// File: contracts/Vouchers.sol



// SPDX-License-Identifier: LGPL-3.0-or-later

pragma solidity 0.7.6;

import "@openzeppelin/contracts/utils/Address.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol";
import "@openzeppelin/contracts/utils/Pausable.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import "./interfaces/IVoucherKernel.sol";
import "./interfaces/ICashier.sol";
import "./interfaces/IVouchers.sol";

//preparing for ERC-1066, ERC-1444, EIP-838

/**
 * @title Vouchers implemented as ERC-721
 */
contract Vouchers is IVouchers, ERC721, Ownable, Pausable {
    using Address for address;
    using Strings for uint256;

    //min security
    address private voucherKernelAddress; //address of the VoucherKernel contract
    address private cashierAddress; //address of the Cashier contract
    string private contractUri;

    event LogVoucherKernelSet(address _newVoucherKernel, address _triggeredBy);
    event LogCashierSet(address _newCashier, address _triggeredBy);
    event LogUriSet(string _newUri, address _triggeredBy);
    event LogContractUriSet(string _contractUri, address _triggeredBy);

    modifier onlyFromVoucherKernel() {
        require(msg.sender == voucherKernelAddress, "UNAUTHORIZED_VK");
        _;
    }

    modifier notZeroAddress(address _address) {
        require(_address != address(0), "ZERO_ADDRESS");
        _;
    }

    /**
     * @notice Construct and initialze the contract. 
     * @param baseURI_ base metadata uri
     * @param name_ token name
     * @param symbol_ token symbol
     * @param _cashierAddress address of the associated Cashier contract
     * @param _voucherKernelAddress address of the associated Voucher Kernel contract
     */
    constructor(string memory baseURI_, string memory name_, string memory symbol_, address _cashierAddress, address _voucherKernelAddress) 
        ERC721(name_, symbol_) notZeroAddress(_cashierAddress) notZeroAddress(_voucherKernelAddress)
    {
        _setBaseURI(baseURI_);

        cashierAddress = _cashierAddress;
        voucherKernelAddress = _voucherKernelAddress;
    }

    /**
     * @notice Pause the process of interaction with voucherID's (ERC-721), in case of emergency.
     * Only BR contract is in control of this function.
     */
    function pause() external override onlyOwner {
        _pause();
    }

    /**
     * @notice Unpause the process of interaction with voucherID's (ERC-721).
     * Only BR contract is in control of this function.
     */
    function unpause() external override onlyOwner {
        _unpause();
    }

    /**
     * @notice Safely transfers the ownership of a given token ID to another address
     * If the target address is a contract, it must implement `onERC721Received`
     * Requires the msg.sender to be the owner, approved, or operator
     * @dev ERC-721
     * @param _from current owner of the token
     * @param _to address to receive the ownership of the given token ID
     * @param _tokenId uint256 ID of the token to be transferred
     * @param _data bytes data to send along with a safe transfer check
     */
     function safeTransferFrom(
        address _from,
        address _to,
        uint256 _tokenId,
        bytes memory _data
    ) public override (ERC721, IERC721)  
    {
        transferFrom(_from, _to, _tokenId);

        _doSafeTransferAcceptanceCheck(
            _from,
            _to,
            _tokenId,
            _data
        );
    }
    /**
     * @notice Transfers the ownership of a given token ID to another address.
     * Usage of this method is discouraged, use `safeTransferFrom` whenever possible.
     * Requires the msg.sender to be the owner, approved, or operator.
     * @dev ERC-721
     * @param _from current owner of the token
     * @param _to address to receive the ownership of the given token ID
     * @param _tokenId uint256 ID of the token to be transferred
     */
    function transferFrom(
        address _from,
        address _to,
        uint256 _tokenId
    ) public 
      override (ERC721, IERC721) 
    {
        super.transferFrom(_from, _to, _tokenId);
        require(IVoucherKernel(voucherKernelAddress).isVoucherTransferable(_tokenId), "FUNDS_RELEASED");

        ICashier(cashierAddress).onVoucherTransfer(
            _from,
            _to,
            _tokenId
        );
    }

    /**
     * @notice Function to mint tokens.
     * @dev ERC-721
     * @param _to The address that will receive the minted tokens.
     * @param _tokenId The token id to mint.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(address _to, uint256 _tokenId)
        external
        override
        onlyFromVoucherKernel
        returns (bool)
    {
        super._mint(_to, _tokenId);
        _doSafeTransferAcceptanceCheck(
            address(0),
            _to,
            _tokenId,
            ""
        );
        return true;
    }

    /* Burning ERC-721 is not allowed, as a voucher (being an ERC-721 token) has a final state and shouldn't be destroyed. */

    // // // // // // // //
    // METADATA EXTENSIONS
    // // // // // // // //

    /**
     * @notice Setting the URL prefix for tokens metadata
     * @param _newUri   New prefix to be used
     */

    function setTokenURI(string memory _newUri) external onlyOwner {
        require(bytes(_newUri).length != 0, "INVALID_VALUE");
        super._setBaseURI(_newUri);
        emit LogUriSet(_newUri, _msgSender());
    }

    /**
     * @notice Setting a contractURI for OpenSea collections integration.
     * @param _contractUri   The contract URI to be used
     */
    function setContractUri(string memory _contractUri) external onlyOwner {
        require(bytes(_contractUri).length != 0, "INVALID_VALUE");
        contractUri = _contractUri;
        emit LogContractUriSet(_contractUri, _msgSender());
    }

    // // // // // // // //
    // UTILS
    // // // // // // // //

    /**
     * @notice Set the address of the VoucherKernel contract
     * @param _voucherKernelAddress   The address of the Voucher Kernel contract
     */
    function setVoucherKernelAddress(address _voucherKernelAddress)
        external
        override
        onlyOwner
        notZeroAddress(_voucherKernelAddress)
        whenPaused
    {
        voucherKernelAddress = _voucherKernelAddress;

        emit LogVoucherKernelSet(_voucherKernelAddress, msg.sender);
    }

    /**
     * @notice Set the address of the cashier contract
     * @param _cashierAddress   The Cashier contract
     */
    function setCashierAddress(address _cashierAddress)
        external
        override
        onlyOwner
        notZeroAddress(_cashierAddress)
        whenPaused
    {
        cashierAddress = _cashierAddress;
        emit LogCashierSet(_cashierAddress, msg.sender);
    }

