// File: contracts/liquidityMining/KyberFairLaunch.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.7.6;
pragma abicoder v2;

import {ReentrancyGuard} from '@openzeppelin/contracts/utils/ReentrancyGuard.sol';
import {SafeMath} from '@openzeppelin/contracts/math/SafeMath.sol';
import {SafeERC20} from '@openzeppelin/contracts/token/ERC20/SafeERC20.sol';
import {SafeCast} from '@openzeppelin/contracts/utils/SafeCast.sol';
import {IERC20Ext} from '@kyber.network/utils-sc/contracts/IERC20Ext.sol';
import {PermissionAdmin} from '@kyber.network/utils-sc/contracts/PermissionAdmin.sol';
import {IKyberFairLaunch} from '../interfaces/liquidityMining/IKyberFairLaunch.sol';
import {IKyberRewardLocker} from '../interfaces/liquidityMining/IKyberRewardLocker.sol';

/// FairLaunch contract for Kyber DMM Liquidity Mining program
/// Allow stakers to stake LP tokens and receive reward tokens
/// Allow extend or renew a pool to continue/restart the LM program
/// When harvesting, rewards will be transferred to a RewardLocker
/// Support multiple reward tokens, reward tokens must be distinct and immutable
contract KyberFairLaunch is IKyberFairLaunch, PermissionAdmin, ReentrancyGuard {
  using SafeMath for uint256;
  using SafeCast for uint256;
  using SafeERC20 for IERC20Ext;

  uint256 internal constant PRECISION = 1e12;

  struct UserRewardData {
    uint256 unclaimedReward;
    uint256 lastRewardPerShare;
  }
  // Info of each user.
  struct UserInfo {
    uint256 amount; // How many Staking tokens the user has provided.
    mapping (uint256 => UserRewardData) userRewardData;
    //
    // Basically, any point in time, the amount of reward token
    // entitled to a user but is pending to be distributed is:
    //
    //   pending reward = user.unclaimAmount + (user.amount * (pool.accRewardPerShare - user.lastRewardPerShare)
    //
    // Whenever a user deposits or withdraws Staking tokens to a pool. Here's what happens:
    //   1. The pool's `accRewardPerShare` (and `lastRewardBlock`) gets updated.
    //   2. User receives the pending reward sent to his/her address.
    //   3. User's `lastRewardPerShare` gets updated.
    //   4. User's `amount` gets updated.
  }

  struct PoolRewardData {
    uint256 rewardPerBlock;
    uint256 accRewardPerShare;
  }
  // Info of each pool
  // poolRewardData: reward data for each reward token
  //      rewardPerBlock: amount of reward token per block
  //      accRewardPerShare: accumulated reward per share of token
  // totalStake: total amount of stakeToken has been staked
  // stakeToken: token to stake, should be an ERC20 token
  // startBlock: the block that the reward starts
  // endBlock: the block that the reward ends
  // lastRewardBlock: last block number that rewards distribution occurs
  struct PoolInfo {
    uint256 totalStake;
    address stakeToken;
    uint32 startBlock;
    uint32 endBlock;
    uint32 lastRewardBlock;
    mapping (uint256 => PoolRewardData) poolRewardData;
  }

  // check if a pool exists for a stakeToken
  mapping(address => bool) public poolExists;
  // contract for locking reward
  IKyberRewardLocker public immutable rewardLocker;
  // list reward tokens, use 0x0 for native token, shouldn't be too many reward tokens
  // don't validate values or length by trusting the deployer
  address[] public rewardTokens;

  // Info of each pool.
  uint256 public override poolLength;
  mapping(uint256 => PoolInfo) internal poolInfo;
  // Info of each user that stakes Staking tokens.
  mapping(uint256 => mapping(address => UserInfo)) internal userInfo;

  event AddNewPool(
    address indexed stakeToken,
    uint32 indexed startBlock,
    uint32 indexed endBlock,
    uint256[] rewardPerBlocks
  );
  event RenewPool(
    uint256 indexed pid,
    uint32 indexed startBlock,
    uint32 indexed endBlock,
    uint256[] rewardPerBlocks
  );
  event UpdatePool(
    uint256 indexed pid,
    uint32 indexed endBlock,
    uint256[] rewardPerBlocks
  );
  event Deposit(
    address indexed user,
    uint256 indexed pid,
    uint256 indexed blockNumber,
    uint256 amount
  );
  event Withdraw(
    address indexed user,
    uint256 indexed pid,
    uint256 indexed blockNumber,
    uint256 amount
  );
  event Harvest(
    address indexed user,
    uint256 indexed pid,
    address indexed rewardToken,
    uint256 lockedAmount,
    uint256 blockNumber
  );
  event EmergencyWithdraw(
    address indexed user,
    uint256 indexed pid,
    uint256 indexed blockNumber,
    uint256 amount
  );

  constructor(
    address _admin,
    address[] memory _rewardTokens,
    IKyberRewardLocker _rewardLocker
  ) PermissionAdmin(_admin) {
    rewardTokens = _rewardTokens;
    rewardLocker = _rewardLocker;

