// File: contracts/SaxToken.sol



//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

import "./WhiteListable.sol";
import "./Restrictable.sol";
import "./ERC1404.sol";

contract SaxToken is ERC1404, WhiteListable, Restrictable {

    // Token Details
    string constant TOKEN_NAME = "SAX";
    string constant TOKEN_SYMBOL = "SAX";
    uint8 constant TOKEN_DECIMALS = 18;

    // Token supply - 1 Million Tokens, with 18 decimal precision
    uint256 constant MILLION = 100000000;
    uint256 constant TOKEN_SUPPLY = MILLION * (10 ** uint256(TOKEN_DECIMALS));

    // ERC1404 Error codes and messages
    uint8 public constant SUCCESS_CODE = 0;
    uint8 public constant FAILURE_NON_WHITELIST = 1;
    string public constant SUCCESS_MESSAGE = "SUCCESS";
    string public constant FAILURE_NON_WHITELIST_MESSAGE = "The transfer was restricted due to white list configuration.";
    string public constant UNKNOWN_ERROR = "Unknown Error Code";


    /**
    Constructor for the token to set readable details and mint all tokens
    to the contract creator.
     */
    constructor(address owner)
        ERC20(TOKEN_NAME, TOKEN_SYMBOL)
    {		
        _transferOwnership(owner);
        _mint(owner, TOKEN_SUPPLY);
    }

    /**
    This function detects whether a transfer should be restricted and not allowed.
    If the function returns SUCCESS_CODE (0) then it should be allowed.
     */
    function detectTransferRestriction (address from, address to, uint256)
        public
        override
        view
        returns (uint8)
    {               
        // If the restrictions have been disabled by the owner, then just return success
        // Logic defined in Restrictable parent class
        if(!isRestrictionEnabled()) {
            return SUCCESS_CODE;
        }

        // If the contract owner is transferring, then ignore reistrictions        
        if(from == owner()) {
            return SUCCESS_CODE;
        }

        // Restrictions are enabled, so verify the whitelist config allows the transfer.
        // Logic defined in Whitelistable parent class
        if(!checkWhitelistAllowed(from, to)) {
            return FAILURE_NON_WHITELIST;
        }

        // If no restrictions were triggered return success
        return SUCCESS_CODE;
    }
    
    /**
    This function allows a wallet or other client to get a human readable string to show
    a user if a transfer was restricted.  It should return enough information for the user
    to know why it failed.
     */
    function messageForTransferRestriction (uint8 restrictionCode)
        public
        override
        pure
        returns (string memory)
    {
        if (restrictionCode == SUCCESS_CODE) {
            return SUCCESS_MESSAGE;
        }

        if (restrictionCode == FAILURE_NON_WHITELIST) {
            return FAILURE_NON_WHITELIST_MESSAGE;
        }

        // An unknown error code was passed in.
        return UNKNOWN_ERROR;
    }

    /**
    Evaluates whether a transfer should be allowed or not.
     */
    modifier notRestricted (address from, address to, uint256 value) {        
        uint8 restrictionCode = detectTransferRestriction(from, to, value);
        require(restrictionCode == SUCCESS_CODE, messageForTransferRestriction(restrictionCode));
        _;
    }

    /**
    Overrides the parent class token transfer function to enforce restrictions.
     */
    function transfer (address to, uint256 value)
        public
        override
        notRestricted(msg.sender, to, value)
        returns (bool success)
    {
        success = super.transfer(to, value);
    }

    /**
    Overrides the parent class token transferFrom function to enforce restrictions.
     */
    function transferFrom (address from, address to, uint256 value)
        public
        override
        notRestricted(from, to, value)
        returns (bool success)
    {
        success = super.transferFrom(from, to, value);
    }
}

// File: contracts/WhiteListable.sol



//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

import "@openzeppelin/contracts/token/ERC20/ERC20.sol";
import "./Administratable.sol";

/**
Keeps track of whitelists and can check if sender and reciever are configured to allow a transfer.
Only administrators can update the whitelists.
Any address can only be a member of one whitelist at a time.
 */
contract WhiteListable is Administratable {
    // Zero is reserved for indicating it is not on a whitelist
    uint8 constant NO_WHITELIST = 0;

    // The mapping to keep track of which whitelist any address belongs to.
    // 0 is reserved for no whitelist and is the default for all addresses.
    mapping (address => uint8) public addressWhitelists;

    // The mapping to keep track of each whitelist's outbound whitelist flags.
    // Boolean flag indicates whether outbound transfers are enabled.
    mapping(uint8 => mapping (uint8 => bool)) public outboundWhitelistsEnabled;

    // Events to allow tracking add/remove.
    event AddressAddedToWhitelist(address indexed addedAddress, uint8 indexed whitelist, address indexed addedBy);
    event AddressRemovedFromWhitelist(address indexed removedAddress, uint8 indexed whitelist, address indexed removedBy);
    event OutboundWhitelistUpdated(address indexed updatedBy, uint8 indexed sourceWhitelist, uint8 indexed destinationWhitelist, bool from, bool to);

