//////// This is the official eUSD smart contract.
//// The eUSD token contract utilizes the eFIAT protocol - a not-for-profit,
//// fully transparent, publicly auditable protocol designed to migrate fiat
//// currencies to the Ethereum blockchain without banks, escrow accounts or reserves.

//// The eFIAT protocol relies on Proof of Burn, meaning any eUSD can only
//// be created by burning Ether at market value. Because Ether is denominated also
//// in USD value, the burning of Ether can be regarded as burning of US Dollars,
//// where Ether serves only as the medium of value transfer and verifiable proof
//// that actual value has ben permanently migrated and not replicated. This means
//// eUSD can never be used to redeem any Ether burned in the eUSD creation process!

// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

pragma solidity ^0.4.24;


/**
 * @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 OwnershipRenounced(address indexed previousOwner);
  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 relinquish control of the contract.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(owner);
    owner = address(0);
  }

  /**
   * @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 {
    _transferOwnership(_newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
}
/**
 * @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 c) {
    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    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 a / b;
  }

  /**
  * @dev Subtracts 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 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}


contract ERC20 {
    function totalSupply() public view returns (uint256);
    function balanceOf(address who) public view returns (uint256);
    function transfer(address to, uint256 value) public returns (bool);
    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);
    event Transfer(address indexed from, address indexed to, uint256 value);
}

contract Oracle {
    function callOracle(address _src, uint256 _amount) public;
}

/**
 * @title eUSD
 */
contract eUSD is Ownable, ERC20 {
    using SafeMath for uint256;

    string public name = "ETHUSD";
    string public symbol = "EUSD";
    uint8 public decimals = 18;

    uint256 totalSupply_;

    mapping(address => uint256) balances;
    mapping(address => mapping (address => uint256)) internal allowed;

    Oracle oracle;

    event Mint(address indexed to, uint256 amount);

    /**
    * @dev fallback function which receives ether and sends it to oracle
    **/
    function () payable public {
        require(address(oracle) != address(0));
        require(msg.value >= 20 finney); //0.02 ETH
        address(oracle).transfer(address(this).balance);
        oracle.callOracle(msg.sender, msg.value);
    }

    /**
    * @dev set new oracle address
    * @param _oracle The new oracle contract address.
    */
    function setOracle(address _oracle) public onlyOwner {
        oracle = Oracle(_oracle);
    }

    /**
    * @dev callback function - oracle sends amount of eUSD tokens to mint
    * @param _src Mint eUSD tokens to address.
    * @param _amount Amount of minted eUSD tokens
    */
    function calculatedTokens(address _src, uint256 _amount) public {
        require(msg.sender == address(oracle));
        mint(_src, _amount);
    }

    /**
    * @dev transfer eUSD token for a specified address
    * @param _to The address to transfer to.
    * @param _value The amount of eUSD tokens to be spent.
    */
    function transfer(address _to, uint256 _value) public returns (bool) {
        require(_to != address(0));
        require(_value <= balances[msg.sender]);

        balances[msg.sender] = balances[msg.sender].sub(_value);
        balances[_to] = balances[_to].add(_value);
        emit Transfer(msg.sender, _to, _value);
        return true;
    }

    /**
   * @dev Transfer eUSD 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 eUSD 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 eUSD 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.
     * @param _spender The address which will spend the funds.
     * @param _value The amount of eUSD 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 Increase the amount of eUSD 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)
     * @param _spender The address which will spend the funds.
     * @param _addedValue The amount of eUSD 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 eUSD 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 eUSD 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;
    }

    /**
   * @dev Function to mint eUSD tokens
   * @param _to The address that will receive minted eUSD tokens.
   * @param _amount The amount of eUSD tokens to mint.
   */
    function mint(address _to, uint256 _amount) private returns (bool){
        totalSupply_ = totalSupply_.add(_amount);
        balances[_to] = balances[_to].add(_amount);
        emit Mint(_to, _amount);
        emit Transfer(address(0), _to, _amount);
        return true;
    }

    /**
    * @dev Gets the balance of the specified address.
    * @param _owner The address to query the the balance of.
    */
    function balanceOf(address _owner) public view returns (uint256) {
        return balances[_owner];
    }

    /**
    * @dev total number of tokens in existence
    */
    function totalSupply() public view returns (uint256) {
        return totalSupply_;
    }

    /**
     * @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.
     */
    function allowance(address _owner, address _spender) public view returns (uint256) {
        return allowed[_owner][_spender];
    }
}