pragma solidity 0.4.24;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
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;
  }
}


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @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 Basic token
 * @dev Basic version of StandardToken, with no allowances.
 */
contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping(address => uint256) balances;

  uint256 totalSupply_;

  /**
  * @dev total number of tokens in existence
  */
  function totalSupply() public view returns (uint256) {
    return totalSupply_;
  }

  /**
  * @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) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[msg.sender]);

    // SafeMath.sub will throw if there is not enough balance.
    balances[msg.sender] = balances[msg.sender].sub(_value);
    balances[_to] = balances[_to].add(_value);
    emit Transfer(msg.sender, _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) public view returns (uint256 balance) {
    return balances[_owner];
  }

}


/**
 * @title Burnable Token
 * @dev Token that can be irreversibly burned (destroyed).
 */
contract BurnableToken is BasicToken {

  event Burn(address indexed burner, uint256 value);

  /**
   * @dev Burns a specific amount of tokens.
   * @param _value The amount of token to be burned.
   */
  function burn(uint256 _value) public {
    require(_value <= balances[msg.sender]);
    // no need to require value <= totalSupply, since that would imply the
    // sender's balance is greater than the totalSupply, which *should* be an assertion failure

    address burner = msg.sender;
    balances[burner] = balances[burner].sub(_value);
    totalSupply_ = totalSupply_.sub(_value);
    emit Burn(burner, _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 Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * @dev https://github.com/ethereum/EIPs/issues/20
 * @dev Based on code by FirstBlood: https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 */
contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;


  /**
   * @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 amount of tokens to be transferred
   */
  function transferFrom(address _from, address _to, uint256 _value) public returns (bool) {
    require(_to != address(0));
    require(_value <= balances[_from]);
    require(_value <= allowed[_from][msg.sender]);

    balances[_from] = balances[_from].sub(_value);
    balances[_to] = balances[_to].add(_value);
    allowed[_from][msg.sender] = allowed[_from][msg.sender].sub(_value);
    emit Transfer(_from, _to, _value);
    return true;
  }

  /**
   * @dev Approve the passed address to spend the specified amount of tokens on behalf of msg.sender.
   *
   * Beware that changing an allowance with this method brings the risk that someone may use both the old
   * and the new allowance by unfortunate transaction ordering. One possible solution to mitigate this
   * race condition is to first reduce the spender's allowance to 0 and set the desired value afterwards:
   * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
   * @param _spender The address which will spend the funds.
   * @param _value The amount of tokens to be spent.
   */
  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit 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 specifying the amount of tokens still available for the spender.
   */
  function allowance(address _owner, address _spender) public view returns (uint256) {
    return allowed[_owner][_spender];
  }

  /**
   * @dev Increase the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To increment
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  function increaseApproval(address _spender, uint _addedValue) public returns (bool) {
    allowed[msg.sender][_spender] = allowed[msg.sender][_spender].add(_addedValue);
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

  /**
   * @dev Decrease the amount of tokens that an owner allowed to a spender.
   *
   * approve should be called when allowed[_spender] == 0. To decrement
   * allowed value is better to use this function to avoid 2 calls (and wait until
   * the first transaction is mined)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _subtractedValue The amount of tokens to decrease the allowance by.
   */
  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);
    }
    emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
    return true;
  }

}



/**
 * @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.
   */
  constructor() 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));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}


/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    emit Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    emit Unpause();
  }
}


/**
 * @title Pausable token
 * @dev StandardToken modified with pausable transfers.
 **/
contract PausableToken is StandardToken, Pausable {

  function transfer(address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transfer(_to, _value);
  }

  function transferFrom(address _from, address _to, uint256 _value) public whenNotPaused returns (bool) {
    return super.transferFrom(_from, _to, _value);
  }

  function approve(address _spender, uint256 _value) public whenNotPaused returns (bool) {
    return super.approve(_spender, _value);
  }

  function increaseApproval(address _spender, uint _addedValue) public whenNotPaused returns (bool success) {
    return super.increaseApproval(_spender, _addedValue);
  }

  function decreaseApproval(address _spender, uint _subtractedValue) public whenNotPaused returns (bool success) {
    return super.decreaseApproval(_spender, _subtractedValue);
  }
}


contract MintableAndPausableToken is PausableToken {
    uint8 public constant decimals = 18;
    uint256 public maxTokenSupply = 2000000000 * 10 ** uint256(decimals);

    bool public mintingFinished = false;
    
    event Mint(address indexed to, uint256 amount);
    event MintFinished();
    event MintStarted();

    modifier canMint() {
        require(!mintingFinished);
        _;
    }

    modifier checkMaxSupply(uint256 _amount) {
        require(maxTokenSupply >= totalSupply_.add(_amount));
        _;
    }

    modifier cannotMint() {
        require(mintingFinished);
        _;
    }

    function mint(address _to, uint256 _amount)
        external
        onlyOwner
        canMint
        checkMaxSupply (_amount)
        whenNotPaused
        returns (bool)
    {
        totalSupply_ = totalSupply_.add(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Mint(_to, _amount);
        emit Transfer(address(0), _to, _amount);
        return true;
    }

    function finishMinting() external onlyOwner canMint returns (bool) {
        mintingFinished = true;
        emit MintFinished();
        return true;
    }

    function startMinting() external onlyOwner cannotMint returns (bool) {
        mintingFinished = false;
        emit MintStarted();
        return true;
    }
}


