// Vulnerability label: locked
pragma solidity ^0.4.21;
  
   // ----------------------------------------------------------------------------
   // 'FIXED' 'Example Fixed Supply Token' token contract
   //
   // Symbol      : vista
   // Name        : Vista Token
   // Total supply: 1,000,000,000.000000000000000000
   // Decimals    : 18
  //
  // Enjoy.
  //
  // Tony 2018-03-08
  // ----------------------------------------------------------------------------
  
  
  // ----------------------------------------------------------------------------
  // Safe maths
  // ----------------------------------------------------------------------------
  library SafeMath {
      function add(uint a, uint b) internal pure returns (uint c) {
          c = a + b;
          require(c >= a);
      }
      function sub(uint a, uint b) internal pure returns (uint c) {
          require(b <= a);
          c = a - b;
      }
      function mul(uint a, uint b) internal pure returns (uint c) {
          c = a * b;
          require(a == 0 || c / a == b);
      }
      function div(uint a, uint b) internal pure returns (uint c) {
          require(b > 0);
          c = a / b;
      }
  }
  
  
  // ----------------------------------------------------------------------------
  // ERC Token Standard #20 Interface
  // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
  // ----------------------------------------------------------------------------
  contract ERC20Interface {
      function totalSupply() public constant returns (uint);
      function balanceOf(address tokenOwner) public constant returns (uint balance);
      function allowance(address tokenOwner, address spender) public constant returns (uint remaining);
      function transfer(address to, uint tokens) public returns (bool success);
      function approve(address spender, uint tokens) public returns (bool success);
      function transferFrom(address from, address to, uint tokens) public returns (bool success);
  
      event Transfer(address indexed from, address indexed to, uint tokens);
      event Approval(address indexed tokenOwner, address indexed spender, uint tokens);
  }
  
  
  // ----------------------------------------------------------------------------
  // Contract function to receive approval and execute function in one call
  //
  // Borrowed from MiniMeToken
  // ----------------------------------------------------------------------------
  contract ApproveAndCallFallBack {
      function receiveApproval(address from, uint256 tokens, address token, bytes data) public;
  }
  
  
  // ----------------------------------------------------------------------------
  // Owned contract
  // ----------------------------------------------------------------------------
  contract Owned {
      address public owner;
      address public newOwner;
  
      event OwnershipTransferred(address indexed _from, address indexed _to);
  
      function Owned() public {
          owner = msg.sender;
      }
  
      modifier onlyOwner {
          require(msg.sender == owner);
          _;
      }
  
      function transferOwnership(address _newOwner) public onlyOwner {
          newOwner = _newOwner;
      }
      function acceptOwnership() public {
          require(msg.sender == newOwner);
          OwnershipTransferred(owner, newOwner);
          owner = newOwner;
          newOwner = address(0);
      }
  }
  
  
  // ----------------------------------------------------------------------------
  // ERC20 Token, with the addition of symbol, name and decimals and an
  // initial fixed supply
 // ----------------------------------------------------------------------------
 contract VistaToken is ERC20Interface, Owned {
     using SafeMath for uint;
 
     string public symbol;
     string public  name;
     uint8 public decimals;
     uint public _totalSupply;
 
     mapping(address => uint) balances;
     mapping(address => mapping(address => uint)) allowed;
 
 
     // ------------------------------------------------------------------------
     // Constructor
     // ------------------------------------------------------------------------
     function VistaToken() public {
         symbol = "vista";
         name = "Vista Token";
         decimals = 18;
         _totalSupply = 1000000000 * 10**uint(decimals);
         balances[owner] = _totalSupply;
         Transfer(address(0), owner, _totalSupply);
     }
 
 
     // ------------------------------------------------------------------------
     // Total supply
     // ------------------------------------------------------------------------
     function totalSupply() public constant returns (uint) {
         return _totalSupply  - balances[address(0)];
     }
 
 
     // ------------------------------------------------------------------------
     // Get the token balance for account `tokenOwner`
     // ------------------------------------------------------------------------
     function balanceOf(address tokenOwner) public constant returns (uint balance) {
         return balances[tokenOwner];
     }
 
 
     // ------------------------------------------------------------------------
     // Transfer the balance from token owner's account to `to` account
     // - Owner's account must have sufficient balance to transfer
     // - 0 value transfers are allowed
     // ------------------------------------------------------------------------
     function transfer(address to, uint tokens) public returns (bool success) {
         balances[msg.sender] = balances[msg.sender].sub(tokens);
         balances[to] = balances[to].add(tokens);
         Transfer(msg.sender, to, tokens);
         return true;
     }
 
 
     // ------------------------------------------------------------------------
     // Token owner can approve for `spender` to transferFrom(...) `tokens`
     // from the token owner's account
     //
     // https://github.com/ethereum/EIPs/blob/master/EIPS/eip-20-token-standard.md
     // recommends that there are no checks for the approval double-spend attack
     // as this should be implemented in user interfaces 
     // ------------------------------------------------------------------------
     function approve(address spender, uint tokens) public returns (bool success) {
         allowed[msg.sender][spender] = tokens;
         Approval(msg.sender, spender, tokens);
         return true;
     }
 
 
     // ------------------------------------------------------------------------
     // Transfer `tokens` from the `from` account to the `to` account
     // 
     // The calling account must already have sufficient tokens approve(...)-d
     // for spending from the `from` account and
     // - From account must have sufficient balance to transfer
     // - Spender must have sufficient allowance to transfer
     // - 0 value transfers are allowed
     // ------------------------------------------------------------------------
     function transferFrom(address from, address to, uint tokens) public returns (bool success) {
         balances[from] = balances[from].sub(tokens);
         allowed[from][msg.sender] = allowed[from][msg.sender].sub(tokens);
         balances[to] = balances[to].add(tokens);
         Transfer(from, to, tokens);
         return true;
     }
 
 
     // ------------------------------------------------------------------------
     // Returns the amount of tokens approved by the owner that can be
     // transferred to the spender's account
     // ------------------------------------------------------------------------
     function allowance(address tokenOwner, address spender) public constant returns (uint remaining) {
         return allowed[tokenOwner][spender];
     }
 
 
     // ------------------------------------------------------------------------
     // Token owner can approve for `spender` to transferFrom(...) `tokens`
     // from the token owner's account. The `spender` contract function
     // `receiveApproval(...)` is then executed
     // ------------------------------------------------------------------------
     function approveAndCall(address spender, uint tokens, bytes data) public returns (bool success) {
         allowed[msg.sender][spender] = tokens;
         Approval(msg.sender, spender, tokens);
         ApproveAndCallFallBack(spender).receiveApproval(msg.sender, tokens, this, data);
         return true;
     }
 
 
     // ------------------------------------------------------------------------
     // Don't accept ETH
     // ------------------------------------------------------------------------
     function () public payable {
         revert();
     }
 
 
     // ------------------------------------------------------------------------
     // Owner can transfer out any accidentally sent ERC20 tokens
     // ------------------------------------------------------------------------
     function transferAnyERC20Token(address tokenAddress, uint tokens) public onlyOwner returns (bool success) {
         return ERC20Interface(tokenAddress).transfer(owner, tokens);
     }
 }