    // approve allowance to reward locker
    for(uint256 i = 0; i < _rewardTokens.length; i++) {
      if (_rewardTokens[i] != address(0)) {
        IERC20Ext(_rewardTokens[i]).safeApprove(address(_rewardLocker), type(uint256).max);
      }
    }
  }

  receive() external payable {}

  /**
   * @dev Allow admin to withdraw only reward tokens
   */
  function adminWithdraw(uint256 rewardTokenIndex, uint256 amount) external onlyAdmin {
    IERC20Ext rewardToken = IERC20Ext(rewardTokens[rewardTokenIndex]);
    if (rewardToken == IERC20Ext(0)) {
      (bool success, ) = msg.sender.call{ value: amount }('');
      require(success, 'transfer reward token failed');
    } else {
      rewardToken.safeTransfer(msg.sender, amount);
    }
  }

  /**
   * @dev Add a new lp to the pool. Can only be called by the admin.
   * @param _stakeToken: token to be staked to the pool
   * @param _startBlock: block where the reward starts
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool for each reward token
   */
  function addPool(
    address _stakeToken,
    uint32 _startBlock,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external override onlyAdmin {
    require(!poolExists[_stakeToken], 'add: duplicated pool');
    require(_stakeToken != address(0), 'add: invalid stake token');
    require(rewardTokens.length == _rewardPerBlocks.length, 'add: invalid length');

    require(_startBlock > block.number && _endBlock > _startBlock, 'add: invalid blocks');

    poolInfo[poolLength].stakeToken = _stakeToken;
    poolInfo[poolLength].startBlock = _startBlock;
    poolInfo[poolLength].endBlock = _endBlock;
    poolInfo[poolLength].lastRewardBlock = _startBlock;

    for(uint256 i = 0; i < _rewardPerBlocks.length; i++) {
      poolInfo[poolLength].poolRewardData[i] = PoolRewardData({
        rewardPerBlock: _rewardPerBlocks[i],
        accRewardPerShare: 0
      });
    }

    poolLength++;

    poolExists[_stakeToken] = true;

    emit AddNewPool(_stakeToken, _startBlock, _endBlock, _rewardPerBlocks);
  }

  /**
   * @dev Renew a pool to start another liquidity mining program
   * @param _pid: id of the pool to renew, must be pool that has not started or already ended
   * @param _startBlock: block where the reward starts
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool
   *   0 if we want to stop the pool from accumulating rewards
   */
  function renewPool(
    uint256 _pid,
    uint32 _startBlock,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external override onlyAdmin {
    updatePoolRewards(_pid);

    PoolInfo storage pool = poolInfo[_pid];
    // check if pool has not started or already ended
    require(
      pool.startBlock > block.number || pool.endBlock < block.number,
      'renew: invalid pool state to renew'
    );
    // checking data of new pool
    require(rewardTokens.length == _rewardPerBlocks.length, 'renew: invalid length');
    require(_startBlock > block.number && _endBlock > _startBlock, 'renew: invalid blocks');

    pool.startBlock = _startBlock;
    pool.endBlock = _endBlock;
    pool.lastRewardBlock = _startBlock;

    for(uint256 i = 0; i < _rewardPerBlocks.length; i++) {
      pool.poolRewardData[i].rewardPerBlock = _rewardPerBlocks[i];
    }

    emit RenewPool(_pid, _startBlock, _endBlock, _rewardPerBlocks);
  }

  /**
   * @dev Update a pool, allow to change end block, reward per block
   * @param _pid: pool id to be renew
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool,
   *   0 if we want to stop the pool from accumulating rewards
   */
  function updatePool(
    uint256 _pid,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external override onlyAdmin {
    updatePoolRewards(_pid);

    PoolInfo storage pool = poolInfo[_pid];

