// File: contracts/MerkleVault.sol



pragma solidity 0.8.6;

// SPDX-License-Identifier: MIT

import { Pausable } from "@openzeppelin/contracts/security/Pausable.sol";
import { ReentrancyGuard } from "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import { Ownable } from "@openzeppelin/contracts/access/Ownable.sol";
import { MerkleProof } from "@openzeppelin/contracts/utils/cryptography/MerkleProof.sol";
import { IERC20 } from "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import { IMerkleVault } from "./IMerkleVault.sol";

/// @title Funds distribution vault driven by MerkleTrees
/// @author KnownOrigin Labs Ltd.
contract MerkleVault is IMerkleVault, Pausable, ReentrancyGuard, Ownable {

    // All the information anyone needs to verify the validity of a merkle tree
    struct MerkleTreeMetadata {
        bytes32 root;
        string dataIPFSHash;
    }

    /// @notice Active merkle tree version / pointer
    uint256 public merkleVersion;

    /// @notice Merkle version -> merkle tree metadata
    mapping(uint256 => MerkleTreeMetadata) public merkleVersionMetadata;

    /// @notice Beneficiary -> Merkle version -> Whether the beneficiary has claimed their funds
    mapping(address => mapping(uint256 => bool)) public fundsClaimed;

    /// @notice Sets up the contract in a paused state
    constructor() {
        // Starting paused means claiming can be enabled by calling `unpauseClaiming()` later
        _pause();
    }

    /// @notice Owner can pause claiming to permit updating the merkle tree to a new version i.e. stop front-running
    function pauseClaiming() onlyOwner external {
        _pause();
    }

    /// @notice Owner can unpause claiming
    function unpauseClaiming() onlyOwner external {
        _unpause();
    }

    /// @notice Update the merkle tree to a new version as the contract owner
    /// @param _metadata Root and IPFS hash of the merkle tree used for the contract
    function updateMerkleTree(MerkleTreeMetadata calldata _metadata) external whenPaused onlyOwner {
        _updateMerkleTree(_metadata);
    }

    /// @notice Allows a beneficiary to claim ETH or ERC20 tokens provided they have a node in the Merkle tree
    /// @param _index Nonce assigned to beneficiary
    /// @param _token Contract address or zero address if claiming ETH
    /// @param _amount Amount being claimed - must be exact
    /// @param _merkleProof Proof for the claim
    function claim(
        uint256 _index,
        address _token,
        uint256 _amount,
        bytes32[] calldata _merkleProof
    ) external override whenNotPaused nonReentrant {
        _claim(_index, _token, _amount, payable(msg.sender), _merkleProof);
    }

    /// @notice Allows anyone to trigger a claim on behalf of a beneficiary
    /// @param _index Nonce assigned to beneficiary
    /// @param _token Contract address or zero address if claiming ETH
    /// @param _amount Amount being claimed - must be exact
    /// @param _merkleProof Proof for the claim
    function claimFor(
        uint256 _index,
        address _token,
        uint256 _amount,
        address payable _claimant,
        bytes32[] calldata _merkleProof
    ) external whenNotPaused nonReentrant {
        _claim(_index, _token, _amount, _claimant, _merkleProof);
    }

    /// NOTE: This receive will fail for payments that only forward the minimum 21k GAS
    /// However, the gas use of this method is only circa 22,111 so not much more is needed
    receive() external payable {
        emit ETHReceived(msg.value);
    }

    /// @notice Externally verify whether a node is part of merkle tree before doing claim
    function isPartOfMerkleTree(
        uint256 _index,
        address _token,
        address _account,
        uint256 _amount,
        bytes32[] calldata _merkleProof
    ) external view returns (bool) {
        bytes32 node = keccak256(abi.encodePacked(_index, _token, _account, _amount));
        return MerkleProof.verify(_merkleProof, merkleVersionMetadata[merkleVersion].root, node);
    }

    // Update the merkle tree version whilst validating the new metadata
    function _updateMerkleTree(MerkleTreeMetadata memory _metadata) internal {
        require(bytes(_metadata.dataIPFSHash).length == 46, "Invalid IPFS hash");

        merkleVersion += 1;
        merkleVersionMetadata[merkleVersion] = _metadata;

        emit MerkleTreeUpdated(merkleVersion);
    }

    // process a claim
    function _claim(
        uint256 _index,
        address _token,
        uint256 _amount,
        address payable _claimant,
        bytes32[] calldata _merkleProof
    ) internal {
        require(!fundsClaimed[_claimant][merkleVersion], "Funds have been claimed");

        bytes32 node = keccak256(abi.encodePacked(_index, _token, _claimant, _amount));
        require(
            MerkleProof.verify(_merkleProof, merkleVersionMetadata[merkleVersion].root, node),
            "Merkle verification failed"
        );

        fundsClaimed[_claimant][merkleVersion] = true;

        // If token is zero - this is a claim for ETH. Otherwise its an ERC20 claim
        if (_token == address(0)) {
            (bool ethTransferSuccessful,) = _claimant.call{value: _amount}("");
            require(ethTransferSuccessful, "ETH transfer failed");
        } else {
            IERC20(_token).transfer(_claimant, _amount);
        }

        emit TokensClaimed(_token, _amount);
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../utils/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/security/ReentrancyGuard.sol



// SPDX-License-Identifier: MIT

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 make 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/access/Ownable.sol



// SPDX-License-Identifier: MIT

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

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// File: @openzeppelin/contracts/utils/cryptography/MerkleProof.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev These functions deal with verification of Merkle Trees proofs.
 *
 * The proofs can be generated using the JavaScript library
 * https://github.com/miguelmota/merkletreejs[merkletreejs].
 * Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
 *
 * See `test/utils/cryptography/MerkleProof.test.js` for some examples.
 */
library MerkleProof {
    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     */
    function verify(
        bytes32[] memory proof,
        bytes32 root,
        bytes32 leaf
    ) internal pure returns (bool) {
        bytes32 computedHash = leaf;

        for (uint256 i = 0; i < proof.length; i++) {
            bytes32 proofElement = proof[i];

            if (computedHash <= proofElement) {
                // Hash(current computed hash + current element of the proof)
                computedHash = keccak256(abi.encodePacked(computedHash, proofElement));
            } else {
                // Hash(current element of the proof + current computed hash)
                computedHash = keccak256(abi.encodePacked(proofElement, computedHash));
            }
        }

        // Check if the computed hash (root) is equal to the provided root
        return computedHash == root;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

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

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

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

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

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

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

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

// File: contracts/IMerkleVault.sol



pragma solidity 0.8.6;

// SPDX-License-Identifier: MIT

interface IMerkleVault {
    event MerkleTreeUpdated(uint256 newVersion);
    event ETHReceived(uint256 amount);
    event TokensClaimed(address indexed token, uint256 amount);

    function claim(uint256 _index, address _token, uint256 _amount, bytes32[] calldata _merkleProof) external;
}

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



// SPDX-License-Identifier: MIT

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;
    }
}