pragma solidity ^0.4.25;

/**
 * @title SafeMath
 * @dev Math operations with safety checks that revert on error
 */
contract SafeMath {
  function safeMul(uint256 a, uint256 b) pure internal returns (uint256) {
    //uint256 c = a * b;
    //require(a == 0 || c / a == b);
    //return c;
    
    // 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;
  }

  function safeDiv(uint256 a, uint256 b) pure internal returns (uint256) {
    //require(b > 0);
    //uint256 c = a / b;
    //require(a == b * c + a % b);
    //return c;
    
    require(b > 0); // Solidity only automatically asserts 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;
  }

  function safeSub(uint256 a, uint256 b) pure internal returns (uint256) {
    //require(b <= a);
    //return a - b;
    require(b <= a);
    uint256 c = a - b;

    return c;
  }

  function safeAdd(uint256 a, uint256 b) pure internal returns (uint256) {
    //uint256 c = a + b;
    //require(c>=a && c>=b);
    //return c;
    
    uint256 c = a + b;
    require(c >= a);

    return c;
  }
  
  function mod(uint256 a, uint256 b) internal pure returns (uint256) {
    require(b != 0);
    return a % b;
  }

  /*function assert(bool assertion) internal {
    if (!assertion) {
      throw;
    }
  }*/
}
/**
 * Smart Token Contract modified and developed by Marco Sanna,
 * blockchain developer of Namacoin ICO Project.
 */
contract Namacoin is SafeMath{
    string public name;
    string public symbol;
    uint8 public decimals;
    uint256 public totalSupply;
	address public owner;

    /* This creates an array with all balances */
    mapping (address => uint256) public balanceOf;
	mapping (address => uint256) public freezeOf;
    mapping (address => mapping (address => uint256)) public allowance;

    /* This generates a public event on the blockchain that will notify clients */
    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 the amount frozen */
    event Freeze(address indexed from, uint256 value);
	
	/* This notifies clients about the amount unfrozen */
    event Unfreeze(address indexed from, uint256 value);
	
	/* This notifies clients that owner withdraw the ether */
	event Withdraw(address indexed from, uint256 value);
	
	/* This notifies the first creation of the contract */
	event Creation(address indexed owner, uint256 value);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    constructor(
        uint256 initialSupply,
        string tokenName,
        uint8 decimalUnits,
        string tokenSymbol
        ) public {
        balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens
        emit Creation(msg.sender, initialSupply);                // Notify anyone that the Tokes was create 
        totalSupply = initialSupply;                        // Update total supply
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
        decimals = decimalUnits;                            // Amount of decimals for display purposes
		owner = msg.sender;
    }

    /* Send coins */
    function transfer(address _to, uint256 _value) public {
        require(_to != 0x0);
        require(_value > 0);
        require(balanceOf[msg.sender] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        
        //if (_to == 0x0) throw;                               // Prevent transfer to 0x0 address. Use burn() instead
		//if (_value <= 0) throw; 
        //if (balanceOf[msg.sender] < _value) throw;           // Check if the sender has enough
        //if (balanceOf[_to] + _value < balanceOf[_to]) throw; // Check for overflows
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                     // Subtract from the sender
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                            // Add the same to the recipient
        emit Transfer(msg.sender, _to, _value);                   // Notify anyone listening that this transfer took place
    }

    /* Allow another contract to spend some tokens in your behalf */
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
            
        require(_value > 0);
		//if (_value <= 0) throw; 
        allowance[msg.sender][_spender] = _value;
        return true;
    }
       

    /* A contract attempts to get the coins */
    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        
        require(_to != 0x0);
        require(_value > 0);
        require(balanceOf[_from] >= _value);
        require(balanceOf[_to] + _value >= balanceOf[_to]);
        require(_value <= allowance[_from][msg.sender]);
        
        //if (_to == 0x0) throw;                                // Prevent transfer to 0x0 address. Use burn() instead
		//if (_value <= 0) throw; 
        //if (balanceOf[_from] < _value) throw;                 // Check if the sender has enough
        //if (balanceOf[_to] + _value < balanceOf[_to]) throw;  // Check for overflows
        //if (_value > allowance[_from][msg.sender]) throw;     // Check allowance
        balanceOf[_from] = SafeMath.safeSub(balanceOf[_from], _value);                           // Subtract from the sender
        balanceOf[_to] = SafeMath.safeAdd(balanceOf[_to], _value);                             // Add the same to the recipient
        allowance[_from][msg.sender] = SafeMath.safeSub(allowance[_from][msg.sender], _value);
        emit Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);
        require(_value > 0);
        //if (balanceOf[msg.sender] < _value) throw;            // Check if the sender has enough
		//if (_value <= 0) throw; 
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                      // Subtract from the sender
        totalSupply = SafeMath.safeSub(totalSupply,_value);                                // Updates totalSupply
        emit Burn(msg.sender, _value);
        return true;
    }
	
	function freeze(uint256 _value) public returns (bool success) {
	    require(balanceOf[msg.sender] >= _value);
	    require(_value > 0);
        //if (balanceOf[msg.sender] < _value) throw;            // Check if the sender has enough
		//if (_value <= 0) throw; 
        balanceOf[msg.sender] = SafeMath.safeSub(balanceOf[msg.sender], _value);                      // Subtract from the sender
        freezeOf[msg.sender] = SafeMath.safeAdd(freezeOf[msg.sender], _value);                                // Updates totalSupply
        emit Freeze(msg.sender, _value);
        return true;
    }
	
	function unfreeze(uint256 _value) public returns (bool success) {
	    require(freezeOf[msg.sender] >= _value);
	    require(_value > 0);
        //if (freezeOf[msg.sender] < _value) throw;            // Check if the sender has enough
		//if (_value <= 0) throw; 
        freezeOf[msg.sender] = SafeMath.safeSub(freezeOf[msg.sender], _value);                      // Subtract from the sender
		balanceOf[msg.sender] = SafeMath.safeAdd(balanceOf[msg.sender], _value);
        emit Unfreeze(msg.sender, _value);
        return true;
    }
	
	// transfer balance to owner
	function withdrawEther(uint256 amount) public returns (bool success){
	    require(msg.sender == owner);
	    //require(amount > 0);
		//if(msg.sender != owner)throw;
		owner.transfer(amount);
		emit Withdraw(msg.sender, amount);
		return true;
	}
	
	// can accept ether
	function() public payable {
    }
}