    // should call renew pool if the pool has ended
    require(pool.endBlock > block.number, 'update: pool already ended');
    require(rewardTokens.length == _rewardPerBlocks.length, 'update: invalid length');
    require(_endBlock > block.number && _endBlock > pool.startBlock, 'update: invalid end block');

    pool.endBlock = _endBlock;
    for(uint256 i = 0; i < _rewardPerBlocks.length; i++) {
      pool.poolRewardData[i].rewardPerBlock = _rewardPerBlocks[i];
    }

    emit UpdatePool(_pid, _endBlock, _rewardPerBlocks);
  }

  /**
   * @dev Deposit tokens to accumulate rewards
   * @param _pid: id of the pool
   * @param _amount: amount of stakeToken to be deposited
   * @param _shouldHarvest: whether to harvest the reward or not
   */
  function deposit(
    uint256 _pid,
    uint256 _amount,
    bool _shouldHarvest
  ) external override nonReentrant {
    // update pool rewards, user's rewards
    updatePoolRewards(_pid);
    _updateUserReward(msg.sender, _pid, _shouldHarvest);

    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][msg.sender];

    // collect stakeToken
    IERC20Ext(pool.stakeToken).safeTransferFrom(msg.sender, address(this), _amount);

    // update user staked amount, and total staked amount for the pool
    user.amount = user.amount.add(_amount);
    pool.totalStake = pool.totalStake.add(_amount);

    emit Deposit(msg.sender, _pid, block.number, _amount);
  }

  /**
   * @dev Withdraw token (of the sender) from pool, also harvest rewards
   * @param _pid: id of the pool
   * @param _amount: amount of stakeToken to withdraw
   */
  function withdraw(uint256 _pid, uint256 _amount) external override nonReentrant {
    _withdraw(_pid, _amount);
  }

  /**
   * @dev Withdraw all tokens (of the sender) from pool, also harvest reward
   * @param _pid: id of the pool
   */
  function withdrawAll(uint256 _pid) external override nonReentrant {
    _withdraw(_pid, userInfo[_pid][msg.sender].amount);
  }

  /**
   * @notice EMERGENCY USAGE ONLY, USER'S REWARDS WILL BE RESET
   * @dev Emergency withdrawal function to allow withdraw all deposited tokens (of the sender)
   *   and reset all rewards
   * @param _pid: id of the pool
   */
  function emergencyWithdraw(uint256 _pid) external override nonReentrant {
    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][msg.sender];
    uint256 amount = user.amount;

    user.amount = 0;
    for(uint256 i = 0; i < rewardTokens.length; i++) {
      UserRewardData storage rewardData = user.userRewardData[i];
      rewardData.lastRewardPerShare = 0;
      rewardData.unclaimedReward = 0;
    }

    pool.totalStake = pool.totalStake.sub(amount);

    if (amount > 0) {
      IERC20Ext(pool.stakeToken).safeTransfer(msg.sender, amount);
    }

    emit EmergencyWithdraw(msg.sender, _pid, block.number, amount);
  }

  /**
   * @dev Harvest rewards from multiple pools for the sender
   *   combine rewards from all pools and only transfer once to save gas
   */
  function harvestMultiplePools(uint256[] calldata _pids) external override {
    address[] memory rTokens = rewardTokens;
    uint256[] memory totalRewards = new uint256[](rTokens.length);
    address account = msg.sender;
    uint256 pid;

    for (uint256 i = 0; i < _pids.length; i++) {
      pid = _pids[i];
      updatePoolRewards(pid);
      // update user reward without harvesting
      _updateUserReward(account, pid, false);

      for(uint256 j = 0; j < rTokens.length; j++) {
        uint256 reward = userInfo[pid][account].userRewardData[j].unclaimedReward;
        if (reward > 0) {
          totalRewards[j] = totalRewards[j].add(reward);
          userInfo[pid][account].userRewardData[j].unclaimedReward = 0;
          emit Harvest(account, pid, rTokens[j], reward, block.number);
        }
      }
    }

    for(uint256 i = 0; i < totalRewards.length; i++) {
      if (totalRewards[i] > 0) {
        _lockReward(IERC20Ext(rTokens[i]), account, totalRewards[i]);
      }
    }
  }

