// File: contracts/token/Ticket.sol



// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.6.0 <0.7.0;

import "sortition-sum-tree-factory/contracts/SortitionSumTreeFactory.sol";
import "@pooltogether/uniform-random-number/contracts/UniformRandomNumber.sol";

import "./ControlledToken.sol";
import "./TicketInterface.sol";

contract Ticket is ControlledToken, TicketInterface {
  using SortitionSumTreeFactory for SortitionSumTreeFactory.SortitionSumTrees;

  bytes32 constant private TREE_KEY = keccak256("PoolTogether/Ticket");
  uint256 constant private MAX_TREE_LEAVES = 5;

  // Ticket-weighted odds
  SortitionSumTreeFactory.SortitionSumTrees internal sortitionSumTrees;

  /// @notice Initializes the Controlled Token with Token Details and the Controller
  /// @param _name The name of the Token
  /// @param _symbol The symbol for the Token
  /// @param _decimals The number of decimals for the Token
  /// @param _controller Address of the Controller contract for minting & burning
  function initialize(
    string memory _name,
    string memory _symbol,
    uint8 _decimals,
    TokenControllerInterface _controller
  )
    public
    virtual
    override
    initializer
  {
    super.initialize(_name, _symbol, _decimals, _controller);
    sortitionSumTrees.createTree(TREE_KEY, MAX_TREE_LEAVES);
  }

  /// @notice Returns the user's chance of winning.
  function chanceOf(address user) external view returns (uint256) {
    return sortitionSumTrees.stakeOf(TREE_KEY, bytes32(uint256(user)));
  }

  /// @notice Selects a user using a random number.  The random number will be uniformly bounded to the ticket totalSupply.
  /// @param randomNumber The random number to use to select a user.
  /// @return The winner
  function draw(uint256 randomNumber) external view override returns (address) {
    uint256 bound = totalSupply();
    address selected;
    if (bound == 0) {
      selected = address(0);
    } else {
      uint256 token = UniformRandomNumber.uniform(randomNumber, bound);
      selected = address(uint256(sortitionSumTrees.draw(TREE_KEY, token)));
    }
    return selected;
  }

  /// @dev Controller hook to provide notifications & rule validations on token transfers to the controller.
  /// This includes minting and burning.
  /// May be overridden to provide more granular control over operator-burning
  /// @param from Address of the account sending the tokens (address(0x0) on minting)
  /// @param to Address of the account receiving the tokens (address(0x0) on burning)
  /// @param amount Amount of tokens being transferred
  function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
    super._beforeTokenTransfer(from, to, amount);

    // optimize: ignore transfers to self
    if (from == to) {
      return;
    }

    if (from != address(0)) {
      uint256 fromBalance = balanceOf(from).sub(amount);
      sortitionSumTrees.set(TREE_KEY, fromBalance, bytes32(uint256(from)));
    }

    if (to != address(0)) {
      uint256 toBalance = balanceOf(to).add(amount);
      sortitionSumTrees.set(TREE_KEY, toBalance, bytes32(uint256(to)));
    }
  }

}
// File: sortition-sum-tree-factory/contracts/SortitionSumTreeFactory.sol



/**
 *  @reviewers: [@clesaege, @unknownunknown1, @ferittuncer]
 *  @auditors: []
 *  @bounties: [<14 days 10 ETH max payout>]
 *  @deployments: []
 */

pragma solidity ^0.6.0;

/**
 *  @title SortitionSumTreeFactory
 *  @author Enrique Piqueras - <epiquerass@gmail.com>
 *  @dev A factory of trees that keep track of staked values for sortition.
 */
library SortitionSumTreeFactory {
    /* Structs */

    struct SortitionSumTree {
        uint K; // The maximum number of childs per node.
        // We use this to keep track of vacant positions in the tree after removing a leaf. This is for keeping the tree as balanced as possible without spending gas on moving nodes around.
        uint[] stack;
        uint[] nodes;
        // Two-way mapping of IDs to node indexes. Note that node index 0 is reserved for the root node, and means the ID does not have a node.
        mapping(bytes32 => uint) IDsToNodeIndexes;
        mapping(uint => bytes32) nodeIndexesToIDs;
    }

