/**
 *Submitted for verification at Etherscan.io on 2021-09-15
*/

/**
 *Submitted for verification at Etherscan.io on 2021-07-12
*/

// SPDX-License-Identifier: UNLICENSED
pragma solidity >=0.6.12 <0.7.0;

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 * 
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {UpgradeableProxy-constructor}.
 * 
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {

    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || _isConstructor() || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }

    /// @dev Returns true if and only if the function is running in the constructor
    function _isConstructor() private view returns (bool) {
        // extcodesize checks the size of the code stored in an address, and
        // address returns the current address. Since the code is still not
        // deployed when running a constructor, any checks on its code size will
        // yield zero, making it an effective way to detect if a contract is
        // under construction or not.
        address self = address(this);
        uint256 cs;
        // solhint-disable-next-line no-inline-assembly
        assembly { cs := extcodesize(self) }
        return cs == 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 GSN 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 ContextUpgradeable is Initializable {
    function __Context_init() internal initializer {
        __Context_init_unchained();
    }

    function __Context_init_unchained() internal initializer {
    }
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
    uint256[50] private __gap;
}

/**
 * @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.
 */
contract OwnableUpgradeable is Initializable, ContextUpgradeable {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    function __Ownable_init() internal initializer {
        __Context_init_unchained();
        __Ownable_init_unchained();
    }

    function __Ownable_init_unchained() internal initializer {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view 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 {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
    uint256[49] private __gap;
}

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMathUpgradeable {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20Upgradeable {
    /**
     * @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);
}

/**
 * @dev These functions deal with verification of Merkle trees (hash trees),
 */
library MerkleProofUpgradeable {
    /**
     * @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;
    }
}

// Allows anyone to claim a token if they exist in a merkle root.
interface IMerkleDistributor {
    // Returns true if the index has been marked claimed.
    function isClaimed(uint256 index) external view returns (bool);
    // 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;

    // This event is triggered whenever a call to #claim succeeds.
    event Claimed(uint256 index, address account, uint256 amount);
}

contract MerkleDistributor is Initializable, IMerkleDistributor {
    address public token;
    bytes32 public merkleRoot;

    // This is a packed array of booleans.
    mapping(uint256 => uint256) internal claimedBitMap;

    function __MerkleDistributor_init(address token_, bytes32 merkleRoot_) public initializer {
        token = token_;
        merkleRoot = merkleRoot_;
    }

    function isClaimed(uint256 index) public override view returns (bool) {
        uint256 claimedWordIndex = index / 256;
        uint256 claimedBitIndex = index % 256;
        uint256 claimedWord = claimedBitMap[claimedWordIndex];
        uint256 mask = (1 << claimedBitIndex);
        return claimedWord & mask == mask;
    }

    function _setClaimed(uint256 index) internal {
        uint256 claimedWordIndex = index / 256;
        uint256 claimedBitIndex = index % 256;
        claimedBitMap[claimedWordIndex] = claimedBitMap[claimedWordIndex] | (1 << claimedBitIndex);
    }

    function claim(
        uint256 index,
        address account,
        uint256 amount,
        bytes32[] calldata merkleProof
    ) external virtual override {
        require(!isClaimed(index), "MerkleDistributor: Drop already claimed.");

        // Verify the merkle proof.
        bytes32 node = keccak256(abi.encodePacked(index, account, amount));
        require(MerkleProofUpgradeable.verify(merkleProof, merkleRoot, node), "MerkleDistributor: Invalid proof.");

        // Mark it claimed and send the token.
        _setClaimed(index);
        require(IERC20Upgradeable(token).transfer(account, amount), "MerkleDistributor: Transfer failed.");

        emit Claimed(index, account, amount);
    }
}

contract TokenDistributor is MerkleDistributor, OwnableUpgradeable {
    using SafeMathUpgradeable for uint256;
    uint256 public constant MAX_BPS = 10000;

    uint256 public claimsStart;
    uint256 public gracePeriod;

    uint256 public epochDuration;
    uint256 public rewardReductionPerEpoch;
    uint256 public currentRewardRate;
    uint256 public finalEpoch;

    address public rewardsEscrow;

    event Claimed(uint256 index, address indexed account, uint256 amount, uint256 userClaim, uint256 rewardsEscrowClaim);

    function initialize(
        address token_,
        bytes32 merkleRoot_,
        uint256 epochDuration_,
        uint256 rewardReductionPerEpoch_,
        uint256 claimsStart_,
        uint256 gracePeriod_,
        address rewardsEscrow_,
        address owner_
    ) public initializer {
        __MerkleDistributor_init(token_, merkleRoot_);

