pragma solidity ^0.6.9;

interface Callable {
	function tokenCallback(address _from, uint256 _tokens, bytes calldata _data) external returns (bool);
}

contract StakingToken {
	uint256 constant private FLOAT_SCALAR = 2**64;
	uint256 constant private INITIAL_SUPPLY = 2e27;   // 2 Billion Total/Max Supply
	uint256 constant private BURN_RATE = 1;            // 1% per tx
	uint256 constant private SUPPLY_FLOOR = 1;         // 1% of 2B = 20M
	uint256 constant private MIN_FREEZE_AMOUNT = 1e20; // 100 minimum
	string constant public name = "UniversalCoin X";
	string constant public symbol = "UVCX";
	uint8 constant public decimals = 18;

	struct User {
		bool whitelisted;
		uint256 balance;
		uint256 frozen;
		mapping(address => uint256) allowance;
		int256 scaledPayout;
	}

	struct Info {
		uint256 totalSupply;
		uint256 totalFrozen;
		mapping(address => User) users;
		uint256 scaledPayoutPerToken;
		address admin;
	}

	Info private info;

	event Transfer(address indexed from, address indexed to, uint256 tokens);
	event Approval(address indexed owner, address indexed spender, uint256 tokens);
	event Whitelist(address indexed user, bool status);
	event Freeze(address indexed owner, uint256 tokens);
	event Unfreeze(address indexed owner, uint256 tokens);
	event Collect(address indexed owner, uint256 tokens);
	event Burn(uint256 tokens);


	constructor() public {
		info.admin = msg.sender;
		info.totalSupply = INITIAL_SUPPLY;
		info.users[msg.sender].balance = INITIAL_SUPPLY;
		emit Transfer(address(0x0), msg.sender, INITIAL_SUPPLY);
		whitelist(msg.sender, true);
	}

	function freeze(uint256 _tokens) external {_freeze(_tokens);}
	function unfreeze(uint256 _tokens) external {_unfreeze(_tokens);}

	function collect() external returns (uint256) {
		uint256 _dividends = dividendsOf(msg.sender);
		require(_dividends >= 0, 'Cannot collect -ve dividends');
		info.users[msg.sender].scaledPayout += int256(_dividends * FLOAT_SCALAR);
		info.users[msg.sender].balance += _dividends;
		emit Transfer(address(this), msg.sender, _dividends);
		emit Collect(msg.sender, _dividends);
		return _dividends;
	}

	function burn(uint256 _tokens) external {
		require(balanceOf(msg.sender) >= _tokens, 'Trying to burn more than you have');
		info.users[msg.sender].balance -= _tokens;
		uint256 _burnedAmount = _tokens;
		if (info.totalFrozen > 0) {
			_burnedAmount /= 2; //50% of burn redirected amongst frozen holders
			info.scaledPayoutPerToken += _burnedAmount * FLOAT_SCALAR / info.totalFrozen;
			emit Transfer(msg.sender, address(this), _burnedAmount);
		}
		info.totalSupply -= _burnedAmount;
		emit Transfer(msg.sender, address(0x0), _burnedAmount);
		emit Burn(_burnedAmount);
	}

	function distribute(uint256 _tokens) external {
		require(info.totalFrozen > 0, 'Must have more than 0 frozen to distribute');
		require(balanceOf(msg.sender) >= _tokens, 'Must have enough tokens to distribute');
		info.users[msg.sender].balance -= _tokens;
		info.scaledPayoutPerToken += _tokens * FLOAT_SCALAR / info.totalFrozen;
		emit Transfer(msg.sender, address(this), _tokens);
	}

	function transfer(address _to, uint256 _tokens) external returns (bool) {
		_transfer(msg.sender, _to, _tokens);
		return true;
	}

	function approve(address _spender, uint256 _tokens) external returns (bool) {
		info.users[msg.sender].allowance[_spender] = _tokens;
		emit Approval(msg.sender, _spender, _tokens);
		return true;
	}

	function transferFrom(address _from, address _to, uint256 _tokens) external returns (bool) {
		require(info.users[_from].allowance[msg.sender] >= _tokens, 'Need to have enough allowance to send');
		info.users[_from].allowance[msg.sender] -= _tokens;
		_transfer(_from, _to, _tokens);
		return true;
	}

