// SPDX-License-Identifier: UNLICENSED
// Audit on 5-Jan-2021 by Keno and BoringCrypto

// P1 - P3: OK
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;
// solhint-disable avoid-low-level-calls

import "./libraries/BoringERC20.sol";

// T1 - T4: OK
contract BaseBoringBatchable {
    function _getRevertMsg(bytes memory _returnData) internal pure returns (string memory) {
        // If the _res length is less than 68, then the transaction failed silently (without a revert message)
        if (_returnData.length < 68) return "Transaction reverted silently";

        assembly {
            // Slice the sighash.
            _returnData := add(_returnData, 0x04)
        }
        return abi.decode(_returnData, (string)); // All that remains is the revert string
    }    
    
    // F3 - F9: OK
    // F1: External is ok here because this is the batch function, adding it to a batch makes no sense
    // F2: Calls in the batch may be payable, delegatecall operates in the same context, so each call in the batch has access to msg.value
    // C1 - C21: OK
    // C3: The length of the loop is fully under user control, so can't be exploited
    // C7: Delegatecall is only used on the same contract, so it's safe
    function batch(bytes[] calldata calls, bool revertOnFail) external payable returns(bool[] memory successes, bytes[] memory results) {
        // Interactions
        successes = new bool[](calls.length);
        results = new bytes[](calls.length);
        for (uint256 i = 0; i < calls.length; i++) {
            (bool success, bytes memory result) = address(this).delegatecall(calls[i]);
            require(success || !revertOnFail, _getRevertMsg(result));
            successes[i] = success;
            results[i] = result;
        }
    }
}

// T1 - T4: OK
contract BoringBatchable is BaseBoringBatchable {
    // F1 - F9: OK
    // F6: Parameters can be used front-run the permit and the user's permit will fail (due to nonce or other revert)
    //     if part of a batch this could be used to grief once as the second call would not need the permit
    // C1 - C21: OK
    function permitToken(IERC20 token, address from, address to, uint256 amount, uint256 deadline, uint8 v, bytes32 r, bytes32 s) public {
        // Interactions
        // X1 - X5
        token.permit(from, to, amount, deadline, v, r, s);
    }
}

// SPDX-License-Identifier: MIT
// Audit on 5-Jan-2021 by Keno and BoringCrypto

// P1 - P3: OK
pragma solidity 0.6.12;

// Source: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol + Claimable.sol
// Edited by BoringCrypto

// T1 - T4: OK
contract BoringOwnableData {
    // V1 - V5: OK
    address public owner;
    // V1 - V5: OK
    address public pendingOwner;
}

// T1 - T4: OK
contract BoringOwnable is BoringOwnableData {
    // E1: OK
    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    constructor () public {
        owner = msg.sender;
        emit OwnershipTransferred(address(0), msg.sender);
    }

    // F1 - F9: OK
    // C1 - C21: OK
    function transferOwnership(address newOwner, bool direct, bool renounce) public onlyOwner {
        if (direct) {
            // Checks
            require(newOwner != address(0) || renounce, "Ownable: zero address");

            // Effects
            emit OwnershipTransferred(owner, newOwner);
            owner = newOwner;
            pendingOwner = address(0);
        } else {
            // Effects
            pendingOwner = newOwner;
        }
    }

    // F1 - F9: OK
    // C1 - C21: OK
    function claimOwnership() public {
        address _pendingOwner = pendingOwner;
        
        // Checks
        require(msg.sender == _pendingOwner, "Ownable: caller != pending owner");

        // Effects
        emit OwnershipTransferred(owner, _pendingOwner);
        owner = _pendingOwner;
        pendingOwner = address(0);
    }

    // M1 - M5: OK
    // C1 - C21: OK
    modifier onlyOwner() {
        require(msg.sender == owner, "Ownable: caller is not the owner");
        _;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;

interface IERC20 {
    function totalSupply() external view returns (uint256);
    function balanceOf(address account) external view returns (uint256);
    function allowance(address owner, address spender) external view returns (uint256);
    function approve(address spender, uint256 amount) external returns (bool);
    event Transfer(address indexed from, address indexed to, uint256 value);
    event Approval(address indexed owner, address indexed spender, uint256 value);

