pragma solidity ^0.4.26;

/**
 * Math operations with safety checks
 */
contract SafeMath {
  function safeMul(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a * b;
    assert(a == 0 || c / a == b);
    return c;
  }

  function safeDiv(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b > 0);
    uint256 c = a / b;
    assert(a == b * c + a % b);
    return c;
  }

  function safeSub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  function safeAdd(uint256 a, uint256 b) internal pure returns (uint256) {
    uint256 c = a + b;
    assert(c>=a && c>=b);
    return c;
  }

}
contract FOSS 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 */
    constructor(
        uint256 initialSupply,
        string tokenName,
        uint8 decimalUnits,
        string tokenSymbol
        ) public{
        balanceOf[msg.sender] = initialSupply;              // Give the creator all initial tokens
        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 returns (bool success) {
        require(_to != 0x0);                                // Prevent transfer to 0x0 address. Use burn() instead
        require(_value > 0);
        require(balanceOf[msg.sender] >= _value);           // Check if the sender has enough
        require(balanceOf[_to] + _value >= balanceOf[_to]); // 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
        return true;
    }

    /* Allow another contract to spend some tokens in your behalf */
    function approve(address _spender, uint256 _value) public returns (bool success){
		    require(_value > 0);
        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);                                // Prevent transfer to 0x0 address. Use burn() instead
        require(_value > 0);
        require(balanceOf[_from] >= _value);                // Check if the sender has enough
        require(balanceOf[_to] + _value >= balanceOf[_to]); // Check for overflows
        require(_value <= allowance[_from][msg.sender]);    // 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);           // Check if the sender has enough
        require(_value > 0);
        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 burnFrom(address _from, uint256 _value) public returns (bool success) {
        require(balanceOf[_from] >= _value);                // Check if the sender has enough
        require(_value > 0);
        require(_value <= allowance[_from][msg.sender]);    // Check allowance
        balanceOf[_from] -= _value;                         // Subtract from the sender
        totalSupply -= _value;                              // Updates totalSupply
        emit Burn(_from, _value);
        return true;
    }

    function freeze(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);            // Check if the sender has enough
        require(_value > 0);
        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);            // Check if the sender has enough
        require(_value > 0);
        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;
    }

    function withdrawEther(uint256 amount) public {
      require(msg.sender == owner);
      owner.transfer(amount);
    }

    function transferOwnership(address newOwner) public returns (bool success) {
      require(msg.sender == owner );
      owner = newOwner;
      return true;
    }

    function () public payable {
      revert();
    }
}