    /* Storage */

    struct SortitionSumTrees {
        mapping(bytes32 => SortitionSumTree) sortitionSumTrees;
    }

    /* internal */

    /**
     *  @dev Create a sortition sum tree at the specified key.
     *  @param _key The key of the new tree.
     *  @param _K The number of children each node in the tree should have.
     */
    function createTree(SortitionSumTrees storage self, bytes32 _key, uint _K) internal {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];
        require(tree.K == 0, "Tree already exists.");
        require(_K > 1, "K must be greater than one.");
        tree.K = _K;
        tree.stack = new uint[](0);
        tree.nodes = new uint[](0);
        tree.nodes.push(0);
    }

    /**
     *  @dev Set a value of a tree.
     *  @param _key The key of the tree.
     *  @param _value The new value.
     *  @param _ID The ID of the value.
     *  `O(log_k(n))` where
     *  `k` is the maximum number of childs per node in the tree,
     *   and `n` is the maximum number of nodes ever appended.
     */
    function set(SortitionSumTrees storage self, bytes32 _key, uint _value, bytes32 _ID) internal {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];
        uint treeIndex = tree.IDsToNodeIndexes[_ID];

        if (treeIndex == 0) { // No existing node.
            if (_value != 0) { // Non zero value.
                // Append.
                // Add node.
                if (tree.stack.length == 0) { // No vacant spots.
                    // Get the index and append the value.
                    treeIndex = tree.nodes.length;
                    tree.nodes.push(_value);

                    // Potentially append a new node and make the parent a sum node.
                    if (treeIndex != 1 && (treeIndex - 1) % tree.K == 0) { // Is first child.
                        uint parentIndex = treeIndex / tree.K;
                        bytes32 parentID = tree.nodeIndexesToIDs[parentIndex];
                        uint newIndex = treeIndex + 1;
                        tree.nodes.push(tree.nodes[parentIndex]);
                        delete tree.nodeIndexesToIDs[parentIndex];
                        tree.IDsToNodeIndexes[parentID] = newIndex;
                        tree.nodeIndexesToIDs[newIndex] = parentID;
                    }
                } else { // Some vacant spot.
                    // Pop the stack and append the value.
                    treeIndex = tree.stack[tree.stack.length - 1];
                    tree.stack.pop();
                    tree.nodes[treeIndex] = _value;
                }

                // Add label.
                tree.IDsToNodeIndexes[_ID] = treeIndex;
                tree.nodeIndexesToIDs[treeIndex] = _ID;

                updateParents(self, _key, treeIndex, true, _value);
            }
        } else { // Existing node.
            if (_value == 0) { // Zero value.
                // Remove.
                // Remember value and set to 0.
                uint value = tree.nodes[treeIndex];
                tree.nodes[treeIndex] = 0;

                // Push to stack.
                tree.stack.push(treeIndex);

                // Clear label.
                delete tree.IDsToNodeIndexes[_ID];
                delete tree.nodeIndexesToIDs[treeIndex];

                updateParents(self, _key, treeIndex, false, value);
            } else if (_value != tree.nodes[treeIndex]) { // New, non zero value.
                // Set.
                bool plusOrMinus = tree.nodes[treeIndex] <= _value;
                uint plusOrMinusValue = plusOrMinus ? _value - tree.nodes[treeIndex] : tree.nodes[treeIndex] - _value;
                tree.nodes[treeIndex] = _value;

                updateParents(self, _key, treeIndex, plusOrMinus, plusOrMinusValue);
            }
        }
    }

