// SPDX-License-Identifier: MIT

pragma solidity 0.8.3;



// Part: OpenZeppelin/openzeppelin-contracts@4.1.0/Context

/*
 * @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;
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.1.0/IERC20

/**
 * @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);
}

// Part: OpenZeppelin/openzeppelin-contracts@4.1.0/IERC20Metadata

/**
 * @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);
}

// Part: OpenZeppelin/openzeppelin-contracts@4.1.0/Ownable

/**
 * @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;
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.1.0/ERC20

/**
 * @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 { }
}

// Part: ControllerInterface

interface ControllerInterface {
    function mint(address to, uint amount) external returns (bool);
    function burn(uint value) external returns (bool);
    function isCustodian(address addr) external view returns (bool);
    function isBroker(address addr) external view returns (bool);
    function getToken() external view returns (ERC20);
}

// File: Bridge.sol

contract Bridge is Ownable {

    enum RequestStatus {PENDING, CANCELED, APPROVED, REJECTED}

    struct Request {
        address requester; // sender of the request.
        uint amount; // amount of token to mint/burn.
        string depositAddress; // custodian's asset address in mint, broker's asset address in burn.
        string txid; // asset txid for sending/redeeming asset in the mint/burn process.
        uint nonce; // serial number allocated for each request.
        uint timestamp; // time of the request creation.
        RequestStatus status; // status of the request.
    }

    ControllerInterface public controller;

    // mapping between broker to the corresponding custodian deposit address, used in the minting process.
    // by using a different deposit address per broker the custodian can identify which broker deposited.
    mapping(address=>string) public custodianDepositAddress;

    // mapping between broker to the its deposit address where the asset should be moved to, used in the burning process.
    mapping(address=>string) public brokerDepositAddress;

    // mapping between a mint request hash and the corresponding request nonce. 
    mapping(bytes32=>uint) public mintRequestNonce;

    // mapping between a burn request hash and the corresponding request nonce.
    mapping(bytes32=>uint) public burnRequestNonce;

    Request[] public mintRequests;
    Request[] public burnRequests;

    constructor(address _controller) {
        require(_controller != address(0), "invalid _controller address");
        controller = ControllerInterface(_controller);
        transferOwnership(_controller);
    }

    modifier onlyBroker() {
        require(controller.isBroker(msg.sender), "sender not a broker.");
        _;
    }

    modifier onlyCustodian() {
        require(controller.isCustodian(msg.sender), "sender not a custodian.");
        _;
    }

    event CustodianDepositAddressSet(address indexed broker, address indexed sender, string depositAddress);

    function setCustodianDepositAddress(
        address broker,
        string memory depositAddress
    )
        external
        onlyCustodian
        returns (bool) 
    {
        require(broker != address(0), "invalid broker address");
        require(controller.isBroker(broker), "broker address is not a real broker.");
        require(!isEmptyString(depositAddress), "invalid asset deposit address");

        custodianDepositAddress[broker] = depositAddress;
        emit CustodianDepositAddressSet(broker, msg.sender, depositAddress);
        return true;
    }

    event BrokerDepositAddressSet(address indexed broker, string depositAddress);

    function setBrokerDepositAddress(string memory depositAddress) external onlyBroker returns (bool) {
        require(!isEmptyString(depositAddress), "invalid asset deposit address");

        brokerDepositAddress[msg.sender] = depositAddress;
        emit BrokerDepositAddressSet(msg.sender, depositAddress);
        return true; 
    }

    event MintRequestAdd(
        uint indexed nonce,
        address indexed requester,
        uint amount,
        string depositAddress,
        string txid,
        uint timestamp,
        bytes32 requestHash
    );

    function addMintRequest(
        uint amount,
        string memory txid,
        string memory depositAddress
    )
        external
        onlyBroker
        returns (bool)
    {
        require(!isEmptyString(depositAddress), "invalid asset deposit address"); 
        require(compareStrings(depositAddress, custodianDepositAddress[msg.sender]), "wrong asset deposit address");

        uint nonce = mintRequests.length;
        uint timestamp = getTimestamp();

