// SPDX-License-Identifier: MIT

/*
   ____  ____  ______   _____                           
   / __ \/ __ \/_  __/  / __(_)___  ____ _____  ________ 
  / /_/ / / / / / /    / /_/ / __ \/ __ `/ __ \/ ___/ _ \
 / ____/ /_/ / / /    / __/ / / / / /_/ / / / / /__/  __/
/_/    \____/ /_/    /_/ /_/_/ /_/\__,_/_/ /_/\___/\___/ 

* POT.Finance: YuanYangPot.sol
* Token distribution contract for POT tokens
*
*/

// File: node_modules\@openzeppelin\contracts\token\ERC20\IERC20.sol

pragma solidity ^0.6.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: node_modules\@openzeppelin\contracts\math\SafeMath.sol

pragma solidity ^0.6.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be 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;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: node_modules\@openzeppelin\contracts\utils\Address.sol

pragma solidity ^0.6.2;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return _functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: weiValue }(data);
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// File: @openzeppelin\contracts\token\ERC20\SafeERC20.sol

pragma solidity ^0.6.0;




/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: node_modules\@openzeppelin\contracts\GSN\Context.sol

pragma solidity ^0.6.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
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;
    }
}

// File: @openzeppelin\contracts\access\Ownable.sol

pragma solidity ^0.6.0;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(_owner == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin\contracts\token\ERC20\ERC20.sol

pragma solidity ^0.6.0;





/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;
    using Address for address;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name, string memory symbol) public {
        _name = name;
        _symbol = symbol;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20};
     *
     * Requirements:
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    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;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    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;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    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);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements
     *
     * - `to` cannot be the zero address.
     */
    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);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    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);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    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);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

// File: contracts\HotpotBaseToken.sol

pragma solidity ^0.6.12;



contract HotpotBaseToken is ERC20, Ownable {
	constructor(string memory name, string memory symbol) public ERC20(name, symbol) {}

	/// @notice Creates `_amount` token to `_to`. Must only be called by the owner.
	function mint(address _to, uint256 _amount) public onlyOwner {
		_mint(_to, _amount);
	}
}

// File: contracts\IYuanYangPot.sol

pragma solidity ^0.6.12;


/**
 * @dev Interface of the YuanYangPot.
 */
interface IYuanYangPot {
	/**
	 * @dev Hotpot Base created per block
	 */
	function hotpotBasePerBlock() external view returns (uint256);

	/**
	 * @dev The Hotpot Base Token
	 */
	function hotpotBaseTotalSupply() external view returns (uint256);

	/**
	 * @dev The block number when Hotpot mining starts.
	 */
	function startBlock() external view returns (uint256);
	
	/**
	 * @dev Update reward vairables for all pools.
	 */
	function massUpdatePools() external;

	/**
	 * @dev Update the Hotpot Base distribution speed.
	 */
	function setHotpotBasePerBlock(uint256 _hotpotBasePerBlock) external;

	/**
	 * @dev Update the distributio share of RED soups; WHITE share = 100% - RED share
	 */
	function setRedPotShare(uint256 _redPotShare) external;

	/**
	 * @dev Update if HotPot is in Circuit Breaker mode. Reward claims are suspended during CB
	 */
	function setCircuitBreaker(bool _isInCircuitBreaker) external;

	/**
	 * @dev Add a new lp to the pool.
	 * XXX DO NOT add the same LP token more than once. Rewards will be messed up if you do.
	 */
	function addPool(
		uint256 _allocPoint,
		IERC20 _lpToken,
		bool _isRed,
		bool _withUpdate
	) external;

	/**
	 * @dev Update the given pool's Hotpot allocation point.
	 */
	function setPool(
		uint256 _pid,
		uint256 _allocPoint,
		bool _withUpdate
	) external;

	/**
	 * @dev Update the tip rate on reward distribution.
	 */
	function setTipRate(uint256 _tipRate) external;

	/**
	 * @dev Transfers ownership of the pot to a new account (`newOwner`).
	 */
	function transferPotOwnership(address newOwner) external;
}

