pragma solidity ^0.4.8;

/**
 * Math operations with safety checks
 */
contract SafeMath {
    function safeMul(uint256 a, uint256 b) internal returns (uint256) {
        uint256 c = a * b;
        assert(a == 0 || c / a == b);
        return c;
    }

    function safeDiv(uint256 a, uint256 b) internal returns (uint256) {
        assert(b > 0);
        uint256 c = a / b;
        assert(a == b * c + a % b);
        return c;
    }

    function safeSub(uint256 a, uint256 b) internal returns (uint256) {
        assert(b <= a);
        return a - b;
    }

    function safeAdd(uint256 a, uint256 b) internal returns (uint256) {
        uint256 c = a + b;
        assert(c>=a && c>=b);
        return c;
    }

    function assert(bool assertion) internal {
        if (!assertion) {
            throw;
        }
    }
}
contract VDN 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);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    function VDN(
        uint256 _totalSupply,
        string _name,
        uint8 _decimals,
        string _symbol
    ) {
        balanceOf[msg.sender] = _totalSupply;              // Give the creator all initial tokens
        totalSupply = _totalSupply;                        // Update total supply
        name = _name;                                   // Set the name for display purposes
        symbol = _symbol;                               // Set the symbol for display purposes
        decimals = _decimals;                            // Amount of decimals for display purposes
        owner = msg.sender;
    }

    /* Send coins */
    function transfer(address _to, uint256 _value) {
        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
        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)
    returns (bool success) {
        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) returns (bool success) {
        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);
        Transfer(_from, _to, _value);
        return true;
    }

    function burn(uint256 _value) returns (bool success) {
        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
        Burn(msg.sender, _value);
        return true;
    }

    function freeze(uint256 _value) returns (bool success) {
        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
        Freeze(msg.sender, _value);
        return true;
    }

    function unfreeze(uint256 _value) returns (bool success) {
        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);
        Unfreeze(msg.sender, _value);
        return true;
    }

    // transfer balance to owner
    function withdrawEther(uint256 amount) {
        if(msg.sender != owner)throw;
        owner.transfer(amount);
    }

    // can accept ether
    function() payable {
    }
}