    /**
    Sets an address's white list ID.  Only administrators should be allowed to update this.
    If an address is on an existing whitelist, it will just get updated to the new value (removed from previous).
     */
    function addToWhitelist(address addressToAdd, uint8 whitelist) public onlyAdministrator {
        // Verify the whitelist is valid
        require(whitelist != NO_WHITELIST, "Invalid whitelist ID supplied");

        // Save off the previous white list
        uint8 previousWhitelist = addressWhitelists[addressToAdd];

        // Set the address's white list ID
        addressWhitelists[addressToAdd] = whitelist;        

        // If the previous whitelist existed then we want to indicate it has been removed
        if(previousWhitelist != NO_WHITELIST) {
            // Emit the event for tracking
            emit AddressRemovedFromWhitelist(addressToAdd, previousWhitelist, msg.sender);
        }

        // Emit the event for new whitelist
        emit AddressAddedToWhitelist(addressToAdd, whitelist, msg.sender);
    }

    /**
    Clears out an address's white list ID.  Only administrators should be allowed to update this.
     */
    function removeFromWhitelist(address addressToRemove) public onlyAdministrator {
        // Save off the previous white list
        uint8 previousWhitelist = addressWhitelists[addressToRemove];

        // Zero out the previous white list
        addressWhitelists[addressToRemove] = NO_WHITELIST;

        // Emit the event for tracking
        emit AddressRemovedFromWhitelist(addressToRemove, previousWhitelist, msg.sender);
    }

    /**
    Sets the flag to indicate whether source whitelist is allowed to send to destination whitelist.
    Only administrators should be allowed to update this.
     */
    function updateOutboundWhitelistEnabled(uint8 sourceWhitelist, uint8 destinationWhitelist, bool newEnabledValue) public onlyAdministrator {
        // Get the old enabled flag
        bool oldEnabledValue = outboundWhitelistsEnabled[sourceWhitelist][destinationWhitelist];

        // Update to the new value
        outboundWhitelistsEnabled[sourceWhitelist][destinationWhitelist] = newEnabledValue;

        // Emit event for tracking
        emit OutboundWhitelistUpdated(msg.sender, sourceWhitelist, destinationWhitelist, oldEnabledValue, newEnabledValue);
    }

    /**
    Determine if the a sender is allowed to send to the receiver.
    The source whitelist must be enabled to send to the whitelist where the receive exists.
     */
    function checkWhitelistAllowed(address sender, address receiver) public view returns (bool) {
        // First get each address white list
        uint8 senderWhiteList = addressWhitelists[sender];
        uint8 receiverWhiteList = addressWhitelists[receiver];

        // If either address is not on a white list then the check should fail
        if(senderWhiteList == NO_WHITELIST || receiverWhiteList == NO_WHITELIST){
            return false;
        }

        // Determine if the sending whitelist is allowed to send to the destination whitelist        
        return outboundWhitelistsEnabled[senderWhiteList][receiverWhiteList];
    }
}
// File: contracts/Restrictable.sol



//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

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

/**
Restrictions start off as enabled.
Once they are disabled, they cannot be re-enabled.
Only the owner may disable restrictions.
 */
contract Restrictable is Ownable {
    // State variable to track whether restrictions are enabled.  Defaults to true.
    bool private _restrictionsEnabled = true;

    // Event emitted when flag is disabled
    event RestrictionsDisabled(address indexed owner);

    /**
    View function to determine if restrictions are enabled
     */
    function isRestrictionEnabled() public view returns (bool) {
        return _restrictionsEnabled;
    }

    /**
    Function to update the enabled flag on restrictions to disabled.  Only the owner should be able to call.
    This is a permanent change that cannot be undone
     */
    function disableRestrictions() public onlyOwner {
        require(_restrictionsEnabled, "Restrictions are already disabled.");
        
        // Set the flag
        _restrictionsEnabled = false;

        // Trigger the event
        emit RestrictionsDisabled(msg.sender);
    }
}

// File: contracts/ERC1404.sol



//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;
import "@openzeppelin/contracts/token/ERC20/ERC20.sol";

abstract contract ERC1404 is ERC20{
    /// @notice Detects if a transfer will be reverted and if so returns an appropriate reference code
    /// @param from Sending address
    /// @param to Receiving address
    /// @param value Amount of tokens being transferred
    /// @return Code by which to reference message for rejection reasoning
    /// @dev Overwrite with your custom transfer restriction logic
    function detectTransferRestriction (address from, address to, uint256 value) virtual public view returns (uint8);

    /// @notice Returns a human-readable message for a given restriction code
    /// @param restrictionCode Identifier for looking up a message
    /// @return Text showing the restriction's reasoning
    /// @dev Overwrite with your custom message and restrictionCode handling
    function messageForTransferRestriction (uint8 restrictionCode) virtual public view returns (string memory);
}
// File: @openzeppelin/contracts/token/ERC20/ERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/ERC20.sol)

