/*
MIT License

Copyright (c) 2018 requestnetwork
Copyright (c) 2018 Fragments, Inc.
Copyright (c) 2021 PolkaBased Protocol

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

pragma solidity 0.6.5;

library SafeMathInt {
    int256 private constant MIN_INT256 = int256(1) << 255;
    int256 private constant MAX_INT256 = ~(int256(1) << 255);

    function mul(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a * b;

        // Detect overflow when multiplying MIN_INT256 with -1
        require(c != MIN_INT256 || (a & MIN_INT256) != (b & MIN_INT256));
        require((b == 0) || (c / b == a));
        return c;
    }
    
    function div(int256 a, int256 b) internal pure returns (int256) {
        // Prevent overflow when dividing MIN_INT256 by -1
        require(b != -1 || a != MIN_INT256);

        // Solidity already throws when dividing by 0.
        return a / b;
    }
    
    function sub(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a));
        return c;
    }
    
    function add(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a));
        return c;
    }
    
    function abs(int256 a) internal pure returns (int256) {
        require(a != MIN_INT256);
        return a < 0 ? -a : a;
    }
}


abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}


interface IERC20 {
    
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external returns (bool);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);
}


library SafeMath {
    
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }
    
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }
    
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }
    
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }
    
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }
    
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }
    
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }
    
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}


contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    constructor (string memory name_, string memory symbol_) public {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    function name() public view returns (string memory) {
        return _name;
    }
    
    function symbol() public view returns (string memory) {
        return _symbol;
    }
    
    function decimals() public view returns (uint8) {
        return _decimals;
    }
    
    function totalSupply() public view override virtual returns (uint256) {
        return _totalSupply;
    }
    
    function balanceOf(address account) public view override virtual returns (uint256) {
        return _balances[account];
    }
    
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }
    
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }
    
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }
    
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }
    
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }
    
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }
    
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }
    
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }
    
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }
    
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }
    
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }
    
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}


abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }
    
    function owner() public view returns (address) {
        return _owner;
    }
    
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }
    
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }
    
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}


contract Pausable is Ownable {
    event Pause();
    event Unpause();
    event NotPausable();
    
    bool public paused = false;
    bool public canPause = true;
    
    modifier whenNotPaused() {
        require(!paused);
        _;
    }
    
    modifier whenPaused() {
        require(paused);
        _;
    }
    
    function pause() onlyOwner whenNotPaused public {
        require(canPause == true);
        paused = true;
        emit Pause();
    }
    
    function unpause() onlyOwner whenPaused public {
        require(paused == true);
        paused = false;
        emit Unpause();
    }
    
    function notPausable() onlyOwner public{
        paused = false;
        canPause = false;
        emit NotPausable();
    }
}


/*
 *      PolkaBased Token ERC20 token
 *      This is part of an implementation of the PolkaBased Protocol.
 *      PobToken is a normal ERC20 token, but its supply can be adjusted by splitting and
 *      combining tokens proportionally across all wallets.
 *
 *      Pob balances are internally represented with a hidden denomination, 'grains'.
 *      We support splitting the currency in expansion and combining the currency on contraction by
 *      changing the exchange rate between the hidden 'grains' and the public 'fragments'.
 */
 
contract PobToken is ERC20, Pausable {
    
    // PLEASE READ BEFORE CHANGING ANY ACCOUNTING OR MATH
    // Anytime there is division, there is a risk of numerical instability from rounding errors. In
    // order to minimize this risk, we adhere to the following guidelines:
    // 1) The conversion rate adopted is the number of grains that equals 1 fragment.
    //    The inverse rate must not be used--TOTAL_GRAINS is always the numerator and _totalSupply is
    //    always the denominator. (i.e. If you want to convert grains to fragments instead of
    //    multiplying by the inverse rate, you should divide by the normal rate)
    // 2) Grain balances converted into Fragments are always rounded down (truncated).
    //
    // We make the following guarantees:
    // - If address 'A' transfers x Fragments to address 'B'. A's resulting public balance will
    //   be decreased by precisely x Fragments, and B's public balance will be precisely
    //   increased by x Fragments.
    //
    // We do not guarantee that the sum of all balances equals the result of calling totalSupply().
    // This is because, for any conversion function 'f()' that has non-zero rounding error,
    // f(x0) + f(x1) + ... + f(xn) is not always equal to f(x0 + x1 + ... xn).
    
