pragma solidity ^0.4.16;

interface tokenRecipient { function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external; }

library SafeMath {
  function mul(uint256 _a, uint256 _b) internal pure returns (uint256) {
    if (_a == 0) {
      return 0;
    }
    uint256 c = _a * _b;
    require(c / _a == _b);
    return c;
  }

  function div(uint256 _a, uint256 _b) internal pure returns (uint256) {
    require(_b > 0); 
    uint256 c = _a / _b;
    return c;
  }

  function sub(uint256 _a, uint256 _b) internal pure returns (uint256) {
    require(_b <= _a);
    uint256 c = _a - _b;
    return c;
  }

  function add(uint256 _a, uint256 _b) internal pure returns (uint256) {
    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;
  }
}


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 TokenERC20 {
    // Public variables of the token
    string public name;
    string public symbol;
    uint8 public decimals = 8;
    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    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);


    constructor(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) public {
        totalSupply = initialSupply * 10 ** uint256(decimals);  
        balanceOf[msg.sender] = totalSupply;                
        name = tokenName;                                  
        symbol = tokenSymbol;                              
    }

    function _transfer(address _from, address _to, uint _value) internal {
        // Prevent transfer to 0x0 address. Use burn() instead
        require(_to != 0x0);
        // Check if the sender has enough
        require(balanceOf[_from] >= _value);
        // Check for overflows
        require(balanceOf[_to] + _value > balanceOf[_to]);
        // Save this for an assertion in the future
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        // Subtract from the sender
        balanceOf[_from] = SafeMath.sub(balanceOf[_from],_value);
        // Add the same to the recipient
        balanceOf[_to] = SafeMath.add(balanceOf[_to],_value);
        emit Transfer(_from, _to, _value);
        // Asserts are used to use static analysis to find bugs in your code. They should never fail
        assert(balanceOf[_from] + balanceOf[_to] == previousBalances);
    }

    function transfer(address _to, uint256 _value) public {
        _transfer(msg.sender, _to, _value);
    }

    function transferFrom(address _from, address _to, uint256 _value) public returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] = SafeMath.sub(allowance[_from][msg.sender],_value);
        _transfer(_from, _to, _value);
        return true;
    }
    
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        require((_value == 0) || (allowance[msg.sender][_spender] == 0));
        allowance[msg.sender][_spender] = _value;
        return true;
    }

    function approveAndCall(address _spender, uint256 _value, bytes _extraData)
        public
        returns (bool success) {
        tokenRecipient spender = tokenRecipient(_spender);
        if (approve(_spender, _value)) {
            spender.receiveApproval(msg.sender, _value, this, _extraData);
            return true;
        }
    }

    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
        balanceOf[msg.sender] = SafeMath.sub(balanceOf[msg.sender],_value);            // Subtract from the sender
        totalSupply = SafeMath.sub(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 targeted balance is enough
        require(_value <= allowance[_from][msg.sender]);                                    // Check allowance
        balanceOf[_from] = SafeMath.sub(balanceOf[_from],_value);                           // Subtract from the targeted balance
        allowance[_from][msg.sender] = SafeMath.sub(allowance[_from][msg.sender],_value);   // Subtract from the sender's allowance
        totalSupply = SafeMath.sub(totalSupply,_value);                                     // Update totalSupply
        emit Burn(_from, _value);
        return true;
    }
}


contract ESTT is owned, TokenERC20 {

    mapping (address => bool) public frozenAccount;

    /* This generates a public event on the blockchain that will notify clients */
    event FrozenFunds(address target, bool frozen);

    /* Initializes contract with initial supply tokens to the creator of the contract */
    constructor(
        uint256 initialSupply,
        string tokenName,
        string tokenSymbol
    ) TokenERC20(initialSupply, tokenName, tokenSymbol) public {}

    /* Internal transfer, only can be called by this contract */
    function _transfer(address _from, address _to, uint _value) internal {
        require (_to != 0x0);                                              // Prevent transfer to 0x0 address. Use burn() instead
        require (balanceOf[_from] >= _value);                              // Check if the sender has enough
        require (balanceOf[_to] + _value > balanceOf[_to]);                // Check for overflows
        require(!frozenAccount[_from]);                                    // Check if sender is frozen
        require(!frozenAccount[_to]);                                      // Check if recipient is frozen
        balanceOf[_from] = SafeMath.sub(balanceOf[_from],_value);          // Subtract from the sender
        balanceOf[_to] = SafeMath.add(balanceOf[_to],_value);              // Add the same to the recipient
        emit Transfer(_from, _to, _value);
    }

    function mintToken(address target, uint256 mintedAmount) onlyOwner public {
        balanceOf[target] = SafeMath.add(balanceOf[target],mintedAmount);
        totalSupply = SafeMath.add(totalSupply,mintedAmount); 
        emit Transfer(0, this, mintedAmount);
        emit Transfer(this, target, mintedAmount);
    }

    function freezeAccount(address target, bool freeze) onlyOwner public {
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }

}