// File: contracts/Airdrop/Airdrop.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "@openzeppelin/contracts-4.4.1/token/ERC20/IERC20.sol";
import "../utils/Owned.sol";
import "@openzeppelin/contracts-4.4.1/utils/cryptography/MerkleProof.sol";
import "../utils/Pausable.sol";

/**
 * Contract which implements a merkle airdrop for a given token
 * Based on an account balance snapshot stored in a merkle tree
 */
contract Airdrop is Owned, Pausable {
    IERC20 public token;

    bytes32 public root; // merkle tree root

    uint256 public startTime;

    mapping(uint256 => uint256) public _claimed;

    constructor(
        address _owner,
        IERC20 _token,
        bytes32 _root
    ) Owned(_owner) Pausable() {
        token = _token;
        root = _root;
        startTime = block.timestamp;
    }

    // Check if a given reward has already been claimed
    function claimed(uint256 index) public view returns (uint256 claimedBlock, uint256 claimedMask) {
        claimedBlock = _claimed[index / 256];
        claimedMask = (uint256(1) << uint256(index % 256));
        require((claimedBlock & claimedMask) == 0, "Tokens have already been claimed");
    }

    // helper for the dapp
    function canClaim(uint256 index) external view returns (bool) {
        uint256 claimedBlock = _claimed[index / 256];
        uint256 claimedMask = (uint256(1) << uint256(index % 256));
        return ((claimedBlock & claimedMask) == 0);
    }

    // Get airdrop tokens assigned to address
    // Requires sending merkle proof to the function
    function claim(
        uint256 index,
        uint256 amount,
        bytes32[] memory merkleProof
    ) public notPaused {
        require(token.balanceOf(address(this)) > amount, "Contract doesnt have enough tokens");

        // Make sure the tokens have not already been redeemed
        (uint256 claimedBlock, uint256 claimedMask) = claimed(index);
        _claimed[index / 256] = claimedBlock | claimedMask;

        // Compute the merkle leaf from index, recipient and amount
        bytes32 leaf = keccak256(abi.encodePacked(index, msg.sender, amount));
        // verify the proof is valid
        require(MerkleProof.verify(merkleProof, root, leaf), "Proof is not valid");
        // Redeem!
        token.transfer(msg.sender, amount);
        emit Claim(msg.sender, amount, block.timestamp);
    }

    function _selfDestruct(address payable beneficiary) external onlyOwner {
        token.transfer(beneficiary, token.balanceOf(address(this)));
        selfdestruct(beneficiary);
    }

    event Claim(address claimer, uint256 amount, uint timestamp);
}

// File: @openzeppelin/contracts-4.4.1/token/ERC20/IERC20.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/IERC20.sol)

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/utils/Owned.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract Owned {
    address public owner;
    address public nominatedOwner;

    constructor(address _owner) {
        require(_owner != address(0), "Owner address cannot be 0");
        owner = _owner;
        emit OwnerChanged(address(0), _owner);
    }

    function nominateNewOwner(address _owner) external onlyOwner {
        nominatedOwner = _owner;
        emit OwnerNominated(_owner);
    }

    function acceptOwnership() external {
        require(msg.sender == nominatedOwner, "You must be nominated before you can accept ownership");
        emit OwnerChanged(owner, nominatedOwner);
        owner = nominatedOwner;
        nominatedOwner = address(0);
    }

    modifier onlyOwner {
        _onlyOwner();
        _;
    }

    function _onlyOwner() private view {
        require(msg.sender == owner, "Only the contract owner may perform this action");
    }

    event OwnerNominated(address newOwner);
    event OwnerChanged(address oldOwner, address newOwner);
}

// File: @openzeppelin/contracts-4.4.1/utils/cryptography/MerkleProof.sol



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

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) {
        return processProof(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merklee tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leafs & pre-images are assumed to be sorted.
     *
     * _Available since v4.4._
     */
    function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
        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));
            }
        }
        return computedHash;
    }
}

// File: contracts/utils/Pausable.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;
// Inheritance
import "./Owned.sol";

abstract contract Pausable is Owned {
    uint public lastPauseTime;
    bool public paused;

    constructor() {
        // This contract is abstract, and thus cannot be instantiated directly
        require(owner != address(0), "Owner must be set");
        // Paused will be false, and lastPauseTime will be 0 upon initialisation
    }

    /**
     * @notice Change the paused state of the contract
     * @dev Only the contract owner may call this.
     */
    function setPaused(bool _paused) external onlyOwner {
        // Ensure we're actually changing the state before we do anything
        if (_paused == paused) {
            return;
        }

        // Set our paused state.
        paused = _paused;

        // If applicable, set the last pause time.
        if (paused) {
            lastPauseTime = block.timestamp;
        }

        // Let everyone know that our pause state has changed.
        emit PauseChanged(paused);
    }

    event PauseChanged(bool isPaused);

    modifier notPaused {
        require(!paused, "This action cannot be performed while the contract is paused");
        _;
    }
}