    // EIP 2612
    function permit(address owner, address spender, uint256 value, uint256 deadline, uint8 v, bytes32 r, bytes32 s) external;
}

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.6.12;

import "../interfaces/IERC20.sol";

library BoringERC20 {
    function safeSymbol(IERC20 token) internal view returns(string memory) {
        (bool success, bytes memory data) = address(token).staticcall(abi.encodeWithSelector(0x95d89b41));
        return success && data.length > 0 ? abi.decode(data, (string)) : "???";
    }

    function safeName(IERC20 token) internal view returns(string memory) {
        (bool success, bytes memory data) = address(token).staticcall(abi.encodeWithSelector(0x06fdde03));
        return success && data.length > 0 ? abi.decode(data, (string)) : "???";
    }

    function safeDecimals(IERC20 token) internal view returns (uint8) {
        (bool success, bytes memory data) = address(token).staticcall(abi.encodeWithSelector(0x313ce567));
        return success && data.length == 32 ? abi.decode(data, (uint8)) : 18;
    }

    function safeTransfer(IERC20 token, address to, uint256 amount) internal {
        (bool success, bytes memory data) = address(token).call(abi.encodeWithSelector(0xa9059cbb, to, amount));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "BoringERC20: Transfer failed");
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 amount) internal {
        (bool success, bytes memory data) = address(token).call(abi.encodeWithSelector(0x23b872dd, from, to, amount));
        require(success && (data.length == 0 || abi.decode(data, (bool))), "BoringERC20: TransferFrom failed");
    }
}

// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;
// a library for performing overflow-safe math, updated with awesomeness from of DappHub (https://github.com/dapphub/ds-math)
library BoringMath {
    function add(uint256 a, uint256 b) internal pure returns (uint256 c) {require((c = a + b) >= b, "BoringMath: Add Overflow");}
    function sub(uint256 a, uint256 b) internal pure returns (uint256 c) {require((c = a - b) <= a, "BoringMath: Underflow");}
    function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {require(b == 0 || (c = a * b)/b == a, "BoringMath: Mul Overflow");}
    function to128(uint256 a) internal pure returns (uint128 c) {
        require(a <= uint128(-1), "BoringMath: uint128 Overflow");
        c = uint128(a);
    }
    function to64(uint256 a) internal pure returns (uint64 c) {
        require(a <= uint64(-1), "BoringMath: uint64 Overflow");
        c = uint64(a);
    }
    function to32(uint256 a) internal pure returns (uint32 c) {
        require(a <= uint32(-1), "BoringMath: uint32 Overflow");
        c = uint32(a);
    }
}

library BoringMath128 {
    function add(uint128 a, uint128 b) internal pure returns (uint128 c) {require((c = a + b) >= b, "BoringMath: Add Overflow");}
    function sub(uint128 a, uint128 b) internal pure returns (uint128 c) {require((c = a - b) <= a, "BoringMath: Underflow");}
}

library BoringMath64 {
    function add(uint64 a, uint64 b) internal pure returns (uint64 c) {require((c = a + b) >= b, "BoringMath: Add Overflow");}
    function sub(uint64 a, uint64 b) internal pure returns (uint64 c) {require((c = a - b) <= a, "BoringMath: Underflow");}
}

library BoringMath32 {
    function add(uint32 a, uint32 b) internal pure returns (uint32 c) {require((c = a + b) >= b, "BoringMath: Add Overflow");}
    function sub(uint32 a, uint32 b) internal pure returns (uint32 c) {require((c = a - b) <= a, "BoringMath: Underflow");}
}