    /**
     * @notice Get the address of Voucher Kernel contract
     * @return Address of Voucher Kernel contract
     */
    function getVoucherKernelAddress() 
        external 
        view 
        override
        returns (address)
    {
        return voucherKernelAddress;
    }

    /**
     * @notice Get the address of Cashier contract
     * @return Address of Cashier address
     */
    function getCashierAddress() 
        external 
        view 
        override
        returns (address)
    {
        return cashierAddress;
    }

    /**
     * @notice Check successful transfer if recipient is a contract
     * @dev ERC-721
     * https://github.com/OpenZeppelin/openzeppelin-contracts/blob/v4.4.0-rc.0/contracts/token/ERC721/ERC721.sol
     * @param _from     Address of sender
     * @param _to       Address of recipient
     * @param _tokenId  ID of the token
     * @param _data     Optional data
     */
    function _doSafeTransferAcceptanceCheck(
        address _from,
        address _to,
        uint256 _tokenId,
        bytes memory _data
    ) internal {
        if (_to.isContract()) {
            try IERC721Receiver(_to).onERC721Received(_msgSender(), _from, _tokenId, _data) returns (bytes4 response) {
                if (response != IERC721Receiver.onERC721Received.selector) {
                    revert("ERC721: transfer to non ERC721Receiver implementer");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC721: transfer to non ERC721Receiver implementer");
            }
        }
    }

    /**
     * @notice Get the contractURI for Opensea collections integration
     * @return Contract URI
     */
    function contractURI() public view returns (string memory) {
        return contractUri;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "../utils/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

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

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: @openzeppelin/contracts/token/ERC721/ERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "../../utils/Context.sol";
import "./IERC721.sol";
import "./IERC721Metadata.sol";
import "./IERC721Enumerable.sol";
import "./IERC721Receiver.sol";
import "../../introspection/ERC165.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";
import "../../utils/EnumerableSet.sol";
import "../../utils/EnumerableMap.sol";
import "../../utils/Strings.sol";

/**
 * @title ERC721 Non-Fungible Token Standard basic implementation
 * @dev see https://eips.ethereum.org/EIPS/eip-721
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata, IERC721Enumerable {
    using SafeMath for uint256;
    using Address for address;
    using EnumerableSet for EnumerableSet.UintSet;
    using EnumerableMap for EnumerableMap.UintToAddressMap;
    using Strings for uint256;

    // Equals to `bytes4(keccak256("onERC721Received(address,address,uint256,bytes)"))`
    // which can be also obtained as `IERC721Receiver(0).onERC721Received.selector`
    bytes4 private constant _ERC721_RECEIVED = 0x150b7a02;

    // Mapping from holder address to their (enumerable) set of owned tokens
    mapping (address => EnumerableSet.UintSet) private _holderTokens;

    // Enumerable mapping from token ids to their owners
    EnumerableMap.UintToAddressMap private _tokenOwners;

    // Mapping from token ID to approved address
    mapping (uint256 => address) private _tokenApprovals;

    // Mapping from owner to operator approvals
    mapping (address => mapping (address => bool)) private _operatorApprovals;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Optional mapping for token URIs
    mapping (uint256 => string) private _tokenURIs;

    // Base URI
    string private _baseURI;

    /*
     *     bytes4(keccak256('balanceOf(address)')) == 0x70a08231
     *     bytes4(keccak256('ownerOf(uint256)')) == 0x6352211e
     *     bytes4(keccak256('approve(address,uint256)')) == 0x095ea7b3
     *     bytes4(keccak256('getApproved(uint256)')) == 0x081812fc
     *     bytes4(keccak256('setApprovalForAll(address,bool)')) == 0xa22cb465
     *     bytes4(keccak256('isApprovedForAll(address,address)')) == 0xe985e9c5
     *     bytes4(keccak256('transferFrom(address,address,uint256)')) == 0x23b872dd
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256)')) == 0x42842e0e
     *     bytes4(keccak256('safeTransferFrom(address,address,uint256,bytes)')) == 0xb88d4fde
     *
     *     => 0x70a08231 ^ 0x6352211e ^ 0x095ea7b3 ^ 0x081812fc ^
     *        0xa22cb465 ^ 0xe985e9c5 ^ 0x23b872dd ^ 0x42842e0e ^ 0xb88d4fde == 0x80ac58cd
     */
    bytes4 private constant _INTERFACE_ID_ERC721 = 0x80ac58cd;

    /*
     *     bytes4(keccak256('name()')) == 0x06fdde03
     *     bytes4(keccak256('symbol()')) == 0x95d89b41
     *     bytes4(keccak256('tokenURI(uint256)')) == 0xc87b56dd
     *
     *     => 0x06fdde03 ^ 0x95d89b41 ^ 0xc87b56dd == 0x5b5e139f
     */
    bytes4 private constant _INTERFACE_ID_ERC721_METADATA = 0x5b5e139f;

    /*
     *     bytes4(keccak256('totalSupply()')) == 0x18160ddd
     *     bytes4(keccak256('tokenOfOwnerByIndex(address,uint256)')) == 0x2f745c59
     *     bytes4(keccak256('tokenByIndex(uint256)')) == 0x4f6ccce7
     *
     *     => 0x18160ddd ^ 0x2f745c59 ^ 0x4f6ccce7 == 0x780e9d63
     */
    bytes4 private constant _INTERFACE_ID_ERC721_ENUMERABLE = 0x780e9d63;

    /**
     * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
     */
    constructor (string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;

        // register the supported interfaces to conform to ERC721 via ERC165
        _registerInterface(_INTERFACE_ID_ERC721);
        _registerInterface(_INTERFACE_ID_ERC721_METADATA);
        _registerInterface(_INTERFACE_ID_ERC721_ENUMERABLE);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _holderTokens[owner].length();
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        return _tokenOwners.get(tokenId, "ERC721: owner query for nonexistent token");
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory _tokenURI = _tokenURIs[tokenId];
        string memory base = baseURI();

        // If there is no base URI, return the token URI.
        if (bytes(base).length == 0) {
            return _tokenURI;
        }
        // If both are set, concatenate the baseURI and tokenURI (via abi.encodePacked).
        if (bytes(_tokenURI).length > 0) {
            return string(abi.encodePacked(base, _tokenURI));
        }
        // If there is a baseURI but no tokenURI, concatenate the tokenID to the baseURI.
        return string(abi.encodePacked(base, tokenId.toString()));
    }