// File: contracts\YuanYangPot.sol

pragma solidity ^0.6.12;






contract YuanYangPot is IYuanYangPot, Ownable {
	using SafeMath for uint256;
	using SafeERC20 for IERC20;

	// Info of each user.
	struct UserInfo {
		uint256 amount; // How many LP tokens the user has provided.
		uint256 rewardOffset; // Reward offset. See explanation below.
		uint256 reward; // Reward accrued.
		//
		// We do some fancy math here. Basically, any point in time, the amount of tokens
		// entitled to a user but is pending to be distributed is:
		//
		//   pending reward = (user.amount * pool.accHotpotBasePerShare) - user.rewardOffset
		//
		// Whenever a user deposits or withdraws LP tokens to a pool. Here's what happens:
		//   1. The pool's `accHotpotBasePerShare` (and `lastRewardBlock`) gets updated.
		//   2. User's `amount` gets updated.
		//   3. User's `rewardOffset` gets updated.
	}

	// Info of each pool.
	struct PoolInfo {
		IERC20 lpToken; // Address of LP token contract.
		uint256 allocPoint; // How many allocation points assigned to this pool. Hotpot to distribute per block.
		bool isRed; // If the pool is in Red soup, otherwise in White soup.
		uint256 lastRewardBlock; // Last block number that Hotpot Base distribution occurs.
		uint256 accHotpotBasePerShare; // Accumulated Hotpot Base per share, times 1e12. See below.
	}

	// The Hotpot Base Token
	HotpotBaseToken public hotpotBase;
	// Dev address.
	address public devAddr;
	// Hotpot Base created per block.
	uint256 private _hotpotBasePerBlock;
	// Share of Hotpot Base production by Red Soup, times 1e12.
	uint256 public redPotShare = 5e11;
	// Tip rate for frontend providers, times 1e12.
	uint256 public tipRate;
	// Determine if the HGB rewards can be collected.
	bool public inCircuitBreaker = false;

	// Info of each pool.
	PoolInfo[] public poolInfo;
	// Info of each user that stakes LP tokens.
	mapping(uint256 => mapping(address => UserInfo)) public userInfo;
	// Total allocation points. Must be the sum of all allocation points in RED soup.
	uint256 public totalRedAllocPoint = 0;
	// Total allocation points. Must be the sum of all allocation points in WHITE soup.
	uint256 public totalWhiteAllocPoint = 0;
	// The block number when Hotpot mining starts.
	uint256 private _startBlock;

	event Deposit(address indexed user, uint256 indexed pid, uint256 amount);
	event Withdraw(address indexed user, uint256 indexed pid, uint256 amount);
	event EmergencyWithdraw(address indexed user, uint256 indexed pid, uint256 amount);
	event ClaimReward(
		address indexed user,
		uint256 indexed pid,
		address indexed waiter,
		uint256 amount
	);

	constructor(
		HotpotBaseToken _hotpotBase,
		address _devAddr,
		uint256 __hotpotBasePerBlock,
		uint256 __startBlock,
		uint256 _tipRate
	) public {
		hotpotBase = _hotpotBase;
		devAddr = _devAddr;
		_hotpotBasePerBlock = __hotpotBasePerBlock;
		_startBlock = __startBlock;
		tipRate = _tipRate;
	}

	function hotpotBasePerBlock() external override view returns (uint256) {
		return _hotpotBasePerBlock;
	}

	function hotpotBaseTotalSupply() external override view returns (uint256) {
		return hotpotBase.totalSupply();
	}

	function startBlock() external override view returns (uint256) {
		return _startBlock;
	}

	function poolLength() external view returns (uint256) {
		return poolInfo.length;
	}

