// Sources flattened with hardhat v2.6.4 https://hardhat.org

// File contracts/interfaces/IERC20.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.9;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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 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 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 Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() 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 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);
}


// File contracts/interfaces/IMerkleDistributor.sol

// Allows anyone to claim a token if they exist in a merkle root.
interface IMerkleDistributor {
    // This event is triggered whenever a call to #claim succeeds.
    event Claimed(address account, uint256 amount, uint256 indexed index);

    // Claim the given amount of the token to the given address. Reverts if the inputs are invalid.
    function claim(
        uint256 index,
        address account,
        uint256 amount,
        bytes32[] calldata merkleProof
    ) external;

    // Returns true if the index has been marked claimed.
    function isClaimed(uint256 index) external view returns (bool);

    // Returns the merkle root of the merkle tree containing account balances available to claim.
    function merkleRoot() external view returns (bytes32);

    // Returns the address of the token distributed by this contract.
    function token() external view returns (address);
}


// File contracts/libraries/BitMaps.sol

/**
 * @dev Library for managing uint256 to bool mapping in a compact and efficient way, providing the keys are sequential.
 * Largelly inspired by Uniswap's https://github.com/Uniswap/merkle-distributor/blob/master/contracts/MerkleDistributor.sol[merkle-distributor].
 */
library BitMaps {
    struct BitMap {
        mapping(uint256 => uint256) _data;
    }

    /**
     * @dev Returns whether the bit at `index` is set.
     */
    function _get(BitMap storage bitmap, uint256 index)
        internal
        view
        returns (bool)
    {
        uint256 bucket = index >> 8;
        uint256 mask = 1 << (index & 0xff);
        return bitmap._data[bucket] & mask != 0;
    }

    /**
     * @dev Sets the bit at `index`.
     */
    function _set(BitMap storage bitmap, uint256 index) internal {
        uint256 bucket = index >> 8;
        uint256 mask = 1 << (index & 0xff);
        bitmap._data[bucket] |= mask;
    }
}


// File contracts/libraries/MerkleProof.sol

/**
 * @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 contracts/core/MerkleDistributor.sol

/**
 * MerkleDistributor Error Codes
 * M1: cannot claim a drop that has already been claimed
 * M2: cannot process claim, merkle proof is invalid
 * M3: token transfer failed, claim is valid
 */

/**
 * @title MerkleDistributor
 */
contract MerkleDistributor is IMerkleDistributor {
    using BitMaps for BitMaps.BitMap;

    BitMaps.BitMap private claimedBitMap;

    address public immutable override token;
    bytes32 public immutable override merkleRoot;

    constructor(address _token, bytes32 _merkleRoot) {
        token = _token;
        merkleRoot = _merkleRoot;
    }

    function claim(
        uint256 index,
        address account,
        uint256 amount,
        bytes32[] calldata merkleProof
    ) external override {
        require(!isClaimed(index), "M1");

        // Verify the merkle proof.
        bytes32 node = keccak256(abi.encodePacked(index, account, amount));
        require(MerkleProof._verify(merkleProof, merkleRoot, node), "M2");

        // Mark it claimed and send the token.
        claimedBitMap._set(index);
        require(IERC20(token).transfer(account, amount), "M3");

        emit Claimed(account, amount, index);
    }

    function isClaimed(uint256 index) public view override returns (bool) {
        return claimedBitMap._get(index);
    }
}