// File: contracts/Downpayment.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

import {Ownable} from "@openzeppelin/contracts/access/Ownable.sol";
import {ReentrancyGuard} from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import {EnumerableSet} from "@openzeppelin/contracts/utils/structs/EnumerableSet.sol";
import {Counters} from "@openzeppelin/contracts/utils/Counters.sol";
import {IERC20, SafeERC20} from "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";

import {IAaveLendPoolAddressesProvider} from "./interfaces/IAaveLendPoolAddressesProvider.sol";
import {IAaveLendPool} from "./interfaces/IAaveLendPool.sol";
import {ILendPool} from "./interfaces/ILendPool.sol";
import {ILendPoolAddressesProvider} from "./interfaces/ILendPoolAddressesProvider.sol";
import {IWETH} from "./interfaces/IWETH.sol";
import {IDownpayment} from "./interfaces/IDownpayment.sol";

import {PercentageMath} from "./libraries/PercentageMath.sol";

contract Downpayment is Ownable, ReentrancyGuard, IDownpayment {
    using SafeERC20 for IERC20;
    using EnumerableSet for EnumerableSet.AddressSet;
    using Counters for Counters.Counter;

    EnumerableSet.AddressSet private _whitelistedAdapters;

    IAaveLendPoolAddressesProvider public immutable aaveAddressesProvider;
    IWETH public immutable override WETH;
    ILendPoolAddressesProvider public bendAddressesProvider;
    address public feeCollector;

    event AdapterRemoved(address indexed adapter);
    event AdapterWhitelisted(address indexed adapter);

    event FeeUpdated(address indexed adapter, uint256 indexed newFee);

    mapping(address => Counters.Counter) internal _nonces;
    mapping(address => uint256) private fees;

    modifier onlyWhitelisted(address adapter) {
        require(_whitelistedAdapters.contains(adapter), "Adapter: not whitelisted");
        _;
    }

    constructor(
        address _aaveAddressesProvider,
        address _bendAddressesProvider,
        address _feeCollector,
        address _weth
    ) {
        aaveAddressesProvider = IAaveLendPoolAddressesProvider(_aaveAddressesProvider);
        bendAddressesProvider = ILendPoolAddressesProvider(_bendAddressesProvider);
        feeCollector = _feeCollector;
        WETH = IWETH(_weth);
    }

    function buy(
        address adapter,
        uint256 borrowAmount,
        bytes calldata data,
        Sig calldata sig
    ) external payable override onlyWhitelisted(adapter) nonReentrant {
        if (msg.value > 0) {
            // Wrap ETH sent to this contract
            WETH.deposit{value: msg.value}();
            // Sent WETH back to sender
            IERC20(address(WETH)).safeTransfer(msg.sender, msg.value);
        }
        IAaveLendPool aavePool = IAaveLendPool(aaveAddressesProvider.getLendingPool());
        address[] memory assets = new address[](1);
        assets[0] = address(WETH);
        uint256[] memory amounts = new uint256[](1);
        amounts[0] = borrowAmount;
        uint256[] memory modes = new uint256[](1);
        modes[0] = 0;
        bytes memory dataWithSignature = abi.encode(data, msg.sender, sig.v, sig.r, sig.s);
        aavePool.flashLoan(adapter, assets, amounts, modes, address(0), dataWithSignature, 0);
        _incrementNonce(msg.sender);
    }

    function addAdapter(address adapter) external override onlyOwner {
        require(adapter != address(0), "Adapter: can not be null address");
        require(!_whitelistedAdapters.contains(adapter), "Adapter: already whitelisted");
        _whitelistedAdapters.add(adapter);
        emit AdapterWhitelisted(adapter);
    }

    function removeAdapter(address adapter) external override onlyOwner onlyWhitelisted(adapter) {
        _whitelistedAdapters.remove(adapter);

        emit AdapterRemoved(adapter);
    }

    function updateFee(address adapter, uint256 _newFee) external onlyOwner onlyWhitelisted(adapter) {
        require(_newFee <= PercentageMath.PERCENTAGE_FACTOR, "Fee overflow");
        fees[adapter] = _newFee;
        emit FeeUpdated(adapter, _newFee);
    }