    /* internal Views */

    /**
     *  @dev Query the leaves of a tree. Note that if `startIndex == 0`, the tree is empty and the root node will be returned.
     *  @param _key The key of the tree to get the leaves from.
     *  @param _cursor The pagination cursor.
     *  @param _count The number of items to return.
     *  @return startIndex The index at which leaves start
     *  @return values The values of the returned leaves
     *  @return hasMore Whether there are more for pagination.
     *  `O(n)` where
     *  `n` is the maximum number of nodes ever appended.
     */
    function queryLeafs(
        SortitionSumTrees storage self,
        bytes32 _key,
        uint _cursor,
        uint _count
    ) internal view returns(uint startIndex, uint[] memory values, bool hasMore) {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];

        // Find the start index.
        for (uint i = 0; i < tree.nodes.length; i++) {
            if ((tree.K * i) + 1 >= tree.nodes.length) {
                startIndex = i;
                break;
            }
        }

        // Get the values.
        uint loopStartIndex = startIndex + _cursor;
        values = new uint[](loopStartIndex + _count > tree.nodes.length ? tree.nodes.length - loopStartIndex : _count);
        uint valuesIndex = 0;
        for (uint j = loopStartIndex; j < tree.nodes.length; j++) {
            if (valuesIndex < _count) {
                values[valuesIndex] = tree.nodes[j];
                valuesIndex++;
            } else {
                hasMore = true;
                break;
            }
        }
    }

    /**
     *  @dev Draw an ID from a tree using a number. Note that this function reverts if the sum of all values in the tree is 0.
     *  @param _key The key of the tree.
     *  @param _drawnNumber The drawn number.
     *  @return ID The drawn ID.
     *  `O(k * log_k(n))` where
     *  `k` is the maximum number of childs per node in the tree,
     *   and `n` is the maximum number of nodes ever appended.
     */
    function draw(SortitionSumTrees storage self, bytes32 _key, uint _drawnNumber) internal view returns(bytes32 ID) {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];
        uint treeIndex = 0;
        uint currentDrawnNumber = _drawnNumber % tree.nodes[0];

        while ((tree.K * treeIndex) + 1 < tree.nodes.length)  // While it still has children.
            for (uint i = 1; i <= tree.K; i++) { // Loop over children.
                uint nodeIndex = (tree.K * treeIndex) + i;
                uint nodeValue = tree.nodes[nodeIndex];

                if (currentDrawnNumber >= nodeValue) currentDrawnNumber -= nodeValue; // Go to the next child.
                else { // Pick this child.
                    treeIndex = nodeIndex;
                    break;
                }
            }
        
        ID = tree.nodeIndexesToIDs[treeIndex];
    }

    /** @dev Gets a specified ID's associated value.
     *  @param _key The key of the tree.
     *  @param _ID The ID of the value.
     *  @return value The associated value.
     */
    function stakeOf(SortitionSumTrees storage self, bytes32 _key, bytes32 _ID) internal view returns(uint value) {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];
        uint treeIndex = tree.IDsToNodeIndexes[_ID];

        if (treeIndex == 0) value = 0;
        else value = tree.nodes[treeIndex];
    }

    function total(SortitionSumTrees storage self, bytes32 _key) internal view returns (uint) {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];
        if (tree.nodes.length == 0) {
            return 0;
        } else {
            return tree.nodes[0];
        }
    }

    /* Private */

    /**
     *  @dev Update all the parents of a node.
     *  @param _key The key of the tree to update.
     *  @param _treeIndex The index of the node to start from.
     *  @param _plusOrMinus Wether to add (true) or substract (false).
     *  @param _value The value to add or substract.
     *  `O(log_k(n))` where
     *  `k` is the maximum number of childs per node in the tree,
     *   and `n` is the maximum number of nodes ever appended.
     */
    function updateParents(SortitionSumTrees storage self, bytes32 _key, uint _treeIndex, bool _plusOrMinus, uint _value) private {
        SortitionSumTree storage tree = self.sortitionSumTrees[_key];

        uint parentIndex = _treeIndex;
        while (parentIndex != 0) {
            parentIndex = (parentIndex - 1) / tree.K;
            tree.nodes[parentIndex] = _plusOrMinus ? tree.nodes[parentIndex] + _value : tree.nodes[parentIndex] - _value;
        }
    }
}

// File: @pooltogether/uniform-random-number/contracts/UniformRandomNumber.sol



/**
Copyright 2019 PoolTogether LLC

This file is part of PoolTogether.