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;

import "@boringcrypto/boring-solidity/contracts/libraries/BoringMath.sol";
import "@boringcrypto/boring-solidity/contracts/BoringBatchable.sol";
import "@boringcrypto/boring-solidity/contracts/BoringOwnable.sol";
import "./libraries/SignedSafeMath.sol";
import "./interfaces/IRewarder.sol";
import "./interfaces/IMasterChef.sol";

/// @notice The (older) MasterChef contract gives out a constant number of SYNAPSE tokens per block.
/// It is the only address with minting rights for SYNAPSE.
/// The idea for this MasterChef V2 (MCV2) contract is therefore to be the owner of a dummy token
/// that is deposited into the MasterChef V1 (MCV1) contract.
/// The allocation point for this pool on MCV1 is the total allocation point for all pools that receive double incentives.
contract MiniChefV2 is BoringOwnable, BoringBatchable {
    using BoringMath for uint256;
    using BoringMath128 for uint128;
    using BoringERC20 for IERC20;
    using SignedSafeMath for int256;

    /// @notice Info of each MCV2 user.
    /// `amount` LP token amount the user has provided.
    /// `rewardDebt` The amount of SYNAPSE entitled to the user.
    struct UserInfo {
        uint256 amount;
        int256 rewardDebt;
    }

    /// @notice Info of each MCV2 pool.
    /// `allocPoint` The amount of allocation points assigned to the pool.
    /// Also known as the amount of SYNAPSE to distribute per block.
    struct PoolInfo {
        uint128 accSynapsePerShare;
        uint64 lastRewardTime;
        uint64 allocPoint;
    }

    /// @notice Address of SYNAPSE contract.
    IERC20 public immutable SYNAPSE;

    /// @notice Info of each MCV2 pool.
    PoolInfo[] public poolInfo;
    /// @notice Address of the LP token for each MCV2 pool.
    IERC20[] public lpToken;
    /// @notice Address of each `IRewarder` contract in MCV2.
    IRewarder[] public rewarder;

    /// @notice Info of each user that stakes LP tokens.
    mapping (uint256 => mapping (address => UserInfo)) public userInfo;
    /// @dev Total allocation points. Must be the sum of all allocation points in all pools.
    uint256 public totalAllocPoint;

    uint256 public synapsePerSecond;
    uint256 private constant ACC_SYNAPSE_PRECISION = 1e12;

    event Deposit(address indexed user, uint256 indexed pid, uint256 amount, address indexed to);
    event Withdraw(address indexed user, uint256 indexed pid, uint256 amount, address indexed to);
    event EmergencyWithdraw(address indexed user, uint256 indexed pid, uint256 amount, address indexed to);
    event Harvest(address indexed user, uint256 indexed pid, uint256 amount);
    event LogPoolAddition(uint256 indexed pid, uint256 allocPoint, IERC20 indexed lpToken, IRewarder indexed rewarder);
    event LogSetPool(uint256 indexed pid, uint256 allocPoint, IRewarder indexed rewarder, bool overwrite);
    event LogUpdatePool(uint256 indexed pid, uint64 lastRewardTime, uint256 lpSupply, uint256 accSynapsePerShare);
    event LogSynapsePerSecond(uint256 synapsePerSecond);

    /// @param _synapse The SYNAPSE token contract address.
    constructor(IERC20 _synapse) public {
        SYNAPSE = _synapse;
    }

    /// @notice Returns the number of MCV2 pools.
    function poolLength() public view returns (uint256 pools) {
        pools = poolInfo.length;
    }

    /// @notice Add a new LP to the pool. Can only be called by the owner.
    /// DO NOT add the same LP token more than once. Rewards will be messed up if you do.
    /// @param allocPoint AP of the new pool.
    /// @param _lpToken Address of the LP ERC-20 token.
    /// @param _rewarder Address of the rewarder delegate.
    function add(uint256 allocPoint, IERC20 _lpToken, IRewarder _rewarder) public onlyOwner {
        totalAllocPoint = totalAllocPoint.add(allocPoint);
        lpToken.push(_lpToken);
        rewarder.push(_rewarder);

        poolInfo.push(PoolInfo({
            allocPoint: allocPoint.to64(),
            lastRewardTime: block.timestamp.to64(),
            accSynapsePerShare: 0
        }));
        emit LogPoolAddition(lpToken.length.sub(1), allocPoint, _lpToken, _rewarder);
    }