    // external view functions
    function getBendLendPool() external view returns (ILendPool) {
        return ILendPool(bendAddressesProvider.getLendPool());
    }

    function getAaveLendPool() external view returns (IAaveLendPool) {
        return IAaveLendPool(aaveAddressesProvider.getLendingPool());
    }

    function nonces(address owner) external view returns (uint256) {
        return _nonces[owner].current();
    }

    function isAdapterWhitelisted(address adapter) external view override returns (bool) {
        return _whitelistedAdapters.contains(adapter);
    }

    function viewCountWhitelistedAdapters() external view override returns (uint256) {
        return _whitelistedAdapters.length();
    }

    function viewWhitelistedAdapters(uint256 cursor, uint256 size)
        external
        view
        override
        returns (address[] memory, uint256)
    {
        uint256 length = size;
        if (length > _whitelistedAdapters.length() - cursor) {
            length = _whitelistedAdapters.length() - cursor;
        }
        address[] memory whitelistedAdapters = new address[](length);

        for (uint256 i = 0; i < length; i++) {
            whitelistedAdapters[i] = _whitelistedAdapters.at(cursor + i);
        }
        return (whitelistedAdapters, cursor + length);
    }

    function getFee(address adapter) external view override onlyWhitelisted(adapter) returns (uint256) {
        return fees[adapter];
    }

    function getFeeCollector() external view returns (address) {
        return feeCollector;
    }

    // internal functions
    function _incrementNonce(address owner) internal {
        Counters.Counter storage nonce = _nonces[owner];
        nonce.increment();
    }
}

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



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

pragma solidity ^0.8.0;

import "../utils/Context.sol";

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

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

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

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

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

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

// File: @openzeppelin/contracts/security/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (utils/structs/EnumerableSet.sol)

pragma solidity ^0.8.0;

/**
 * @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;

            if (lastIndex != toDeleteIndex) {
                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] = valueIndex; // Replace lastValue's index to valueIndex
            }

            // 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) {
        return set._values[index];
    }

    /**
     * @dev Return the entire set in an array
     *
     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
     */
    function _values(Set storage set) private view returns (bytes32[] memory) {
        return set._values;
    }

    // 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);
    }

    /**
     * @dev Return the entire set in an array
     *
     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
     */
    function values(Bytes32Set storage set) internal view returns (bytes32[] memory) {
        return _values(set._inner);
    }

    // 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))));
    }

    /**
     * @dev Return the entire set in an array
     *
     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
     */
    function values(AddressSet storage set) internal view returns (address[] memory) {
        bytes32[] memory store = _values(set._inner);
        address[] memory result;

        assembly {
            result := store
        }

        return result;
    }

    // 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));
    }

    /**
     * @dev Return the entire set in an array
     *
     * WARNING: This operation will copy the entire storage to memory, which can be quite expensive. This is designed
     * to mostly be used by view accessors that are queried without any gas fees. Developers should keep in mind that
     * this function has an unbounded cost, and using it as part of a state-changing function may render the function
     * uncallable if the set grows to a point where copying to memory consumes too much gas to fit in a block.
     */
    function values(UintSet storage set) internal view returns (uint256[] memory) {
        bytes32[] memory store = _values(set._inner);
        uint256[] memory result;

        assembly {
            result := store
        }

        return result;
    }
}

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



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

pragma solidity ^0.8.0;

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 */
library Counters {
    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

// File: @openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/utils/SafeERC20.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using Address for address;

    function safeTransfer(
        IERC20 token,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(
        IERC20 token,
        address from,
        address to,
        uint256 value
    ) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        require(
            (value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        uint256 newAllowance = token.allowance(address(this), spender) + value;
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(
        IERC20 token,
        address spender,
        uint256 value
    ) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            uint256 newAllowance = oldAllowance - value;
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
        }
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) {
            // Return data is optional
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: contracts/interfaces/IAaveLendPoolAddressesProvider.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

/**
 * @title IAaveLendPoolAddressesProvider contract
 * @dev Main registry of addresses part of or connected to the aave protocol, including permissioned roles
 * - Acting also as factory of proxies and admin of those, so with right to change its implementations
 * - Owned by the Aave Governance
 * @author Bend
 **/
interface IAaveLendPoolAddressesProvider {
    function getLendingPool() external view returns (address);
}