PoolTogether is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation under version 3 of the License.

PoolTogether is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with PoolTogether.  If not, see <https://www.gnu.org/licenses/>.
*/

pragma solidity >=0.6.0 <0.8.0;

/**
 * @author Brendan Asselstine
 * @notice A library that uses entropy to select a random number within a bound.  Compensates for modulo bias.
 * @dev Thanks to https://medium.com/hownetworks/dont-waste-cycles-with-modulo-bias-35b6fdafcf94
 */
library UniformRandomNumber {
  /// @notice Select a random number without modulo bias using a random seed and upper bound
  /// @param _entropy The seed for randomness
  /// @param _upperBound The upper bound of the desired number
  /// @return A random number less than the _upperBound
  function uniform(uint256 _entropy, uint256 _upperBound) internal pure returns (uint256) {
    require(_upperBound > 0, "UniformRand/min-bound");
    uint256 min = -_upperBound % _upperBound;
    uint256 random = _entropy;
    while (true) {
      if (random >= min) {
        break;
      }
      random = uint256(keccak256(abi.encodePacked(random)));
    }
    return random % _upperBound;
  }
}
// File: contracts/token/ControlledToken.sol



// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.6.0 <0.7.0;

import "@openzeppelin/contracts-upgradeable/drafts/ERC20PermitUpgradeable.sol";

import "./TokenControllerInterface.sol";
import "./ControlledTokenInterface.sol";

/// @title Controlled ERC20 Token
/// @notice ERC20 Tokens with a controller for minting & burning
contract ControlledToken is ERC20PermitUpgradeable, ControlledTokenInterface {

  /// @notice Interface to the contract responsible for controlling mint/burn
  TokenControllerInterface public override controller;

  /// @notice Initializes the Controlled Token with Token Details and the Controller
  /// @param _name The name of the Token
  /// @param _symbol The symbol for the Token
  /// @param _decimals The number of decimals for the Token
  /// @param _controller Address of the Controller contract for minting & burning
  function initialize(
    string memory _name,
    string memory _symbol,
    uint8 _decimals,
    TokenControllerInterface _controller
  )
    public
    virtual
    initializer
  {
    __ERC20_init(_name, _symbol);
    __ERC20Permit_init("PoolTogether ControlledToken");
    controller = _controller;
    _setupDecimals(_decimals);
  }

  /// @notice Allows the controller to mint tokens for a user account
  /// @dev May be overridden to provide more granular control over minting
  /// @param _user Address of the receiver of the minted tokens
  /// @param _amount Amount of tokens to mint
  function controllerMint(address _user, uint256 _amount) external virtual override onlyController {
    _mint(_user, _amount);
  }

  /// @notice Allows the controller to burn tokens from a user account
  /// @dev May be overridden to provide more granular control over burning
  /// @param _user Address of the holder account to burn tokens from
  /// @param _amount Amount of tokens to burn
  function controllerBurn(address _user, uint256 _amount) external virtual override onlyController {
    _burn(_user, _amount);
  }

  /// @notice Allows an operator via the controller to burn tokens on behalf of a user account
  /// @dev May be overridden to provide more granular control over operator-burning
  /// @param _operator Address of the operator performing the burn action via the controller contract
  /// @param _user Address of the holder account to burn tokens from
  /// @param _amount Amount of tokens to burn
  function controllerBurnFrom(address _operator, address _user, uint256 _amount) external virtual override onlyController {
    if (_operator != _user) {
      uint256 decreasedAllowance = allowance(_user, _operator).sub(_amount, "ControlledToken/exceeds-allowance");
      _approve(_user, _operator, decreasedAllowance);
    }
    _burn(_user, _amount);
  }

