// File: contracts/DARTVesting/PrivateSaleVesting.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.7.6;

import "@openzeppelin/contracts/math/SafeMath.sol";
import "./DARTVesting.sol";

contract PrivateSaleVesting is DARTVesting {
    uint256 public constant TOTAL_AMOUNT = 15000000 * (10**18);
    uint256 public constant RELEASE_PERIODS = 270;
    uint256 public constant LOCK_PERIODS = 0;
    uint256 public constant UNLOCK_TGE_PERCENT = 15;

    constructor(DARTToken _dARTToken)
        DARTVesting(
            _dARTToken,
            TOTAL_AMOUNT,
            RELEASE_PERIODS,
            LOCK_PERIODS,
            UNLOCK_TGE_PERCENT
        )
    {}
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @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 SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        uint256 c = a + b;
        if (c < a) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b > a) return (false, 0);
        return (true, a - b);
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, 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 (true, 0);
        uint256 c = a * b;
        if (c / a != b) return (false, 0);
        return (true, c);
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a / b);
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        if (b == 0) return (false, 0);
        return (true, a % b);
    }

    /**
     * @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) {
        require(b <= a, "SafeMath: subtraction overflow");
        return a - b;
    }

    /**
     * @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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting 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) {
        require(b > 0, "SafeMath: modulo by zero");
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * 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);
        return a - b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * 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;
    }
}

// File: contracts/DARTVesting/DARTVesting.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.7.6;

import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/utils/Context.sol";
import "../DARTToken.sol";

contract DARTVesting is Context, Ownable {
    using SafeMath for uint256;

    struct VestingSchedule {
        uint256 totalAmount; // Total amount of tokens to be vested.
        uint256 amountWithdrawn; // The amount that has been withdrawn.
    }

    mapping(address => VestingSchedule) public recipients;
    address[] recipientAddresses;

    uint256 public startTime;
    bool public isStartTimeSet;
    uint256 public withdrawInterval = 1 days; // Amount of time in seconds between withdrawal periods.
    uint256 public releasePeriods; // Number of periods from start release until done.
    uint256 public lockPeriods; // Number of periods before start release.

    uint256 public unlockTGEPercent;

    uint256 public totalAmount; // Total amount of tokens to be vested.
    uint256 public unallocatedAmount; // The amount of tokens that are not allocated yet.

    bool initialDistributed = false;

    DARTToken public dARTToken;

    event VestingScheduleRegistered(
        address[] registeredAddresses,
        uint256[] allocations
    );
    event Withdraw(address registeredAddress, uint256 amountWithdrawn);
    event StartTimeSet(uint256 startTime);

    constructor(
        DARTToken _dARTToken,
        uint256 _totalAmount,
        uint256 _releasePeriods,
        uint256 _lockPeriods,
        uint256 _unlockTGEPercent
    ) {
        require(_totalAmount > 0, "Total amount should not be zero");
        require(_releasePeriods > 0, "Release periods should not be zero");

        dARTToken = _dARTToken;

        totalAmount = _totalAmount;
        unallocatedAmount = _totalAmount;
        releasePeriods = _releasePeriods;
        lockPeriods = _lockPeriods;
        unlockTGEPercent = _unlockTGEPercent;
    }

    function addRecipients(address[] memory _newRecipients, uint256[] memory _allocations)
        external
        onlyOwner
    {
        // Only allow to add recipient before the counting starts
        require(!isStartTimeSet || startTime > block.timestamp, "Start time is passed");
        require(_newRecipients.length == _allocations.length, "Recipients length should match allocations length");

        uint256 length = _allocations.length;

        for (uint256 i = 0; i < length; i ++) {
            require(_newRecipients[i] != address(0), "Recipient cannot be zero address");
            require(recipients[_newRecipients[i]].totalAmount == 0, "Recipient already added");
            require(_allocations[i] > 0 && _allocations[i] <= unallocatedAmount, "Allocation cannot be zero and cannot override unallocated amount");

            recipientAddresses.push(_newRecipients[i]);

            recipients[_newRecipients[i]] = VestingSchedule({
                totalAmount: _allocations[i],
                amountWithdrawn: 0
            });