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 Contracts guidelines: functions revert
 * instead 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 default 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:
     *
     * - `to` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address to, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _transfer(owner, to, 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}.
     *
     * NOTE: If `amount` is the maximum `uint256`, the allowance is not updated on
     * `transferFrom`. This is semantically equivalent to an infinite approval.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        address owner = _msgSender();
        _approve(owner, 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}.
     *
     * NOTE: Does not update the allowance if the current allowance
     * is the maximum `uint256`.
     *
     * Requirements:
     *
     * - `from` and `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     * - the caller must have allowance for ``from``'s tokens of at least
     * `amount`.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) public virtual override returns (bool) {
        address spender = _msgSender();
        _spendAllowance(from, spender, amount);
        _transfer(from, to, 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) {
        address owner = _msgSender();
        _approve(owner, spender, allowance(owner, 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) {
        address owner = _msgSender();
        uint256 currentAllowance = allowance(owner, spender);
        require(currentAllowance >= subtractedValue, "ERC20: decreased allowance below zero");
        unchecked {
            _approve(owner, spender, currentAllowance - subtractedValue);
        }

        return true;
    }

    /**
     * @dev Moves `amount` of tokens from `sender` to `recipient`.
     *
     * This 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:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `from` must have a balance of at least `amount`.
     */
    function _transfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC20: transfer from the zero address");
        require(to != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(from, to, amount);

        uint256 fromBalance = _balances[from];
        require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
        unchecked {
            _balances[from] = fromBalance - amount;
        }
        _balances[to] += amount;

        emit Transfer(from, to, amount);

        _afterTokenTransfer(from, to, 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:
     *
     * - `account` 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);

        _afterTokenTransfer(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");
        unchecked {
            _balances[account] = accountBalance - amount;
        }
        _totalSupply -= amount;

        emit Transfer(account, address(0), amount);

        _afterTokenTransfer(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 Updates `owner` s allowance for `spender` based on spent `amount`.
     *
     * Does not update the allowance amount in case of infinite allowance.
     * Revert if not enough allowance is available.
     *
     * Might emit an {Approval} event.
     */
    function _spendAllowance(
        address owner,
        address spender,
        uint256 amount
    ) internal virtual {
        uint256 currentAllowance = allowance(owner, spender);
        if (currentAllowance != type(uint256).max) {
            require(currentAllowance >= amount, "ERC20: insufficient allowance");
            unchecked {
                _approve(owner, spender, currentAllowance - 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 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 {}

    /**
     * @dev Hook that is called after any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * has been transferred to `to`.
     * - when `from` is zero, `amount` tokens have been minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens have been 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 _afterTokenTransfer(
        address from,
        address to,
        uint256 amount
    ) internal virtual {}
}

// File: contracts/Administratable.sol



//SPDX-License-Identifier: Unlicense
pragma solidity ^0.8.0;

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

/**
This contract allows a list of administrators to be tracked.  This list can then be enforced
on functions with administrative permissions.  Only the owner of the contract should be allowed
to modify the administrator list.
 */
contract Administratable is Ownable {

    // The mapping to track administrator accounts - true is reserved for admin addresses.
    mapping (address => bool) public administrators;

    // Events to allow tracking add/remove.
    event AdminAdded(address indexed addedAdmin, address indexed addedBy);
    event AdminRemoved(address indexed removedAdmin, address indexed removedBy);

    /**
    Function modifier to enforce administrative permissions.
     */
    modifier onlyAdministrator() {
        require(isAdministrator(msg.sender), "Calling account is not an administrator.");
        _;
    }

    /**
    Determine if the message sender is in the administrators list.
     */
    function isAdministrator(address addressToTest) public view returns (bool) {
        return administrators[addressToTest];
    }

    /**
    Add an admin to the list.  This should only be callable by the owner of the contract.
     */
    function addAdmin(address adminToAdd) public onlyOwner {
        // Verify the account is not already an admin
        require(administrators[adminToAdd] == false, "Account to be added to admin list is already an admin");

        // Set the address mapping to true to indicate it is an administrator account.
        administrators[adminToAdd] = true;

        // Emit the event for any watchers.
        emit AdminAdded(adminToAdd, msg.sender);
    }

    /**
    Remove an admin from the list.  This should only be callable by the owner of the contract.
     */
    function removeAdmin(address adminToRemove) public onlyOwner {
        // Verify the account is an admin
        require(administrators[adminToRemove] == true, "Account to be removed from admin list is not already an admin");

        // Set the address mapping to false to indicate it is NOT an administrator account.  
        administrators[adminToRemove] = false;

        // Emit the event for any watchers.
        emit AdminRemoved(adminToRemove, msg.sender);
    }
}
// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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);

    /**
     * @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 `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, 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 `from` to `to` 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 from,
        address to,
        uint256 amount
    ) external returns (bool);
}

// File: @openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

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);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

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) {
        return msg.data;
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

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() {
        _transferOwnership(_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 {
        _transferOwnership(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");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}