    /**
    * @dev Returns the base URI set via {_setBaseURI}. This will be
    * automatically added as a prefix in {tokenURI} to each token's URI, or
    * to the token ID if no specific URI is set for that token ID.
    */
    function baseURI() public view virtual returns (string memory) {
        return _baseURI;
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        return _holderTokens[owner].at(index);
    }

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        // _tokenOwners are indexed by tokenIds, so .length() returns the number of tokenIds
        return _tokenOwners.length();
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        (uint256 tokenId, ) = _tokenOwners.at(index);
        return tokenId;
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ERC721.ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(_msgSender() == owner || ERC721.isApprovedForAll(owner, _msgSender()),
            "ERC721: approve caller is not owner nor approved for all"
        );

        _approve(to, tokenId);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view virtual override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(operator != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC721-isApprovedForAll}.
     */
    function isApprovedForAll(address owner, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(address from, address to, uint256 tokenId) public virtual override {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes memory _data) public virtual override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * `_data` is additional data, it has no specified format and it is sent in call to `to`.
     *
     * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
     * implement alternative mechanisms to perform token transfer, such as signature-based.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeTransfer(address from, address to, uint256 tokenId, bytes memory _data) internal virtual {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _tokenOwners.contains(tokenId);
    }

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721.ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || ERC721.isApprovedForAll(owner, spender));
    }

    /**
     * @dev Safely mints `tokenId` and transfers it to `to`.
     *
     * Requirements:
     d*
     * - `tokenId` must not exist.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
     * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
     */
    function _safeMint(address to, uint256 tokenId, bytes memory _data) internal virtual {
        _mint(to, tokenId);
        require(_checkOnERC721Received(address(0), to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Mints `tokenId` and transfers it to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
     *
     * Requirements:
     *
     * - `tokenId` must not exist.
     * - `to` cannot be the zero address.
     *
     * Emits a {Transfer} event.
     */
    function _mint(address to, uint256 tokenId) internal virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _beforeTokenTransfer(address(0), to, tokenId);

        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @dev Destroys `tokenId`.
     * The approval is cleared when the token is burned.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     *
     * Emits a {Transfer} event.
     */
    function _burn(uint256 tokenId) internal virtual {
        address owner = ERC721.ownerOf(tokenId); // internal owner

        _beforeTokenTransfer(owner, address(0), tokenId);

        // Clear approvals
        _approve(address(0), tokenId);

        // Clear metadata (if any)
        if (bytes(_tokenURIs[tokenId]).length != 0) {
            delete _tokenURIs[tokenId];
        }

        _holderTokens[owner].remove(tokenId);

        _tokenOwners.remove(tokenId);

        emit Transfer(owner, address(0), tokenId);
    }

    /**
     * @dev Transfers `tokenId` from `from` to `to`.
     *  As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     *
     * Emits a {Transfer} event.
     */
    function _transfer(address from, address to, uint256 tokenId) internal virtual {
        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own"); // internal owner
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        _holderTokens[from].remove(tokenId);
        _holderTokens[to].add(tokenId);

        _tokenOwners.set(tokenId, to);

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Sets `_tokenURI` as the tokenURI of `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _setTokenURI(uint256 tokenId, string memory _tokenURI) internal virtual {
        require(_exists(tokenId), "ERC721Metadata: URI set of nonexistent token");
        _tokenURIs[tokenId] = _tokenURI;
    }

    /**
     * @dev Internal function to set the base URI for all token IDs. It is
     * automatically added as a prefix to the value returned in {tokenURI},
     * or to the token ID if {tokenURI} is empty.
     */
    function _setBaseURI(string memory baseURI_) internal virtual {
        _baseURI = baseURI_;
    }

    /**
     * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
     * The call is not executed if the target address is not a contract.
     *
     * @param from address representing the previous owner of the given token ID
     * @param to target address that will receive the tokens
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes optional data to send along with the call
     * @return bool whether the call correctly returned the expected magic value
     */
    function _checkOnERC721Received(address from, address to, uint256 tokenId, bytes memory _data)
        private returns (bool)
    {
        if (!to.isContract()) {
            return true;
        }
        bytes memory returndata = to.functionCall(abi.encodeWithSelector(
            IERC721Receiver(to).onERC721Received.selector,
            _msgSender(),
            from,
            tokenId,
            _data
        ), "ERC721: transfer to non ERC721Receiver implementer");
        bytes4 retval = abi.decode(returndata, (bytes4));
        return (retval == _ERC721_RECEIVED);
    }

    /**
     * @dev Approve `to` to operate on `tokenId`
     *
     * Emits an {Approval} event.
     */
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId); // internal owner
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 tokenId) internal virtual { }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
     */
    function onERC721Received(address operator, address from, uint256 tokenId, bytes calldata data) external returns (bytes4);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "./Context.sol";

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor () {
        _paused = false;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!paused(), "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        require(paused(), "Pausable: not paused");
        _;
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev String operations.
 */
library Strings {
    /**
     * @dev Converts a `uint256` to its ASCII `string` representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        uint256 index = digits - 1;
        temp = value;
        while (temp != 0) {
            buffer[index--] = bytes1(uint8(48 + temp % 10));
            temp /= 10;
        }
        return string(buffer);
    }
}

// File: contracts/interfaces/IVoucherKernel.sol



// SPDX-License-Identifier: LGPL-3.0-or-later
pragma solidity 0.7.6;

import "./../UsingHelpers.sol";

interface IVoucherKernel {
    /**
     * @notice Pause the process of interaction with voucherID's (ERC-721), in case of emergency.
     * Only Cashier contract is in control of this function.
     */
    function pause() external;

    /**
     * @notice Unpause the process of interaction with voucherID's (ERC-721).
     * Only Cashier contract is in control of this function.
     */
    function unpause() external;

    /**
     * @notice Creating a new promise for goods or services.
     * Can be reused, e.g. for making different batches of these (but not in prototype).
     * @param _seller      seller of the promise
     * @param _validFrom   Start of valid period
     * @param _validTo     End of valid period
     * @param _price       Price (payment amount)
     * @param _depositSe   Seller's deposit
     * @param _depositBu   Buyer's deposit
     */
    function createTokenSupplyId(
        address _seller,
        uint256 _validFrom,
        uint256 _validTo,
        uint256 _price,
        uint256 _depositSe,
        uint256 _depositBu,
        uint256 _quantity
    ) external returns (uint256);

