (address => TokenGrant[]) public grants;

  event NewTokenGrant(address indexed from, address indexed to, uint256 value, uint256 grantId);

  /**
   * @dev Grant tokens to a specified address
   * @param _to address The address which the tokens will be granted to.
   * @param _value uint256 The amount of tokens to be granted.
   * @param _start uint64 Time of the beginning of the grant.
   * @param _cliff uint64 Time of the cliff period.
   * @param _vesting uint64 The vesting period.
   */
  function grantVestedTokens(
    address _to,
    uint256 _value,
    uint64 _start,
    uint64 _cliff,
    uint64 _vesting,
    bool _revokable,
    bool _burnsOnRevoke
  ) public {

    // Check for date inconsistencies that may cause unexpected behavior
    if (_cliff < _start || _vesting < _cliff) {
      throw;
    }

    if (tokenGrantsCount(_to) > MAX_GRANTS_PER_ADDRESS) throw;   // To prevent a user being spammed and have his balance locked (out of gas attack when calculating vesting).

    uint count = grants[_to].push(
                TokenGrant(
                  _revokable ? msg.sender : 0, // avoid storing an extra 20 bytes when it is non-revokable
                  _value,
                  _cliff,
                  _vesting,
                  _start,
                  _revokable,
                  _burnsOnRevoke
                )
              );

    transfer(_to, _value);

    NewTokenGrant(msg.sender, _to, _value, count - 1);
  }

  /**
   * @dev Revoke the grant of tokens of a specifed address.
   * @param _holder The address which will have its tokens revoked.
   * @param _grantId The id of the token grant.
   */
  function revokeTokenGrant(address _holder, uint _grantId) public {
    TokenGrant grant = grants[_holder][_grantId];

    if (!grant.revokable) { // Check if grant was revokable
      throw;
    }

    if (grant.granter != msg.sender) { // Only granter can revoke it
      throw;
    }

    address receiver = grant.burnsOnRevoke ? 0xdead : msg.sender;

    uint256 nonVested = nonVestedTokens(grant, uint64(now));

    // remove grant from array
    delete grants[_holder][_grantId];
    grants[_holder][_grantId] = grants[_holder][grants[_holder].length.sub(1)];
    grants[_holder].length -= 1;

    balances[receiver] = balances[receiver].add(nonVested);
    balances[_holder] = balances[_holder].sub(nonVested);

    Transfer(_holder, receiver, nonVested);
  }


  /**
   * @dev Calculate the total amount of transferable tokens of a holder at a given time
   * @param holder address The address of the holder
   * @param time uint64 The specific time.
   * @return An uint representing a holder's total amount of transferable tokens.
   */
  function transferableTokens(address holder, uint64 time) constant public returns (uint256) {
    uint256 grantIndex = tokenGrantsCount(holder);

    if (grantIndex == 0) return balanceOf(holder); // shortcut for holder without grants

    // Iterate through all the grants the holder has, and add all non-vested tokens
    uint256 nonVested = 0;
    for (uint256 i = 0; i < grantIndex; i++) {
      nonVested = SafeMath.add(nonVested, nonVestedTokens(grants[holder][i], time));
    }

    // Balance - totalNonVested is the amount of tokens a holder can transfer at any given time
    uint256 vestedTransferable = SafeMath.sub(balanceOf(holder), nonVested);

    // Return the minimum of how many vested can transfer and other value
    // in case there are other limiting transferability factors (default is balanceOf)
    return SafeMath.min256(vestedTransferable, super.transferableTokens(holder, time));
  }

  /**
   * @dev Check the amount of grants that an address has.
   * @param _holder The holder of the grants.
   * @return A uint representing the total amount of grants.
   */
  function tokenGrantsCount(address _holder) constant returns (uint index) {
    return grants[_holder].length;
  }