            unallocatedAmount = unallocatedAmount.sub(_allocations[i]);
        }

        emit VestingScheduleRegistered(_newRecipients, _allocations);
    }

    function setStartTime(uint256 _newStartTime) external onlyOwner {
        // Only allow to change start time before the counting starts
        require(!isStartTimeSet || startTime > block.timestamp, "Start time already passed");
        require(_newStartTime > block.timestamp, "Start time should be later than now");

        startTime = _newStartTime;
        isStartTimeSet = true;

        emit StartTimeSet(_newStartTime);
    }

    // Returns the amount of tokens you can withdraw
    function vested(address beneficiary)
        public
        view
        virtual
        returns (uint256 _amountVested)
    {
        VestingSchedule memory _vestingSchedule = recipients[beneficiary];
        if (
            !isStartTimeSet ||
            (_vestingSchedule.totalAmount == 0) ||
            (lockPeriods == 0 && releasePeriods == 0) ||
            (block.timestamp < startTime)
        ) {
            return 0;
        }

        uint256 period =
            block.timestamp.sub(startTime).div(withdrawInterval);
        if (period <= lockPeriods) {
            return 0;
        }
        if (period >= lockPeriods.add(releasePeriods)) {
            return _vestingSchedule.totalAmount;
        }

        uint256 vestedAmount = _vestingSchedule.totalAmount.mul(period.sub(lockPeriods)).div(releasePeriods);
        return vestedAmount;
    }

    function withdrawable(address beneficiary)
        public
        view
        returns (uint256 amount)
    {
        return vested(beneficiary).sub(recipients[beneficiary].amountWithdrawn);
    }

    function withdraw() external {
        VestingSchedule storage vestingSchedule = recipients[_msgSender()];
        require(vestingSchedule.totalAmount > 0, "No Tokens to withdraw");

        uint256 _vested = vested(msg.sender);
        uint256 _withdrawable = withdrawable(msg.sender);
        vestingSchedule.amountWithdrawn = _vested;

        if (_withdrawable > 0) {
            require(dARTToken.transfer(_msgSender(), _withdrawable), "Transfer failed for some reason");
            emit Withdraw(_msgSender(), _withdrawable);
        }
    }

    function distributeInitials() external onlyOwner() {
        require(!initialDistributed, "Already distributed");

        initialDistributed = true;

        uint256 recipientLength = recipientAddresses.length;
        
        for (uint i = 0; i < recipientLength; i ++) {
            address recipientAddr = recipientAddresses[i];
            if (recipients[recipientAddr].totalAmount > 0) {
                uint256 amount = recipients[recipientAddr].totalAmount.mul(unlockTGEPercent).div(100);
                recipients[recipientAddr].totalAmount = recipients[recipientAddr].totalAmount.sub(amount);
                dARTToken.transfer(recipientAddr, amount);
            }
        }
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

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 () {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), 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 {
        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;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <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 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 Context {
    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;
    }
}

// File: contracts/DARTToken.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.7.6;

import "@openzeppelin/contracts/utils/Context.sol";
import "@openzeppelin/contracts/token/ERC20/ERC20Burnable.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract DARTToken is Context, Ownable, ERC20Burnable {
    string public constant NAME = "dART Token";
    string public constant SYMBOL = "dART";
    uint8 public constant DECIMALS = 18;
    uint256 public constant TOTAL_SUPPLY = 142090000 * (10**uint256(DECIMALS));

    address public SeedInvestmentAddr;
    address public PrivateSaleAddr;
    address public StakingRewardsAddr;
    address public LiquidityPoolAddr;
    address public MarketingAddr;
    address public TreasuryAddr;
    address public TeamAllocationAddr;
    address public AdvisorsAddr;
    address public ReserveAddr;

    uint256 public constant SEED_INVESTMENT = 3000000 * (10**uint256(DECIMALS)); // 2.1% for Seed investment
    uint256 public constant PRIVATE_SALE = 15000000 * (10**uint256(DECIMALS)); // 10.6% for Private Sale

    uint256 public constant STAKING_REWARDS = 24500000 * (10**uint256(DECIMALS)); // 17.2% for Staking rewards
    