    /**
     * @notice Creates a Payment method struct recording the details on how the seller requires to receive Price and Deposits for a certain Voucher Set.
     * @param _tokenIdSupply     _tokenIdSupply of the voucher set this is related to
     * @param _paymentMethod  might be ETHETH, ETHTKN, TKNETH or TKNTKN
     * @param _tokenPrice   token address which will hold the funds for the price of the voucher
     * @param _tokenDeposits   token address which will hold the funds for the deposits of the voucher
     */
    function createPaymentMethod(
        uint256 _tokenIdSupply,
        PaymentMethod _paymentMethod,
        address _tokenPrice,
        address _tokenDeposits
    ) external;

    /**
     * @notice Mark voucher token that the payment was released
     * @param _tokenIdVoucher   ID of the voucher token
     */
    function setPaymentReleased(uint256 _tokenIdVoucher) external;

    /**
     * @notice Mark voucher token that the deposits were released
     * @param _tokenIdVoucher   ID of the voucher token
     */
    function setDepositsReleased(uint256 _tokenIdVoucher) external;

    /**
     * @notice Redemption of the vouchers promise
     * @param _tokenIdVoucher   ID of the voucher
     * @param _messageSender owner of the voucher
     */
    function redeem(uint256 _tokenIdVoucher, address _messageSender) external;

    /**
     * @notice Refunding a voucher
     * @param _tokenIdVoucher   ID of the voucher
     * @param _messageSender owner of the voucher
     */
    function refund(uint256 _tokenIdVoucher, address _messageSender) external;

    /**
     * @notice Issue a complain for a voucher
     * @param _tokenIdVoucher   ID of the voucher
     * @param _messageSender owner of the voucher
     */
    function complain(uint256 _tokenIdVoucher, address _messageSender) external;

    /**
     * @notice Cancel/Fault transaction by the Seller, admitting to a fault or backing out of the deal
     * @param _tokenIdVoucher   ID of the voucher
     * @param _messageSender owner of the voucher set (seller)
     */
    function cancelOrFault(uint256 _tokenIdVoucher, address _messageSender)
        external;

    /**
     * @notice Cancel/Fault transaction by the Seller, cancelling the remaining uncommitted voucher set so that seller prevents buyers from committing to vouchers for items no longer in exchange.
     * @param _tokenIdSupply   ID of the voucher
     * @param _issuer   owner of the voucher
     */
    function cancelOrFaultVoucherSet(uint256 _tokenIdSupply, address _issuer)
        external
        returns (uint256);

    /**
     * @notice Fill Voucher Order, iff funds paid, then extract & mint NFT to the voucher holder
     * @param _tokenIdSupply   ID of the supply token (ERC-1155)
     * @param _issuer          Address of the token's issuer
     * @param _holder          Address of the recipient of the voucher (ERC-721)
     * @param _paymentMethod   method being used for that particular order that needs to be fulfilled
     */
    function fillOrder(
        uint256 _tokenIdSupply,
        address _issuer,
        address _holder,
        PaymentMethod _paymentMethod
    ) external;

    /**
     * @notice Mark voucher token as expired
     * @param _tokenIdVoucher   ID of the voucher token
     */
    function triggerExpiration(uint256 _tokenIdVoucher) external;

    /**
     * @notice Mark voucher token to the final status
     * @param _tokenIdVoucher   ID of the voucher token
     */
    function triggerFinalizeVoucher(uint256 _tokenIdVoucher) external;

    /**
     * @notice Set the address of the new holder of a _tokenIdSupply on transfer
     * @param _tokenIdSupply   _tokenIdSupply which will be transferred
     * @param _newSeller   new holder of the supply
     */
    function setSupplyHolderOnTransfer(
        uint256 _tokenIdSupply,
        address _newSeller
    ) external;

    /**
     * @notice Set the general cancelOrFault period, should be used sparingly as it has significant consequences. Here done simply for demo purposes.
     * @param _cancelFaultPeriod   the new value for cancelOrFault period (in number of seconds)
     */
    function setCancelFaultPeriod(uint256 _cancelFaultPeriod) external;

    /**
     * @notice Set the address of the Boson Router contract
     * @param _bosonRouterAddress   The address of the BR contract
     */
    function setBosonRouterAddress(address _bosonRouterAddress) external;

    /**
     * @notice Set the address of the Cashier contract
     * @param _cashierAddress   The address of the Cashier contract
     */
    function setCashierAddress(address _cashierAddress) external;

    /**
     * @notice Set the address of the Vouchers token contract, an ERC721 contract
     * @param _voucherTokenAddress   The address of the Vouchers token contract
     */
    function setVoucherTokenAddress(address _voucherTokenAddress) external;

    /**
     * @notice Set the address of the Voucher Sets token contract, an ERC1155 contract
     * @param _voucherSetTokenAddress   The address of the Voucher Sets token contract
     */
    function setVoucherSetTokenAddress(address _voucherSetTokenAddress)
        external;

    /**
     * @notice Set the general complain period, should be used sparingly as it has significant consequences. Here done simply for demo purposes.
     * @param _complainPeriod   the new value for complain period (in number of seconds)
     */
    function setComplainPeriod(uint256 _complainPeriod) external;

    /**
     * @notice Get the promise ID at specific index
     * @param _idx  Index in the array of promise keys
     * @return      Promise ID
     */
    function getPromiseKey(uint256 _idx) external view returns (bytes32);

    /**
     * @notice Get the address of the token where the price for the supply is held
     * @param _tokenIdSupply   ID of the voucher token
     * @return                  Address of the token
     */
    function getVoucherPriceToken(uint256 _tokenIdSupply)
        external
        view
        returns (address);

    /**
     * @notice Get the address of the token where the deposits for the supply are held
     * @param _tokenIdSupply   ID of the voucher token
     * @return                  Address of the token
     */
    function getVoucherDepositToken(uint256 _tokenIdSupply)
        external
        view
        returns (address);

