// File: cache/solpp-generated-contracts/MigratorFull.sol



pragma solidity 0.8.0;

// SPDX-License-Identifier: MIT



import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "./tacoswapv2/interfaces/ITacoswapV2Pair.sol";
import "./tacoswapv2/interfaces/ITacoswapV2Factory.sol";
import "./interfaces/IMasterChef.sol";
import "./interfaces/IETacoChef.sol";
import "./MigratorDummy.sol";


/**
 *@title MigratorFull contract
 * - Users can:
 *   #Migrate` migrates LP tokens from TacoChef to eTacoChef
 *   #migrateUserInfo
 * - only owner can
 *   #MigratePools
 **/

contract MigratorFull {
    IMasterChef public oldChef;
    IETacoChef public newChef;
    MigratorDummy public dummyMigrator;

    address public uniFactory;
    address public sushiFactory;
    ITacoswapV2Factory public factory;

    uint256 public desiredLiquidity = type(uint256).max;

    IERC20 public taco;
    IERC20 public etaco;

    mapping(address => bool) public isMigrated;

    /**
     *  @param _oldChef The address of TacoChef contract.
     *  @param _newChef The address of eTacoChef.
     *  @param _dummyMigrator The address of MigratorDummy.
     *  @param _uniFactory The address of UniSwapV2Factory.
     *  @param _sushiFactory The address of SushiSwapFactory.
     *  @param _factory The address of TacoSwapFactory.
     *  @param tacoToken_ The address of TacoToken
     *  @param etaco_ The address of eTacoToken
     **/
    constructor(
        address _oldChef,
        address _newChef,
        address _dummyMigrator,
        address _uniFactory,
        address _sushiFactory,
        address _factory,
        address tacoToken_,
        address etaco_
    ) {
        require(_oldChef != address(0x0), "Migrator::set zero address");
        require(_dummyMigrator != address(0x0), "Migrator::set zero address");
        require(_newChef != address(0x0), "Migrator::set zero address");
        require(_uniFactory != address(0x0), "Migrator::set zero address");
        require(_sushiFactory != address(0x0), "Migrator::set zero address");
        require(tacoToken_ != address(0x0), "TacoToETaco::set zero address");
        require(etaco_ != address(0x0), "TacoToETaco::set zero address");
        taco = IERC20(tacoToken_);
        etaco = IERC20(etaco_);
        uniFactory = _uniFactory;
        sushiFactory = _sushiFactory;
        oldChef = IMasterChef(_oldChef);
        newChef = IETacoChef(_newChef);
        dummyMigrator = MigratorDummy(_dummyMigrator);
        factory = ITacoswapV2Factory(_factory);
    }

    function migrateLP(ITacoswapV2Pair orig) public returns (ITacoswapV2Pair) {
        require(msg.sender == address(newChef), "not from master chef");
        require(
            orig.factory() == uniFactory || orig.factory() == sushiFactory,
            "Migrator: not from old factory"
        );

        address token0 = orig.token0();
        address token1 = orig.token1();
        ITacoswapV2Pair pair = ITacoswapV2Pair(factory.getPair(token0, token1));
        if (pair == ITacoswapV2Pair(address(0))) {
            pair = ITacoswapV2Pair(factory.createPair(token0, token1));
        }
        uint256 lp = orig.balanceOf(msg.sender);
        if (lp == 0) return pair;
        desiredLiquidity = lp;
        orig.transferFrom(msg.sender, address(orig), lp);
        orig.burn(address(pair));
        pair.mint(msg.sender);
        desiredLiquidity = type(uint256).max;
        return pair;
    }

    /**
     *  @dev Migrates UserInfo from TacoChef to eTacoChef.
     *   Can be called by user one time only.
     **/
    function migrateUserInfo() external {
        require(!isMigrated[msg.sender], "Migrator: Already migrated");
        uint256 oldPoolLength = oldChef.poolLength();
        for (uint256 i = 0; i < oldPoolLength; i++) {
            (uint256 amount, ) = oldChef.userInfo(i, msg.sender);
            if (amount == 0) continue;
            newChef.setUser(i, msg.sender, amount, 0);
        }
        swap();
        isMigrated[msg.sender] = true;
    }

    /**
     *  @dev Migrates UserInfo from TacoChef to eTacoChef.
     *   Can be called by user one time and required to call deposit function.
     **/
    function swap() public {
        uint256 _amount = taco.balanceOf(msg.sender);
        taco.transferFrom(msg.sender, address(this), _amount);
        etaco.transfer(msg.sender, _amount);
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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: cache/solpp-generated-contracts/tacoswapv2/interfaces/ITacoswapV2Pair.sol



pragma solidity >=0.5.0;

// SPDX-License-Identifier: GPL-3.0



interface ITacoswapV2Pair {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    function name() external pure returns (string memory);
    function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;

    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, uint amount0, uint amount1, address indexed to);
    event Swap(
        address indexed sender,
        uint amount0In,
        uint amount1In,
        uint amount0Out,
        uint amount1Out,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1, uint32 blockTimestampLast);
    function price0CumulativeLast() external view returns (uint);
    function price1CumulativeLast() external view returns (uint);
    function kLast() external view returns (uint);

    function mint(address to) external returns (uint liquidity);
    function burn(address to) external returns (uint amount0, uint amount1);
    function swap(uint amount0Out, uint amount1Out, address to, bytes calldata data) external;
    function skim(address to) external;
    function sync() external;

    function initialize(address, address) external;
}
// File: cache/solpp-generated-contracts/tacoswapv2/interfaces/ITacoswapV2Factory.sol



pragma solidity >=0.5.0;