  /// @dev Function modifier to ensure that the caller is the controller contract
  modifier onlyController {
    require(_msgSender() == address(controller), "ControlledToken/only-controller");
    _;
  }

  /// @dev Controller hook to provide notifications & rule validations on token transfers to the controller.
  /// This includes minting and burning.
  /// May be overridden to provide more granular control over operator-burning
  /// @param from Address of the account sending the tokens (address(0x0) on minting)
  /// @param to Address of the account receiving the tokens (address(0x0) on burning)
  /// @param amount Amount of tokens being transferred
  function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual override {
    controller.beforeTokenTransfer(from, to, amount);
  }
}

// File: contracts/token/TicketInterface.sol



// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.5.0 <0.7.0;

/// @title Interface that allows a user to draw an address using an index
interface TicketInterface {
  /// @notice Selects a user using a random number.  The random number will be uniformly bounded to the ticket totalSupply.
  /// @param randomNumber The random number to use to select a user.
  /// @return The winner
  function draw(uint256 randomNumber) external view returns (address);
}
// File: @openzeppelin/contracts-upgradeable/drafts/ERC20PermitUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.5 <0.8.0;

import "../token/ERC20/ERC20Upgradeable.sol";
import "./IERC20PermitUpgradeable.sol";
import "../cryptography/ECDSAUpgradeable.sol";
import "../utils/CountersUpgradeable.sol";
import "./EIP712Upgradeable.sol";
import "../proxy/Initializable.sol";

/**
 * @dev Implementation of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on `{IERC20-approve}`, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 *
 * _Available since v3.4._
 */
abstract contract ERC20PermitUpgradeable is Initializable, ERC20Upgradeable, IERC20PermitUpgradeable, EIP712Upgradeable {
    using CountersUpgradeable for CountersUpgradeable.Counter;

    mapping (address => CountersUpgradeable.Counter) private _nonces;

    // solhint-disable-next-line var-name-mixedcase
    bytes32 private _PERMIT_TYPEHASH;

    /**
     * @dev Initializes the {EIP712} domain separator using the `name` parameter, and setting `version` to `"1"`.
     *
     * It's a good idea to use the same `name` that is defined as the ERC20 token name.
     */
    function __ERC20Permit_init(string memory name) internal initializer {
        __Context_init_unchained();
        __EIP712_init_unchained(name, "1");
        __ERC20Permit_init_unchained(name);
    }

    function __ERC20Permit_init_unchained(string memory name) internal initializer {
        _PERMIT_TYPEHASH = keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");
    }

    /**
     * @dev See {IERC20Permit-permit}.
     */
    function permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) public virtual override {
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= deadline, "ERC20Permit: expired deadline");

        bytes32 structHash = keccak256(
            abi.encode(
                _PERMIT_TYPEHASH,
                owner,
                spender,
                value,
                _nonces[owner].current(),
                deadline
            )
        );

        bytes32 hash = _hashTypedDataV4(structHash);

        address signer = ECDSAUpgradeable.recover(hash, v, r, s);
        require(signer == owner, "ERC20Permit: invalid signature");

        _nonces[owner].increment();
        _approve(owner, spender, value);
    }

    /**
     * @dev See {IERC20Permit-nonces}.
     */
    function nonces(address owner) public view override returns (uint256) {
        return _nonces[owner].current();
    }

    /**
     * @dev See {IERC20Permit-DOMAIN_SEPARATOR}.
     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view override returns (bytes32) {
        return _domainSeparatorV4();
    }
    uint256[49] private __gap;
}

// File: contracts/token/TokenControllerInterface.sol



// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.5.0 <0.7.0;