    /**
     * @notice Get Buyer costs required to make an order for a supply token
     * @param _tokenIdSupply   ID of the supply token
     * @return                  returns a tuple (Payment amount, Buyer's deposit)
     */
    function getBuyerOrderCosts(uint256 _tokenIdSupply)
        external
        view
        returns (uint256, uint256);

    /**
     * @notice Get Seller deposit
     * @param _tokenIdSupply   ID of the supply token
     * @return                  returns sellers deposit
     */
    function getSellerDeposit(uint256 _tokenIdSupply)
        external
        view
        returns (uint256);

    /**
     * @notice Get the promise ID from a voucher token
     * @param _tokenIdVoucher   ID of the voucher token
     * @return                  ID of the promise
     */
    function getIdSupplyFromVoucher(uint256 _tokenIdVoucher)
        external
        pure
        returns (uint256);

    /**
     * @notice Get the promise ID from a voucher token
     * @param _tokenIdVoucher   ID of the voucher token
     * @return                  ID of the promise
     */
    function getPromiseIdFromVoucherId(uint256 _tokenIdVoucher)
        external
        view
        returns (bytes32);

    /**
     * @notice Get all necessary funds for a supply token
     * @param _tokenIdSupply   ID of the supply token
     * @return                  returns a tuple (Payment amount, Seller's deposit, Buyer's deposit)
     */
    function getOrderCosts(uint256 _tokenIdSupply)
        external
        view
        returns (
            uint256,
            uint256,
            uint256
        );

    /**
     * @notice Get the remaining quantity left in supply of tokens (e.g ERC-721 left in ERC-1155) of an account
     * @param _tokenSupplyId  Token supply ID
     * @param _owner    holder of the Token Supply
     * @return          remaining quantity
     */
    function getRemQtyForSupply(uint256 _tokenSupplyId, address _owner)
        external
        view
        returns (uint256);

    /**
     * @notice Get the payment method for a particular _tokenIdSupply
     * @param _tokenIdSupply   ID of the voucher supply token
     * @return                  payment method
     */
    function getVoucherPaymentMethod(uint256 _tokenIdSupply)
        external
        view
        returns (PaymentMethod);

    /**
     * @notice Get the current status of a voucher
     * @param _tokenIdVoucher   ID of the voucher token
     * @return                  Status of the voucher (via enum)
     */
    function getVoucherStatus(uint256 _tokenIdVoucher)
        external
        view
        returns (
            uint8,
            bool,
            bool,
            uint256,
            uint256
        );

    /**
     * @notice Get the holder of a supply
     * @param _tokenIdSupply    _tokenIdSupply ID of the order (aka VoucherSet) which is mapped to the corresponding Promise.
     * @return                  Address of the holder
     */
    function getSupplyHolder(uint256 _tokenIdSupply)
        external
        view
        returns (address);

    /**
     * @notice Get the holder of a voucher
     * @param _tokenIdVoucher   ID of the voucher token
     * @return                  Address of the holder
     */
    function getVoucherHolder(uint256 _tokenIdVoucher)
        external
        view
        returns (address);

    /**
     * @notice Checks whether a voucher is in valid period for redemption (between start date and end date)
     * @param _tokenIdVoucher ID of the voucher token
     */
    function isInValidityPeriod(uint256 _tokenIdVoucher)
        external
        view
        returns (bool);

    /**
     * @notice Checks whether a voucher is in valid state to be transferred. If either payments or deposits are released, voucher could not be transferred
     * @param _tokenIdVoucher ID of the voucher token
     */
    function isVoucherTransferable(uint256 _tokenIdVoucher)
        external
        view
        returns (bool);

    /**
     * @notice Get address of the Boson Router contract to which this contract points
     * @return Address of the Boson Router contract
     */
    function getBosonRouterAddress() external view returns (address);

    /**
     * @notice Get address of the Cashier contract to which this contract points
     * @return Address of the Cashier contract
     */
    function getCashierAddress() external view returns (address);

    /**
     * @notice Get the token nonce for a seller
     * @param _seller Address of the seller
     * @return The seller's
     */
    function getTokenNonce(address _seller) external view returns (uint256);

    /**
     * @notice Get the current type Id
     * @return type Id
     */
    function getTypeId() external view returns (uint256);

    /**
     * @notice Get the complain period
     * @return complain period
     */
    function getComplainPeriod() external view returns (uint256);

    /**
     * @notice Get the cancel or fault period
     * @return cancel or fault period
     */
    function getCancelFaultPeriod() external view returns (uint256);

    /**
     * @notice Get promise data not retrieved by other accessor functions
     * @param _promiseKey   ID of the promise
     * @return promise data not returned by other accessor methods
     */
    function getPromiseData(bytes32 _promiseKey)
        external
        view
        returns (
            bytes32,
            uint256,
            uint256,
            uint256,
            uint256
        );

    /**
     * @notice Get the promise ID from a voucher set
     * @param _tokenIdSupply   ID of the voucher token
     * @return                  ID of the promise
     */
    function getPromiseIdFromSupplyId(uint256 _tokenIdSupply)
        external
        view
        returns (bytes32);

    /**
     * @notice Get the address of the Vouchers token contract, an ERC721 contract
     * @return Address of Vouchers contract
     */
    function getVoucherTokenAddress() external view returns (address);

    /**
     * @notice Get the address of the VoucherSets token contract, an ERC155 contract
     * @return Address of VoucherSets contract
     */
    function getVoucherSetTokenAddress() external view returns (address);
}

// File: contracts/interfaces/ICashier.sol



// SPDX-License-Identifier: LGPL-3.0-or-later

pragma solidity 0.7.6;

import "./../UsingHelpers.sol";

interface ICashier {
    /**
     * @notice Pause the Cashier && the Voucher Kernel contracts in case of emergency.
     * All functions related to creating new batch, requestVoucher or withdraw will be paused, hence cannot be executed.
     * There is special function for withdrawing funds if contract is paused.
     */
    function pause() external;

    /**
     * @notice Unpause the Cashier && the Voucher Kernel contracts.
     * All functions related to creating new batch, requestVoucher or withdraw will be unpaused.
     */
    function unpause() external;

    function canUnpause() external view returns (bool);

    /**
     * @notice Trigger withdrawals of what funds are releasable
     * The caller of this function triggers transfers to all involved entities (pool, issuer, token holder), also paying for gas.
     * @dev This function would be optimized a lot, here verbose for readability.
     * @param _tokenIdVoucher  ID of a voucher token (ERC-721) to try withdraw funds from
     */
    function withdraw(uint256 _tokenIdVoucher) external;

