// File: /home/euphemia/work/axion/axion-contracts/contracts/SubBalances.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "@openzeppelin/contracts/access/AccessControl.sol";
import "./interfaces/IToken.sol";
import "./interfaces/IAuction.sol";
import "./interfaces/IForeignSwap.sol";
import "./interfaces/IBPD.sol";
import "./interfaces/ISubBalances.sol";


contract SubBalances is ISubBalances, AccessControl {
	using SafeMath for uint256;

    event PoolCreated(
        uint256 paydayTime,
        uint256 poolAmount
    );

    bytes32 public constant SETTER_ROLE = keccak256("SETTER_ROLE");
    bytes32 public constant STAKING_ROLE = keccak256("CALLER_ROLE");

    struct StakeSession {
    	address staker;
    	uint256 shares;
    	// uint256 sessionId;
    	uint256 start;
    	uint256 end;
    	uint256 finishTime;
        bool[5] payDayEligible;
    	bool withdrawn;
    }

    struct SubBalance {
    	// mapping (address => uint256[]) userStakings;
    	// mapping (uint256 => StakeSession) stakeSessions;
    	uint256 totalShares;
    	uint256 totalWithdrawAmount;
    	uint256 payDayTime;
    	// uint256 payDayEnd;
        uint256 requiredStakePeriod;
    	bool minted;
    }

    SubBalance[5] public subBalanceList;

    address public mainToken;
    address public foreignSwap;
	address public bigPayDayPool;
	address public auction;
	uint256 public startTimestamp;
    uint256 public stepTimestamp;
    uint256 public basePeriod;
    uint256[5] public PERIODS;

	uint256 public currentSharesTotalSupply;

    // Users
    mapping (address => uint256[]) userStakings;
    mapping (uint256 => StakeSession) stakeSessions;

    modifier onlySetter() {
        require(hasRole(SETTER_ROLE, _msgSender()), "Caller is not a setter");
        _;
    }

    constructor(address _setter) public {
        _setupRole(SETTER_ROLE, _setter);
    }

    function init(
        address _mainToken,
        address _foreignSwap,
        address _bigPayDayPool,
        address _auction,
        address _staking,
        uint256 _stepTimestamp,
        uint256 _basePeriod
    ) public
      onlySetter
    {
        _setupRole(STAKING_ROLE, _staking);
        mainToken = _mainToken;
        foreignSwap = _foreignSwap;
        bigPayDayPool = _bigPayDayPool;
        auction = _auction;
        stepTimestamp = _stepTimestamp;
        basePeriod = _basePeriod;
    	startTimestamp = now;

    	for (uint256 i = 0; i < subBalanceList.length; i++) {
            PERIODS[i] = _basePeriod.mul(i.add(1));
    		SubBalance storage subBalance = subBalanceList[i];
            subBalance.payDayTime = startTimestamp.add(stepTimestamp.mul(PERIODS[i]));
    		// subBalance.payDayEnd = subBalance.payDayStart.add(stepTimestamp);
            subBalance.requiredStakePeriod = PERIODS[i];
    	}
        renounceRole(SETTER_ROLE, _msgSender());
    }

    function getStartTimes() public view returns (uint256[5] memory startTimes) {
        for (uint256 i = 0; i < subBalanceList.length; i ++) {
            startTimes[i] = subBalanceList[i].payDayTime;
        }
    }

    function getPoolsMinted() public view returns (bool[5] memory poolsMinted) {
        for (uint256 i = 0; i < subBalanceList.length; i ++) {
            poolsMinted[i] = subBalanceList[i].minted;
        }
    }

    function getPoolsMintedAmounts() public view returns (uint256[5] memory poolsMintedAmounts) {
        for (uint256 i = 0; i < subBalanceList.length; i ++) {
            poolsMintedAmounts[i] = subBalanceList[i].totalWithdrawAmount;
        }
    }

    function getClosestYearShares() public view returns (uint256 shareAmount) {
        for (uint256 i = 0; i < subBalanceList.length; i++) {
            if (!subBalanceList[i].minted) {
                continue;
            } else {
                shareAmount = subBalanceList[i].totalShares;
                return shareAmount;
            }

