/*
You should inherit from StandardToken or, for a token like you would want to
deploy in something like Mist, see HumanStandardToken.sol.
(This implements ONLY the standard functions and NOTHING else.
If you deploy this, you won't have anything useful.)

Implements ERC 20 Token standard: https://github.com/ethereum/EIPs/issues/20
based on the https://github.com/ConsenSys/Tokens/blob/master/contracts/StandardToken.sol
.*/
pragma solidity ^0.4.18;

import "./EIP20Token.sol";

contract EIP20StandardToken is EIP20Token {

  uint256 constant MAX_UINT256 = 2 ** 256 - 1;

  function transfer(address _to, uint256 _value) public returns(bool success) {
    //Default assumes totalSupply can't be over max (2^256 - 1).
    //If your token leaves out totalSupply and can issue more tokens as time goes on, you need to check if it doesn't wrap.
    //Replace the if with this one instead.
    //require(balances[msg.sender] >= _value && balances[_to] + _value > balances[_to]);
    require(balances[msg.sender] >= _value);
    balances[msg.sender] -= _value;
    balances[_to] += _value;
    Transfer(msg.sender, _to, _value);
    return true;
  }

  function transferFrom(address _from, address _to, uint256 _value) public returns(bool success) {
    //same as above. Replace this line with the following if you want to protect against wrapping uints.
    //require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value > balances[_to]);
    uint256 allowance = allowed[_from][msg.sender];
    require(balances[_from] >= _value && allowance >= _value);
    balances[_to] += _value;
    balances[_from] -= _value;
    if (allowance < MAX_UINT256) {
      allowed[_from][msg.sender] -= _value;
    }
    Transfer(_from, _to, _value);
    return true;
  }

  function balanceOf(address _owner) constant public returns(uint256 balance) {
    return balances[_owner];
  }

  function approve(address _spender, uint256 _value) public returns(bool success) {
    allowed[msg.sender][_spender] = _value;
    Approval(msg.sender, _spender, _value);
    return true;
  }

  function allowance(address _owner, address _spender) public constant returns(uint256 remaining) {
    return allowed[_owner][_spender];
  }

  mapping(address => uint256) balances;
  mapping(address => mapping(address => uint256)) allowed;
}