        Request memory request = Request({
            requester: msg.sender,
            amount: amount,
            depositAddress: depositAddress,
            txid: txid,
            nonce: nonce,
            timestamp: timestamp,
            status: RequestStatus.PENDING
        });

        bytes32 requestHash = calcRequestHash(request);
        mintRequestNonce[requestHash] = nonce; 
        mintRequests.push(request);

        emit MintRequestAdd(nonce, msg.sender, amount, depositAddress, txid, timestamp, requestHash);
        return true;
    }

    event MintRequestCancel(uint indexed nonce, address indexed requester, bytes32 requestHash);

    function cancelMintRequest(bytes32 requestHash) external onlyBroker returns (bool) {
        uint nonce;
        Request memory request;

        (nonce, request) = getPendingMintRequest(requestHash);

        require(msg.sender == request.requester, "cancel sender is different than pending request initiator");
        mintRequests[nonce].status = RequestStatus.CANCELED;

        emit MintRequestCancel(nonce, msg.sender, requestHash);
        return true;
    }

    event MintConfirmed(
        uint indexed nonce,
        address indexed requester,
        uint amount,
        string depositAddress,
        string txid,
        uint timestamp,
        bytes32 requestHash
    );

    function confirmMintRequest(bytes32 requestHash) external onlyCustodian returns (bool) {
        uint nonce;
        Request memory request;

        (nonce, request) = getPendingMintRequest(requestHash);

        mintRequests[nonce].status = RequestStatus.APPROVED;
        require(controller.mint(request.requester, request.amount), "mint failed");

        emit MintConfirmed(
            request.nonce,
            request.requester,
            request.amount,
            request.depositAddress,
            request.txid,
            request.timestamp,
            requestHash
        );
        return true;
    }

    event MintRejected(
        uint indexed nonce,
        address indexed requester,
        uint amount,
        string depositAddress,
        string txid,
        uint timestamp,
        bytes32 requestHash
    );

    function rejectMintRequest(bytes32 requestHash) external onlyCustodian returns (bool) {
        uint nonce;
        Request memory request;

        (nonce, request) = getPendingMintRequest(requestHash);

        mintRequests[nonce].status = RequestStatus.REJECTED;

        emit MintRejected(
            request.nonce,
            request.requester,
            request.amount,
            request.depositAddress,
            request.txid,
            request.timestamp,
            requestHash
        );
        return true;
    }

    event Burned(
        uint indexed nonce,
        address indexed requester,
        uint amount,
        string depositAddress,
        uint timestamp,
        bytes32 requestHash
    );

    function burn(uint amount) external onlyBroker returns (bool) {
        string memory depositAddress = brokerDepositAddress[msg.sender];
        require(!isEmptyString(depositAddress), "broker asset deposit address was not set");

        uint nonce = burnRequests.length;
        uint timestamp = getTimestamp();

        // set txid as empty since it is not known yet.
        string memory txid = "";
        Request memory request = Request({
            requester: msg.sender,
            amount: amount,
            depositAddress: depositAddress,
            txid: txid,
            nonce: nonce,
            timestamp: timestamp,
            status: RequestStatus.PENDING
        });

        bytes32 requestHash = calcRequestHash(request);
        burnRequestNonce[requestHash] = nonce; 
        burnRequests.push(request);

        require(controller.getToken().transferFrom(msg.sender, address(controller), amount), "transfer tokens to burn failed");
        require(controller.burn(amount), "burn failed");

        emit Burned(nonce, msg.sender, amount, depositAddress, timestamp, requestHash);
        return true;
    }

    event BurnConfirmed(
        uint indexed nonce,
        address indexed requester,
        uint amount,
        string depositAddress,
        string txid,
        uint timestamp,
        bytes32 inputRequestHash
    );

    function confirmBurnRequest(bytes32 requestHash, string memory txid) external onlyCustodian returns (bool) {
        uint nonce;
        Request memory request;

