// File: contracts/HATToken.sol



// SPDX-License-Identifier: MIT
pragma solidity 0.8.6;
import "openzeppelin-solidity/contracts/utils/math/SafeMath.sol";
import "openzeppelin-solidity/contracts/token/ERC20/IERC20.sol";


contract HATToken is IERC20 {

    struct PendingMinter {
        uint256 seedAmount;
        uint256 setMinterPendingAt;
    }

    /// @notice A checkpoint for marking number of votes from a given block
    struct Checkpoint {
        uint32 fromBlock;
        uint96 votes;
    }

    /// @notice EIP-20 token name for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant name = "hats.finance";

    /// @notice EIP-20 token symbol for this token
    // solhint-disable-next-line const-name-snakecase
    string public constant symbol = "HAT";

    /// @notice EIP-20 token decimals for this token
    // solhint-disable-next-line const-name-snakecase
    uint8 public constant decimals = 18;

    /// @notice Total number of tokens in circulation
    uint public override totalSupply;

    address public governance;
    address public governancePending;
    uint256 public setGovernancePendingAt;
    uint256 public immutable timeLockDelay;
    uint256 public constant CAP = 10000000e18;

    /// @notice Address which may mint new tokens
    /// minter -> minting seedAmount
    mapping (address => uint256) public minters;

    /// @notice Address which may mint new tokens
    /// minter -> minting seedAmount
    mapping (address => PendingMinter) public pendingMinters;

    // @notice Allowance amounts on behalf of others
    mapping (address => mapping (address => uint96)) internal allowances;

    // @notice Official record of token balances for each account
    mapping (address => uint96) internal balances;

    /// @notice A record of each accounts delegate
    mapping (address => address) public delegates;

    /// @notice A record of votes checkpoints for each account, by index
    mapping (address => mapping (uint32 => Checkpoint)) public checkpoints;

    /// @notice The number of checkpoints for each account
    mapping (address => uint32) public numCheckpoints;

    /// @notice A record of states for signing / validating signatures
    mapping (address => uint) public nonces;

    /// @notice The EIP-712 typehash for the contract's domain
    bytes32 public constant DOMAIN_TYPEHASH =
    keccak256("EIP712Domain(string name,uint256 chainId,address verifyingContract)");

    /// @notice The EIP-712 typehash for the delegation struct used by the contract
    bytes32 public constant DELEGATION_TYPEHASH =
    keccak256("Delegation(address delegatee,uint256 nonce,uint256 expiry)");

    /// @notice The EIP-712 typehash for the permit struct used by the contract
    bytes32 public constant PERMIT_TYPEHASH =
    keccak256("Permit(address owner,address spender,uint256 value,uint256 nonce,uint256 deadline)");

    /// @notice An event thats emitted when a new minter address is pending
    event MinterPending(address indexed minter, uint256 seedAmount, uint256 at);
    /// @notice An event thats emitted when the minter address is changed
    event MinterChanged(address indexed minter, uint256 seedAmount);
    /// @notice An event thats emitted when a new governance address is pending
    event GovernancePending(address indexed oldGovernance, address indexed newGovernance, uint256 at);
    /// @notice An event thats emitted when a new governance address is set
    event GovernanceChanged(address indexed oldGovernance, address indexed newGovernance);
    /// @notice An event thats emitted when an account changes its delegate
    event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);
    /// @notice An event thats emitted when a delegate account's vote balance changes
    event DelegateVotesChanged(address indexed delegate, uint previousBalance, uint newBalance);

    /**
     * @notice Construct a new HAT token
     */
    // solhint-disable-next-line func-visibility
    constructor(address _governance, uint256 _timeLockDelay) {
        governance = _governance;
        timeLockDelay = _timeLockDelay;
    }

    function setPendingGovernance(address _governance) external {
        require(msg.sender == governance, "HAT:!governance");
        require(_governance != address(0), "HAT:!_governance");
        governancePending = _governance;
        // solhint-disable-next-line not-rely-on-time
        setGovernancePendingAt = block.timestamp;
        emit GovernancePending(governance, _governance, setGovernancePendingAt);
    }

    function confirmGovernance() external {
        require(msg.sender == governance, "HAT:!governance");
        require(setGovernancePendingAt > 0, "HAT:!governancePending");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp - setGovernancePendingAt > timeLockDelay,
        "HAT: cannot confirm governance at this time");
        emit GovernanceChanged(governance, governancePending);
        governance = governancePending;
        setGovernancePendingAt = 0;
    }

    function setPendingMinter(address _minter, uint256 _cap) external {
        require(msg.sender == governance, "HAT::!governance");
        pendingMinters[_minter].seedAmount = _cap;
        // solhint-disable-next-line not-rely-on-time
        pendingMinters[_minter].setMinterPendingAt = block.timestamp;
        emit MinterPending(_minter, _cap, pendingMinters[_minter].setMinterPendingAt);
    }