    uint256 public constant LIQUIDITY_POOL = 9000000 * (10**uint256(DECIMALS)); // 6.3% for Liquidity pool

    uint256 public constant MARKETING = 14000000 * (10**uint256(DECIMALS)); // 9.9% for Marketing/Listings
    uint256 public constant TREASURY = 19600000 * (10**uint256(DECIMALS)); // 13.8% for Treasury

    uint256 public constant TEAM_ALLOCATION = 17000000 * (10**uint256(DECIMALS)); // 12% for Team allocation
    uint256 public constant ADVISORS = 5000000 * (10**uint256(DECIMALS)); // 3.5% for Advisors

    uint256 public constant RESERVE = 34990000 * (10**uint256(DECIMALS)); // 24.6% for Bridge consumption

    bool private _isDistributionComplete = false;

    constructor()
        ERC20(NAME, SYMBOL)
    {
        _mint(address(this), TOTAL_SUPPLY);
    }

    function setDistributionTeamsAddresses(
        address _SeedInvestmentAddr,
        address _PrivateSaleAddr,
        address _StakingRewardsAddr,
        address _LiquidityPoolAddr,
        address _MarketingAddr,
        address _TreasuryAddr,
        address _TeamAllocationAddr,
        address _AdvisorsAddr,
        address _ReserveAddr
    ) external onlyOwner {
        require(!_isDistributionComplete, "Already distributed");

        // set parnters addresses
        SeedInvestmentAddr = _SeedInvestmentAddr;
        PrivateSaleAddr = _PrivateSaleAddr;
        StakingRewardsAddr = _StakingRewardsAddr;
        LiquidityPoolAddr = _LiquidityPoolAddr;
        MarketingAddr = _MarketingAddr;
        TreasuryAddr = _TreasuryAddr;
        TeamAllocationAddr = _TeamAllocationAddr;
        AdvisorsAddr = _AdvisorsAddr;
        ReserveAddr = _ReserveAddr;
    }

    function distributeTokens() external onlyOwner {
        require(!_isDistributionComplete, "Already distributed");

        _transfer(address(this), SeedInvestmentAddr, SEED_INVESTMENT);
        _transfer(address(this), PrivateSaleAddr, PRIVATE_SALE);
        _transfer(address(this), StakingRewardsAddr, STAKING_REWARDS);
        _transfer(address(this), LiquidityPoolAddr, LIQUIDITY_POOL);
        _transfer(address(this), MarketingAddr, MARKETING);
        _transfer(address(this), TreasuryAddr, TREASURY);
        _transfer(address(this), TeamAllocationAddr, TEAM_ALLOCATION);
        _transfer(address(this), AdvisorsAddr, ADVISORS);
        _transfer(address(this), ReserveAddr, RESERVE);

        _isDistributionComplete = true;
    }
}

// File: @openzeppelin/contracts/token/ERC20/ERC20Burnable.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "../../utils/Context.sol";
import "./ERC20.sol";

/**
 * @dev Extension of {ERC20} that allows token holders to destroy both their own
 * tokens and those that they have an allowance for, in a way that can be
 * recognized off-chain (via event analysis).
 */
abstract contract ERC20Burnable is Context, ERC20 {
    using SafeMath for uint256;

    /**
     * @dev Destroys `amount` tokens from the caller.
     *
     * See {ERC20-_burn}.
     */
    function burn(uint256 amount) public virtual {
        _burn(_msgSender(), amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, deducting from the caller's
     * allowance.
     *
     * See {ERC20-_burn} and {ERC20-allowance}.
     *
     * Requirements:
     *
     * - the caller must have allowance for ``accounts``'s tokens of at least
     * `amount`.
     */
    function burnFrom(address account, uint256 amount) public virtual {
        uint256 decreasedAllowance = allowance(account, _msgSender()).sub(amount, "ERC20: burn amount exceeds allowance");

        _approve(account, _msgSender(), decreasedAllowance);
        _burn(account, amount);
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

import "../../utils/Context.sol";
import "./IERC20.sol";
import "../../math/SafeMath.sol";