	// Add a new lp to the pool.
	// XXX DO NOT add the same LP token more than once. Rewards will be messed up if you do.
	function addPool(
		uint256 _allocPoint,
		IERC20 _lpToken,
		bool _isRed,
		bool _withUpdate
	) public override onlyOwner {
		if (_withUpdate) {
			massUpdatePools();
		}
		uint256 blockNumber = getBlockNumber();
		uint256 lastRewardBlock = blockNumber > _startBlock ? blockNumber : _startBlock;
		if (_isRed) {
			totalRedAllocPoint = totalRedAllocPoint.add(_allocPoint);
		} else {
			totalWhiteAllocPoint = totalWhiteAllocPoint.add(_allocPoint);
		}
		poolInfo.push(
			PoolInfo({
				lpToken: _lpToken,
				allocPoint: _allocPoint,
				isRed: _isRed,
				lastRewardBlock: lastRewardBlock,
				accHotpotBasePerShare: 0
			})
		);
	}

	// Update the given pool's Hotpot allocation point.
	function setPool(
		uint256 _pid,
		uint256 _allocPoint,
		bool _withUpdate
	) public override onlyOwner {
		if (_withUpdate) {
			massUpdatePools();
		}

		if (_pid >= poolInfo.length) return;

		if (poolInfo[_pid].isRed) {
			totalRedAllocPoint = totalRedAllocPoint.sub(poolInfo[_pid].allocPoint).add(_allocPoint);
		} else {
			totalWhiteAllocPoint = totalWhiteAllocPoint.sub(poolInfo[_pid].allocPoint).add(
				_allocPoint
			);
		}
		poolInfo[_pid].allocPoint = _allocPoint;
	}

	// Update if Hotpot is in Circuit Breaker mode. Reward claims are suspended during CB - see getReward()
	function setCircuitBreaker(bool _inCircuitBreaker) public override onlyOwner {
		inCircuitBreaker = _inCircuitBreaker;
	}

	// Update the Hotpot Base distribution speed.
	function setHotpotBasePerBlock(uint256 __hotpotBasePerBlock) public override onlyOwner {
		_hotpotBasePerBlock = __hotpotBasePerBlock;
	}

	// Update the tip rate on reward distribution - see getReward().
	function setTipRate(uint256 _tipRate) public override onlyOwner {
		require(_tipRate < 1e12, 'tipRate: too high');
		tipRate = _tipRate;
	}

	// Update the distributio share of RED soups; WHITE share = 100% - RED share
	function setRedPotShare(uint256 _redPotShare) public override onlyOwner {
		require(_redPotShare < 1e12, 'redPotShare: too high');
		redPotShare = _redPotShare;
	}

	// Return reward Hotpot Base amount over the given _from to _to block for pool _pid.
	function getPoolHotpotBaseReward(
		uint256 _from,
		uint256 _to,
		uint256 _pid
	) public view returns (uint256) {
		PoolInfo storage pool = poolInfo[_pid];
		uint256 totalHotpotBaseReward = _to.sub(_from).mul(_hotpotBasePerBlock);
		if (pool.isRed) {
			return
				totalHotpotBaseReward
					.mul(pool.allocPoint)
					.mul(redPotShare)
					.div(totalRedAllocPoint)
					.div(1e12);
		} else {
			return
				totalHotpotBaseReward
					.mul(pool.allocPoint)
					.mul(uint256(1e12).sub(redPotShare))
					.div(totalWhiteAllocPoint)
					.div(1e12);
		}
	}

	// View function to see earned Hotpot Base on frontend.
	function earned(uint256 _pid, address _user) public view returns (uint256) {
		PoolInfo storage pool = poolInfo[_pid];
		UserInfo storage user = userInfo[_pid][_user];
		uint256 accHotpotBasePerShare = pool.accHotpotBasePerShare;
		uint256 lpSupply = pool.lpToken.balanceOf(address(this));
		uint256 blockNumber = getBlockNumber();
		if (blockNumber > pool.lastRewardBlock && lpSupply != 0) {
			uint256 hotpotBaseReward = getPoolHotpotBaseReward(
				pool.lastRewardBlock,
				blockNumber,
				_pid
			);
			accHotpotBasePerShare = accHotpotBasePerShare.add(
				hotpotBaseReward.mul(1e12).div(lpSupply)
			);
		}
		return
			user.amount.mul(accHotpotBasePerShare).div(1e12).add(user.reward).sub(user.rewardOffset);
	}