    function confirmMinter(address _minter) external {
        require(msg.sender == governance, "HAT::mint: only the governance can confirm minter");
        require(pendingMinters[_minter].setMinterPendingAt > 0, "HAT:: no pending minter was set");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp - pendingMinters[_minter].setMinterPendingAt > timeLockDelay,
        "HATToken: cannot confirm at this time");
        minters[_minter] = pendingMinters[_minter].seedAmount;
        pendingMinters[_minter].setMinterPendingAt = 0;
        emit MinterChanged(_minter, pendingMinters[_minter].seedAmount);
    }

    function burn(uint256 _amount) external {
        return _burn(msg.sender, _amount);
    }

    function mint(address _account, uint _amount) external {
        require(minters[msg.sender] >= _amount, "HATToken: amount greater than limitation");
        minters[msg.sender] = SafeMath.sub(minters[msg.sender], _amount);
        _mint(_account, _amount);
    }

    /**
     * @notice Get the number of tokens `spender` is approved to spend on behalf of `account`
     * @param account The address of the account holding the funds
     * @param spender The address of the account spending the funds
     * @return The number of tokens approved
     */
    function allowance(address account, address spender) external override view returns (uint) {
        return allowances[account][spender];
    }

    /**
     * @notice Approve `spender` to transfer up to `amount` from `src`
     * @dev This will overwrite the approval amount for `spender`
     *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
     * @param spender The address of the account which may transfer tokens
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @return Whether or not the approval succeeded
     */
    function approve(address spender, uint rawAmount) external override returns (bool) {
        uint96 amount;
        if (rawAmount == type(uint256).max) {
            amount = type(uint96).max;
        } else {
            amount = safe96(rawAmount, "HAT::approve: amount exceeds 96 bits");
        }

        allowances[msg.sender][spender] = amount;

        emit Approval(msg.sender, spender, 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, uint addedValue) external virtual returns (bool) {
        require(spender != address(0), "HAT: increaseAllowance to the zero address");
        uint96 valueToAdd = safe96(addedValue, "HAT::increaseAllowance: addedValue exceeds 96 bits");
        allowances[msg.sender][spender] =
        add96(allowances[msg.sender][spender], valueToAdd, "HAT::increaseAllowance: overflows");
        emit Approval(msg.sender, spender, allowances[msg.sender][spender]);
        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, uint subtractedValue) external virtual returns (bool) {
        require(spender != address(0), "HAT: decreaseAllowance to the zero address");
        uint96 valueTosubtract = safe96(subtractedValue, "HAT::decreaseAllowance: subtractedValue exceeds 96 bits");
        allowances[msg.sender][spender] = sub96(allowances[msg.sender][spender], valueTosubtract,
        "HAT::decreaseAllowance: spender allowance is less than subtractedValue");
        emit Approval(msg.sender, spender, allowances[msg.sender][spender]);
        return true;
    }

    /**
     * @notice Triggers an approval from owner to spends
     * @param owner The address to approve from
     * @param spender The address to be approved
     * @param rawAmount The number of tokens that are approved (2^256-1 means infinite)
     * @param deadline The time at which to expire the signature
     * @param v The recovery byte of the signature
     * @param r Half of the ECDSA signature pair
     * @param s Half of the ECDSA signature pair
     */
    function permit(address owner, address spender, uint rawAmount, uint deadline, uint8 v, bytes32 r, bytes32 s) external {
        uint96 amount;
        if (rawAmount == type(uint256).max) {
            amount = type(uint96).max;
        } else {
            amount = safe96(rawAmount, "HAT::permit: amount exceeds 96 bits");
        }

        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(PERMIT_TYPEHASH, owner, spender, rawAmount, nonces[owner]++, deadline));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "HAT::permit: invalid signature");
        require(signatory == owner, "HAT::permit: unauthorized");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= deadline, "HAT::permit: signature expired");

        allowances[owner][spender] = amount;

        emit Approval(owner, spender, amount);
    }

    /**
     * @notice Get the number of tokens held by the `account`
     * @param account The address of the account to get the balance of
     * @return The number of tokens held
     */
    function balanceOf(address account) external view override returns (uint) {
        return balances[account];
    }

    /**
     * @notice Transfer `amount` tokens from `msg.sender` to `dst`
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transfer(address dst, uint rawAmount) external override returns (bool) {
        uint96 amount = safe96(rawAmount, "HAT::transfer: amount exceeds 96 bits");
        _transferTokens(msg.sender, dst, amount);
        return true;
    }