    /// @notice Update the given pool's SYNAPSE allocation point and `IRewarder` contract. Can only be called by the owner.
    /// @param _pid The index of the pool. See `poolInfo`.
    /// @param _allocPoint New AP of the pool.
    /// @param _rewarder Address of the rewarder delegate.
    /// @param overwrite True if _rewarder should be `set`. Otherwise `_rewarder` is ignored.
    function set(uint256 _pid, uint256 _allocPoint, IRewarder _rewarder, bool overwrite) public onlyOwner {
        totalAllocPoint = totalAllocPoint.sub(poolInfo[_pid].allocPoint).add(_allocPoint);
        poolInfo[_pid].allocPoint = _allocPoint.to64();
        if (overwrite) { rewarder[_pid] = _rewarder; }
        emit LogSetPool(_pid, _allocPoint, overwrite ? _rewarder : rewarder[_pid], overwrite);
    }

    /// @notice Sets the synapse per second to be distributed. Can only be called by the owner.
    /// @param _synapsePerSecond The amount of Synapse to be distributed per second.
    function setSynapsePerSecond(uint256 _synapsePerSecond) public onlyOwner {
        synapsePerSecond = _synapsePerSecond;
        emit LogSynapsePerSecond(_synapsePerSecond);
    }

    /// @notice View function to see pending SYNAPSE on frontend.
    /// @param _pid The index of the pool. See `poolInfo`.
    /// @param _user Address of user.
    /// @return pending SYNAPSE reward for a given user.
    function pendingSynapse(uint256 _pid, address _user) external view returns (uint256 pending) {
        PoolInfo memory pool = poolInfo[_pid];
        UserInfo storage user = userInfo[_pid][_user];
        uint256 accSynapsePerShare = pool.accSynapsePerShare;
        uint256 lpSupply = lpToken[_pid].balanceOf(address(this));
        if (block.timestamp > pool.lastRewardTime && lpSupply != 0) {
            uint256 time = block.timestamp.sub(pool.lastRewardTime);
            uint256 synapseReward = time.mul(synapsePerSecond).mul(pool.allocPoint) / totalAllocPoint;
            accSynapsePerShare = accSynapsePerShare.add(synapseReward.mul(ACC_SYNAPSE_PRECISION) / lpSupply);
        }
        pending = int256(user.amount.mul(accSynapsePerShare) / ACC_SYNAPSE_PRECISION).sub(user.rewardDebt).toUInt256();
    }

    /// @notice Update reward variables for all pools. Be careful of gas spending!
    /// @param pids Pool IDs of all to be updated. Make sure to update all active pools.
    function massUpdatePools(uint256[] calldata pids) external {
        uint256 len = pids.length;
        for (uint256 i = 0; i < len; ++i) {
            updatePool(pids[i]);
        }
    }

    /// @notice Update reward variables of the given pool.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @return pool Returns the pool that was updated.
    function updatePool(uint256 pid) public returns (PoolInfo memory pool) {
        pool = poolInfo[pid];
        if (block.timestamp > pool.lastRewardTime) {
            uint256 lpSupply = lpToken[pid].balanceOf(address(this));
            if (lpSupply > 0) {
                uint256 time = block.timestamp.sub(pool.lastRewardTime);
                uint256 synapseReward = time.mul(synapsePerSecond).mul(pool.allocPoint) / totalAllocPoint;
                pool.accSynapsePerShare = pool.accSynapsePerShare.add((synapseReward.mul(ACC_SYNAPSE_PRECISION) / lpSupply).to128());
            }
            pool.lastRewardTime = block.timestamp.to64();
            poolInfo[pid] = pool;
            emit LogUpdatePool(pid, pool.lastRewardTime, lpSupply, pool.accSynapsePerShare);
        }
    }

