// SPDX-License-Identifier: UNLICENSED

pragma solidity 0.7.6;



// Part: IERC20

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

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

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

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

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

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

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

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

// File: MerkleDistributorSdt.sol

// MerkleDistributor for distributing SDT to veCRV holders
// Based on the EMN refund contract by banteg - https://github.com/banteg/your-eminence
contract MerkleDistributorSdt {
    bytes32[] public merkleRoots;
    bytes32 public pendingMerkleRoot;
    uint256 public lastRoot;

    // reward token
    address
        public constant rewardToken = 0x73968b9a57c6E53d41345FD57a6E6ae27d6CDB2F;
    // admin address which can propose adding a new merkle root
    address public proposalAuthority;
    // admin address which approves or rejects a proposed merkle root
    address public reviewAuthority;

    event Claimed(
        uint256 merkleIndex,
        uint256 index,
        address account,
        uint256 amount
    );

    // This is a packed array of booleans.
    mapping(uint256 => mapping(uint256 => uint256)) private claimedBitMap;

    constructor(address _proposalAuthority, address _reviewAuthority) public {
        proposalAuthority = _proposalAuthority;
        reviewAuthority = _reviewAuthority;
    }

    function setProposalAuthority(address _account) public {
        require(msg.sender == proposalAuthority);
        proposalAuthority = _account;
    }

    function setReviewAuthority(address _account) public {
        require(msg.sender == reviewAuthority);
        reviewAuthority = _account;
    }

    // Each week, the proposal authority calls to submit the merkle root for a new airdrop.
    function proposeMerkleRoot(bytes32 _merkleRoot) public {
        require(msg.sender == proposalAuthority);
        require(pendingMerkleRoot == 0x00);
        require(block.timestamp > lastRoot + 604800);
        pendingMerkleRoot = _merkleRoot;
    }

    // After validating the correctness of the pending merkle root, the reviewing authority
    // calls to confirm it and the distribution may begin.
    function reviewPendingMerkleRoot(bool _approved) public {
        require(msg.sender == reviewAuthority);
        require(pendingMerkleRoot != 0x00);
        if (_approved) {
            merkleRoots.push(pendingMerkleRoot);
            lastRoot = block.timestamp;
        }
        delete pendingMerkleRoot;
    }

    function isClaimed(uint256 merkleIndex, uint256 index)
        public
        view
        returns (bool)
    {
        uint256 claimedWordIndex = index / 256;
        uint256 claimedBitIndex = index % 256;
        uint256 claimedWord = claimedBitMap[merkleIndex][claimedWordIndex];
        uint256 mask = (1 << claimedBitIndex);
        return claimedWord & mask == mask;
    }

    function _setClaimed(uint256 merkleIndex, uint256 index) private {
        uint256 claimedWordIndex = index / 256;
        uint256 claimedBitIndex = index % 256;
        claimedBitMap[merkleIndex][claimedWordIndex] =
            claimedBitMap[merkleIndex][claimedWordIndex] |
            (1 << claimedBitIndex);
    }

    function claim(
        uint256 merkleIndex,
        uint256 index,
        uint256 amount,
        bytes32[] calldata merkleProof
    ) external {
        require(
            merkleIndex < merkleRoots.length,
            "MerkleDistributor: Invalid merkleIndex"
        );
        require(
            !isClaimed(merkleIndex, index),
            "MerkleDistributor: Drop already claimed."
        );

        // Verify the merkle proof.
        bytes32 node = keccak256(abi.encodePacked(index, msg.sender, amount));
        require(
            verify(merkleProof, merkleRoots[merkleIndex], node),
            "MerkleDistributor: Invalid proof."
        );

        // Mark it claimed and send the token.
        _setClaimed(merkleIndex, index);
        IERC20(rewardToken).transfer(msg.sender, amount);

        emit Claimed(merkleIndex, index, msg.sender, amount);
    }

    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;
    }
}