    /**
     * @notice Transfer `amount` tokens from `src` to `dst`
     * @param src The address of the source account
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function transferFrom(address src, address dst, uint rawAmount) external override returns (bool) {
        address spender = msg.sender;
        uint96 spenderAllowance = allowances[src][spender];
        uint96 amount = safe96(rawAmount, "HAT::approve: amount exceeds 96 bits");

        if (spender != src && spenderAllowance != type(uint96).max) {
            uint96 newAllowance = sub96(spenderAllowance, amount,
            "HAT::transferFrom: transfer amount exceeds spender allowance");
            allowances[src][spender] = newAllowance;

            emit Approval(src, spender, newAllowance);
        }

        _transferTokens(src, dst, amount);
        return true;
    }

    /**
     * @notice Delegate votes from `msg.sender` to `delegatee`
     * @param delegatee The address to delegate votes to
     */
    function delegate(address delegatee) external {
        return _delegate(msg.sender, delegatee);
    }

    /**
     * @notice Delegates votes from signatory to `delegatee`
     * @param delegatee The address to delegate votes to
     * @param nonce The contract state required to match the signature
     * @param expiry The time at which to expire the signature
     * @param v The recovery byte of the signature
     * @param r Half of the ECDSA signature pair
     * @param s Half of the ECDSA signature pair
     */
    function delegateBySig(address delegatee, uint nonce, uint expiry, uint8 v, bytes32 r, bytes32 s) external {
        bytes32 domainSeparator = keccak256(abi.encode(DOMAIN_TYPEHASH, keccak256(bytes(name)), getChainId(), address(this)));
        bytes32 structHash = keccak256(abi.encode(DELEGATION_TYPEHASH, delegatee, nonce, expiry));
        bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
        address signatory = ecrecover(digest, v, r, s);
        require(signatory != address(0), "HAT::delegateBySig: invalid signature");
        require(nonce == nonces[signatory]++, "HAT::delegateBySig: invalid nonce");
        // solhint-disable-next-line not-rely-on-time
        require(block.timestamp <= expiry, "HAT::delegateBySig: signature expired");
        return _delegate(signatory, delegatee);
    }

    /**
     * @notice Gets the current votes balance for `account`
     * @param account The address to get votes balance
     * @return The number of current votes for `account`
     */
    function getCurrentVotes(address account) external view returns (uint96) {
        uint32 nCheckpoints = numCheckpoints[account];
        return nCheckpoints > 0 ? checkpoints[account][nCheckpoints - 1].votes : 0;
    }

    /**
     * @notice Determine the prior number of votes for an account as of a block number
     * @dev Block number must be a finalized block or else this function will revert to prevent misinformation.
     * @param account The address of the account to check
     * @param blockNumber The block number to get the vote balance at
     * @return The number of votes the account had as of the given block
     */
    function getPriorVotes(address account, uint blockNumber) external view returns (uint96) {
        require(blockNumber < block.number, "HAT::getPriorVotes: not yet determined");

        uint32 nCheckpoints = numCheckpoints[account];
        if (nCheckpoints == 0) {
            return 0;
        }

        // First check most recent balance
        if (checkpoints[account][nCheckpoints - 1].fromBlock <= blockNumber) {
            return checkpoints[account][nCheckpoints - 1].votes;
        }

        // Next check implicit zero balance
        if (checkpoints[account][0].fromBlock > blockNumber) {
            return 0;
        }

        uint32 lower = 0;
        uint32 upper = nCheckpoints - 1;
        while (upper > lower) {
            uint32 center = upper - (upper - lower) / 2; // ceil, avoiding overflow
            Checkpoint memory cp = checkpoints[account][center];
            if (cp.fromBlock == blockNumber) {
                return cp.votes;
            } else if (cp.fromBlock < blockNumber) {
                lower = center;
            } else {
                upper = center - 1;
            }
        }
        return checkpoints[account][lower].votes;
    }

    /**
     * @notice Mint new tokens
     * @param dst The address of the destination account
     * @param rawAmount The number of tokens to be minted
     */
    function _mint(address dst, uint rawAmount) internal {
        require(dst != address(0), "HAT::mint: cannot transfer to the zero address");
        require(SafeMath.add(totalSupply, rawAmount) <= CAP, "ERC20Capped: CAP exceeded");

        // mint the amount
        uint96 amount = safe96(rawAmount, "HAT::mint: amount exceeds 96 bits");
        totalSupply = safe96(SafeMath.add(totalSupply, amount), "HAT::mint: totalSupply exceeds 96 bits");

        // transfer the amount to the recipient
        balances[dst] = add96(balances[dst], amount, "HAT::mint: transfer amount overflows");
        emit Transfer(address(0), dst, amount);

        // move delegates
        _moveDelegates(address(0), delegates[dst], amount);
    }