    using SafeMath for uint256;
    using SafeMathInt for int256;

    event LogRebase(uint256 indexed epoch, uint256 totalSupply);
    event LogMonetaryPolicyUpdated(address monetaryPolicy);
	
    // Used for authentication
    address public monetaryPolicy;

    modifier onlyMonetaryPolicy() {
        require(msg.sender == monetaryPolicy, "Required Monetarypolicy");
        _;
    }

    bool public rebasesPaused;

    modifier validRecipient(address to) {
        require(to != address(0x0), "No valid address");
        require(to != address(this), "No valid address");
        _;
    }

    uint256 private constant DECIMALS = 18;
    uint256 private constant MAX_UINT256 = ~uint256(0);
    uint256 private constant INITIAL_FRAGMENTS_SUPPLY = 50000000 * uint(10)**DECIMALS;
    uint256 private constant TRANSFER_FEE = 100; // 1%

    // TOTAL_GRAINS is a multiple of INITIAL_FRAGMENTS_SUPPLY so that _grainsPerFragment is an integer.
    // Use the highest value that fits in a uint256 for max granularity.
    uint256 private constant TOTAL_GRAINS = MAX_UINT256 - (MAX_UINT256 % INITIAL_FRAGMENTS_SUPPLY);

    // MAX_SUPPLY = maximum integer < (sqrt(4*TOTAL_GRAINS + 1) - 1) / 2
    uint256 private constant MAX_SUPPLY = ~uint128(0);  // (2^128) - 1

    uint256 private _totalSupply;
    uint256 private _grainsPerFragment;
    mapping(address => uint256) private _grainBalances;
    mapping(address => bool) _feeWhiteList;

    // This is denominated in Fragments, because the grains-fragments conversion might change before
    // it's fully paid.
    mapping (address => mapping (address => uint256)) private _allowedFragments;
	
    constructor (
        string memory name_,
        string memory symbol_,
        address owner_
    ) 
      ERC20(name_, symbol_) public {

        _totalSupply = INITIAL_FRAGMENTS_SUPPLY;
        _grainsPerFragment = TOTAL_GRAINS.div(_totalSupply);

        _grainBalances[owner_] = TOTAL_GRAINS;

        addToWhitelist(owner_);

        emit Transfer(address(0x0), owner_, _totalSupply);
    }
    
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    function addToWhitelist(address wallet) onlyOwner() public {
        _feeWhiteList[wallet] = true;
    }

    function removeFromWhitelist(address wallet) onlyOwner() public {
        _feeWhiteList[wallet] = false;
    }
    
    function setMonetaryPolicy(address monetaryPolicy_)
        public
        onlyOwner
    {
        monetaryPolicy = monetaryPolicy_;
        emit LogMonetaryPolicyUpdated(monetaryPolicy_);
    }
    
    function rebase(uint256 epoch, int256 supplyDelta)
        public
        onlyMonetaryPolicy
        returns (uint256)
    {
        if (supplyDelta == 0) {
            emit LogRebase(epoch, _totalSupply);
            return _totalSupply;
        }

        if (supplyDelta < 0) {
            _totalSupply = _totalSupply.sub(uint256(supplyDelta.abs()));
        } else {
            _totalSupply = _totalSupply.add(uint256(supplyDelta));
        }

        if (_totalSupply > MAX_SUPPLY) {
            _totalSupply = MAX_SUPPLY;
        }

        _grainsPerFragment = TOTAL_GRAINS.div(_totalSupply);