  /**
   * @dev Get pending rewards of a user from a pool, mostly for front-end
   * @param _pid: id of the pool
   * @param _user: user to check for pending rewards
   */
  function pendingRewards(uint256 _pid, address _user)
    external
    override
    view
    returns (uint256[] memory rewards)
  {
    uint256 rTokensLength = rewardTokens.length;
    rewards = new uint256[](rTokensLength);
    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][_user];
    uint256 _totalStake = pool.totalStake;
    uint256 _poolLastRewardBlock = pool.lastRewardBlock;
    uint32 lastAccountedBlock = _lastAccountedRewardBlock(_pid);
    for(uint256 i = 0; i < rTokensLength; i++) {
      uint256 _accRewardPerShare = pool.poolRewardData[i].accRewardPerShare;
      if (lastAccountedBlock > _poolLastRewardBlock && _totalStake != 0) {
        uint256 reward = (lastAccountedBlock - _poolLastRewardBlock)
          .mul(pool.poolRewardData[i].rewardPerBlock);
        _accRewardPerShare = _accRewardPerShare.add(reward.mul(PRECISION) / _totalStake);
      }

      rewards[i] = user.amount.mul(
        _accRewardPerShare.sub(user.userRewardData[i].lastRewardPerShare)
        ) / PRECISION;
      rewards[i] = rewards[i].add(user.userRewardData[i].unclaimedReward);
    }
  }

  /**
   * @dev Return list reward tokens
   */
  function getRewardTokens() external override view returns (address[] memory) {
    return rewardTokens;
  }

  /**
   * @dev Return full details of a pool
   */
  function getPoolInfo(uint256 _pid)
    external override view
    returns (
      uint256 totalStake,
      address stakeToken,
      uint32 startBlock,
      uint32 endBlock,
      uint32 lastRewardBlock,
      uint256[] memory rewardPerBlocks,
      uint256[] memory accRewardPerShares
    )
  {
    PoolInfo storage pool = poolInfo[_pid];
    (
      totalStake,
      stakeToken,
      startBlock,
      endBlock,
      lastRewardBlock
    ) = (
      pool.totalStake,
      pool.stakeToken,
      pool.startBlock,
      pool.endBlock,
      pool.lastRewardBlock
    );
    rewardPerBlocks = new uint256[](rewardTokens.length);
    accRewardPerShares = new uint256[](rewardTokens.length);
    for(uint256 i = 0; i < rewardTokens.length; i++) {
      rewardPerBlocks[i] = pool.poolRewardData[i].rewardPerBlock;
      accRewardPerShares[i] = pool.poolRewardData[i].accRewardPerShare;
    }
  }

  /**
   * @dev Return user's info including deposited amount and reward data
   */
  function getUserInfo(uint256 _pid, address _account)
    external override view
    returns (
      uint256 amount,
      uint256[] memory unclaimedRewards,
      uint256[] memory lastRewardPerShares
    )
  {
    UserInfo storage user = userInfo[_pid][_account];
    amount = user.amount;
    unclaimedRewards = new uint256[](rewardTokens.length);
    lastRewardPerShares = new uint256[](rewardTokens.length);
    for(uint256 i = 0; i < rewardTokens.length; i++) {
      unclaimedRewards[i] = user.userRewardData[i].unclaimedReward;
      lastRewardPerShares[i] = user.userRewardData[i].lastRewardPerShare;
    }
  }

  /**
   * @dev Harvest rewards from a pool for the sender
   * @param _pid: id of the pool
   */
  function harvest(uint256 _pid) public override {
    updatePoolRewards(_pid);
    _updateUserReward(msg.sender, _pid, true);
  }

  /**
   * @dev Update rewards for one pool
   */
  function updatePoolRewards(uint256 _pid) public override {
    require(_pid < poolLength, 'invalid pool id');
    PoolInfo storage pool = poolInfo[_pid];
    uint32 lastAccountedBlock = _lastAccountedRewardBlock(_pid);
    if (lastAccountedBlock <= pool.lastRewardBlock) return;
    uint256 _totalStake = pool.totalStake;
    if (_totalStake == 0) {
      pool.lastRewardBlock = lastAccountedBlock;
      return;
    }
    uint256 numberBlocks = lastAccountedBlock - pool.lastRewardBlock;
    for(uint256 i = 0; i < rewardTokens.length; i++) {
      PoolRewardData storage rewardData = pool.poolRewardData[i];
      uint256 reward = numberBlocks.mul(rewardData.rewardPerBlock);
      rewardData.accRewardPerShare = rewardData.accRewardPerShare.add(reward.mul(PRECISION) / _totalStake);
    }
    pool.lastRewardBlock = lastAccountedBlock;
  }

  /**
   * @dev Withdraw _amount of stakeToken from pool _pid, also harvest reward for the sender
   */
  function _withdraw(uint256 _pid, uint256 _amount) internal {
    PoolInfo storage pool = poolInfo[_pid];
    UserInfo storage user = userInfo[_pid][msg.sender];
    require(user.amount >= _amount, 'withdraw: insufficient amount');