	function transferAndCall(address _to, uint256 _tokens, bytes calldata _data) external returns (bool) {
		uint256 _transferred = _transfer(msg.sender, _to, _tokens);
		uint32 _size;
		assembly {_size := extcodesize(_to)}
		if (_size > 0) {require(Callable(_to).tokenCallback(msg.sender, _transferred, _data), 'More than 0 data in the transfer');}
		return true;
	}

	function bulkTransfer(address[] calldata _receivers, uint256[] calldata _amounts) external {
		require(_receivers.length == _amounts.length, 'Need equal amounts of receivers and values');
		for (uint256 i = 0; i < _receivers.length; i++) {_transfer(msg.sender, _receivers[i], _amounts[i]);}
	}

	function whitelist(address _user, bool _status) public {
		require(msg.sender == info.admin, 'Only admins can whitelist');
		info.users[_user].whitelisted = _status;
		emit Whitelist(_user, _status);
	}

	function totalSupply() public view returns (uint256) {return info.totalSupply;}
	function totalFrozen() public view returns (uint256) {return info.totalFrozen;}
	function balanceOf(address _user) public view returns (uint256) {return info.users[_user].balance - frozenOf(_user);}
	function frozenOf(address _user) public view returns (uint256) {return info.users[_user].frozen;}
	function dividendsOf(address _user) public view returns (uint256) {return uint256(int256(info.scaledPayoutPerToken * info.users[_user].frozen) - info.users[_user].scaledPayout) / FLOAT_SCALAR;}
	function allowance(address _user, address _spender) public view returns (uint256) {return info.users[_user].allowance[_spender];}
	function isWhitelisted(address _user) public view returns (bool) {return info.users[_user].whitelisted;}
	function allInfoFor(address _user) public view returns (uint256 totalTokenSupply, uint256 totalTokensFrozen, uint256 userBalance, uint256 userFrozen, uint256 userDividends) {return (totalSupply(), totalFrozen(), balanceOf(_user), frozenOf(_user), dividendsOf(_user));}

	function _transfer(address _from, address _to, uint256 _tokens) internal returns (uint256) {
		require(balanceOf(_from) >= _tokens, 'Trying to send more than you have');
		info.users[_from].balance -= _tokens;
		uint256 _burnedAmount = _tokens * BURN_RATE / 100;
		if (totalSupply() - _burnedAmount < INITIAL_SUPPLY * SUPPLY_FLOOR / 100 || isWhitelisted(_from)) {_burnedAmount = 0;}
		uint256 _transferred = _tokens - _burnedAmount;
		info.users[_to].balance += _transferred;
		emit Transfer(_from, _to, _transferred);
		if (_burnedAmount > 0) {
			if (info.totalFrozen > 0) {
				_burnedAmount /= 2;
				info.scaledPayoutPerToken += _burnedAmount * FLOAT_SCALAR / info.totalFrozen;
				emit Transfer(_from, address(this), _burnedAmount);
			}
			info.totalSupply -= _burnedAmount;
			emit Transfer(_from, address(0x0), _burnedAmount);
			emit Burn(_burnedAmount);
		}
		return _transferred;
	}

	function _freeze(uint256 _amount) internal {
		require(balanceOf(msg.sender) >= _amount, 'Trying to freeze more than you have');
		require(frozenOf(msg.sender) + _amount >= MIN_FREEZE_AMOUNT, 'Trying to freeze less than the minimum');
		info.totalFrozen += _amount;
		info.users[msg.sender].frozen += _amount;
		info.users[msg.sender].scaledPayout += int256(_amount * info.scaledPayoutPerToken);
		emit Transfer(msg.sender, address(this), _amount);
		emit Freeze(msg.sender, _amount);
	}

	function _unfreeze(uint256 _amount) internal {
		require(frozenOf(msg.sender) >= _amount, 'Trying to unfreeze more than you can');
		uint256 _burnedAmount = _amount * BURN_RATE / 100;
		info.scaledPayoutPerToken += _burnedAmount * FLOAT_SCALAR / info.totalFrozen;
		info.totalFrozen -= _amount;
		info.users[msg.sender].balance -= _burnedAmount;
		info.users[msg.sender].frozen -= _amount;
		info.users[msg.sender].scaledPayout -= int256(_amount * info.scaledPayoutPerToken);
		emit Transfer(address(this), msg.sender, _amount - _burnedAmount);
		emit Unfreeze(msg.sender, _amount);
	}
}

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