/**
 * @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) {
    if (a == 0) {
      return 0;
    }
    uint256 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 c;
  }

  /**
  * @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) {
    uint256 c = a + b;
    assert(c >= a);
    return c;
  }
}

contract owned {
    address public owner;
    constructor() public {
        owner = msg.sender;
    }
    modifier onlyOwner {
        require(msg.sender == owner);
        _;
    }
    function transferOwnership(address _newOwner) onlyOwner public {
        owner = _newOwner;
    }
}

contract GOG is owned {

    using SafeMath for uint256;
    // Public variables of the GOG token
    string public name;
    string public symbol;
    uint8 public decimals = 6;
    // 6 decimals for GOG
    uint256 public totalSupply;
    bool public paused;

    // This creates an array with all balances
    mapping (address => uint256) public balances;
    // this creates an 2 x 2 array with allowances
    mapping (address => mapping (address => uint256)) public allowance;
    
    // This generates a public event on the blockchain that will notify clients transfering of funds
    event Transfer(address indexed from, address indexed to, uint256 value);
    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);
    // This notifies clients about approval of allowances
    event Approval(address indexed owner, address indexed spender, uint256 value);
    event Pause(address indexed owner);
    event Unpause(address indexed owner);

    modifier onlyUnpaused() {
      require(!paused);
      _;
    }

    /**
     * Constrctor function
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor() public {
        totalSupply = 10000000000000000;               // GOG's total supply is 10 billion with 6 decimals
        balances[msg.sender] = totalSupply;          // Give the creator all initial tokens
        name = "GoGlobe Token";                       // Token name is GoGlobe Token
        symbol = "GOG";                               // token symbol is GOG
    }

    /**
     * get the balance of account
     * @param _owner The account address
     */
    function balanceOf(address _owner) view public returns (uint256) {
        return balances[_owner];
    }

    /**
     * @dev Aprove the passed address to spend the specified amount of tokens on behalf of msg.sender.
     * @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 onlyUnpaused returns (bool) {
        require((_value == 0) || (allowance[msg.sender][_spender] == 0));
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }
    
      /**
   * @dev Increase the amount of 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)
   * From MonolithDAO Token.sol
   * @param _spender The address which will spend the funds.
   * @param _addedValue The amount of tokens to increase the allowance by.
   */
  function increaseApproval(address _spender, uint _addedValue) public onlyUnpaused returns (bool) {
    allowance[msg.sender][_spender] = allowance[msg.sender][_spender].add(_addedValue);
    emit Approval(msg.sender, _spender, allowance[msg.sender][_spender]);
    return true;
  }

  /**
   * @dev Decrease the amount of 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 tokens to decrease the allowance by.
   */
  function decreaseApproval(address _spender, uint _subtractedValue) public onlyUnpaused returns (bool) {
    uint oldValue = allowance[msg.sender][_spender];
    if (_subtractedValue > oldValue) {
      allowance[msg.sender][_spender] = 0;
    } else {
      allowance[msg.sender][_spender] = oldValue.sub(_subtractedValue);
    }
    emit Approval(msg.sender, _spender, allowance[msg.sender][_spender]);
    return true;
  }

    /**
     * @dev Function to check the amount of tokens that an owner allowance 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 specifing the amount of tokens still avaible for the spender.
     */
    function allowance(address _owner, address _spender) view public returns (uint256) {
        return allowance[_owner][_spender];
    }

    /**
     * Internal transfer, only can be called by this contract
     */
    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != address(0));

        // Check if the sender has enough
        require(balances[_from] >= _value);
        // Save this for an assertion in the future
        uint previousBalances = balances[_from].add(balances[_to]);
        // Subtract from the sender
        balances[_from] = balances[_from].sub(_value);
        // Add the same to the recipient
        balances[_to] = balances[_to].add(_value);
        emit Transfer(_from, _to, _value);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balances[_from] + balances[_to] == previousBalances);
    }

    /**
     * Transfer tokens
     * Send `_value` tokens to `_to` from your account
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transfer(address _to, uint256 _value) public onlyUnpaused {
        _transfer(msg.sender, _to, _value);
    }

    /**
     * Transfer tokens from other address
     * Send `_value` tokens to `_to` on behalf of `_from`
     * @param _from The address of the sender
     * @param _to The address of the recipient
     * @param _value the amount to send
     */
    function transferFrom(address _from, address _to, uint256 _value) public onlyUnpaused returns (bool) {
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);
        _transfer(_from, _to, _value);
        return true;
    }

    /**
     * Destroy tokens
     * Remove `_value` tokens from the system irreversibly
     * @param _value the amount of money to burn
     */
    function burn(uint256 _value) public onlyUnpaused returns (bool) {
        require(balances[msg.sender] >= _value);   // Check if the sender has enough
        balances[msg.sender] = balances[msg.sender].sub(_value);            // Subtract from the sender
        totalSupply = totalSupply.sub(_value);                      // Updates totalSupply
        emit Burn(msg.sender, _value);
        return true;
    }

    /**
     * Destroy tokens from other account
     * Remove `_value` tokens from the system irreversibly on behalf of `_from`.
     * @param _from the address of the sender
     * @param _value the amount of money to burn
     */
    function burnFrom(address _from, uint256 _value) public onlyUnpaused returns (bool) {
        require(balances[_from] >= _value);                // Check if the targeted balance is enough
        require(_value <= allowance[_from][msg.sender]);    // Check allowance
        balances[_from] = balances[_from].sub(_value);                         // Subtract from the targeted balance
        allowance[_from][msg.sender] = allowance[_from][msg.sender].sub(_value);             // Subtract from the sender's allowance
        totalSupply = totalSupply.sub(_value);                              // Update totalSupply
        emit Burn(_from, _value);
        return true;
    }

    function pause() public onlyOwner returns (bool) {
      paused = true;
      return true;
    }

    function unPause() public onlyOwner returns (bool) {
      paused = false;
      return true;
    }
}