// File: contracts/interfaces/IAaveLendPool.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

interface IAaveLendPool {
    /**
     * @dev Allows smartcontracts to access the liquidity of the pool within one transaction,
     * as long as the amount taken plus a fee is returned.
     * IMPORTANT There are security concerns for developers of flashloan receiver contracts that must be kept into consideration.
     * For further details please visit https://developers.aave.com
     * @param receiverAddress The address of the contract receiving the funds, implementing the IFlashLoanReceiver interface
     * @param assets The addresses of the assets being flash-borrowed
     * @param amounts The amounts amounts being flash-borrowed
     * @param modes Types of the debt to open if the flash loan is not returned:
     *   0 -> Don't open any debt, just revert if funds can't be transferred from the receiver
     *   1 -> Open debt at stable rate for the value of the amount flash-borrowed to the `onBehalfOf` address
     *   2 -> Open debt at variable rate for the value of the amount flash-borrowed to the `onBehalfOf` address
     * @param onBehalfOf The address  that will receive the debt in the case of using on `modes` 1 or 2
     * @param params Variadic packed params to pass to the receiver as extra information
     * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
     *   0 if the action is executed directly by the user, without any middle-man
     **/
    function flashLoan(
        address receiverAddress,
        address[] calldata assets,
        uint256[] calldata amounts,
        uint256[] calldata modes,
        address onBehalfOf,
        bytes calldata params,
        uint16 referralCode
    ) external;
}

// File: contracts/interfaces/ILendPool.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

import {ILendPoolAddressesProvider} from "./ILendPoolAddressesProvider.sol";

interface ILendPool {
    /**
     * @dev Deposits an `amount` of underlying asset into the reserve, receiving in return overlying bTokens.
     * - E.g. User deposits 100 USDC and gets in return 100 bUSDC
     * @param reserve The address of the underlying asset to deposit
     * @param amount The amount to be deposited
     * @param onBehalfOf The address that will receive the bTokens, same as msg.sender if the user
     *   wants to receive them on his own wallet, or a different address if the beneficiary of bTokens
     *   is a different wallet
     * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
     *   0 if the action is executed directly by the user, without any middle-man
     **/
    function deposit(
        address reserve,
        uint256 amount,
        address onBehalfOf,
        uint16 referralCode
    ) external;

    /**
     * @dev Allows users to borrow a specific `amount` of the reserve underlying asset, provided that the borrower
     * already deposited enough collateral
     * - E.g. User borrows 100 USDC, receiving the 100 USDC in his wallet
     *   and lock collateral asset in contract
     * @param reserveAsset The address of the underlying asset to borrow
     * @param amount The amount to be borrowed
     * @param nftAsset The address of the underlying NFT used as collateral
     * @param nftTokenId The token ID of the underlying NFT used as collateral
     * @param onBehalfOf Address of the user who will receive the loan. Should be the address of the borrower itself
     * calling the function if he wants to borrow against his own collateral, or the address of the credit delegator
     * if he has been given credit delegation allowance
     * @param referralCode Code used to register the integrator originating the operation, for potential rewards.
     *   0 if the action is executed directly by the user, without any middle-man
     **/
    function borrow(
        address reserveAsset,
        uint256 amount,
        address nftAsset,
        uint256 nftTokenId,
        address onBehalfOf,
        uint16 referralCode
    ) external;

    /**
     * @notice Repays a borrowed `amount` on a specific reserve, burning the equivalent loan owned
     * - E.g. User repays 100 USDC, burning loan and receives collateral asset
     * @param nftAsset The address of the underlying NFT used as collateral
     * @param nftTokenId The token ID of the underlying NFT used as collateral
     * @param amount The amount to repay
     * @return The final amount repaid, loan is burned or not
     **/
    function repay(
        address nftAsset,
        uint256 nftTokenId,
        uint256 amount
    ) external returns (uint256, bool);