    // update pool reward and harvest
    updatePoolRewards(_pid);
    _updateUserReward(msg.sender, _pid, true);

    user.amount = user.amount.sub(_amount);
    pool.totalStake = pool.totalStake.sub(_amount);

    IERC20Ext(pool.stakeToken).safeTransfer(msg.sender, _amount);

    emit Withdraw(msg.sender, _pid, block.number, user.amount);
  }

  /**
   * @dev Update reward of _to address from pool _pid, harvest if needed
   */
  function _updateUserReward(
    address _to,
    uint256 _pid,
    bool shouldHarvest
  ) internal {
    uint256 userAmount = userInfo[_pid][_to].amount;
    uint256 rTokensLength = rewardTokens.length;

    if (userAmount == 0) {
      // update user last reward per share to the latest pool reward per share
      // by right if user.amount is 0, user.unclaimedReward should be 0 as well,
      // except when user uses emergencyWithdraw function
      for(uint256 i = 0; i < rTokensLength; i++) {
        userInfo[_pid][_to].userRewardData[i].lastRewardPerShare =
          poolInfo[_pid].poolRewardData[i].accRewardPerShare;
      }
      return;
    }

    for(uint256 i = 0; i < rTokensLength; i++) {
      uint256 lastAccRewardPerShare = poolInfo[_pid].poolRewardData[i].accRewardPerShare;
      UserRewardData storage rewardData = userInfo[_pid][_to].userRewardData[i];
      // user's unclaim reward + user's amount * (pool's accRewardPerShare - user's lastRewardPerShare) / precision
      uint256 _pending = userAmount.mul(lastAccRewardPerShare.sub(rewardData.lastRewardPerShare)) / PRECISION;
      _pending = _pending.add(rewardData.unclaimedReward);

      rewardData.unclaimedReward = shouldHarvest ? 0 : _pending;
      // update user last reward per share to the latest pool reward per share
      rewardData.lastRewardPerShare = lastAccRewardPerShare;

      if (shouldHarvest && _pending > 0) {
        _lockReward(IERC20Ext(rewardTokens[i]), _to, _pending);
        emit Harvest(_to, _pid, rewardTokens[i], _pending, block.number);
      }
    }
  }

  /**
   * @dev Returns last accounted reward block, either the current block number or the endBlock of the pool
   */
  function _lastAccountedRewardBlock(uint256 _pid) internal view returns (uint32 _value) {
    _value = poolInfo[_pid].endBlock;
    if (_value > block.number) _value = block.number.toUint32();
  }

  /**
   * @dev Call locker contract to lock rewards
   */
  function _lockReward(IERC20Ext token, address _account, uint256 _amount) internal {
    uint256 value = token == IERC20Ext(0) ? _amount : 0;
    rewardLocker.lock{ value: value }(token, _account, _amount);
  }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// 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: @openzeppelin/contracts/token/ERC20/SafeERC20.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

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

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function _callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "SafeERC20: low-level call failed");
        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;


/**
 * @dev Wrappers over Solidity's uintXX/intXX casting operators with added overflow
 * checks.
 *
 * Downcasting from uint256/int256 in Solidity does not revert on overflow. This can
 * easily result in undesired exploitation or bugs, since developers usually
 * assume that overflows raise errors. `SafeCast` restores this intuition by
 * reverting the transaction when such 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.
 *
 * Can be combined with {SafeMath} and {SignedSafeMath} to extend it to smaller types, by performing
 * all math on `uint256` and `int256` and then downcasting.
 */
library SafeCast {

    /**
     * @dev Returns the downcasted uint128 from uint256, reverting on
     * overflow (when the input is greater than largest uint128).
     *
     * Counterpart to Solidity's `uint128` operator.
     *
     * Requirements:
     *
     * - input must fit into 128 bits
     */
    function toUint128(uint256 value) internal pure returns (uint128) {
        require(value < 2**128, "SafeCast: value doesn\'t fit in 128 bits");
        return uint128(value);
    }

    /**
     * @dev Returns the downcasted uint64 from uint256, reverting on
     * overflow (when the input is greater than largest uint64).
     *
     * Counterpart to Solidity's `uint64` operator.
     *
     * Requirements:
     *
     * - input must fit into 64 bits
     */
    function toUint64(uint256 value) internal pure returns (uint64) {
        require(value < 2**64, "SafeCast: value doesn\'t fit in 64 bits");
        return uint64(value);
    }

