pragma solidity ^0.4.19;

/**
* Token for SpringRole PreMint. This token is usable on the mainnet
* Go to https://beta.springrole.com to start!
* At the time of writing this contract, this token can be used for reserving vanity URL.
* More features will be added soon.
*/


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  uint256 public totalSupply;
  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);
}


contract StandardToken is ERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) public balances;
    mapping (address => mapping (address => uint256)) public allowed;

    /**
    * @dev transfer token for a specified address
    * @param _to The address to transfer to.
    * @param _value The amount to be transferred.
    */
    function transfer(address _to, uint256 _value) returns (bool success) {
        require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
    * @dev Transfer tokens from one address to another
    * @param _from address The address which you want to send tokens from
    * @param _to address The address which you want to transfer to
    * @param _value uint256 the amout of tokens to be transfered
    */
    function transferFrom(address _from, address _to, uint256 _value) returns (bool success) {
        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]);
        balances[_to] = balances[_to].add(_value);
        balances[_from] = balances[_from].sub(_value);
        allowed[_from][msg.sender] -= allowed[_from][msg.sender].sub(_value);
        Transfer(_from, _to, _value);
        return true;
    }

    /**
    * @dev Gets the balance of the specified address.
    * @param _owner The address to query the the balance of.
    * @return An uint256 representing the amount owned by the passed address.
    */
    function balanceOf(address _owner) constant returns (uint256 balance) {
        return balances[_owner];
    }

    /**
    * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
    * This only works when the allowance is 0. Cannot be used to change allowance. 
    * https://github.com/ethereum/EIPs/issues/738#issuecomment-336277632
    * @param _spender The address which will spend the funds.
    * @param _value The amount of tokens to be spent.
    */
    function approve(address _spender, uint256 _value) returns (bool success) {
        require(allowed[msg.sender][_spender] == 0);
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
    * @dev Function to check the amount of tokens that an owner allowed to a spender.
    * @param _owner address The address which owns the funds.
    * @param _spender address The address which will spend the funds.
    * @return A uint256 specifing the amount of tokens still available for the spender.
    */
    function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
      return allowed[_owner][_spender];
    }

    /**
     * To increment allowed value is better to use this function.
     * From MonolithDAO Token.sol
     */
    function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
        allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }

    function decreaseApproval(address _spender, uint _subtractedValue) public returns (bool) {
        uint oldValue = allowed[msg.sender][_spender];
        if (_subtractedValue > oldValue) {
            allowed[msg.sender][_spender] = 0;
        } else {
            allowed[msg.sender][_spender] = oldValue.sub(_subtractedValue);
        }
        Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
        return true;
    }
}

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() {
    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) onlyOwner public {
    require(newOwner != address(0));
    OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

library SafeMath {
  function mul(uint256 a, uint256 b) internal constant returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function div(uint256 a, uint256 b) internal constant 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;
  }

  function sub(uint256 a, uint256 b) internal constant returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function add(uint256 a, uint256 b) internal constant returns (uint256) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

/* Contract class for adding removing whitelisted contracts */
contract WhiteListedContracts is Ownable {
  mapping (address => bool ) white_listed_contracts;

  //modifer to check if the contract given is white listed or not
  modifier whitelistedContractsOnly() {
    require(white_listed_contracts[msg.sender]);
    _;
  }

  //add a contract to whitelist
  function addWhiteListedContracts (address _address) onlyOwner public {
    white_listed_contracts[_address] = true;
  }

  //remove contract from whitelist
  function removeWhiteListedContracts (address _address) onlyOwner public {
    white_listed_contracts[_address] = false;
  }
}

/* Contract class to mint tokens and transfer */
contract SRTToken is Ownable,StandardToken,WhiteListedContracts {
  using SafeMath for uint256;

  string constant public name = 'SpringRole Pre Mint Token';
  string constant public symbol = 'SRPMT';
  uint constant public decimals = 18;
  uint256 public totalSupply;
  uint256 public maxSupply;

  /* Contructor function to set maxSupply*/
  function SRTToken(uint256 _maxSupply){
    maxSupply = _maxSupply.mul(10**decimals);
  }

  /*
  do transfer function will allow transfer from a _to to _from provided if the call
  comes from whitelisted contracts only
  */
  function doTransfer(address _from, address _to, uint256 _value) whitelistedContractsOnly public returns (bool){
    require(balances[_from] >= _value && balances[_to] + _value > balances[_to]);
    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    Transfer(_from, _to, _value);
    return true;
  }

  /**
 * @dev Function to mint tokens
 * @param _amount The amount of tokens to mint.
 * @return A boolean that indicates if the operation was successful.
 */
  function mint(uint256 _amount) onlyOwner public returns (bool) {
    require (maxSupply >= (totalSupply.add(_amount)));
    totalSupply = totalSupply.add(_amount);
    balances[msg.sender] = balances[msg.sender].add(_amount);
    Transfer(address(0), msg.sender, _amount);
    return true;
  }

}