        (nonce, request) = getPendingBurnRequest(requestHash);

        burnRequests[nonce].txid = txid;
        burnRequests[nonce].status = RequestStatus.APPROVED;
        burnRequestNonce[calcRequestHash(burnRequests[nonce])] = nonce;

        emit BurnConfirmed(
            request.nonce,
            request.requester,
            request.amount,
            request.depositAddress,
            txid,
            request.timestamp,
            requestHash
        );
        return true;
    }

    function getMintRequest(uint nonce)
        external
        view
        returns (
            uint requestNonce,
            address requester,
            uint amount,
            string memory depositAddress,
            string memory txid,
            uint timestamp,
            string memory status,
            bytes32 requestHash
        )
    {
        Request memory request = mintRequests[nonce];
        string memory statusString = getStatusString(request.status); 

        requestNonce = request.nonce;
        requester = request.requester;
        amount = request.amount;
        depositAddress = request.depositAddress;
        txid = request.txid;
        timestamp = request.timestamp;
        status = statusString;
        requestHash = calcRequestHash(request);
    }

    function getMintRequestsLength() external view returns (uint length) {
        return mintRequests.length;
    }

    function getBurnRequest(uint nonce)
        external
        view
        returns (
            uint requestNonce,
            address requester,
            uint amount,
            string memory depositAddress,
            string memory txid,
            uint timestamp,
            string memory status,
            bytes32 requestHash
        )
    {
        Request storage request = burnRequests[nonce];
        string memory statusString = getStatusString(request.status); 

        requestNonce = request.nonce;
        requester = request.requester;
        amount = request.amount;
        depositAddress = request.depositAddress;
        txid = request.txid;
        timestamp = request.timestamp;
        status = statusString;
        requestHash = calcRequestHash(request);
    }

    function getBurnRequestsLength() external view returns (uint length) {
        return burnRequests.length;
    }

    function getTimestamp() internal view returns (uint) {
        // timestamp is only used for data maintaining purpose, it is not relied on for critical logic.
        return block.timestamp; // solhint-disable-line not-rely-on-time
    }

    function getPendingMintRequest(bytes32 requestHash) internal view returns (uint nonce, Request memory request) {
        require(requestHash != 0, "request hash is 0");
        nonce = mintRequestNonce[requestHash];
        request = mintRequests[nonce];
        validatePendingRequest(request, requestHash);
    }

    function getPendingBurnRequest(bytes32 requestHash) internal view returns (uint nonce, Request memory request) {
        require(requestHash != 0, "request hash is 0");
        nonce = burnRequestNonce[requestHash];
        request = burnRequests[nonce];
        validatePendingRequest(request, requestHash);
    }

    function validatePendingRequest(Request memory request, bytes32 requestHash) internal pure {
        require(request.status == RequestStatus.PENDING, "request is not pending");
        require(requestHash == calcRequestHash(request), "given request hash does not match a pending request");
    }

    function calcRequestHash(Request memory request) internal pure returns (bytes32) {
        return keccak256(abi.encode(
            request.requester,
            request.amount,
            request.depositAddress,
            request.txid,
            request.nonce,
            request.timestamp
        ));
    }

    function compareStrings (string memory a, string memory b) internal pure returns (bool) {
        return (keccak256(abi.encodePacked(a)) == keccak256(abi.encodePacked(b)));
    }

    function isEmptyString (string memory a) internal pure returns (bool) {
        return (compareStrings(a, ""));
    }

    function getStatusString(RequestStatus status) internal pure returns (string memory) {
        if (status == RequestStatus.PENDING) {
            return "pending";
        } else if (status == RequestStatus.CANCELED) {
            return "canceled";
        } else if (status == RequestStatus.APPROVED) {
            return "approved";
        } else if (status == RequestStatus.REJECTED) {
            return "rejected";
        } else {
            // this fallback can never be reached.
            return "unknown";
        }
    }
}