            // return 0;
        }
    }

    function getSessionStats(uint256 sessionId) 
        public 
        view 
        returns (address staker, uint256 shares, uint256 start, uint256 sessionEnd, bool withdrawn) 
    {
        StakeSession storage stakeSession = stakeSessions[sessionId];
        staker = stakeSession.staker;
        shares = stakeSession.shares;
        start = stakeSession.start;
        if (stakeSession.finishTime > 0) {
            sessionEnd = stakeSession.finishTime;
        } else {
            sessionEnd = stakeSession.end;
        }
        withdrawn = stakeSession.withdrawn;
    }

    function getSessionEligibility(uint256 sessionId) public view returns (bool[5] memory stakePayDays) {
        StakeSession storage stakeSession = stakeSessions[sessionId];
        for (uint256 i = 0; i < subBalanceList.length; i ++) {
            stakePayDays[i] = stakeSession.payDayEligible[i];
        }
    }


    function calculateSessionPayout(uint256 sessionId) public view returns (uint256, uint256) {
        StakeSession storage stakeSession = stakeSessions[sessionId];

        uint256 subBalancePayoutAmount;
        uint256[5] memory bpdRawAmounts = IBPD(bigPayDayPool).getPoolYearAmounts();
        for (uint256 i = 0; i < subBalanceList.length; i++) {
            SubBalance storage subBalance = subBalanceList[i];

            uint256 subBalanceAmount;
            uint256 addAmount;
            if (subBalance.minted) {
                subBalanceAmount = subBalance.totalWithdrawAmount;
            } else {
                (subBalanceAmount, addAmount) = _bpdAmountFromRaw(bpdRawAmounts[i]);
            }
            if (stakeSession.payDayEligible[i]) {
                uint256 stakerShare = stakeSession.shares.mul(1e18).div(subBalance.totalShares);
                uint256 stakerAmount = subBalanceAmount.mul(stakerShare).div(1e18);
                subBalancePayoutAmount = subBalancePayoutAmount.add(stakerAmount);
            }
        }

        uint256 stakingDays = stakeSession.end.sub(stakeSession.start).div(stepTimestamp);
        uint256 stakeEnd;
        if (stakeSession.finishTime != 0) {
            stakeEnd = stakeSession.finishTime;
        } else {
            stakeEnd = stakeSession.end;
        }

        uint256 daysStaked = stakeEnd.sub(stakeSession.start).div(stepTimestamp);

        // Early unstaked
        if (stakingDays > daysStaked) {
            uint256 payoutAmount = subBalancePayoutAmount.mul(daysStaked).div(stakingDays);
            uint256 earlyUnstakePenalty = subBalancePayoutAmount.sub(payoutAmount);
            return (payoutAmount, earlyUnstakePenalty);
        // Unstaked in time, no penalty
        } else if (
            stakingDays <= daysStaked && daysStaked < stakingDays.add(14)
        ) {
            return (subBalancePayoutAmount, 0);
        // Unstaked late
        } else if (
            stakingDays.add(14) <= daysStaked && daysStaked < stakingDays.add(714)
        ) {
            uint256 daysAfterStaking = daysStaked.sub(stakingDays);
            uint256 payoutAmount = subBalancePayoutAmount.mul(uint256(714).sub(daysAfterStaking)).div(700);
            uint256 lateUnstakePenalty = subBalancePayoutAmount.sub(payoutAmount);
            return (payoutAmount, lateUnstakePenalty);
        // Too much time 
        } else if (stakingDays.add(714) <= daysStaked) {
            return (0, subBalancePayoutAmount);
        }

        return (0, 0);
    }

    function withdrawPayout(uint256 sessionId) public {
        StakeSession storage stakeSession = stakeSessions[sessionId];

        require(stakeSession.finishTime != 0, "cannot withdraw before unclaim");
        require(!stakeSession.withdrawn, "already withdrawn");
        require(_msgSender() == stakeSession.staker, "caller not matching sessionId");
        (uint256 payoutAmount, uint256 penaltyAmount) = calculateSessionPayout(sessionId);

        stakeSession.withdrawn = true;

        if (payoutAmount > 0) {
            IERC20(mainToken).transfer(_msgSender(), payoutAmount);
        }

        if (penaltyAmount > 0) {
            IERC20(mainToken).transfer(auction, penaltyAmount);
            IAuction(auction).callIncomeDailyTokensTrigger(penaltyAmount);
        }
    }


    function callIncomeStakerTrigger(
        address staker,
        uint256 sessionId,
        uint256 start,
        uint256 end,
        uint256 shares
    ) external override {
        require(hasRole(STAKING_ROLE, _msgSender()), "SUBBALANCES: Caller is not a staking role");
        require(end > start, 'SUBBALANCES: Stake end must be after stake start');
        uint256 stakeDays = end.sub(start).div(stepTimestamp);