// SPDX-License-Identifier: GPL-3.0



interface ITacoswapV2Factory {

    function feeTo() external view returns (address);
    function feeToSetter() external view returns (address);
    function migrator() external view returns (address);

    function getPair(address tokenA, address tokenB) external view returns (address pair);
    function allPairs(uint) external view returns (address pair);
    function allPairsLength() external view returns (uint);

    function createPair(address tokenA, address tokenB) external returns (address pair);

    function setFeeTo(address) external;
    function setFeeToSetter(address) external;
    function setMigrator(address) external;
}

// File: cache/solpp-generated-contracts/interfaces/IMasterChef.sol



pragma solidity 0.8.0;

// SPDX-License-Identifier: MIT


interface IMasterChef {
    function deposit(uint256, uint256) external;
    function harvest(uint256) external;
    function poolLength() external returns (uint256);
    function userInfo(uint256, address) external returns(uint256, uint256);
    function totalAllocPoint() external view returns(uint256);
    function pendingTaco() external view returns(uint256);
    function poolInfo(uint256) external returns(address, uint256, uint256, uint256);
    function setMigrator(address) external;
    function migrate(uint256) external;
    function massUpdatePools() external;
}

// File: cache/solpp-generated-contracts/interfaces/IETacoChef.sol



pragma solidity 0.8.0;

// SPDX-License-Identifier: MIT


interface IETacoChef {
    function poolLength() external view returns (uint256);

    function startBlock() external view returns (uint256);

    function approveDummies(address) external;

    function getrewardForBlock(uint256) external view returns (uint256);

    function getReward(uint256, uint256) external view returns (uint256);

    function poolInfo(uint256)
        external
        view
        returns (
            address,
            uint256,
            uint256,
            uint256
        );

    function userInfo(uint256, uint256)
        external
        view
        returns (uint256, uint256);

    function pendingeTaco(uint256, address) external view returns (uint256);

    function speedStake(
        uint256,
        uint256,
        uint256,
        uint256,
        uint256,
        uint256
    ) external payable returns (uint256);

    function totalAllocPoint() external view returns (uint256);

    function deposit(uint256, uint256) external;

    function setPool(
        uint256,
        address,
        uint256,
        uint256,
        uint256
    ) external;

    function setUser(
        uint256,
        address,
        uint256,
        uint256
    ) external;
}

// File: cache/solpp-generated-contracts/MigratorDummy.sol



pragma solidity 0.8.0;

// SPDX-License-Identifier: MIT



import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "./tacoswapv2/interfaces/ITacoswapV2Pair.sol";
import "./DummyToken.sol";

/**
 *@title Migrator contract
 * - Users can:
 *   #Migrate` migrates LP tokens from TacoChef to eTacoChef
 *   #migrateUserInfo
 * - only owner can
 *   #MigratePools
 **/

contract MigratorDummy is Ownable {
    /**
     *  @dev Migrates LP tokens from TacoChef to eTacoChef.
     *   Deploy DummyToken. Mint DummyToken with the same amount of LP tokens.
     *   DummyToken is neaded to pass require in TacoChef contracts migrate function.
     **/
    function migrateLP(ITacoswapV2Pair orig) public returns (IERC20) {
        // Transfer all LP tokens from oldMaster to newMaster
        // Deploy dummy token
        // Mint same amount of dummy token for oldMaster

        DummyToken dummyToken = new DummyToken();
        uint256 lp = orig.balanceOf(msg.sender);
        if (lp == 0) return dummyToken;

        orig.transferFrom(msg.sender, owner(), lp);
        dummyToken.mint(msg.sender, lp);
        return dummyToken;
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/Context.sol";
/**
 * @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.
 */
abstract 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 () {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual 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: cache/solpp-generated-contracts/DummyToken.sol



pragma solidity ^0.8.0;

// SPDX-License-Identifier: MIT



import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "@openzeppelin/contracts/access/Ownable.sol";



/**
    *@title DummyToken contract
    * @dev It is deployed only when the Migrate function is called. 
    *  Owner of DummyToken contract is MIgrator contract.
**/
contract DummyToken is ERC20("Dummy.Token", "DMT"), Ownable {

    /// @notice Creates `_amount` token to `_to`. Must only be called by the owner (MasterChef).
    function mint(address _to, uint256 _amount) public onlyOwner {
        _mint(_to, _amount);
    }

    // function _beforeTokenTransfer(address from, address to, uint256 amount) internal override {
    //     require(from == address(0), "ERC20: only minting!");
    // }
}

// File: @openzeppelin/contracts/utils/Context.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/*
 * @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 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC20.sol";
import "./extensions/IERC20Metadata.sol";
import "../../utils/Context.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 ERC20 is Context, IERC20, IERC20Metadata {
    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;

    /**
     * @dev Sets the values for {name} and {symbol}.
     *
     * The defaut value of {decimals} is 18. To select a different value for
     * {decimals} you should overload it.
     *
     * All two of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

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

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual override 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 this function is
     * overridden;
     *
     * 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 override returns (uint8) {
        return 18;
    }

    /**
     * @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);

        uint256 currentAllowance = _allowances[sender][_msgSender()];
        require(currentAllowance >= amount, "ERC20: transfer amount exceeds allowance");
        _approve(sender, _msgSender(), currentAllowance - amount);

        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] + 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) {
        uint256 currentAllowance = _allowances[_msgSender()][spender];
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        _approve(_msgSender(), spender, currentAllowance - subtractedValue);

        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);

        uint256 senderBalance = _balances[sender];
        require(senderBalance >= amount, "ERC20: transfer amount exceeds balance");
        _balances[sender] = senderBalance - amount;
        _balances[recipient] += 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 += amount;
        _balances[account] += 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);

        uint256 accountBalance = _balances[account];
        require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
        _balances[account] = accountBalance - amount;
        _totalSupply -= 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 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: @openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}