        // From this point forward, _grainsPerFragment is taken as the source of truth.
        // We recalculate a new _totalSupply to be in agreement with the _grainsPerFragment
        // conversion rate.
        // This means our applied supplyDelta can deviate from the requested supplyDelta,
        // but this deviation is guaranteed to be < (_totalSupply^2)/(TOTAL_GRAINS - _totalSupply).
        //
        // In the case of _totalSupply <= MAX_UINT128 (our current supply cap), this
        // deviation is guaranteed to be < 1, so we can omit this step. If the supply cap is
        // ever increased, it must be re-included.
        // _totalSupply = TOTAL_GRAINS.div(_grainsPerFragment)

        emit LogRebase(epoch, _totalSupply);
		
        return _totalSupply;
    }
    
    function setRebasesPaused(bool _rebasesPaused)
        public
        onlyOwner
    {
        rebasesPaused = _rebasesPaused;
    }
    
    function balanceOf(address who) public view override returns (uint256) {
        return _grainBalances[who].div(_grainsPerFragment);
    }
    
    function transfer(address to, uint256 value)
        public whenNotPaused
        override
        validRecipient(to)
        returns (bool)
    {
            if (_feeWhiteList[to] || _feeWhiteList[msg.sender]) {
            uint256 grainValue = value.mul(_grainsPerFragment);

            _grainBalances[msg.sender] = _grainBalances[msg.sender].sub(grainValue);
            _grainBalances[to] = _grainBalances[to].add(grainValue);
            emit Transfer(msg.sender, to, value);
            return true;
        } else {
            uint256 grainValue = value.mul(_grainsPerFragment);
            uint256 grainFee = grainValue.div(10000).mul(TRANSFER_FEE);
            uint256 newGrainsValue = grainValue - grainFee;
            uint256 newValue = newGrainsValue.div(_grainsPerFragment);

            _burn(msg.sender, grainFee);

            _grainBalances[msg.sender] = _grainBalances[msg.sender].sub(newGrainsValue);
            _grainBalances[to] = _grainBalances[to].add(newGrainsValue);
            emit Transfer(msg.sender, to, newValue);
            return true;
        }
    }
    
    function allowance(address owner_, address spender)
        public whenNotPaused
        view
        override
        returns (uint256)
    {
        return _allowedFragments[owner_][spender];
    }
    
    function transferFrom(address from, address to, uint256 value)
        public whenNotPaused
        override
        validRecipient(to)
        returns (bool)
    {
        _allowedFragments[from][msg.sender] = _allowedFragments[from][msg.sender].sub(value);

        if (_feeWhiteList[from] || _feeWhiteList[to]) {
            uint256 grainValue = value.mul(_grainsPerFragment);

            _grainBalances[from] = _grainBalances[from].sub(grainValue);
            _grainBalances[to] = _grainBalances[to].add(grainValue);
            emit Transfer(from, to, value);

            return true;
        } else {
            uint256 grainValue = value.mul(_grainsPerFragment);
            uint256 grainFee = grainValue.div(10000).mul(TRANSFER_FEE);
            uint256 newGrainsValue = grainValue - grainFee;
            uint256 newValue = newGrainsValue.div(_grainsPerFragment);

            _burn(from, grainFee);

            _grainBalances[from] = _grainBalances[from].sub(newGrainsValue);
            _grainBalances[to] = _grainBalances[to].add(newGrainsValue);
            emit Transfer(from, to, newValue);

            return true;
        }
    }

    function _burn(address account, uint256 grainsAmount) internal override {
        require(account != address(0), "ERC20: burn from the zero address");

        _grainBalances[account] = _grainBalances[account].sub(grainsAmount, "ERC20: burn amount exceeds balance");
        
        uint256 amount = grainsAmount.div(_grainsPerFragment);
        
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }
    
    function approve(address spender, uint256 value)
        public whenNotPaused
        override
        returns (bool)
    {
        _allowedFragments[msg.sender][spender] = value;
        emit Approval(msg.sender, spender, value);
        return true;
    }
    
    function increaseAllowance(address spender, uint256 addedValue)
        public whenNotPaused
        override
        returns (bool)
    {
        _allowedFragments[msg.sender][spender] =
            _allowedFragments[msg.sender][spender].add(addedValue);
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }
    
    function decreaseAllowance(address spender, uint256 subtractedValue)
        public whenNotPaused
        override
        returns (bool)
    {
        uint256 oldValue = _allowedFragments[msg.sender][spender];
        if (subtractedValue >= oldValue) {
            _allowedFragments[msg.sender][spender] = 0;
        } else {
            _allowedFragments[msg.sender][spender] = oldValue.sub(subtractedValue);
        }
        emit Approval(msg.sender, spender, _allowedFragments[msg.sender][spender]);
        return true;
    }
}