    /**
     * @notice External function for withdrawing deposits. Caller must be the seller of the goods, otherwise reverts.
     * @notice Seller triggers withdrawals of remaining deposits for a given supply, in case the voucher set is no longer in exchange.
     * @param _tokenIdSupply an ID of a supply token (ERC-1155) which will be burned and deposits will be returned for
     * @param _burnedQty burned quantity that the deposits should be withdrawn for
     * @param _messageSender owner of the voucher set
     */
    function withdrawDepositsSe(
        uint256 _tokenIdSupply,
        uint256 _burnedQty,
        address payable _messageSender
    ) external;

    /**
     * @notice Get the amount in escrow of an address
     * @param _account  The address of an account to query
     * @return          The balance in escrow
     */
    function getEscrowAmount(address _account) external view returns (uint256);

    /**
     * @notice Update the amount in escrow of an address with the new value, based on VoucherSet/Voucher interaction
     * @param _account  The address of an account to query
     */
    function addEscrowAmount(address _account) external payable;

    /**
     * @notice Update the amount in escrowTokens of an address with the new value, based on VoucherSet/Voucher interaction
     * @param _token  The address of a token to query
     * @param _account  The address of an account to query
     * @param _newAmount  New amount to be set
     */
    function addEscrowTokensAmount(
        address _token,
        address _account,
        uint256 _newAmount
    ) external;

    /**
     * @notice Hook which will be triggered when a _tokenIdVoucher will be transferred. Escrow funds should be allocated to the new owner.
     * @param _from prev owner of the _tokenIdVoucher
     * @param _to next owner of the _tokenIdVoucher
     * @param _tokenIdVoucher _tokenIdVoucher that has been transferred
     */
    function onVoucherTransfer(
        address _from,
        address _to,
        uint256 _tokenIdVoucher
    ) external;

    /**
     * @notice After the transfer happens the _tokenSupplyId should be updated in the promise. Escrow funds for the deposits (If in ETH) should be allocated to the new owner as well.
     * @param _from prev owner of the _tokenSupplyId
     * @param _to next owner of the _tokenSupplyId
     * @param _tokenSupplyId _tokenSupplyId for transfer
     * @param _value qty which has been transferred
     */
    function onVoucherSetTransfer(
        address _from,
        address _to,
        uint256 _tokenSupplyId,
        uint256 _value
    ) external;

    /**
     * @notice Get the address of Voucher Kernel contract
     * @return Address of Voucher Kernel contract
     */
    function getVoucherKernelAddress() external view returns (address);

    /**
     * @notice Get the address of Boson Router contract
     * @return Address of Boson Router contract
     */
    function getBosonRouterAddress() external view returns (address);

    /**
     * @notice Get the address of the Vouchers contract, an ERC721 contract
     * @return Address of Vouchers contract
     */
    function getVoucherTokenAddress() external view returns (address);

    /**
     * @notice Get the address of the VoucherSets token contract, an ERC155 contract
     * @return Address of VoucherSets contract
     */
    function getVoucherSetTokenAddress() external view returns (address);

    /**
     * @notice Ensure whether or not contract has been set to disaster state
     * @return disasterState
     */
    function isDisasterStateSet() external view returns (bool);

    /**
     * @notice Get the amount in escrow of an address
     * @param _token  The address of a token to query
     * @param _account  The address of an account to query
     * @return          The balance in escrow
     */
    function getEscrowTokensAmount(address _token, address _account)
        external
        view
        returns (uint256);

    /**
     * @notice Set the address of the BR contract
     * @param _bosonRouterAddress   The address of the Cashier contract
     */
    function setBosonRouterAddress(address _bosonRouterAddress) external;

    /**
     * @notice Set the address of the VoucherKernel contract
     * @param _voucherKernelAddress   The address of the VoucherKernel contract
     */
    function setVoucherKernelAddress(address _voucherKernelAddress) external;

    /**
     * @notice Set the address of the Vouchers token contract, an ERC721 contract
     * @param _voucherTokenAddress   The address of the Vouchers token contract
     */
    function setVoucherTokenAddress(address _voucherTokenAddress) external;

    /**
     * @notice Set the address of the Voucher Sets token contract, an ERC1155 contract
     * @param _voucherSetTokenAddress   The address of the Voucher Sets token contract
     */
    function setVoucherSetTokenAddress(address _voucherSetTokenAddress)
        external;
}

// File: contracts/interfaces/IVouchers.sol



// SPDX-License-Identifier: LGPL-3.0-or-later
pragma solidity 0.7.6;

import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721Metadata.sol";

interface IVouchers is IERC721, IERC721Metadata {
    /**
     * @notice Pause the Cashier && the Voucher Kernel contracts in case of emergency.
     * All functions related to creating new batch, requestVoucher or withdraw will be paused, hence cannot be executed.
     * There is special function for withdrawing funds if contract is paused.
     */
    function pause() external;

    /**
     * @notice Unpause the Cashier && the Voucher Kernel contracts.
     * All functions related to creating new batch, requestVoucher or withdraw will be unpaused.
     */
    function unpause() external;

    /**
     * @notice Function to mint tokens.
     * @dev ERC-721
     * @param _to The address that will receive the minted tokens.
     * @param _tokenId The token id to mint.
     * @return A boolean that indicates if the operation was successful.
     */
    function mint(address _to, uint256 _tokenId) external returns (bool);

    /**
     * @notice Set the address of the VoucherKernel contract
     * @param _voucherKernelAddress The address of the Voucher Kernel contract
     */
    function setVoucherKernelAddress(address _voucherKernelAddress) external;

    /**
     * @notice Set the address of the Cashier contract
     * @param _cashierAddress   The address of the Cashier contract
     */
    function setCashierAddress(address _cashierAddress) external;

    /**
     * @notice Get the address of Voucher Kernel contract
     * @return Address of Voucher Kernel contract
     */
    function getVoucherKernelAddress() external view returns (address);

    /**
     * @notice Get the address of Cashier contract
     * @return Address of Cashier address
     */
    function getCashierAddress() external view returns (address);
}

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <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 GSN 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 payable) {
        return msg.sender;
    }