        __Ownable_init();
        transferOwnership(owner_);

        epochDuration = epochDuration_;
        rewardReductionPerEpoch = rewardReductionPerEpoch_;
        claimsStart = claimsStart_;
        gracePeriod = gracePeriod_;

        rewardsEscrow = rewardsEscrow_;

        currentRewardRate = 10000;

        finalEpoch = (currentRewardRate / rewardReductionPerEpoch_) - 1;
    }

    /// ===== View Functions =====
    /// @dev Get grace period end timestamp
    function getGracePeriodEnd() public view returns (uint256) {
        return claimsStart.add(gracePeriod);
    }

    /// @dev Get claims start timestamp
    function getClaimsStartTime() public view returns (uint256) {
        return claimsStart;
    }

    /// @dev Get the next epoch start
    function getNextEpochStart() public view returns (uint256) {
        uint256 epoch = getCurrentEpoch();

        if (epoch == 0) {
            return getGracePeriodEnd();
        } else {
            return getGracePeriodEnd().add(epochDuration.mul(epoch));
        }
    }

    function getTimeUntilNextEpoch() public view returns (uint256) {
        uint256 epoch = getCurrentEpoch();

        if (epoch == 0) {
            return getGracePeriodEnd().sub(now);
        } else {
            return (getGracePeriodEnd().add(epochDuration.mul(epoch))).sub(now);
        }
    }

    /// @dev Get the current epoch number
    function getCurrentEpoch() public view returns (uint256) {
        uint256 gracePeriodEnd = claimsStart.add(gracePeriod);

        if (now < gracePeriodEnd) {
            return 0;
        }
        uint256 secondsPastGracePeriod = now.sub(gracePeriodEnd);
        return (secondsPastGracePeriod / epochDuration).add(1);
    }

    /// @dev Get the rewards % of current epoch
    function getCurrentRewardsRate() public view returns (uint256) {
        uint256 epoch = getCurrentEpoch();
        if (epoch == 0) return MAX_BPS;
        if (epoch > finalEpoch) return 0;
        else return MAX_BPS.sub(epoch.mul(rewardReductionPerEpoch));
    }

    /// @dev Get the rewards % of following epoch
    function getNextEpochRewardsRate() public view returns (uint256) {
        uint256 epoch = getCurrentEpoch().add(1);
        if (epoch == 0) return MAX_BPS;
        if (epoch > finalEpoch) return 0;
        else return MAX_BPS.sub(epoch.mul(rewardReductionPerEpoch));
    }

    /// ===== Public Actions =====

    function claim(
        uint256 index,
        address account,
        uint256 amount,
        bytes32[] calldata merkleProof
    ) external virtual override {
        require(now >= claimsStart, "TokenDistributor: Before claim start.");

        // Intentionally commented out so users can pay gas for others claims
        // require(account == msg.sender, "TokenDistributor: Can only claim for own account.");
        require(getCurrentRewardsRate() > 0, "TokenDistributor: Past rewards claim period.");
        require(!isClaimed(index), "TokenDistributor: Drop already claimed.");

        // Verify the merkle proof.
        bytes32 node = keccak256(abi.encodePacked(index, account, amount));
        require(MerkleProofUpgradeable.verify(merkleProof, merkleRoot, node), "TokenDistributor: Invalid proof.");

        // Mark it claimed and send the token.
        _setClaimed(index);

        require(getCurrentRewardsRate() <= MAX_BPS, "Excessive Rewards Rate");
        uint256 claimable = amount.mul(getCurrentRewardsRate()).div(MAX_BPS);

        require(IERC20Upgradeable(token).transfer(account, claimable), "Transfer to user failed.");
        emit Claimed(index, account, amount, claimable, amount.sub(claimable));
    }

    /// ===== Gated Actions: Owner =====

    /// @notice After claim period is complete, transfer excess funds to rewardsEscrow
    function recycleExcess() external onlyOwner {
        require(getCurrentRewardsRate() == 0 && getCurrentEpoch() > finalEpoch, "Claim period not finished");
        uint256 remainingBalance = IERC20Upgradeable(token).balanceOf(address(this));
        IERC20Upgradeable(token).transfer(rewardsEscrow, remainingBalance);
    }

    function setGracePeriod(uint256 duration) external onlyOwner {
        gracePeriod = duration;
    }
}