pragma solidity ^0.5.7;



/**
 * @title Standard ERC20 token
 *
 * @dev Implementation of the basic standard token.
 * https://eips.ethereum.org/EIPS/eip-20
 * Originally based on code by FirstBlood:
 * https://github.com/Firstbloodio/token/blob/master/smart_contract/FirstBloodToken.sol
 *
 * This implementation emits additional Approval events, allowing applications to reconstruct the allowance status for
 * all accounts just by listening to said events. Note that this isn't required by the specification, and other
 * compliant implementations may not do it.
 */



 contract Ownable {
     address private _owner;

     event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

     /**
      * @dev The Ownable constructor sets the original `owner` of the contract to the sender
      * account.
      */
     constructor () internal {
         _owner = msg.sender;
         emit OwnershipTransferred(address(0), _owner);
     }

     /**
      * @return the address of the owner.
      */
     function owner() public view returns (address) {
         return _owner;
     }

     /**
      * @dev Throws if called by any account other than the owner.
      */
     modifier onlyOwner() {
         require(isOwner());
         _;
     }

     /**
      * @return true if `msg.sender` is the owner of the contract.
      */
     function isOwner() public view returns (bool) {
         return msg.sender == _owner;
     }

     /**
      * @dev Allows the current owner to relinquish control of the contract.
      * It will not be possible to call the functions with the `onlyOwner`
      * modifier anymore.
      * @notice Renouncing ownership will leave the contract without an owner,
      * thereby removing any functionality that is only available to the owner.
      */
     function renounceOwnership() public onlyOwner {
         emit OwnershipTransferred(_owner, address(0));
         _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;
     }
 }



 contract Pausable is Ownable {
   event Pause();
   event Unpause();

   bool public paused = false;


   /**
    * @dev Modifier to make a function callable only when the contract is not paused.
    */
   modifier whenNotPaused() {
     require(!paused);
     _;
   }

   /**
    * @dev Modifier to make a function callable only when the contract is paused.
    */
   modifier whenPaused() {
     require(paused);
     _;
   }

   /**
    * @dev called by the owner to pause, triggers stopped state
    */
   function pause() onlyOwner whenNotPaused public {
     paused = true;
     emit Pause();
   }

   /**
    * @dev called by the owner to unpause, returns to normal state
    */
   function unpause() onlyOwner whenPaused public {
     paused = false;
     emit Unpause();
   }
 }


contract IERC20 {
    function transfer(address to, uint256 value) external returns (bool);

    function approve(address spender, uint256 value) external returns (bool);

    function transferFrom(address from, address to, uint256 value) external returns (bool);

    function totalSupply() external view returns (uint256);

    function balanceOf(address who) external view returns (uint256);

    function allowance(address owner, address spender) external view returns (uint256);

    event Transfer(address indexed from, address indexed to, uint256 value);

    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract ERC20 is IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) public _balances;

    mapping (address => mapping (address => uint256)) private _allowed;

    uint256 public totalSupply;


    /**
     * @dev Gets the balance of the specified address.
     * @param owner The address to query the balance of.
     * @return A uint256 representing the amount owned by the passed address.
     */
    function balanceOf(address owner) public view returns (uint256) {
        return _balances[owner];
    }

    /**
     * @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.
     * @return A uint256 specifying the amount of tokens still available for the spender.
     */
    function allowance(address owner, address spender) public view returns (uint256) {
        return _allowed[owner][spender];
    }

    /**
     * @dev Transfer token to a specified address
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
    function transfer(address to, uint256 value) public returns (bool) {
        _transfer(msg.sender, to, value);
        return true;
    }

    /**
     * @dev Approve the passed address to spend the specified amount of 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:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     * @param spender The address which will spend the funds.
     * @param value The amount of tokens to be spent.
     */
    function approve(address spender, uint256 value) public returns (bool) {
        _approve(msg.sender, spender, value);
        return true;
    }

    /**
     * @dev Transfer tokens from one address to another.
     * Note that while this function emits an Approval event, this is not required as per the specification,
     * and other compliant implementations may not emit the event.
     * @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 tokens to be transferred
     */
    function transferFrom(address from, address to, uint256 value) public returns (bool) {
        _transfer(from, to, value);
        _approve(from, msg.sender, _allowed[from][msg.sender].sub(value));
        return true;
    }

    /**
     * @dev Increase the amount of tokens that an owner allowed to a spender.
     * approve should be called when _allowed[msg.sender][spender] == 0. To increment
     * allowed value is better to use this function to avoid 2 calls (and wait until
     * the first transaction is mined)
     * From MonolithDAO Token.sol
     * Emits an Approval event.
     * @param spender The address which will spend the funds.
     * @param addedValue The amount of tokens to increase the allowance by.
     */
    function increaseAllowance(address spender, uint256 addedValue) public returns (bool) {
        _approve(msg.sender, spender, _allowed[msg.sender][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Decrease the amount of tokens that an owner allowed to a spender.
     * approve should be called when _allowed[msg.sender][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
     * Emits an Approval event.
     * @param spender The address which will spend the funds.
     * @param subtractedValue The amount of tokens to decrease the allowance by.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public returns (bool) {
        _approve(msg.sender, spender, _allowed[msg.sender][spender].sub(subtractedValue));
        return true;
    }