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

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "../../introspection/IERC165.sol";

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address from, address to, uint256 tokenId) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
      * @dev Safely transfers `tokenId` token from `from` to `to`.
      *
      * Requirements:
      *
      * - `from` cannot be the zero address.
      * - `to` cannot be the zero address.
      * - `tokenId` token must exist and be owned by `from`.
      * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
      * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
      *
      * Emits a {Transfer} event.
      */
    function safeTransferFrom(address from, address to, uint256 tokenId, bytes calldata data) external;
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Metadata.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "./IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {

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

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

    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

// File: @openzeppelin/contracts/token/ERC721/IERC721Enumerable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "./IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {

    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

// File: @openzeppelin/contracts/introspection/ERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts may inherit from this and call {_registerInterface} to declare
 * their support of an interface.
 */
abstract contract ERC165 is IERC165 {
    /*
     * bytes4(keccak256('supportsInterface(bytes4)')) == 0x01ffc9a7
     */
    bytes4 private constant _INTERFACE_ID_ERC165 = 0x01ffc9a7;

    /**
     * @dev Mapping of interface ids to whether or not it's supported.
     */
    mapping(bytes4 => bool) private _supportedInterfaces;

    constructor () {
        // Derived contracts need only register support for their own interfaces,
        // we register support for ERC165 itself here
        _registerInterface(_INTERFACE_ID_ERC165);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     *
     * Time complexity O(1), guaranteed to always use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return _supportedInterfaces[interfaceId];
    }

    /**
     * @dev Registers the contract as an implementer of the interface defined by
     * `interfaceId`. Support of the actual ERC165 interface is automatic and
     * registering its interface id is not required.
     *
     * See {IERC165-supportsInterface}.
     *
     * Requirements:
     *
     * - `interfaceId` cannot be the ERC165 invalid interface (`0xffffffff`).
     */
    function _registerInterface(bytes4 interfaceId) internal virtual {
        require(interfaceId != 0xffffffff, "ERC165: invalid interface id");
        _supportedInterfaces[interfaceId] = true;
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
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) {
        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) {
        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) {
        // 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) {
        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) {
        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) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");
        return c;
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        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) {
        if (a == 0) return 0;
        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");
        return c;
    }

    /**
     * @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. 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) internal pure returns (uint256) {
        require(b > 0, "SafeMath: division by zero");
        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) {
        require(b > 0, "SafeMath: modulo by zero");
        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) {
        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.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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) {
        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) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.3.0, sets of type `bytes32` (`Bytes32Set`), `address` (`AddressSet`)
 * and `uint256` (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // Bytes32Set