        // Skipping user if period less that year
        if (stakeDays >= basePeriod) {

            // Setting pay day eligibility for user in advance when he stakes
            bool[5] memory stakerPayDays;
            for (uint256 i = 0; i < subBalanceList.length; i++) {
                SubBalance storage subBalance = subBalanceList[i];  

                // Setting eligibility only if payday is not passed and stake end more that this pay day
                if (subBalance.payDayTime > start && end > subBalance.payDayTime) {
                    stakerPayDays[i] = true;

                    subBalance.totalShares = subBalance.totalShares.add(shares);
                }

            }

            // Saving user
            stakeSessions[sessionId] = StakeSession({
                staker: staker,
                shares: shares,
                start: start,
                end: end,
                finishTime: 0,
                payDayEligible: stakerPayDays,
                withdrawn: false
            });
            userStakings[staker].push(sessionId);

        }

        // Adding to shares
        currentSharesTotalSupply = currentSharesTotalSupply.add(shares);            

	}

    function callOutcomeStakerTrigger(
        address staker,
        uint256 sessionId,
        uint256 start,
        uint256 end,
        uint256 shares
    ) 
        external
        override
    {
        (staker);
        require(hasRole(STAKING_ROLE, _msgSender()), "SUBBALANCES: Caller is not a staking role");
        require(end > start, 'SUBBALANCES: Stake end must be after stake start');
        uint256 stakeDays = end.sub(start).div(stepTimestamp);
        uint256 realStakeEnd = now;
        // uint256 daysStaked = realStakeEnd.sub(stakeStart).div(stepTimestamp);

        if (stakeDays >= basePeriod) {
            StakeSession storage stakeSession = stakeSessions[sessionId];

            // Rechecking eligibility of paydays
            for (uint256 i = 0; i < subBalanceList.length; i++) {
                SubBalance storage subBalance = subBalanceList[i];  

                // Removing from payday if unstaked before
                if (realStakeEnd < subBalance.payDayTime) {
                    stakeSession.payDayEligible[i] = false;

                    if (shares > subBalance.totalShares) {
                        subBalance.totalShares = 0;
                    } else {
                        subBalance.totalShares = subBalance.totalShares.sub(shares);
                    }
                }
            }


            // Setting real stake end
            stakeSessions[sessionId].finishTime = realStakeEnd;

        }

        // Substract shares from total
        if (shares > currentSharesTotalSupply) {
            currentSharesTotalSupply = 0;
        } else {
            currentSharesTotalSupply = currentSharesTotalSupply.sub(shares);
        }

    }


    // Pool logic
    function generatePool() external returns (bool) {
    	for (uint256 i = 0; i < subBalanceList.length; i++) {
    		SubBalance storage subBalance = subBalanceList[i];

    		if (now > subBalance.payDayTime && !subBalance.minted) {
    			uint256 yearTokens = getPoolFromBPD(i);
    			(uint256 bpdTokens, uint256 addAmount) = _bpdAmountFromRaw(yearTokens);

    			IToken(mainToken).mint(address(this), addAmount);
    			subBalance.totalWithdrawAmount = bpdTokens;
    			subBalance.minted = true;

                emit PoolCreated(now, bpdTokens);
                return true;
    		}
    	}
    }


    // Pool logic
    function getPoolFromBPD(uint256 poolNumber) internal returns (uint256 poolAmount) {
    	poolAmount = IBPD(bigPayDayPool).transferYearlyPool(poolNumber);
    }

    // Pool logic
    function _bpdAmountFromRaw(uint256 yearTokenAmount) internal view returns (uint256 totalAmount, uint256 addAmount) {
    	uint256 currentTokenTotalSupply = IERC20(mainToken).totalSupply();

        uint256 inflation = uint256(8).mul(currentTokenTotalSupply.add(currentSharesTotalSupply)).div(36500);

        
        uint256 criticalMassCoeff = IForeignSwap(foreignSwap).getCurrentClaimedAmount().mul(1e18).div(
            IForeignSwap(foreignSwap).getTotalSnapshotAmount());

       uint256 viralityCoeff = IForeignSwap(foreignSwap).getCurrentClaimedAddresses().mul(1e18).div(
            IForeignSwap(foreignSwap).getTotalSnapshotAddresses());

        uint256 totalUprisingCoeff = uint256(1e18).add(criticalMassCoeff).add(viralityCoeff);

        totalAmount = yearTokenAmount.add(inflation).mul(totalUprisingCoeff).div(1e18);
        addAmount = totalAmount.sub(yearTokenAmount);
    }