	// Update reward vairables for all pools. Be careful of gas spending!
	function massUpdatePools() public override {
		uint256 length = poolInfo.length;
		for (uint256 pid = 0; pid < length; ++pid) {
			updatePool(pid);
		}
	}

	// Update reward variables of given pool. New Hotpot Base will be minted.
	function updatePool(uint256 _pid) public {
		PoolInfo storage pool = poolInfo[_pid];
		uint256 blockNumber = getBlockNumber();
		if (blockNumber <= pool.lastRewardBlock) {
			return;
		}
		uint256 lpSupply = pool.lpToken.balanceOf(address(this));
		if (lpSupply == 0) {
			pool.lastRewardBlock = blockNumber;
			return;
		}
		uint256 hotpotBaseReward = getPoolHotpotBaseReward(pool.lastRewardBlock, blockNumber, _pid);
		pool.accHotpotBasePerShare = pool.accHotpotBasePerShare.add(
			hotpotBaseReward.mul(1e12).div(lpSupply)
		);
		pool.lastRewardBlock = blockNumber;
	}

	// Deposit LP tokens to YuanYangPot to earn Hotpot Base.
	function deposit(uint256 _pid, uint256 _amount) public {
		address sender = msg.sender;
		PoolInfo storage pool = poolInfo[_pid];
		UserInfo storage user = userInfo[_pid][sender];
		updatePool(_pid);
		if (user.amount > 0) {
			user.reward = earned(_pid, sender);
		}
		pool.lpToken.safeTransferFrom(sender, address(this), _amount);
		user.amount = user.amount.add(_amount);
		user.rewardOffset = user.amount.mul(pool.accHotpotBasePerShare).div(1e12);
		emit Deposit(sender, _pid, _amount);
	}

	// Withdraw LP tokens from YuanYangPot.
	function withdraw(uint256 _pid, uint256 _amount) public {
		address sender = msg.sender;
		PoolInfo storage pool = poolInfo[_pid];
		UserInfo storage user = userInfo[_pid][sender];
		require(user.amount >= _amount, 'withdraw: not good');
		updatePool(_pid);
		user.reward = earned(_pid, sender);
		user.amount = user.amount.sub(_amount);
		user.rewardOffset = user.amount.mul(pool.accHotpotBasePerShare).div(1e12);
		pool.lpToken.safeTransfer(sender, _amount);
		emit Withdraw(sender, _pid, _amount);
	}

	// Claim earned rewards from YuanYangPot.
	function claimReward(uint256 _pid, address _tipTo) public {
		address sender = msg.sender;
		require(!inCircuitBreaker, 'claimReward: halted during Circuit Breaker');
		PoolInfo storage pool = poolInfo[_pid];
		UserInfo storage user = userInfo[_pid][sender];
		updatePool(_pid);
		uint256 pending = earned(_pid, sender);
		user.rewardOffset = user.amount.mul(pool.accHotpotBasePerShare).div(1e12);
		user.reward = 0;
		hotpotBase.mint(devAddr, pending.div(10)); // minted on top of pending
		hotpotBase.mint(_tipTo, pending.mul(tipRate).div(1e12)); // minted on top of pending
		hotpotBase.mint(sender, pending);
		emit ClaimReward(sender, _pid, _tipTo, pending);
	}

	// Withdraw without caring about rewards. EMERGENCY ONLY.
	function emergencyWithdraw(uint256 _pid) public {
		address sender = msg.sender;
		PoolInfo storage pool = poolInfo[_pid];
		UserInfo storage user = userInfo[_pid][sender];
		uint256 amount = user.amount;
		user.rewardOffset = 0;
		user.reward = 0;
		user.amount = 0;
		pool.lpToken.safeTransfer(sender, amount);
		emit EmergencyWithdraw(sender, _pid, amount);
	}

	// Update dev address by the previous dev.
	function dev(address _devAddr) public {
		require(msg.sender == devAddr, 'dev: wut?');
		devAddr = _devAddr;
	}

	function transferPotOwnership(address newOwner) public override {
		transferOwnership(newOwner);
	}

	function getBlockNumber() public virtual view returns (uint256) {
		return block.number;
	}
}