/// @title Controlled ERC20 Token Interface
/// @notice Required interface for Controlled ERC20 Tokens linked to a Prize Pool
/// @dev Defines the spec required to be implemented by a Controlled ERC20 Token
interface TokenControllerInterface {

  /// @dev Controller hook to provide notifications & rule validations on token transfers to the controller.
  /// This includes minting and burning.
  /// @param from Address of the account sending the tokens (address(0x0) on minting)
  /// @param to Address of the account receiving the tokens (address(0x0) on burning)
  /// @param amount Amount of tokens being transferred
  function beforeTokenTransfer(address from, address to, uint256 amount) external;
}

// File: contracts/token/ControlledTokenInterface.sol



// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.6.0 <0.7.0;

import "@openzeppelin/contracts-upgradeable/token/ERC20/IERC20Upgradeable.sol";

import "./TokenControllerInterface.sol";

/// @title Controlled ERC20 Token
/// @notice ERC20 Tokens with a controller for minting & burning
interface ControlledTokenInterface is IERC20Upgradeable {

  /// @notice Interface to the contract responsible for controlling mint/burn
  function controller() external view returns (TokenControllerInterface);

  /// @notice Allows the controller to mint tokens for a user account
  /// @dev May be overridden to provide more granular control over minting
  /// @param _user Address of the receiver of the minted tokens
  /// @param _amount Amount of tokens to mint
  function controllerMint(address _user, uint256 _amount) external;

  /// @notice Allows the controller to burn tokens from a user account
  /// @dev May be overridden to provide more granular control over burning
  /// @param _user Address of the holder account to burn tokens from
  /// @param _amount Amount of tokens to burn
  function controllerBurn(address _user, uint256 _amount) external;

  /// @notice Allows an operator via the controller to burn tokens on behalf of a user account
  /// @dev May be overridden to provide more granular control over operator-burning
  /// @param _operator Address of the operator performing the burn action via the controller contract
  /// @param _user Address of the holder account to burn tokens from
  /// @param _amount Amount of tokens to burn
  function controllerBurnFrom(address _operator, address _user, uint256 _amount) external;
}

// File: @openzeppelin/contracts-upgradeable/token/ERC20/ERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../../utils/ContextUpgradeable.sol";
import "./IERC20Upgradeable.sol";
import "../../math/SafeMathUpgradeable.sol";
import "../../proxy/Initializable.sol";

/**
 * @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 ERC20Upgradeable is Initializable, ContextUpgradeable, IERC20Upgradeable {
    using SafeMathUpgradeable 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;

    /**
     * @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.
     */
    function __ERC20_init(string memory name_, string memory symbol_) internal initializer {
        __Context_init_unchained();
        __ERC20_init_unchained(name_, symbol_);
    }

    function __ERC20_init_unchained(string memory name_, string memory symbol_) internal initializer {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual 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 virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual 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 virtual {
        _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 { }
    uint256[44] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/drafts/IERC20PermitUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on `{IERC20-approve}`, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 */
interface IERC20PermitUpgradeable {
    /**
     * @dev Sets `value` as the allowance of `spender` over `owner`'s tokens,
     * given `owner`'s signed approval.
     *
     * IMPORTANT: The same issues {IERC20-approve} has related to transaction
     * ordering also apply here.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `deadline` must be a timestamp in the future.
     * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`
     * over the EIP712-formatted function arguments.
     * - the signature must use ``owner``'s current nonce (see {nonces}).
     *
     * For more information on the signature format, see the
     * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP
     * section].
     */
    function permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) external;

    /**
     * @dev Returns the current nonce for `owner`. This value must be
     * included whenever a signature is generated for {permit}.
     *
     * Every successful call to {permit} increases ``owner``'s nonce by one. This
     * prevents a signature from being used multiple times.
     */
    function nonces(address owner) external view returns (uint256);

    /**
     * @dev Returns the domain separator used in the encoding of the signature for `permit`, as defined by {EIP712}.
     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view returns (bytes32);
}