}
// File: /home/euphemia/work/axion/axion-contracts/contracts/interfaces/IAuction.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

interface IAuction {
    function callIncomeDailyTokensTrigger(uint256 amount) external;

    function callIncomeWeeklyTokensTrigger(uint256 amount) external;
}

// File: /home/euphemia/work/axion/axion-contracts/contracts/interfaces/IBPD.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

interface IBPD {
    function callIncomeTokensTrigger(uint256 incomeAmountToken) external;
    function transferYearlyPool(uint256 poolNumber) external returns (uint256);
	function getPoolYearAmounts() external view returns (uint256[5] memory poolAmounts);
}

// File: /home/euphemia/work/axion/axion-contracts/contracts/interfaces/IForeignSwap.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

interface IForeignSwap {
    function getCurrentClaimedAmount() external view returns (uint256);

    function getTotalSnapshotAmount() external view returns (uint256);

    function getCurrentClaimedAddresses() external view returns (uint256);

    function getTotalSnapshotAddresses() external view returns (uint256);
}

// File: /home/euphemia/work/axion/axion-contracts/contracts/interfaces/ISubBalances.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

interface ISubBalances {
    function callIncomeStakerTrigger(
        address staker,
        uint256 sessionId,
        uint256 start,
        uint256 end,
        uint256 shares
    ) external;

    function callOutcomeStakerTrigger(
        address staker,
        uint256 sessionId,
        uint256 start,
        uint256 end,
        uint256 shares
    ) external;
}

// File: /home/euphemia/work/axion/axion-contracts/contracts/interfaces/IToken.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

interface IToken {
    function mint(address to, uint256 amount) external;

    function burn(address from, uint256 amount) external;
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/*
 * @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: @openzeppelin/contracts/access/AccessControl.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

import "../utils/EnumerableSet.sol";
import "../utils/Address.sol";
import "../GSN/Context.sol";

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context {
    using EnumerableSet for EnumerableSet.AddressSet;
    using Address for address;

    struct RoleData {
        EnumerableSet.AddressSet members;
        bytes32 adminRole;
    }

    mapping (bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view returns (bool) {
        return _roles[role].members.contains(account);
    }

    /**
     * @dev Returns the number of accounts that have `role`. Can be used
     * together with {getRoleMember} to enumerate all bearers of a role.
     */
    function getRoleMemberCount(bytes32 role) public view returns (uint256) {
        return _roles[role].members.length();
    }

    /**
     * @dev Returns one of the accounts that have `role`. `index` must be a
     * value between 0 and {getRoleMemberCount}, non-inclusive.
     *
     * Role bearers are not sorted in any particular way, and their ordering may
     * change at any point.
     *
     * WARNING: When using {getRoleMember} and {getRoleMemberCount}, make sure
     * you perform all queries on the same block. See the following
     * https://forum.openzeppelin.com/t/iterating-over-elements-on-enumerableset-in-openzeppelin-contracts/2296[forum post]
     * for more information.
     */
    function getRoleMember(bytes32 role, uint256 index) public view returns (address) {
        return _roles[role].members.at(index);
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to grant");

        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) public virtual {
        require(hasRole(_roles[role].adminRole, _msgSender()), "AccessControl: sender must be an admin to revoke");

        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) public virtual {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        emit RoleAdminChanged(role, _roles[role].adminRole, adminRole);
        _roles[role].adminRole = adminRole;
    }

    function _grantRole(bytes32 role, address account) private {
        if (_roles[role].members.add(account)) {
            emit RoleGranted(role, account, _msgSender());
        }
    }

    function _revokeRole(bytes32 role, address account) private {
        if (_roles[role].members.remove(account)) {
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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 ^0.6.2;

/**
 * @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 in 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");
        return _functionCallWithValue(target, data, value, errorMessage);
    }

    function _functionCallWithValue(address target, bytes memory data, uint256 weiValue, string memory errorMessage) private returns (bytes memory) {
        require(isContract(target), "Address: call to non-contract");