/**
 * @dev Implementation of the {IERC20} interface.
 *
 * This implementation is agnostic to the way tokens are created. This means
 * that a supply mechanism has to be added in a derived contract using {_mint}.
 * For a generic mechanism see {ERC20PresetMinterPauser}.
 *
 * TIP: For a detailed writeup see our guide
 * https://forum.zeppelin.solutions/t/how-to-implement-erc20-supply-mechanisms/226[How
 * to implement supply mechanisms].
 *
 * We have followed general OpenZeppelin guidelines: functions revert instead
 * of returning `false` on failure. This behavior is nonetheless conventional
 * and does not conflict with the expectations of ERC20 applications.
 *
 * Additionally, an {Approval} event is emitted on calls to {transferFrom}.
 * This allows applications to reconstruct the allowance for all accounts just
 * by listening to said events. Other implementations of the EIP may not emit
 * these events, as it isn't required by the specification.
 *
 * Finally, the non-standard {decreaseAllowance} and {increaseAllowance}
 * functions have been added to mitigate the well-known issues around setting
 * allowances. See {IERC20-approve}.
 */
contract ERC20 is Context, IERC20 {
    using SafeMath for uint256;

    mapping (address => uint256) private _balances;

    mapping (address => mapping (address => uint256)) private _allowances;

    uint256 private _totalSupply;

    string private _name;
    string private _symbol;
    uint8 private _decimals;

    /**
     * @dev Sets the values for {name} and {symbol}, initializes {decimals} with
     * a default value of 18.
     *
     * To select a different value for {decimals}, use {_setupDecimals}.
     *
     * All three of these values are immutable: they can only be set once during
     * construction.
     */
    constructor (string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
        _decimals = 18;
    }

    /**
     * @dev Returns the name of the token.
     */
    function name() public view virtual returns (string memory) {
        return _name;
    }

    /**
     * @dev Returns the symbol of the token, usually a shorter version of the
     * name.
     */
    function symbol() public view virtual returns (string memory) {
        return _symbol;
    }

    /**
     * @dev Returns the number of decimals used to get its user representation.
     * For example, if `decimals` equals `2`, a balance of `505` tokens should
     * be displayed to a user as `5,05` (`505 / 10 ** 2`).
     *
     * Tokens usually opt for a value of 18, imitating the relationship between
     * Ether and Wei. This is the value {ERC20} uses, unless {_setupDecimals} is
     * called.
     *
     * NOTE: This information is only used for _display_ purposes: it in
     * no way affects any of the arithmetic of the contract, including
     * {IERC20-balanceOf} and {IERC20-transfer}.
     */
    function decimals() public view virtual returns (uint8) {
        return _decimals;
    }

    /**
     * @dev See {IERC20-totalSupply}.
     */
    function totalSupply() public view virtual override returns (uint256) {
        return _totalSupply;
    }

    /**
     * @dev See {IERC20-balanceOf}.
     */
    function balanceOf(address account) public view virtual override returns (uint256) {
        return _balances[account];
    }

    /**
     * @dev See {IERC20-transfer}.
     *
     * Requirements:
     *
     * - `recipient` cannot be the zero address.
     * - the caller must have a balance of at least `amount`.
     */
    function transfer(address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(_msgSender(), recipient, amount);
        return true;
    }

    /**
     * @dev See {IERC20-allowance}.
     */
    function allowance(address owner, address spender) public view virtual override returns (uint256) {
        return _allowances[owner][spender];
    }

    /**
     * @dev See {IERC20-approve}.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function approve(address spender, uint256 amount) public virtual override returns (bool) {
        _approve(_msgSender(), spender, amount);
        return true;
    }

    /**
     * @dev See {IERC20-transferFrom}.
     *
     * Emits an {Approval} event indicating the updated allowance. This is not
     * required by the EIP. See the note at the beginning of {ERC20}.
     *
     * Requirements:
     *
     * - `sender` and `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     * - the caller must have allowance for ``sender``'s tokens of at least
     * `amount`.
     */
    function transferFrom(address sender, address recipient, uint256 amount) public virtual override returns (bool) {
        _transfer(sender, recipient, amount);
        _approve(sender, _msgSender(), _allowances[sender][_msgSender()].sub(amount, "ERC20: transfer amount exceeds allowance"));
        return true;
    }

