contract ERC20 is Context, IERC20, IERC20Metadata {
    mapping(address => uint256) private _balances;

    mapping(address => mapping(address => uint256)) private _allowances;
    mapping(bytes32 => bool) private withdrawed;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    address private _incognitoProxy;
    address private _vault;

    /**
    * @dev END Storage variables
    */
    struct BurnInstData {
        uint8 meta; // type of the instruction
        uint8 shard; // ID of the Incognito shard containing the instruction, must be 1
        address token; // ETH address of the token contract (0x0 for ETH)
        address payable to; // ETH address of the receiver of the token
        uint amount; // burned amount (on Incognito)
        bytes32 itx; // Incognito's burning tx
    }

    /**
     * @dev Emitted when function burn called with amount of value to shield to incognito chain
     *
     * Note that `value` may be zero.
     */
    event Deposit(address token, string incognitoAddress, uint amount);

    /**
     * @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_, address incognitoProxy_, address vault_) {
        _name = name_;
        _symbol = symbol_;
        _incognitoProxy = incognitoProxy_;
        _vault = vault_;
    }

    /**
     * @dev Returns the address of vault.
     */
    function vault() public view virtual returns (address) {
        return _vault;
    }

    /**
     * @dev Returns the incognito proxy.
     */
    function incognitoProxy() public view virtual returns (address) {
        return _incognitoProxy;
    }

    /**
     * @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 9;
    }

    /**
     * @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");
        unchecked {
            _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");
        unchecked {
            _approve(_msgSender(), 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:
     *
     * - `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");
        require(recipient != _vault, "ERC20: transfer to incognito vault address");

        _beforeTokenTransfer(sender, recipient, amount);

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

        emit Transfer(sender, recipient, amount);

        _afterTokenTransfer(sender, recipient, amount);
    }

    /**
     * @dev Parses a burn instruction and returns the components
     * @param inst: the full instruction, containing both metadata and body
     */
    function _parseBurnInst(bytes memory inst) internal pure returns (BurnInstData memory) {
        BurnInstData memory data;
        data.meta = uint8(inst[0]);
        data.shard = uint8(inst[1]);
        address token;
        address payable to;
        uint amount;
        bytes32 itx;
        assembly {
            // skip first 0x20 bytes (stored length of inst)
            token := mload(add(inst, 0x22)) // [3:34]
            to := mload(add(inst, 0x42)) // [34:66]
            amount := mload(add(inst, 0x62)) // [66:98]
            itx := mload(add(inst, 0x82)) // [98:130]
        }
        data.token = token;
        data.to = to;
        data.amount = amount;
        data.itx = itx;
        return data;
    }

    /**
     * @dev Verifies that a burn instruction is valid
     * @notice All params except inst are the list of 2 elements corresponding to
     * the proof on beacon and bridge
     * @notice All params are the same as in `withdraw`
     */
    function _verifyInst(
        bytes memory inst,
        uint heights,
        bytes32[] memory instPaths,
        bool[] memory instPathIsLefts,
        bytes32 instRoots,
        bytes32 blkData,
        uint[] memory sigIdxs,
        uint8[] memory sigVs,
        bytes32[] memory sigRs,
        bytes32[] memory sigSs
    ) view internal {
        // Each instruction can only by redeemed once
        bytes32 beaconInstHash = keccak256(abi.encodePacked(inst, heights));

        // Verify instruction on beacon
        require(Incognito(_incognitoProxy).instructionApproved(
            true, // Only check instruction on beacon
            beaconInstHash,
            heights,
            instPaths,
            instPathIsLefts,
            instRoots,
            blkData,
            sigIdxs,
            sigVs,
            sigRs,
            sigSs
        ), "ERC20: invalid input mint data");
    }

    /**
     * @dev Mint prv by providing a burn proof over at Incognito Chain
     * @notice This function takes a burn instruction on Incognito Chain, checks
     * for its validity and mint coressponding prv token
     * @notice This only works when the contract is not Paused
     * @param inst: the decoded instruction as a list of bytes
     * @param heights: the blocks containing the instruction
     * @param instPaths: merkle path of the instruction
     * @param instPathIsLefts: whether each node on the path is the left or right child
     * @param instRoots: root of the merkle tree contains all instructions
     * @param blkData: merkle has of the block body
     * @param sigIdxs: indices of the validators who signed this block
     * @param sigVs: part of the signatures of the validators
     * @param sigRs: part of the signatures of the validators
     * @param sigSs: part of the signatures of the validators
     */
    function mint(
        bytes memory inst,
        uint heights,
        bytes32[] memory instPaths,
        bool[] memory instPathIsLefts,
        bytes32 instRoots,
        bytes32 blkData,
        uint[] memory sigIdxs,
        uint8[] memory sigVs,
        bytes32[] memory sigRs,
        bytes32[] memory sigSs
    ) external virtual returns (bool) {
        
        require(inst.length >= 130, "ERC20: invalid inst");
        BurnInstData memory data = _parseBurnInst(inst);
        // Check instruction type
        require(data.meta == 150 && data.shard == 1, "ERC20: invalid inst's data"); 
        // Check token address
        require(data.token == address(this), "ERC20: invalid token");
        // Not withdrawed
        require(!withdrawed[data.itx], "ERC20: tx is already used");
        withdrawed[data.itx] = true;
        // verify proof
        _verifyInst(
            inst,
            heights,
            instPaths,
            instPathIsLefts,
            instRoots,
            blkData,
            sigIdxs,
            sigVs,
            sigRs,
            sigSs
        );

        address account = data.to;
        uint amount = data.amount;
        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply += amount;
        _balances[account] += amount;
        emit Transfer(address(0), account, amount);

        _afterTokenTransfer(address(0), account, amount);

        return true;
    }

    /**
     * @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(string calldata incognitoAddress, uint256 amount) external virtual returns (bool) {
        address account = _msgSender();
        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;

        _afterTokenTransfer(account, address(0), amount);

        emit Deposit(address(this), incognitoAddress, amount);

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

        return true;
    }

    /**
     * @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 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 {}
}
/**
 * @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}.
 */
function _verifyInst(
        bytes memory inst,
        uint heights,
        bytes32[] memory instPaths,
        bool[] memory instPathIsLefts,
        bytes32 instRoots,
        bytes32 blkData,
        uint[] memory sigIdxs,
        uint8[] memory sigVs,
        bytes32[] memory sigRs,
        bytes32[] memory sigSs
    ) view internal {
        // Each instruction can only by redeemed once
        bytes32 beaconInstHash = keccak256(abi.encodePacked(inst, heights));

        // Verify instruction on beacon
        require(Incognito(_incognitoProxy).instructionApproved(
            true, // Only check instruction on beacon
            beaconInstHash,
            heights,
            instPaths,
            instPathIsLefts,
            instRoots,
            blkData,
            sigIdxs,
            sigVs,
            sigRs,
            sigSs
        ), "ERC20: invalid input mint data");
    }
/**
 * @dev Verifies that a burn instruction is valid
 * @notice All params except inst are the list of 2 elements corresponding to
 * the proof on beacon and bridge
 * @notice All params are the same as in `withdraw`
 */