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

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



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @dev Library for managing
 * https://en.wikipedia.org/wiki/Set_(abstract_data_type)[sets] of primitive
 * types.
 *
 * Sets have the following properties:
 *
 * - Elements are added, removed, and checked for existence in constant time
 * (O(1)).
 * - Elements are enumerated in O(n). No guarantees are made on the ordering.
 *
 * ```
 * contract Example {
 *     // Add the library methods
 *     using EnumerableSet for EnumerableSet.AddressSet;
 *
 *     // Declare a set state variable
 *     EnumerableSet.AddressSet private mySet;
 * }
 * ```
 *
 * As of v3.0.0, only sets of type `address` (`AddressSet`) and `uint256`
 * (`UintSet`) are supported.
 */
library EnumerableSet {
    // To implement this library for multiple types with as little code
    // repetition as possible, we write it in terms of a generic Set type with
    // bytes32 values.
    // The Set implementation uses private functions, and user-facing
    // implementations (such as AddressSet) are just wrappers around the
    // underlying Set.
    // This means that we can only create new EnumerableSets for types that fit
    // in bytes32.

    struct Set {
        // Storage of set values
        bytes32[] _values;

        // Position of the value in the `values` array, plus 1 because index 0
        // means a value is not in the set.
        mapping (bytes32 => uint256) _indexes;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function _add(Set storage set, bytes32 value) private returns (bool) {
        if (!_contains(set, value)) {
            set._values.push(value);
            // The value is stored at length-1, but we add 1 to all indexes
            // and use 0 as a sentinel value
            set._indexes[value] = set._values.length;
            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function _remove(Set storage set, bytes32 value) private returns (bool) {
        // We read and store the value's index to prevent multiple reads from the same storage slot
        uint256 valueIndex = set._indexes[value];

        if (valueIndex != 0) { // Equivalent to contains(set, value)
            // To delete an element from the _values array in O(1), we swap the element to delete with the last one in
            // the array, and then remove the last element (sometimes called as 'swap and pop').
            // This modifies the order of the array, as noted in {at}.

            uint256 toDeleteIndex = valueIndex - 1;
            uint256 lastIndex = set._values.length - 1;

            // When the value to delete is the last one, the swap operation is unnecessary. However, since this occurs
            // so rarely, we still do the swap anyway to avoid the gas cost of adding an 'if' statement.

            bytes32 lastvalue = set._values[lastIndex];

            // Move the last value to the index where the value to delete is
            set._values[toDeleteIndex] = lastvalue;
            // Update the index for the moved value
            set._indexes[lastvalue] = toDeleteIndex + 1; // All indexes are 1-based

            // Delete the slot where the moved value was stored
            set._values.pop();

            // Delete the index for the deleted slot
            delete set._indexes[value];

            return true;
        } else {
            return false;
        }
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function _contains(Set storage set, bytes32 value) private view returns (bool) {
        return set._indexes[value] != 0;
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function _length(Set storage set) private view returns (uint256) {
        return set._values.length;
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function _at(Set storage set, uint256 index) private view returns (bytes32) {
        require(set._values.length > index, "EnumerableSet: index out of bounds");
        return set._values[index];
    }

    // AddressSet

    struct AddressSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(AddressSet storage set, address value) internal returns (bool) {
        return _add(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(AddressSet storage set, address value) internal returns (bool) {
        return _remove(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(AddressSet storage set, address value) internal view returns (bool) {
        return _contains(set._inner, bytes32(uint256(value)));
    }

    /**
     * @dev Returns the number of values in the set. O(1).
     */
    function length(AddressSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(AddressSet storage set, uint256 index) internal view returns (address) {
        return address(uint256(_at(set._inner, index)));
    }


    // UintSet

    struct UintSet {
        Set _inner;
    }

    /**
     * @dev Add a value to a set. O(1).
     *
     * Returns true if the value was added to the set, that is if it was not
     * already present.
     */
    function add(UintSet storage set, uint256 value) internal returns (bool) {
        return _add(set._inner, bytes32(value));
    }

    /**
     * @dev Removes a value from a set. O(1).
     *
     * Returns true if the value was removed from the set, that is if it was
     * present.
     */
    function remove(UintSet storage set, uint256 value) internal returns (bool) {
        return _remove(set._inner, bytes32(value));
    }

    /**
     * @dev Returns true if the value is in the set. O(1).
     */
    function contains(UintSet storage set, uint256 value) internal view returns (bool) {
        return _contains(set._inner, bytes32(value));
    }

    /**
     * @dev Returns the number of values on the set. O(1).
     */
    function length(UintSet storage set) internal view returns (uint256) {
        return _length(set._inner);
    }

   /**
    * @dev Returns the value stored at position `index` in the set. O(1).
    *
    * Note that there are no guarantees on the ordering of values inside the
    * array, and it may change when more values are added or removed.
    *
    * Requirements:
    *
    * - `index` must be strictly less than {length}.
    */
    function at(UintSet storage set, uint256 index) internal view returns (uint256) {
        return uint256(_at(set._inner, index));
    }
}