// File: @openzeppelin/contracts-upgradeable/cryptography/ECDSAUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
 *
 * These functions can be used to verify that a message was signed by the holder
 * of the private keys of a given address.
 */
library ECDSAUpgradeable {
    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature`. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        // Check the signature length
        if (signature.length != 65) {
            revert("ECDSA: invalid signature length");
        }

        // Divide the signature in r, s and v variables
        bytes32 r;
        bytes32 s;
        uint8 v;

        // ecrecover takes the signature parameters, and the only way to get them
        // currently is to use assembly.
        // solhint-disable-next-line no-inline-assembly
        assembly {
            r := mload(add(signature, 0x20))
            s := mload(add(signature, 0x40))
            v := byte(0, mload(add(signature, 0x60)))
        }

        return recover(hash, v, r, s);
    }

    /**
     * @dev Overload of {ECDSA-recover-bytes32-bytes-} that receives the `v`,
     * `r` and `s` signature fields separately.
     */
    function recover(bytes32 hash, uint8 v, bytes32 r, bytes32 s) internal pure returns (address) {
        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (281): 0 < s < secp256k1n ÷ 2 + 1, and for v in (282): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        require(uint256(s) <= 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0, "ECDSA: invalid signature 's' value");
        require(v == 27 || v == 28, "ECDSA: invalid signature 'v' value");

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(hash, v, r, s);
        require(signer != address(0), "ECDSA: invalid signature");

        return signer;
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
     * replicates the behavior of the
     * https://github.com/ethereum/wiki/wiki/JSON-RPC#eth_sign[`eth_sign`]
     * JSON-RPC method.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }
}

// File: @openzeppelin/contracts-upgradeable/utils/CountersUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../math/SafeMathUpgradeable.sol";

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented or decremented by one. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 * Since it is not possible to overflow a 256 bit integer with increments of one, `increment` can skip the {SafeMath}
 * overflow check, thereby saving gas. This does assume however correct usage, in that the underlying `_value` is never
 * directly accessed.
 */
library CountersUpgradeable {
    using SafeMathUpgradeable for uint256;

    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        // The {SafeMath} overflow check can be skipped here, see the comment at the top
        counter._value += 1;
    }

    function decrement(Counter storage counter) internal {
        counter._value = counter._value.sub(1);
    }
}

// File: @openzeppelin/contracts-upgradeable/drafts/EIP712Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.sol";

/**
 * @dev https://eips.ethereum.org/EIPS/eip-712[EIP 712] is a standard for hashing and signing of typed structured data.
 *
 * The encoding specified in the EIP is very generic, and such a generic implementation in Solidity is not feasible,
 * thus this contract does not implement the encoding itself. Protocols need to implement the type-specific encoding
 * they need in their contracts using a combination of `abi.encode` and `keccak256`.
 *
 * This contract implements the EIP 712 domain separator ({_domainSeparatorV4}) that is used as part of the encoding
 * scheme, and the final step of the encoding to obtain the message digest that is then signed via ECDSA
 * ({_hashTypedDataV4}).
 *
 * The implementation of the domain separator was designed to be as efficient as possible while still properly updating
 * the chain id to protect against replay attacks on an eventual fork of the chain.
 *
 * NOTE: This contract implements the version of the encoding known as "v4", as implemented by the JSON RPC method
 * https://docs.metamask.io/guide/signing-data.html[`eth_signTypedDataV4` in MetaMask].
 *
 * _Available since v3.4._
 */
abstract contract EIP712Upgradeable is Initializable {
    /* solhint-disable var-name-mixedcase */
    bytes32 private _HASHED_NAME;
    bytes32 private _HASHED_VERSION;
    bytes32 private constant _TYPE_HASH = keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)");
    /* solhint-enable var-name-mixedcase */