    /**
     * @dev Returns the downcasted uint32 from uint256, reverting on
     * overflow (when the input is greater than largest uint32).
     *
     * Counterpart to Solidity's `uint32` operator.
     *
     * Requirements:
     *
     * - input must fit into 32 bits
     */
    function toUint32(uint256 value) internal pure returns (uint32) {
        require(value < 2**32, "SafeCast: value doesn\'t fit in 32 bits");
        return uint32(value);
    }

    /**
     * @dev Returns the downcasted uint16 from uint256, reverting on
     * overflow (when the input is greater than largest uint16).
     *
     * Counterpart to Solidity's `uint16` operator.
     *
     * Requirements:
     *
     * - input must fit into 16 bits
     */
    function toUint16(uint256 value) internal pure returns (uint16) {
        require(value < 2**16, "SafeCast: value doesn\'t fit in 16 bits");
        return uint16(value);
    }

    /**
     * @dev Returns the downcasted uint8 from uint256, reverting on
     * overflow (when the input is greater than largest uint8).
     *
     * Counterpart to Solidity's `uint8` operator.
     *
     * Requirements:
     *
     * - input must fit into 8 bits.
     */
    function toUint8(uint256 value) internal pure returns (uint8) {
        require(value < 2**8, "SafeCast: value doesn\'t fit in 8 bits");
        return uint8(value);
    }

    /**
     * @dev Converts a signed int256 into an unsigned uint256.
     *
     * Requirements:
     *
     * - input must be greater than or equal to 0.
     */
    function toUint256(int256 value) internal pure returns (uint256) {
        require(value >= 0, "SafeCast: value must be positive");
        return uint256(value);
    }

    /**
     * @dev Returns the downcasted int128 from int256, reverting on
     * overflow (when the input is less than smallest int128 or
     * greater than largest int128).
     *
     * Counterpart to Solidity's `int128` operator.
     *
     * Requirements:
     *
     * - input must fit into 128 bits
     *
     * _Available since v3.1._
     */
    function toInt128(int256 value) internal pure returns (int128) {
        require(value >= -2**127 && value < 2**127, "SafeCast: value doesn\'t fit in 128 bits");
        return int128(value);
    }

    /**
     * @dev Returns the downcasted int64 from int256, reverting on
     * overflow (when the input is less than smallest int64 or
     * greater than largest int64).
     *
     * Counterpart to Solidity's `int64` operator.
     *
     * Requirements:
     *
     * - input must fit into 64 bits
     *
     * _Available since v3.1._
     */
    function toInt64(int256 value) internal pure returns (int64) {
        require(value >= -2**63 && value < 2**63, "SafeCast: value doesn\'t fit in 64 bits");
        return int64(value);
    }

    /**
     * @dev Returns the downcasted int32 from int256, reverting on
     * overflow (when the input is less than smallest int32 or
     * greater than largest int32).
     *
     * Counterpart to Solidity's `int32` operator.
     *
     * Requirements:
     *
     * - input must fit into 32 bits
     *
     * _Available since v3.1._
     */
    function toInt32(int256 value) internal pure returns (int32) {
        require(value >= -2**31 && value < 2**31, "SafeCast: value doesn\'t fit in 32 bits");
        return int32(value);
    }

    /**
     * @dev Returns the downcasted int16 from int256, reverting on
     * overflow (when the input is less than smallest int16 or
     * greater than largest int16).
     *
     * Counterpart to Solidity's `int16` operator.
     *
     * Requirements:
     *
     * - input must fit into 16 bits
     *
     * _Available since v3.1._
     */
    function toInt16(int256 value) internal pure returns (int16) {
        require(value >= -2**15 && value < 2**15, "SafeCast: value doesn\'t fit in 16 bits");
        return int16(value);
    }

    /**
     * @dev Returns the downcasted int8 from int256, reverting on
     * overflow (when the input is less than smallest int8 or
     * greater than largest int8).
     *
     * Counterpart to Solidity's `int8` operator.
     *
     * Requirements:
     *
     * - input must fit into 8 bits.
     *
     * _Available since v3.1._
     */
    function toInt8(int256 value) internal pure returns (int8) {
        require(value >= -2**7 && value < 2**7, "SafeCast: value doesn\'t fit in 8 bits");
        return int8(value);
    }

    /**
     * @dev Converts an unsigned uint256 into a signed int256.
     *
     * Requirements:
     *
     * - input must be less than or equal to maxInt256.
     */
    function toInt256(uint256 value) internal pure returns (int256) {
        require(value < 2**255, "SafeCast: value doesn't fit in an int256");
        return int256(value);
    }
}