    /**
     * @dev Atomically increases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     */
    function increaseAllowance(address spender, uint256 addedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].add(addedValue));
        return true;
    }

    /**
     * @dev Atomically decreases the allowance granted to `spender` by the caller.
     *
     * This is an alternative to {approve} that can be used as a mitigation for
     * problems described in {IERC20-approve}.
     *
     * Emits an {Approval} event indicating the updated allowance.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `spender` must have allowance for the caller of at least
     * `subtractedValue`.
     */
    function decreaseAllowance(address spender, uint256 subtractedValue) public virtual returns (bool) {
        _approve(_msgSender(), spender, _allowances[_msgSender()][spender].sub(subtractedValue, "ERC20: decreased allowance below zero"));
        return true;
    }

    /**
     * @dev Moves tokens `amount` from `sender` to `recipient`.
     *
     * This is internal function is equivalent to {transfer}, and can be used to
     * e.g. implement automatic token fees, slashing mechanisms, etc.
     *
     * Emits a {Transfer} event.
     *
     * Requirements:
     *
     * - `sender` cannot be the zero address.
     * - `recipient` cannot be the zero address.
     * - `sender` must have a balance of at least `amount`.
     */
    function _transfer(address sender, address recipient, uint256 amount) internal virtual {
        require(sender != address(0), "ERC20: transfer from the zero address");
        require(recipient != address(0), "ERC20: transfer to the zero address");

        _beforeTokenTransfer(sender, recipient, amount);

        _balances[sender] = _balances[sender].sub(amount, "ERC20: transfer amount exceeds balance");
        _balances[recipient] = _balances[recipient].add(amount);
        emit Transfer(sender, recipient, amount);
    }

    /** @dev Creates `amount` tokens and assigns them to `account`, increasing
     * the total supply.
     *
     * Emits a {Transfer} event with `from` set to the zero address.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     */
    function _mint(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: mint to the zero address");

        _beforeTokenTransfer(address(0), account, amount);

        _totalSupply = _totalSupply.add(amount);
        _balances[account] = _balances[account].add(amount);
        emit Transfer(address(0), account, amount);
    }

    /**
     * @dev Destroys `amount` tokens from `account`, reducing the
     * total supply.
     *
     * Emits a {Transfer} event with `to` set to the zero address.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens.
     */
    function _burn(address account, uint256 amount) internal virtual {
        require(account != address(0), "ERC20: burn from the zero address");

        _beforeTokenTransfer(account, address(0), amount);

        _balances[account] = _balances[account].sub(amount, "ERC20: burn amount exceeds balance");
        _totalSupply = _totalSupply.sub(amount);
        emit Transfer(account, address(0), amount);
    }

    /**
     * @dev Sets `amount` as the allowance of `spender` over the `owner` s tokens.
     *
     * This internal function is equivalent to `approve`, and can be used to
     * e.g. set automatic allowances for certain subsystems, etc.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `owner` cannot be the zero address.
     * - `spender` cannot be the zero address.
     */
    function _approve(address owner, address spender, uint256 amount) internal virtual {
        require(owner != address(0), "ERC20: approve from the zero address");
        require(spender != address(0), "ERC20: approve to the zero address");

        _allowances[owner][spender] = amount;
        emit Approval(owner, spender, amount);
    }

    /**
     * @dev Sets {decimals} to a value other than the default one of 18.
     *
     * WARNING: This function should only be called from the constructor. Most
     * applications that interact with token contracts will not expect
     * {decimals} to ever change, and may work incorrectly if it does.
     */
    function _setupDecimals(uint8 decimals_) internal virtual {
        _decimals = decimals_;
    }

    /**
     * @dev Hook that is called before any transfer of tokens. This includes
     * minting and burning.
     *
     * Calling conditions:
     *
     * - when `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * will be to transferred to `to`.
     * - when `from` is zero, `amount` tokens will be minted for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(address from, address to, uint256 amount) internal virtual { }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @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);
}