    /**
     * @dev Returns the loan data of the NFT
     * @param nftAsset The address of the NFT
     * @param reserveAsset The address of the Reserve
     * @return totalCollateralInETH the total collateral in ETH of the NFT
     * @return totalCollateralInReserve the total collateral in Reserve of the NFT
     * @return availableBorrowsInETH the borrowing power in ETH of the NFT
     * @return availableBorrowsInReserve the borrowing power in Reserve of the NFT
     * @return ltv the loan to value of the user
     * @return liquidationThreshold the liquidation threshold of the NFT
     * @return liquidationBonus the liquidation bonus of the NFT
     **/
    function getNftCollateralData(address nftAsset, address reserveAsset)
        external
        view
        returns (
            uint256 totalCollateralInETH,
            uint256 totalCollateralInReserve,
            uint256 availableBorrowsInETH,
            uint256 availableBorrowsInReserve,
            uint256 ltv,
            uint256 liquidationThreshold,
            uint256 liquidationBonus
        );
}

// File: contracts/interfaces/ILendPoolAddressesProvider.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

/**
 * @title LendPoolAddressesProvider contract
 * @dev Main registry of addresses part of or connected to the protocol, including permissioned roles
 * - Acting also as factory of proxies and admin of those, so with right to change its implementations
 * - Owned by the Bend Governance
 * @author Bend
 **/
interface ILendPoolAddressesProvider {
    function getLendPool() external view returns (address);
}

// File: contracts/interfaces/IWETH.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

interface IWETH {
    function deposit() external payable;

    function withdraw(uint256) external;

    function allowance(address, address) external view returns (uint256);

    function approve(address guy, uint256 wad) external returns (bool);

    function transferFrom(
        address src,
        address dst,
        uint256 wad
    ) external returns (bool);

    function transfer(address dst, uint256 wad) external returns (bool);

    function balanceOf(address) external view returns (uint256);
}

// File: contracts/interfaces/IDownpayment.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

import {IWETH} from "./IWETH.sol";
import {ILendPool} from "./ILendPool.sol";
import {IAaveLendPool} from "./IAaveLendPool.sol";

interface IDownpayment {
    struct Sig {
        uint8 v;
        bytes32 r;
        bytes32 s;
    }

    function WETH() external view returns (IWETH);

    function getFee(address adapter) external view returns (uint256);

    function getFeeCollector() external view returns (address);

    function getBendLendPool() external view returns (ILendPool);

    function getAaveLendPool() external view returns (IAaveLendPool);

    function nonces(address owner) external view returns (uint256);

    function isAdapterWhitelisted(address adapter) external view returns (bool);

    function viewCountWhitelistedAdapters() external view returns (uint256);

    function viewWhitelistedAdapters(uint256 cursor, uint256 size) external view returns (address[] memory, uint256);

    function buy(
        address adapter,
        uint256 borrowAmount,
        bytes calldata data,
        Sig calldata sig
    ) external payable;

    function addAdapter(address adapter) external;

    function removeAdapter(address adapter) external;
}

// File: contracts/libraries/PercentageMath.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.8.9;

/**
 * @title PercentageMath library
 * @author Bend
 * @notice Provides functions to perform percentage calculations
 * @dev Percentages are defined by default with 2 decimals of precision (100.00). The precision is indicated by PERCENTAGE_FACTOR
 * @dev Operations are rounded half up
 **/

library PercentageMath {
    uint256 public constant PERCENTAGE_FACTOR = 1e4; //percentage plus two decimals
    uint256 public constant HALF_PERCENT = PERCENTAGE_FACTOR / 2;
    uint256 public constant ONE_PERCENT = 1e2; //100, 1%
    uint256 public constant TEN_PERCENT = 1e3; //1000, 10%
    uint256 public constant ONE_THOUSANDTH_PERCENT = 1e1; //10, 0.1%
    uint256 public constant ONE_TEN_THOUSANDTH_PERCENT = 1; //1, 0.01%

    /**
     * @dev Executes a percentage multiplication
     * @param value The value of which the percentage needs to be calculated
     * @param percentage The percentage of the value to be calculated
     * @return The percentage of value
     **/
    function percentMul(uint256 value, uint256 percentage) internal pure returns (uint256) {
        if (value == 0 || percentage == 0) {
            return 0;
        }

        require(value <= (type(uint256).max - HALF_PERCENT) / percentage, "MATH_MULTIPLICATION_OVERFLOW");

        return (value * percentage + HALF_PERCENT) / PERCENTAGE_FACTOR;
    }
}

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



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

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: @openzeppelin/contracts/token/ERC20/IERC20.sol



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

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

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

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (utils/Address.sol)

pragma solidity ^0.8.1;

/**
 * @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
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 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");

        (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");

        (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");

        (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");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}