// File: @kyber.network/utils-sc/contracts/IERC20Ext.sol



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

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";


/**
 * @dev Interface extending ERC20 standard to include decimals() as
 *      it is optional in the OpenZeppelin IERC20 interface.
 */
interface IERC20Ext is IERC20 {
    /**
     * @dev This function is required as Kyber requires to interact
     *      with token.decimals() with many of its operations.
     */
    function decimals() external view returns (uint8 digits);
}

// File: @kyber.network/utils-sc/contracts/PermissionAdmin.sol



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


abstract contract PermissionAdmin {
    address public admin;
    address public pendingAdmin;

    event AdminClaimed(address newAdmin, address previousAdmin);

    event TransferAdminPending(address pendingAdmin);

    constructor(address _admin) {
        require(_admin != address(0), "admin 0");
        admin = _admin;
    }

    modifier onlyAdmin() {
        require(msg.sender == admin, "only admin");
        _;
    }

    /**
     * @dev Allows the current admin to set the pendingAdmin address.
     * @param newAdmin The address to transfer ownership to.
     */
    function transferAdmin(address newAdmin) public onlyAdmin {
        require(newAdmin != address(0), "new admin 0");
        emit TransferAdminPending(newAdmin);
        pendingAdmin = newAdmin;
    }

    /**
     * @dev Allows the current admin to set the admin in one tx. Useful initial deployment.
     * @param newAdmin The address to transfer ownership to.
     */
    function transferAdminQuickly(address newAdmin) public onlyAdmin {
        require(newAdmin != address(0), "admin 0");
        emit TransferAdminPending(newAdmin);
        emit AdminClaimed(newAdmin, admin);
        admin = newAdmin;
    }

    /**
     * @dev Allows the pendingAdmin address to finalize the change admin process.
     */
    function claimAdmin() public {
        require(pendingAdmin == msg.sender, "not pending");
        emit AdminClaimed(pendingAdmin, admin);
        admin = pendingAdmin;
        pendingAdmin = address(0);
    }
}

// File: contracts/interfaces/liquidityMining/IKyberFairLaunch.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.7.6;
pragma abicoder v2;

interface IKyberFairLaunch {
  /**
   * @dev Add a new lp to the pool. Can only be called by the admin.
   * @param _stakeToken: token to be staked to the pool
   * @param _startBlock: block where the reward starts
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool
   */
  function addPool(
    address _stakeToken,
    uint32 _startBlock,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external;

  /**
   * @dev Renew a pool to start another liquidity mining program
   * @param _pid: id of the pool to renew, must be pool that has not started or already ended
   * @param _startBlock: block where the reward starts
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool
   *   0 if we want to stop the pool from accumulating rewards
   */
  function renewPool(
    uint256 _pid,
    uint32 _startBlock,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external;

  /**
   * @dev Update a pool, allow to change end block, reward per block
   * @param _pid: pool id to be renew
   * @param _endBlock: block where the reward ends
   * @param _rewardPerBlocks: amount of reward token per block for the pool
   *   0 if we want to stop the pool from accumulating rewards
   */
  function updatePool(
    uint256 _pid,
    uint32 _endBlock,
    uint256[] calldata _rewardPerBlocks
  ) external;

  /**
   * @dev deposit to tokens to accumulate rewards
   * @param _pid: id of the pool
   * @param _amount: amount of stakeToken to be deposited
   * @param _shouldHarvest: whether to harvest the reward or not
   */
  function deposit(
    uint256 _pid,
    uint256 _amount,
    bool _shouldHarvest
  ) external;

  /**
   * @dev withdraw token (of the sender) from pool, also harvest reward
   * @param _pid: id of the pool
   * @param _amount: amount of stakeToken to withdraw
   */
  function withdraw(uint256 _pid, uint256 _amount) external;

  /**
   * @dev withdraw all tokens (of the sender) from pool, also harvest reward
   * @param _pid: id of the pool
   */
  function withdrawAll(uint256 _pid) external;

  /**
   * @dev emergency withdrawal function to allow withdraw all deposited token (of the sender)
   *   without harvesting the reward
   * @param _pid: id of the pool
   */
  function emergencyWithdraw(uint256 _pid) external;

  /**
   * @dev harvest reward from pool for the sender
   * @param _pid: id of the pool
   */
  function harvest(uint256 _pid) external;

