/*

  Copyright 2017 ZeroEx Intl.

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.

*/

pragma solidity 0.4.18;

contract Token {

    /// @notice send `_value` token to `_to` from `msg.sender`
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transfer(address _to, uint _value) public returns (bool) {}

    /// @notice send `_value` token to `_to` from `_from` on the condition it is approved by `_from`
    /// @param _from The address of the sender
    /// @param _to The address of the recipient
    /// @param _value The amount of token to be transferred
    /// @return Whether the transfer was successful or not
    function transferFrom(address _from, address _to, uint _value) public returns (bool) {}

    /// @notice `msg.sender` approves `_addr` to spend `_value` tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @param _value The amount of wei to be approved for transfer
    /// @return Whether the approval was successful or not
    function approve(address _spender, uint _value) public returns (bool) {}

    /// @param _owner The address from which the balance will be retrieved
    /// @return The balance
    function balanceOf(address _owner) public view returns (uint) {}

    /// @param _owner The address of the account owning tokens
    /// @param _spender The address of the account able to transfer the tokens
    /// @return Amount of remaining tokens allowed to spent
    function allowance(address _owner, address _spender) public view returns (uint) {}

    event Transfer(address indexed _from, address indexed _to, uint _value);
    event Approval(address indexed _owner, address indexed _spender, uint _value);
}

contract ERC20Token is Token {

    function transfer(address _to, uint _value)
        public
        returns (bool) 
    {
        require(balances[msg.sender] >= _value && balances[_to] + _value >= balances[_to]); 
        balances[msg.sender] -= _value;
        balances[_to] += _value;
        Transfer(msg.sender, _to, _value);
        return true;
    }

    function transferFrom(address _from, address _to, uint _value)
        public 
        returns (bool) 
    {
        require(balances[_from] >= _value && allowed[_from][msg.sender] >= _value && balances[_to] + _value >= balances[_to]); 
        balances[_to] += _value;
        balances[_from] -= _value;
        allowed[_from][msg.sender] -= _value;
        Transfer(_from, _to, _value);
        return true;
    }

    function approve(address _spender, uint _value) 
        public
        returns (bool)
    {
        allowed[msg.sender][_spender] = _value;
        Approval(msg.sender, _spender, _value);
        return true;
    }

    function balanceOf(address _owner)
        public
        view
        returns (uint)
    {
        return balances[_owner];
    }

    function allowance(address _owner, address _spender) 
        public
        view
        returns (uint)
    {
        return allowed[_owner][_spender];
    }

    mapping (address => uint) balances;
    mapping (address => mapping (address => uint)) allowed;
    uint public totalSupply;
}

contract UnlimitedAllowanceToken is ERC20Token {

    uint constant MAX_UINT = 2**256 - 1;

    /// @dev ERC20 transferFrom, modified such that an allowance of MAX_UINT represents an unlimited allowance. See https://github.com/ethereum/EIPs/issues/717
    /// @param _from Address to transfer from.
    /// @param _to Address to transfer to.
    /// @param _value Amount to transfer.
    /// @return Success of transfer.
    function transferFrom(address _from, address _to, uint _value)
        public 
        returns (bool) 
    {
        uint allowance = allowed[_from][msg.sender];
        require(balances[_from] >= _value && allowance >= _value && balances[_to] + _value >= balances[_to]); 
        balances[_to] += _value;
        balances[_from] -= _value;
        if (allowance < MAX_UINT) {
            allowed[_from][msg.sender] -= _value;
        }
        Transfer(_from, _to, _value);
        return true;
    }
}

contract SafeMath {
    function safeMul(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function safeDiv(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a / b;
        return c;
    }

    function safeSub(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        assert(b <= a);
        return a - b;
    }

    function safeAdd(uint a, uint b)
        internal
        pure
        returns (uint256)
    {
        uint c = a + b;
        assert(c >= a);
        return c;
    }

    function max64(uint64 a, uint64 b)
        internal
        pure
        returns (uint256)
    {
        return a >= b ? a : b;
    }

    function min64(uint64 a, uint64 b)
        internal
        pure
        returns (uint256)
    {
        return a < b ? a : b;
    }

    function max256(uint256 a, uint256 b)
        internal
        pure
        returns (uint256)
    {
        return a >= b ? a : b;
    }

    function min256(uint256 a, uint256 b)
        internal
        pure
        returns (uint256)
    {
        return a < b ? a : b;
    }
}

contract EtherToken is UnlimitedAllowanceToken, SafeMath {

    string constant public name = "Ether Token";
    string constant public symbol = "WETH";
    string constant public version = "2.0.0"; // version 1.0.0 deployed on mainnet at 0x2956356cd2a2bf3202f771f50d3d14a367b48070
    uint8 constant public decimals = 18;

    /// @dev Fallback to calling deposit when ether is sent directly to contract.
    function()
        public
        payable
    {
        deposit();
    }

    /// @dev Buys tokens with Ether, exchanging them 1:1.
    function deposit()
        public
        payable
    {
        balances[msg.sender] = safeAdd(balances[msg.sender], msg.value);
        totalSupply = safeAdd(totalSupply, msg.value);
        Transfer(address(0), msg.sender, msg.value);
    }

    /// @dev Sells tokens in exchange for Ether, exchanging them 1:1.
    /// @param _value Number of tokens to sell.
    function withdraw(uint _value)
        public
    {
        balances[msg.sender] = safeSub(balances[msg.sender], _value);
        totalSupply = safeSub(totalSupply, _value);
        require(msg.sender.send(_value));
        Transfer(msg.sender, address(0), _value);
    }
}