pragma solidity ^0.4.0;

contract tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData); }

contract DogTestToken {
   
  string public constant name = "Dog Test Token2";

  string public constant symbol = "DTT";

  uint8 public constant decimals = 18;

  string public constant version = '0.1';

  uint256 public constant totalSupply = 1000000000 * 1000000000000000000;

  address public owner;

  uint256 public constant lockedUntilBlock = 0;

  event Transfer(address indexed _from, address indexed _to, uint256 _value);
  event Approval(address indexed _owner, address indexed _spender, uint256 _value);
  event BlockLockSet(uint256 _value);
  event NewOwner(address _newOwner);
  
  modifier onlyOwner {
    if (msg.sender == owner) {
      _;
    }
  }

  function isLocked() constant returns (bool success) {
    return lockedUntilBlock > block.number;
  }

  modifier blockLock(address _sender) {
    if (!isLocked() || _sender == owner) {
      _;
    }
  }

  modifier checkIfToContract(address _to) {
    if(_to != address(this))  {
      _;
    }
  }    

  function DogTestToken() {
    owner = msg.sender;
    balances[owner] = totalSupply;        
  }

  function approveAndCall(address _spender, uint256 _value, bytes _extraData) returns (bool success) {
    tokenRecipient spender = tokenRecipient(_spender);
    if (approve(_spender, _value)) {
      spender.receiveApproval(msg.sender, _value, this, _extraData);
      return true;
    }
  }

  function transfer(address _to, uint256 _value) blockLock(msg.sender) checkIfToContract(_to) returns (bool success) {
    if (balances[msg.sender] >= _value && _value > 0) {
      balances[msg.sender] -= _value;
      balances[_to] += _value;
      Transfer(msg.sender, _to, _value);
      return true;
    } else {
      return false;
    }
  }

  function transferFrom(address _from, address _to, uint256 _value) blockLock(_from) checkIfToContract(_to) returns (bool success) {
    if (balances[_from] >= _value && allowed[_from][msg.sender] >= _value && _value > 0) {
      balances[_to] += _value;
      balances[_from] -= _value;
      allowed[_from][msg.sender] -= _value;
      Transfer(_from, _to, _value);
      return true;
    } else {
      return false;
    }
  }

  function balanceOf(address _owner) constant returns (uint256 balance) {
    return balances[_owner];
  }

  function approve(address _spender, uint256 _value) returns (bool success) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }

  function allowance(address _owner, address _spender) constant returns (uint256 remaining) {
    return allowed[_owner][_spender];
  }  

  function replaceOwner(address _newOwner) onlyOwner returns (bool success) {
    owner = _newOwner;
    NewOwner(_newOwner);
    return true;
  }

  mapping (address => uint256) balances;
  mapping (address => mapping (address => uint256)) allowed;
}