UpgradeAgent.sol

pragma solidity ^0.4.11;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {
    function mul(uint256 a, uint256 b) internal constant returns (uint256) {
        uint256 c = a * b;
        require(a == 0 || c / a == b);
        return c;
    }

    function div(uint256 a, uint256 b) internal constant returns (uint256) {
        //   require(b > 0); // Solidity automatically throws when dividing by 0
        uint256 c = a / b;
        //   require(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) {
        require(b <= a);
        return a - b;
    }

    function add(uint256 a, uint256 b) internal constant returns (uint256) {
        uint256 c = a + b;
        require(c >= a);
        return c;
    }
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
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;
    }

}


interface UpgradeAgent {
    function upgradeFrom(address _owner, uint256 _value) public;
}

contract OldToken is Ownable {


    using SafeMath for uint;
    address public newTokenAddr;
    uint256 public totalSupply;
    uint256 public totalUpgraded;

    mapping(address => uint256) public balances;
    
    event Upgrade(address indexed _from, address indexed newTokenAddr, uint256 _value);
    
    function OldToken() public {
        balances[msg.sender] = 10000;
        totalSupply = 10000;
    }
    
    function setUpgradeAgent(address _newTokenAddr) public onlyOwner {
        newTokenAddr = _newTokenAddr;
    }

    /**
    * Allow the token holder to upgrade some of their tokens to a new contract.
    */
    function upgrade(uint256 value) public {
      // Validate input value.
        require(value != 0);
        require(newTokenAddr != address(0));
        balances[msg.sender] = balances[msg.sender].sub(value);
        // Take tokens out from circulation
        totalSupply = totalSupply.sub(value);
        totalUpgraded = totalUpgraded.add(value);
        // Upgrade agent reissues the tokens
        UpgradeAgent(newTokenAddr).upgradeFrom(msg.sender, value);
        Upgrade(msg.sender, newTokenAddr, value);
    }
}


contract NewToken {


    using SafeMath for uint;
    address public oldTokenAddr;
    uint256 public totalSupply;
    mapping(address => uint256) public balances;

    function NewToken(address _oldTokenAddr) public {
        oldTokenAddr = _oldTokenAddr;
    }
    /**
    * Allow the new token contract to update the token balances.
    */
    function upgradeFrom(address _from, uint256 value) public {
        // Make sure the call is from old token contract
        require(msg.sender == oldTokenAddr);
        // Validate input value.
        balances[_from] = balances[_from].add(value);
        // Take tokens out from circulation
        totalSupply = totalSupply.add(value);
    }
}