    struct Bytes32Set {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _add(set._inner, value);
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(Bytes32Set storage set, bytes32 value) internal returns (bool) {
        return _remove(set._inner, value);
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(Bytes32Set storage set, bytes32 value) internal view returns (bool) {
        return _contains(set._inner, value);
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(Bytes32Set storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(Bytes32Set storage set, uint256 index) internal view returns (bytes32) {
        return _at(set._inner, index);
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint160(uint256(_at(set._inner, index))));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Library for managing an enumerable variant of Solidity's
 * https://solidity.readthedocs.io/en/latest/types.html#mapping-types[`mapping`]
 * type.
 *
 * Maps have the following properties:
 *
 * - Entries are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Entries are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableMap for EnumerableMap.UintToAddressMap;
 *
 *     // Declare a set state variable
 *     EnumerableMap.UintToAddressMap private myMap;
 * }
 * ```
 *
 * As of v3.0.0, only maps of type `uint256 -> address` (`UintToAddressMap`) are
 * supported.
 */
library EnumerableMap {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Map type with
    // bytes32 keys and values.
    // The Map implementation uses private functions, and user-facing
    // implementations (such as Uint256ToAddressMap) are just wrappers around
    // the underlying Map.
    // This means that we can only create new EnumerableMaps for types that fit
    // in bytes32.

    struct MapEntry {
        bytes32 _key;
        bytes32 _value;
    }

    struct Map {
        // Storage of map keys and values
        MapEntry[] _entries;

        // Position of the entry defined by a key in the `entries` array, plus 1
        // because index 0 means a key is not in the map.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function _set(Map storage map, bytes32 key, bytes32 value) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex == 0) { // Equivalent to !contains(map, key)
            map._entries.push(MapEntry({ _key: key, _value: value }));
            // The entry is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            map._indexes[key] = map._entries.length;
            return true;
        } else {
            map._entries[keyIndex - 1]._value = value;
            return false;
        }
    }

    /**
     * @dev Removes a key-value pair from a map. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function _remove(Map storage map, bytes32 key) private returns (bool) {
        // We read and store the key's index to prevent multiple reads from the same storage slot
        uint256 keyIndex = map._indexes[key];

        if (keyIndex != 0) { // Equivalent to contains(map, key)
            // To delete a key-value pair from the _entries array in O(1), we swap the entry to delete with the last one
            // in the array, and then remove the last entry (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = keyIndex - 1;
            uint256 lastIndex = map._entries.length - 1;

            // When the entry to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            MapEntry storage lastEntry = map._entries[lastIndex];

            // Move the last entry to the index where the entry to delete is
            map._entries[toDeleteIndex] = lastEntry;
            // Update the index for the moved entry
            map._indexes[lastEntry._key] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved entry was stored
            map._entries.pop();

            // Delete the index for the deleted slot
            delete map._indexes[key];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function _contains(Map storage map, bytes32 key) private view returns (bool) {
        return map._indexes[key] != 0;
    }

    /**
     * @dev Returns the number of key-value pairs in the map. O(1).
     */
    function _length(Map storage map) private view returns (uint256) {
        return map._entries.length;
    }

   /**
    * @dev Returns the key-value pair stored at position `index` in the map. O(1).
    *
    * Note that there are no guarantees on the ordering of entries inside the
    * array, and it may change when more entries are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Map storage map, uint256 index) private view returns (bytes32, bytes32) {
        require(map._entries.length > index, "EnumerableMap: index out of bounds");

        MapEntry storage entry = map._entries[index];
        return (entry._key, entry._value);
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     */
    function _tryGet(Map storage map, bytes32 key) private view returns (bool, bytes32) {
        uint256 keyIndex = map._indexes[key];
        if (keyIndex == 0) return (false, 0); // Equivalent to contains(map, key)
        return (true, map._entries[keyIndex - 1]._value); // All indexes are 1-based
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function _get(Map storage map, bytes32 key) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, "EnumerableMap: nonexistent key"); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    /**
     * @dev Same as {_get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {_tryGet}.
     */
    function _get(Map storage map, bytes32 key, string memory errorMessage) private view returns (bytes32) {
        uint256 keyIndex = map._indexes[key];
        require(keyIndex != 0, errorMessage); // Equivalent to contains(map, key)
        return map._entries[keyIndex - 1]._value; // All indexes are 1-based
    }

    // UintToAddressMap

    struct UintToAddressMap {
        Map _inner;
    }

    /**
     * @dev Adds a key-value pair to a map, or updates the value for an existing
     * key. O(1).
     *
     * Returns true if the key was added to the map, that is if it was not
     * already present.
     */
    function set(UintToAddressMap storage map, uint256 key, address value) internal returns (bool) {
        return _set(map._inner, bytes32(key), bytes32(uint256(uint160(value))));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the key was removed from the map, that is if it was present.
     */
    function remove(UintToAddressMap storage map, uint256 key) internal returns (bool) {
        return _remove(map._inner, bytes32(key));
    }

    /**
     * @dev Returns true if the key is in the map. O(1).
     */
    function contains(UintToAddressMap storage map, uint256 key) internal view returns (bool) {
        return _contains(map._inner, bytes32(key));
    }

    /**
     * @dev Returns the number of elements in the map. O(1).
     */
    function length(UintToAddressMap storage map) internal view returns (uint256) {
        return _length(map._inner);
    }

   /**
    * @dev Returns the element stored at position `index` in the set. O(1).
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintToAddressMap storage map, uint256 index) internal view returns (uint256, address) {
        (bytes32 key, bytes32 value) = _at(map._inner, index);
        return (uint256(key), address(uint160(uint256(value))));
    }

    /**
     * @dev Tries to returns the value associated with `key`.  O(1).
     * Does not revert if `key` is not in the map.
     *
     * _Available since v3.4._
     */
    function tryGet(UintToAddressMap storage map, uint256 key) internal view returns (bool, address) {
        (bool success, bytes32 value) = _tryGet(map._inner, bytes32(key));
        return (success, address(uint160(uint256(value))));
    }

    /**
     * @dev Returns the value associated with `key`.  O(1).
     *
     * Requirements:
     *
     * - `key` must be in the map.
     */
    function get(UintToAddressMap storage map, uint256 key) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key)))));
    }

    /**
     * @dev Same as {get}, with a custom error message when `key` is not in the map.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryGet}.
     */
    function get(UintToAddressMap storage map, uint256 key, string memory errorMessage) internal view returns (address) {
        return address(uint160(uint256(_get(map._inner, bytes32(key), errorMessage))));
    }
}

// File: @openzeppelin/contracts/introspection/IERC165.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}

// File: contracts/UsingHelpers.sol



// SPDX-License-Identifier: LGPL-3.0-or-later

pragma solidity 0.7.6;

// Those are the payment methods we are using throughout the system.
// Depending on how to user choose to interact with it's funds we store the method, so we could distribute its tokens afterwise
enum PaymentMethod {
    ETHETH,
    ETHTKN,
    TKNETH,
    TKNTKN
}

enum VoucherState {FINAL, CANCEL_FAULT, COMPLAIN, EXPIRE, REFUND, REDEEM, COMMIT}
/*  Status of the voucher in 8 bits:
    [6:COMMITTED] [5:REDEEMED] [4:REFUNDED] [3:EXPIRED] [2:COMPLAINED] [1:CANCELORFAULT] [0:FINAL]
*/

uint8 constant ONE = 1;

struct VoucherDetails {
    uint256 tokenIdSupply;
    uint256 tokenIdVoucher;
    address issuer;
    address holder;
    uint256 price;
    uint256 depositSe;
    uint256 depositBu;
    uint256 price2pool;
    uint256 deposit2pool;
    uint256 price2issuer;
    uint256 deposit2issuer;
    uint256 price2holder;
    uint256 deposit2holder;
    PaymentMethod paymentMethod;
    VoucherStatus currStatus;
}

struct VoucherStatus {
    uint8 status;
    bool isPaymentReleased;
    bool isDepositsReleased;
    uint256 complainPeriodStart;
    uint256 cancelFaultPeriodStart;
}

/**
    * @notice Based on its lifecycle, voucher can have many different statuses. Checks whether a voucher is in Committed state.
    * @param _status current status of a voucher.
    */
function isStateCommitted(uint8 _status) pure returns (bool) {
    return _status == determineStatus(0, VoucherState.COMMIT);
}

/**
    * @notice Based on its lifecycle, voucher can have many different statuses. Checks whether a voucher is in RedemptionSigned state.
    * @param _status current status of a voucher.
    */
function isStateRedemptionSigned(uint8 _status)
    pure
    returns (bool)
{
    return _status == determineStatus(determineStatus(0, VoucherState.COMMIT), VoucherState.REDEEM);
}

/**
    * @notice Based on its lifecycle, voucher can have many different statuses. Checks whether a voucher is in Refunded state.
    * @param _status current status of a voucher.
    */
function isStateRefunded(uint8 _status) pure returns (bool) {
    return _status == determineStatus(determineStatus(0, VoucherState.COMMIT), VoucherState.REFUND);
}

/**
    * @notice Based on its lifecycle, voucher can have many different statuses. Checks whether a voucher is in Expired state.
    * @param _status current status of a voucher.
    */
function isStateExpired(uint8 _status) pure returns (bool) {
    return _status == determineStatus(determineStatus(0, VoucherState.COMMIT), VoucherState.EXPIRE);
}

/**
    * @notice Based on its lifecycle, voucher can have many different statuses. Checks the current status a voucher is at.
    * @param _status current status of a voucher.
    * @param _idx status to compare.
    */
function isStatus(uint8 _status, VoucherState _idx) pure returns (bool) {
    return (_status >> uint8(_idx)) & ONE == 1;
}

/**
    * @notice Set voucher status.
    * @param _status previous status.
    * @param _changeIdx next status.
    */
function determineStatus(uint8 _status, VoucherState _changeIdx)
    pure
    returns (uint8)
{
    return _status | (ONE << uint8(_changeIdx));
}