/**
 * Token upgrader interface inspired by Lunyr.
 *
 * Token upgrader transfers previous version tokens to a newer version.
 * Token upgrader itself can be the token contract, or just a middle man contract doing the heavy lifting.
 */
contract TokenUpgrader {
    uint public originalSupply;

    /** Interface marker */
    function isTokenUpgrader() external pure returns (bool) {
        return true;
    }

    function upgradeFrom(address _from, uint256 _value) public {}
}


/**
 * A token upgrade mechanism where users can opt-in amount of tokens to the next smart contract revision.
 *
 * First envisioned by Golem and Lunyr projects.
 */


contract UpgradeableToken is MintableAndPausableToken {
    // Contract or person who can set the upgrade path.
    address public upgradeMaster;
    
    // Bollean value needs to be true to start upgrades
    bool private upgradesAllowed;

    // The next contract where the tokens will be migrated.
    TokenUpgrader public tokenUpgrader;

    // How many tokens we have upgraded by now.
    uint public totalUpgraded;

    /**
    * Upgrade states.
    * - NotAllowed: The child contract has not reached a condition where the upgrade can begin
    * - Waiting: Token allows upgrade, but we don't have a new token version
    * - ReadyToUpgrade: The token version is set, but not a single token has been upgraded yet
    * - Upgrading: Token upgrader is set and the balance holders can upgrade their tokens
    */
    enum UpgradeState { NotAllowed, Waiting, ReadyToUpgrade, Upgrading }

    // Somebody has upgraded some of his tokens.
    event Upgrade(address indexed _from, address indexed _to, uint256 _value);

    // New token version available.
    event TokenUpgraderIsSet(address _newToken);

    modifier onlyUpgradeMaster {
        // Only a master can designate the next token
        require(msg.sender == upgradeMaster);
        _;
    }

    modifier notInUpgradingState {
        // Upgrade has already begun for token
        require(getUpgradeState() != UpgradeState.Upgrading);
        _;
    }

    // Do not allow construction without upgrade master set.
    constructor(address _upgradeMaster) public {
        upgradeMaster = _upgradeMaster;
    }

    // set a token upgrader
    function setTokenUpgrader(address _newToken)
        external
        onlyUpgradeMaster
        notInUpgradingState
    {
        require(canUpgrade());
        require(_newToken != address(0));

        tokenUpgrader = TokenUpgrader(_newToken);

        // Handle bad interface
        require(tokenUpgrader.isTokenUpgrader());

        // Make sure that token supplies match in source and target
        require(tokenUpgrader.originalSupply() == totalSupply_);

        emit TokenUpgraderIsSet(tokenUpgrader);
    }

    // Allow the token holder to upgrade some of their tokens to a new contract.
    function upgrade(uint _value) external {
        UpgradeState state = getUpgradeState();
        
        // Check upgrate state 
        require(state == UpgradeState.ReadyToUpgrade || state == UpgradeState.Upgrading);
        // Validate input value
        require(_value != 0);

        balances[msg.sender] = balances[msg.sender].sub(_value);

        // Take tokens out from circulation
        totalSupply_ = totalSupply_.sub(_value);
        totalUpgraded = totalUpgraded.add(_value);

        // Token Upgrader reissues the tokens
        tokenUpgrader.upgradeFrom(msg.sender, _value);
        emit Upgrade(msg.sender, tokenUpgrader, _value);
    }

    /**
    * Change the upgrade master.
    * This allows us to set a new owner for the upgrade mechanism.
    */
    function setUpgradeMaster(address _newMaster) external onlyUpgradeMaster {
        require(_newMaster != address(0));
        upgradeMaster = _newMaster;
    }

    // To be overriden to add functionality
    function allowUpgrades() external onlyUpgradeMaster () {
        upgradesAllowed = true;
    }

    // To be overriden to add functionality
    function rejectUpgrades() external onlyUpgradeMaster () {
        require(!(totalUpgraded > 0));
        upgradesAllowed = false;
    }

    // Get the state of the token upgrade.
    function getUpgradeState() public view returns(UpgradeState) {
        if (!canUpgrade()) return UpgradeState.NotAllowed;
        else if (address(tokenUpgrader) == address(0)) return UpgradeState.Waiting;
        else if (totalUpgraded == 0) return UpgradeState.ReadyToUpgrade;
        else return UpgradeState.Upgrading;
    }

    // To be overriden to add functionality
    function canUpgrade() public view returns(bool) {
        return upgradesAllowed;
    }
}


contract Token is UpgradeableToken, BurnableToken {
    string public name = "KEYOTO";
    string public symbol = "KEYO";

    // For patient incentive programs
    uint256 public INITIAL_SUPPLY;

    event UpdatedTokenInformation(string newName, string newSymbol);

    constructor (address kpoWallet, address _upgradeMaster, uint256 _INITIAL_SUPPLY)
        public
        UpgradeableToken(_upgradeMaster)
    {
        require(maxTokenSupply >= _INITIAL_SUPPLY * (10 ** uint256(decimals)));
        INITIAL_SUPPLY = _INITIAL_SUPPLY * (10 ** uint256(decimals));
        totalSupply_ = INITIAL_SUPPLY;
        balances[kpoWallet] = INITIAL_SUPPLY;
        emit Transfer(address(0), kpoWallet, INITIAL_SUPPLY);
    }

    /**
    * Owner can update token information here
    */
    function setTokenInformation(string _name, string _symbol) external onlyOwner {
        name = _name;
        symbol = _symbol;

        emit UpdatedTokenInformation(name, symbol);
    }

    /**
    * Owner can burn token here
    */
    function burn(uint256 _value) public onlyOwner {
        super.burn(_value);
    }
}