  /**
   * @dev Calculate amount of vested tokens at a specifc time.
   * @param tokens uint256 The amount of tokens grantted.
   * @param time uint64 The time to be checked
   * @param start uint64 A time representing the begining of the grant
   * @param cliff uint64 The cliff period.
   * @param vesting uint64 The vesting period.
   * @return An uint representing the amount of vested tokensof a specif grant.
  */
  function calculateVestedTokens(
    uint256 tokens,
    uint256 time,
    uint256 start,
    uint256 cliff,
    uint256 vesting) constant returns (uint256)
    {
      // Shortcuts for before cliff and after vesting cases.
      if (time < cliff) return 0;
      if (time >= vesting) return tokens;

      // vestedTokens = tokens * (time - start) / (vesting - start)
      uint256 vestedTokens = SafeMath.div(
                                    SafeMath.mul(
                                      tokens,
                                      SafeMath.sub(time, start)
                                      ),
                                    SafeMath.sub(vesting, start)
                                    );

      return vestedTokens;
  }

  /**
   * @dev Get all information about a specifc grant.
   * @param _holder The address which will have its tokens revoked.
   * @param _grantId The id of the token grant.
   * @return Returns all the values that represent a TokenGrant(address, value, start, cliff,
   * revokability, burnsOnRevoke, and vesting) plus the vested value at the current time.
   */
  function tokenGrant(address _holder, uint _grantId) constant returns (address granter, uint256 value, uint256 vested, uint64 start, uint64 cliff, uint64 vesting, bool revokable, bool burnsOnRevoke) {
    TokenGrant grant = grants[_holder][_grantId];

    granter = grant.granter;
    value = grant.value;
    start = grant.start;
    cliff = grant.cliff;
    vesting = grant.vesting;
    revokable = grant.revokable;
    burnsOnRevoke = grant.burnsOnRevoke;

    vested = vestedTokens(grant, uint64(now));
  }

  /**
   * @dev Get the amount of vested tokens at a specific time.
   * @param grant TokenGrant The grant to be checked.
   * @param time The time to be checked
   * @return An uint representing the amount of vested tokens of a specific grant at a specific time.
   */
  function vestedTokens(TokenGrant grant, uint64 time) private constant returns (uint256) {
    return calculateVestedTokens(
      grant.value,
      uint256(time),
      uint256(grant.start),
      uint256(grant.cliff),
      uint256(grant.vesting)
    );
  }

  /**
   * @dev Calculate the amount of non vested tokens at a specific time.
   * @param grant TokenGrant The grant to be checked.
   * @param time uint64 The time to be checked
   * @return An uint representing the amount of non vested tokens of a specifc grant on the 
   * passed time frame.
   */
  function nonVestedTokens(TokenGrant grant, uint64 time) private constant returns (uint256) {
    return grant.value.sub(vestedTokens(grant, time));
  }

  /**
   * @dev Calculate the date when the holder can trasfer all its tokens
   * @param holder address The address of the holder
   * @return An uint representing the date of the last transferable tokens.
   */
  function lastTokenIsTransferableDate(address holder) constant public returns (uint64 date) {
    date = uint64(now);
    uint256 grantIndex = grants[holder].length;
    for (uint256 i = 0; i < grantIndex; i++) {
      date = SafeMath.max64(grants[holder][i].vesting, date);
    }
  }
}
/**
 * @title Vested token
 * @dev Tokens that can be vested for a group of addresses.
 */
function calculateVestedTokens(
    uint256 tokens,
    uint256 time,
    uint256 start,
    uint256 cliff,
    uint256 vesting) constant returns (uint256)
    {
      // Shortcuts for before cliff and after vesting cases.
      if (time < cliff) return 0;
      if (time >= vesting) return tokens;

      // vestedTokens = tokens * (time - start) / (vesting - start)
      uint256 vestedTokens = SafeMath.div(
                                    SafeMath.mul(
                                      tokens,
                                      SafeMath.sub(time, start)
                                      ),
                                    SafeMath.sub(vesting, start)
                                    );

      return vestedTokens;
  }
/**
 * @dev Calculate amount of vested tokens at a specifc time.
 * @param tokens uint256 The amount of tokens grantted.
 * @param time uint64 The time to be checked
 * @param start uint64 A time representing the begining of the grant
 * @param cliff uint64 The cliff period.
 * @param vesting uint64 The vesting period.
 * @return An uint representing the amount of vested tokensof a specif grant.
 */