    /// @notice Deposit LP tokens to MCV2 for SYNAPSE allocation.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @param amount LP token amount to deposit.
    /// @param to The receiver of `amount` deposit benefit.
    function deposit(uint256 pid, uint256 amount, address to) public {
        PoolInfo memory pool = updatePool(pid);
        UserInfo storage user = userInfo[pid][to];

        // Effects
        user.amount = user.amount.add(amount);
        user.rewardDebt = user.rewardDebt.add(int256(amount.mul(pool.accSynapsePerShare) / ACC_SYNAPSE_PRECISION));

        // Interactions
        IRewarder _rewarder = rewarder[pid];
        if (address(_rewarder) != address(0)) {
            _rewarder.onSynapseReward(pid, to, to, 0, user.amount);
        }

        lpToken[pid].safeTransferFrom(msg.sender, address(this), amount);

        emit Deposit(msg.sender, pid, amount, to);
    }

    /// @notice Withdraw LP tokens from MCV2.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @param amount LP token amount to withdraw.
    /// @param to Receiver of the LP tokens.
    function withdraw(uint256 pid, uint256 amount, address to) public {
        PoolInfo memory pool = updatePool(pid);
        UserInfo storage user = userInfo[pid][msg.sender];

        // Effects
        user.rewardDebt = user.rewardDebt.sub(int256(amount.mul(pool.accSynapsePerShare) / ACC_SYNAPSE_PRECISION));
        user.amount = user.amount.sub(amount);

        // Interactions
        IRewarder _rewarder = rewarder[pid];
        if (address(_rewarder) != address(0)) {
            _rewarder.onSynapseReward(pid, msg.sender, to, 0, user.amount);
        }
        
        lpToken[pid].safeTransfer(to, amount);

        emit Withdraw(msg.sender, pid, amount, to);
    }

    /// @notice Harvest proceeds for transaction sender to `to`.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @param to Receiver of SYNAPSE rewards.
    function harvest(uint256 pid, address to) public {
        PoolInfo memory pool = updatePool(pid);
        UserInfo storage user = userInfo[pid][msg.sender];
        int256 accumulatedSynapse = int256(user.amount.mul(pool.accSynapsePerShare) / ACC_SYNAPSE_PRECISION);
        uint256 _pendingSynapse = accumulatedSynapse.sub(user.rewardDebt).toUInt256();

        // Effects
        user.rewardDebt = accumulatedSynapse;

        // Interactions
        if (_pendingSynapse != 0) {
            SYNAPSE.safeTransfer(to, _pendingSynapse);
        }
        
        IRewarder _rewarder = rewarder[pid];
        if (address(_rewarder) != address(0)) {
            _rewarder.onSynapseReward( pid, msg.sender, to, _pendingSynapse, user.amount);
        }

        emit Harvest(msg.sender, pid, _pendingSynapse);
    }
    
    /// @notice Withdraw LP tokens from MCV2 and harvest proceeds for transaction sender to `to`.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @param amount LP token amount to withdraw.
    /// @param to Receiver of the LP tokens and SYNAPSE rewards.
    function withdrawAndHarvest(uint256 pid, uint256 amount, address to) public {
        PoolInfo memory pool = updatePool(pid);
        UserInfo storage user = userInfo[pid][msg.sender];
        int256 accumulatedSynapse = int256(user.amount.mul(pool.accSynapsePerShare) / ACC_SYNAPSE_PRECISION);
        uint256 _pendingSynapse = accumulatedSynapse.sub(user.rewardDebt).toUInt256();

        // Effects
        user.rewardDebt = accumulatedSynapse.sub(int256(amount.mul(pool.accSynapsePerShare) / ACC_SYNAPSE_PRECISION));
        user.amount = user.amount.sub(amount);
        
        // Interactions
        SYNAPSE.safeTransfer(to, _pendingSynapse);