    /**
     * Burn tokens
     * @param src The address of the source account
     * @param rawAmount The number of tokens to be burned
     */
    function _burn(address src, uint rawAmount) internal {
        require(src != address(0), "HAT::burn: cannot burn to the zero address");

        // burn the amount
        uint96 amount = safe96(rawAmount, "HAT::burn: amount exceeds 96 bits");
        totalSupply = safe96(SafeMath.sub(totalSupply, amount), "HAT::mint: totalSupply exceeds 96 bits");

        // reduce the amount from src address
        balances[src] = sub96(balances[src], amount, "HAT::burn: burn amount exceeds balance");
        emit Transfer(src, address(0), amount);

        // move delegates
        _moveDelegates(delegates[src], address(0), amount);
    }

    function _delegate(address delegator, address delegatee) internal {
        address currentDelegate = delegates[delegator];
        uint96 delegatorBalance = balances[delegator];
        delegates[delegator] = delegatee;

        emit DelegateChanged(delegator, currentDelegate, delegatee);

        _moveDelegates(currentDelegate, delegatee, delegatorBalance);
    }

    function _transferTokens(address src, address dst, uint96 amount) internal {
        require(src != address(0), "HAT::_transferTokens: cannot transfer from the zero address");
        require(dst != address(0), "HAT::_transferTokens: cannot transfer to the zero address");

        balances[src] = sub96(balances[src], amount, "HAT::_transferTokens: transfer amount exceeds balance");
        balances[dst] = add96(balances[dst], amount, "HAT::_transferTokens: transfer amount overflows");
        emit Transfer(src, dst, amount);

        _moveDelegates(delegates[src], delegates[dst], amount);
    }

    function _moveDelegates(address srcRep, address dstRep, uint96 amount) internal {
        if (srcRep != dstRep && amount > 0) {
            if (srcRep != address(0)) {
                uint32 srcRepNum = numCheckpoints[srcRep];
                uint96 srcRepOld = srcRepNum > 0 ? checkpoints[srcRep][srcRepNum - 1].votes : 0;
                uint96 srcRepNew = sub96(srcRepOld, amount, "HAT::_moveVotes: vote amount underflows");
                _writeCheckpoint(srcRep, srcRepNum, srcRepOld, srcRepNew);
            }

            if (dstRep != address(0)) {
                uint32 dstRepNum = numCheckpoints[dstRep];
                uint96 dstRepOld = dstRepNum > 0 ? checkpoints[dstRep][dstRepNum - 1].votes : 0;
                uint96 dstRepNew = add96(dstRepOld, amount, "HAT::_moveVotes: vote amount overflows");
                _writeCheckpoint(dstRep, dstRepNum, dstRepOld, dstRepNew);
            }
        }
    }

    function _writeCheckpoint(address delegatee, uint32 nCheckpoints, uint96 oldVotes, uint96 newVotes) internal {
        uint32 blockNumber = safe32(block.number, "HAT::_writeCheckpoint: block number exceeds 32 bits");

        if (nCheckpoints > 0 && checkpoints[delegatee][nCheckpoints - 1].fromBlock == blockNumber) {
            checkpoints[delegatee][nCheckpoints - 1].votes = newVotes;
        } else {
            checkpoints[delegatee][nCheckpoints] = Checkpoint(blockNumber, newVotes);
            numCheckpoints[delegatee] = nCheckpoints + 1;
        }

        emit DelegateVotesChanged(delegatee, oldVotes, newVotes);
    }

    function safe32(uint n, string memory errorMessage) internal pure returns (uint32) {
        require(n < 2**32, errorMessage);
        return uint32(n);
    }

    function safe96(uint n, string memory errorMessage) internal pure returns (uint96) {
        require(n < 2**96, errorMessage);
        return uint96(n);
    }

    function add96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        uint96 c = a + b;
        require(c >= a, errorMessage);
        return c;
    }

    function sub96(uint96 a, uint96 b, string memory errorMessage) internal pure returns (uint96) {
        require(b <= a, errorMessage);
        return a - b;
    }

    function getChainId() internal view returns (uint) {
        uint256 chainId;
        // solhint-disable-next-line no-inline-assembly
        assembly { chainId := chainid() }
        return chainId;
    }
}

// File: openzeppelin-solidity/contracts/utils/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is no longer needed starting with Solidity 0.8. The compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @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) {
        unchecked {
            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) {
        unchecked {
            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) {
        unchecked {
            // 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) {
        unchecked {
            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) {
        unchecked {
            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) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return 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) {
        return a * b;
    }

    /**
     * @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.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        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) {
        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) {
        unchecked {
            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.
     *
     * 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).
     *
     * 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) {
        unchecked {
            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) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

// File: openzeppelin-solidity/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);
}