pragma solidity ^0.4.24;

interface tokenRecipient 
{ 
	function receiveApproval(address _from, uint256 _value, address _token, bytes _extraData) external;
}

contract owned 
{
	
	address public owner;

	constructor() public {
		owner = msg.sender;
	}

	modifier onlyOwner {
		require(msg.sender == owner);
		_;
	}

	function transferOwnership(address newOwner) public onlyOwner {
		owner = newOwner;
	}
}


contract TokenERC20 
{	
    string public name;
    string public symbol;
    uint8 public decimals = 2;

    uint256 public totalSupply;

    // This creates an array with all balances
    mapping (address => uint256) public balanceOf;
    mapping (address => mapping (address => uint256)) public allowance;


    event Transfer(address indexed from, address indexed to, uint256 value);
    
    // This generates a public event on the blockchain that will notify clients
    event Approval(address indexed _owner, address indexed _spender, uint256 _value);

    // This notifies clients about the amount burnt
    event Burn(address indexed from, uint256 value);

	
    /**
     * Constrctor function
     *
     * Initializes contract with initial supply tokens to the creator of the contract
     */
    constructor(uint256 initialSupply, string tokenName, string tokenSymbol, uint8 decimalUnits) public	{
        totalSupply = initialSupply * 10 ** uint256(decimals);  // Update total supply with the decimal amount
        balanceOf[msg.sender] = totalSupply;                // Give the creator all initial tokens
        name = tokenName;                                   // Set the name for display purposes
        symbol = tokenSymbol;                               // Set the symbol for display purposes
		decimals = decimalUnits;							// Set the decimal units of token
    }

    /**
     * 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 != 0x0);
         /* Check if sender has balance and for overflows */
        require(balanceOf[_from] >= _value && balanceOf[_to] + _value >= balanceOf[_to], "Not enough 7s provided");
		// Save this for an assertion in the future
        uint previousBalances = balanceOf[_from] + balanceOf[_to];
        // Subtract from the sender
        balanceOf[_from] -= _value;
        // Add the same to the recipient
        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);
    }

    /**
     * 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 returns (bool success) {
        _transfer(msg.sender, _to, _value);
        return true;
    }

    /**
     * Transfer tokens from other address
     *
     * Send `_value` tokens to `_to` in 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 returns (bool success) {
        require(_value <= allowance[_from][msg.sender]);     // Check allowance
        allowance[_from][msg.sender] -= _value;
        _transfer(_from, _to, _value);
        return true;
    }

    /**
     * Set allowance for other address
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     */
    function approve(address _spender, uint256 _value) public
        returns (bool success) {
        allowance[msg.sender][_spender] = _value;
        emit Approval(msg.sender, _spender, _value);
        return true;
    }

    /**
     * Set allowance for other address and notify
     *
     * Allows `_spender` to spend no more than `_value` tokens in your behalf, and then ping the 
	 * contract about it
     *
     * @param _spender The address authorized to spend
     * @param _value the max amount they can spend
     * @param _extraData some extra information to send to the approved contract
     */
    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;
        }
    }

    /**
     * Destroy tokens
     *
     * Remove `_value` tokens from the system irreversibly
     *
     * @param _value the amount of money to burn
     */
    function burn(uint256 _value) public returns (bool success) {
        require(balanceOf[msg.sender] >= _value);   // Check if the sender has enough
        balanceOf[msg.sender] -= _value;            // Subtract from the sender
        totalSupply -= _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 returns (bool success) {
        require(balanceOf[_from] >= _value);                // Check if the targeted balance is enough
        require(_value <= allowance[_from][msg.sender]);    // Check allowance
        balanceOf[_from] -= _value;                         // Subtract from the targeted balance
        allowance[_from][msg.sender] -= _value;             // Subtract from the sender's allowance
        totalSupply -= _value;                              // Update totalSupply
        emit Burn(_from, _value);
        return true;
    }
}


contract SEVENS is owned, TokenERC20{

	mapping (address => bool) public frozenAccount;
   
	event FrozenFunds(address target, bool frozen);
	
	
	constructor(uint256 initialSupply, string tokenName, string tokenSymbol, uint8 decimalUnits)
		TokenERC20(initialSupply, tokenName, tokenSymbol, decimalUnits) 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 && balanceOf[_to] + _value >= balanceOf[_to], "Not enough 7s provided");
        require(!frozenAccount[_from], "7s account is frozen"); // Check if sender is frozen
        require(!frozenAccount[_to], "7s account is frozen");  	// Check if recipient is frozen
        balanceOf[_from] -= _value;                         	// Subtract from the sender
        balanceOf[_to] += _value;                           	// Add the same to the recipient
        emit Transfer(_from, _to, _value);
    }
	
	
	/*create new tokens in case of account freeze or token burn e.g. on hacks*/
	function mintToken(address target, uint256 mintedAmount) public onlyOwner {
        balanceOf[target] += mintedAmount;
        totalSupply += mintedAmount;
        emit Transfer(0, owner, mintedAmount);
        emit Transfer(owner, target, mintedAmount);
    }

		
	function freezeAccount(address target, bool freeze) public onlyOwner {
        frozenAccount[target] = freeze;
        emit FrozenFunds(target, freeze);
    }
    
}