        IRewarder _rewarder = rewarder[pid];
        if (address(_rewarder) != address(0)) {
            _rewarder.onSynapseReward(pid, msg.sender, to, _pendingSynapse, user.amount);
        }

        lpToken[pid].safeTransfer(to, amount);

        emit Withdraw(msg.sender, pid, amount, to);
        emit Harvest(msg.sender, pid, _pendingSynapse);
    }

    /// @notice Withdraw without caring about rewards. EMERGENCY ONLY.
    /// @param pid The index of the pool. See `poolInfo`.
    /// @param to Receiver of the LP tokens.
    function emergencyWithdraw(uint256 pid, address to) public {
        UserInfo storage user = userInfo[pid][msg.sender];
        uint256 amount = user.amount;
        user.amount = 0;
        user.rewardDebt = 0;

        IRewarder _rewarder = rewarder[pid];
        if (address(_rewarder) != address(0)) {
            _rewarder.onSynapseReward(pid, msg.sender, to, 0, 0);
        }

        // Note: transfer can fail or succeed if `amount` is zero.
        lpToken[pid].safeTransfer(to, amount);
        emit EmergencyWithdraw(msg.sender, pid, amount, to);
    }
}

// SPDX-License-Identifier: MIT
pragma solidity 0.6.12;
pragma experimental ABIEncoderV2;
import "@boringcrypto/boring-solidity/contracts/libraries/BoringERC20.sol";

interface IMasterChef {
    using BoringERC20 for IERC20;
    struct UserInfo {
        uint256 amount;     // How many LP tokens the user has provided.
        uint256 rewardDebt; // Reward debt. See explanation below.
    }

    struct PoolInfo {
        IERC20 lpToken;           // Address of LP token contract.
        uint256 allocPoint;       // How many allocation points assigned to this pool. SYNAPSE to distribute per block.
        uint256 lastRewardBlock;  // Last block number that SYNAPSE distribution occurs.
        uint256 accSynapsePerShare; // Accumulated SYNAPSE per share, times 1e12. See below.
    }

    function poolInfo(uint256 pid) external view returns (IMasterChef.PoolInfo memory);
    function totalAllocPoint() external view returns (uint256);
    function deposit(uint256 _pid, uint256 _amount) external;
}

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;
import "@boringcrypto/boring-solidity/contracts/libraries/BoringERC20.sol";
interface IRewarder {
    using BoringERC20 for IERC20;
    function onSynapseReward(uint256 pid, address user, address recipient, uint256 synapseAmount, uint256 newLpAmount) external;
    function pendingTokens(uint256 pid, address user, uint256 synapseAmount) external view returns (IERC20[] memory, uint256[] memory);
}

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

library SignedSafeMath {
    int256 constant private _INT256_MIN = -2**255;

    /**
     * @dev Returns the multiplication of two signed integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(int256 a, int256 b) internal pure returns (int256) {
        // 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;
        }

        require(!(a == -1 && b == _INT256_MIN), "SignedSafeMath: multiplication overflow");

        int256 c = a * b;
        require(c / a == b, "SignedSafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two signed 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(int256 a, int256 b) internal pure returns (int256) {
        require(b != 0, "SignedSafeMath: division by zero");
        require(!(b == -1 && a == _INT256_MIN), "SignedSafeMath: division overflow");

        int256 c = a / b;

        return c;
    }

    /**
     * @dev Returns the subtraction of two signed integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a - b;
        require((b >= 0 && c <= a) || (b < 0 && c > a), "SignedSafeMath: subtraction overflow");

        return c;
    }

    /**
     * @dev Returns the addition of two signed integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(int256 a, int256 b) internal pure returns (int256) {
        int256 c = a + b;
        require((b >= 0 && c >= a) || (b < 0 && c < a), "SignedSafeMath: addition overflow");

        return c;
    }

    function toUInt256(int256 a) internal pure returns (uint256) {
        require(a >= 0, "Integer < 0");
        return uint256(a);
    }
}