    /**
     * @dev Transfer token for a specified addresses
     * @param from The address to transfer from.
     * @param to The address to transfer to.
     * @param value The amount to be transferred.
     */
    function _transfer(address from, address to, uint256 value) internal {
        require(to != address(0));

        _balances[from] = _balances[from].sub(value);
        _balances[to] = _balances[to].add(value);
        emit Transfer(from, to, value);
    }

    /**
     * @dev Internal function that mints an amount of the token and assigns it to
     * an account. This encapsulates the modification of balances such that the
     * proper events are emitted.
     * @param account The account that will receive the created tokens.
     * @param value The amount that will be created.
     */
    function _mint(address account, uint256 value) internal {
        require(account != address(0));

        totalSupply = totalSupply.add(value);
        _balances[account] = _balances[account].add(value);
        emit Transfer(address(0), account, value);
    }

    /**
     * @dev Internal function that burns an amount of the token of a given
     * account.
     * @param account The account whose tokens will be burnt.
     * @param value The amount that will be burnt.
     */
    function _burn(address account, uint256 value) internal {
        require(account != address(0));

        totalSupply = totalSupply.sub(value);
        _balances[account] = _balances[account].sub(value);
        emit Transfer(account, address(0), value);
    }

    /**
     * @dev Approve an address to spend another addresses' tokens.
     * @param owner The address that owns the tokens.
     * @param spender The address that will spend the tokens.
     * @param value The number of tokens that can be spent.
     */
    function _approve(address owner, address spender, uint256 value) internal {
        require(spender != address(0));
        require(owner != address(0));

        _allowed[owner][spender] = value;
        emit Approval(owner, spender, value);
    }

    /**
     * @dev Internal function that burns an amount of the token of a given
     * account, deducting from the sender's allowance for said account. Uses the
     * internal burn function.
     * Emits an Approval event (reflecting the reduced allowance).
     * @param account The account whose tokens will be burnt.
     * @param value The amount that will be burnt.
     */
    function _burnFrom(address account, uint256 value) internal {
        _burn(account, value);
        _approve(account, msg.sender, _allowed[account][msg.sender].sub(value));
    }

}




contract ERC20Pausable is ERC20, Pausable {
    function transfer(address to, uint256 value) public whenNotPaused returns (bool) {
        return super.transfer(to, value);
    }

    function transferFrom(address from, address to, uint256 value) public whenNotPaused returns (bool) {
        return super.transferFrom(from, to, value);
    }

    function approve(address spender, uint256 value) public whenNotPaused returns (bool) {
        return super.approve(spender, value);
    }

    function increaseAllowance(address spender, uint addedValue) public whenNotPaused returns (bool success) {
        return super.increaseAllowance(spender, addedValue);
    }

    function decreaseAllowance(address spender, uint subtractedValue) public whenNotPaused returns (bool success) {
        return super.decreaseAllowance(spender, subtractedValue);
    }
}






contract SRVcontract is Pausable {
  using SafeMath for uint256;

  mapping(address => uint256) _balances;

  mapping (address => mapping (address => uint256)) internal allowed;

  // the token being sold
  SRVToken public token;
  uint256 constant public tokenDecimals = 18;

  // totalSupply
  uint256 public totalSupply = 1500000000 * (10 ** uint256(tokenDecimals));

  // to send tokens to
  address constant public walletOriginal = 0x4DaD1DD22a3fD0dDBf873f8846925ceC4661f563;



  constructor () public {

    token = createTokenContract();
    token.unpause();
    token.transfer(walletOriginal, totalSupply);



  }



  //
  // Token related operations
  //

  // creates the token to be sold.
  // override this method to have crowdsale of a specific mintable token.
  function createTokenContract() internal returns (SRVToken) {
    return new SRVToken();
  }

  // enable token transferability
  function enableTokenTransferability() external onlyOwner {
    token.unpause();
  }

  // disable token transferability
  function disableTokenTransferability() external onlyOwner {
    token.pause();
  }


}





contract SRVToken is ERC20Pausable {
  string constant public name = "SRV";
  string constant public symbol = "SRV";
  uint256 constant public decimals = 18;
  uint256 constant TOKEN_UNIT = 10 ** uint256(decimals);
  uint256 constant INITIAL_SUPPLY = 1500000000 * TOKEN_UNIT;


  constructor () public {
    // Set untransferable by default to the token
    paused = true;
    // asign all tokens to the contract creator
    totalSupply = INITIAL_SUPPLY;

    _balances[msg.sender] = INITIAL_SUPPLY;
  }

}



library SafeMath {
    /**
    * @dev Multiplies two unsigned integers, reverts on overflow.
    */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring '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;
        }

        uint256 c = a * b;
        require(c / a == b);

        return c;
    }

    /**
    * @dev Integer division of two unsigned integers truncating the quotient, reverts on division by zero.
    */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
    * @dev Subtracts two unsigned integers, reverts on overflow (i.e. if subtrahend is greater than minuend).
    */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }

    /**
    * @dev Adds two unsigned integers, reverts on overflow.
    */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }

    /**
    * @dev Divides two unsigned integers and returns the remainder (unsigned integer modulo),
    * reverts when dividing by zero.
    */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}