    /**
     * @dev Initializes the domain separator and parameter caches.
     *
     * The meaning of `name` and `version` is specified in
     * https://eips.ethereum.org/EIPS/eip-712#definition-of-domainseparator[EIP 712]:
     *
     * - `name`: the user readable name of the signing domain, i.e. the name of the DApp or the protocol.
     * - `version`: the current major version of the signing domain.
     *
     * NOTE: These parameters cannot be changed except through a xref:learn::upgrading-smart-contracts.adoc[smart
     * contract upgrade].
     */
    function __EIP712_init(string memory name, string memory version) internal initializer {
        __EIP712_init_unchained(name, version);
    }

    function __EIP712_init_unchained(string memory name, string memory version) internal initializer {
        bytes32 hashedName = keccak256(bytes(name));
        bytes32 hashedVersion = keccak256(bytes(version));
        _HASHED_NAME = hashedName;
        _HASHED_VERSION = hashedVersion;
    }

    /**
     * @dev Returns the domain separator for the current chain.
     */
    function _domainSeparatorV4() internal view returns (bytes32) {
        return _buildDomainSeparator(_TYPE_HASH, _EIP712NameHash(), _EIP712VersionHash());
    }

    function _buildDomainSeparator(bytes32 typeHash, bytes32 name, bytes32 version) private view returns (bytes32) {
        return keccak256(
            abi.encode(
                typeHash,
                name,
                version,
                _getChainId(),
                address(this)
            )
        );
    }

    /**
     * @dev Given an already https://eips.ethereum.org/EIPS/eip-712#definition-of-hashstruct[hashed struct], this
     * function returns the hash of the fully encoded EIP712 message for this domain.
     *
     * This hash can be used together with {ECDSA-recover} to obtain the signer of a message. For example:
     *
     * ```solidity
     * bytes32 digest = _hashTypedDataV4(keccak256(abi.encode(
     *     keccak256("Mail(address to,string contents)"),
     *     mailTo,
     *     keccak256(bytes(mailContents))
     * )));
     * address signer = ECDSA.recover(digest, signature);
     * ```
     */
    function _hashTypedDataV4(bytes32 structHash) internal view virtual returns (bytes32) {
        return keccak256(abi.encodePacked("\x19\x01", _domainSeparatorV4(), structHash));
    }

    function _getChainId() private view returns (uint256 chainId) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        // solhint-disable-next-line no-inline-assembly
        assembly {
            chainId := chainid()
        }
    }

    /**
     * @dev The hash of the name parameter for the EIP712 domain.
     *
     * NOTE: This function reads from storage by default, but can be redefined to return a constant value if gas costs
     * are a concern.
     */
    function _EIP712NameHash() internal virtual view returns (bytes32) {
        return _HASHED_NAME;
    }

    /**
     * @dev The hash of the version parameter for the EIP712 domain.
     *
     * NOTE: This function reads from storage by default, but can be redefined to return a constant value if gas costs
     * are a concern.
     */
    function _EIP712VersionHash() internal virtual view returns (bytes32) {
        return _HASHED_VERSION;
    }
    uint256[50] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/proxy/Initializable.sol



// SPDX-License-Identifier: MIT

// solhint-disable-next-line compiler-version
pragma solidity >=0.4.24 <0.8.0;

import "../utils/AddressUpgradeable.sol";

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function _isConstructor() private view returns (bool) {
        return !AddressUpgradeable.isContract(address(this));
    }
}

// File: @openzeppelin/contracts-upgradeable/utils/ContextUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;
import "../proxy/Initializable.sol";

/*
 * @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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    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;
    }
    uint256[50] private __gap;
}

// File: @openzeppelin/contracts-upgradeable/token/ERC20/IERC20Upgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20Upgradeable {
    /**
     * @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: @openzeppelin/contracts-upgradeable/math/SafeMathUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 SafeMathUpgradeable {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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: @openzeppelin/contracts-upgradeable/utils/AddressUpgradeable.sol



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library AddressUpgradeable {
    /**
     * @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 on 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");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        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);
            }
        }
    }
}