  /**
   * @dev harvest rewards from multiple pools for the sender
   */
  function harvestMultiplePools(uint256[] calldata _pids) external;

  /**
   * @dev update reward for one pool
   */
  function updatePoolRewards(uint256 _pid) external;

  /**
   * @dev return the total of pools that have been added
   */
  function poolLength() external view returns (uint256);

  /**
   * @dev return full details of a pool
   */
  function getPoolInfo(uint256 _pid)
    external view
    returns(
      uint256 totalStake,
      address stakeToken,
      uint32 startBlock,
      uint32 endBlock,
      uint32 lastRewardBlock,
      uint256[] memory rewardPerBlocks,
      uint256[] memory accRewardPerShares);

  /**
   * @dev get user's info
   */
  function getUserInfo(uint256 _pid, address _account)
    external view
    returns (
      uint256 amount,
      uint256[] memory unclaimedRewards,
      uint256[] memory lastRewardPerShares);

  /**
  * @dev return list reward tokens
  */
  function getRewardTokens() external view returns (address[] memory);
  /**
   * @dev get pending reward of a user from a pool, mostly for front-end
   * @param _pid: id of the pool
   * @param _user: user to check for pending rewards
   */
  function pendingRewards(
    uint256 _pid,
    address _user
   )
    external view
    returns (uint256[] memory rewards);
}

// File: contracts/interfaces/liquidityMining/IKyberRewardLocker.sol



// SPDX-License-Identifier: agpl-3.0
pragma solidity 0.7.6;
pragma abicoder v2;

import {IERC20Ext} from '@kyber.network/utils-sc/contracts/IERC20Ext.sol';

interface IKyberRewardLocker {
  struct VestingSchedule {
    uint64 startBlock;
    uint64 endBlock;
    uint128 quantity;
    uint128 vestedQuantity;
  }

  event VestingEntryCreated(
    IERC20Ext indexed token,
    address indexed beneficiary,
    uint256 startBlock,
    uint256 endBlock,
    uint256 quantity,
    uint256 index
  );

  event VestingEntryQueued(
    uint256 indexed index,
    IERC20Ext indexed token,
    address indexed beneficiary,
    uint256 quantity
  );

  event Vested(
    IERC20Ext indexed token,
    address indexed beneficiary,
    uint256 vestedQuantity,
    uint256 index
  );

  /**
   * @dev queue a vesting schedule starting from now
   */
  function lock(
    IERC20Ext token,
    address account,
    uint256 amount
  ) external payable;

  /**
   * @dev queue a vesting schedule
   */
  function lockWithStartBlock(
    IERC20Ext token,
    address account,
    uint256 quantity,
    uint256 startBlock
  ) external payable;

  /**
   * @dev vest all completed schedules for multiple tokens
   */
  function vestCompletedSchedulesForMultipleTokens(IERC20Ext[] calldata tokens)
    external
    returns (uint256[] memory vestedAmounts);

  /**
   * @dev claim multiple tokens for specific vesting schedule,
   *      if schedule has not ended yet, claiming amounts are linear with vesting blocks
   */
  function vestScheduleForMultipleTokensAtIndices(
    IERC20Ext[] calldata tokens,
    uint256[][] calldata indices
  )
    external
    returns (uint256[] memory vestedAmounts);

  /**
   * @dev for all completed schedule, claim token
   */
  function vestCompletedSchedules(IERC20Ext token) external returns (uint256);

  /**
   * @dev claim token for specific vesting schedule,
   * @dev if schedule has not ended yet, claiming amount is linear with vesting blocks
   */
  function vestScheduleAtIndices(IERC20Ext token, uint256[] calldata indexes)
    external
    returns (uint256);

  /**
   * @dev claim token for specific vesting schedule from startIndex to endIndex
   */
  function vestSchedulesInRange(
    IERC20Ext token,
    uint256 startIndex,
    uint256 endIndex
  ) external returns (uint256);

  /**
   * @dev length of vesting schedules array
   */
  function numVestingSchedules(address account, IERC20Ext token) external view returns (uint256);

  /**
   * @dev get detailed of each vesting schedule
   */
  function getVestingScheduleAtIndex(
    address account,
    IERC20Ext token,
    uint256 index
  ) external view returns (VestingSchedule memory);

  /**
   * @dev get vesting shedules array
   */
  function getVestingSchedules(address account, IERC20Ext token)
    external
    view
    returns (VestingSchedule[] memory schedules);
}

// 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);
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.7.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        require(isContract(target), "Address: delegate call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}