// SPDX-License-Identifier: BSD-3-Clause
pragma solidity 0.6.11;

/**
 * @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;
    }
}

/**
 * @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 v3.3._
     */
    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 v3.3._
     */
    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);
            }
        }
    }
}

/**
 * @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));
    }
}

/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address public owner;


  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    owner = msg.sender;
  }


  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }


  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) onlyOwner public {
    require(newOwner != address(0));
    emit OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }
}

/**
 * @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);
}

/**
 * @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");
        }
    }
}

interface IUniswapV2Router {
  function WETH() external pure returns (address);

  function swapExactTokensForTokens(
      uint amountIn,
      uint amountOutMin,
      address[] calldata path,
      address to,
      uint deadline
  ) external returns (uint[] memory amounts);
  
  function getAmountsOut(uint amountIn, address[] calldata path) external view returns (uint[] memory amounts);
}

//interface BuybackContract {
//    function depositByContract(address account, uint amount) external;
//}

contract ConstantReturnStaking is Ownable {
    using Address for address;
    using SafeMath for uint;
    using EnumerableSet for EnumerableSet.AddressSet;
    using SafeERC20 for IERC20;
    
    event Stake(address account, uint amount);
    event Unstake(address account, uint amount);
    
    event RewardsTransferred(address indexed holder, uint amount);
    event ReferralFeeTransferred(address indexed referrer, uint amount);
    event Reinvest(address indexed holder, uint amount);
    
    event StakingFeeChanged(uint newFee);
    event UnstakingFeeChanged(uint newFee);
    event ReferralFeeChanged(uint newFee);
    event UniswapV2RouterChanged(address router);
    event LockupTimeChanged(uint _newLockupTime);
    
    event TrustedDepositContractAdded(address contractAddress);
    event TrustedDepositContractRemoved(address contractAddress);
    //event BuybackContractChanged(address contractAddress);
    event FeeRecipientAddressChanged(address newAddress);
    
    event EmergencyDeclared(address indexed owner);
    
    // ============================= CONTRACT VARIABLES ==============================
    
    // stake token contract address
    address public TRUSTED_DEPOSIT_TOKEN_ADDRESS = 0x961C8c0B1aaD0c0b10a51FeF6a867E3091BCef17;
    address public TRUSTED_REWARD_TOKEN_ADDRESS = 0xBD100d061E120b2c67A24453CF6368E63f1Be056;
    //address public TRUSTED_BUYBACK_CONTRACT_ADDRESS;
    
    // earnings reward rate
    uint public REWARD_RATE_X_100 = 4000;
    uint public REWARD_INTERVAL = 365 days;
    
    // staking fee
    uint public STAKING_FEE_RATE_X_100 = 0;
    
    // unstaking fee 
    uint public UNSTAKING_FEE_RATE_X_100 = 0;
    
    // this portion of earned rewards go to referrer
    uint public REFERRAL_FEE_RATE_X_100 = 500;
    
    // unstaking possible after LOCKUP_TIME
    uint public LOCKUP_TIME = 60 days;
    
    uint public constant EMERGENCY_WAIT_TIME = 3 days;

    // If there are any undistributed or unclaimed tokens left in contract after this time
    // Admin can claim them
    uint public constant adminCanClaimAfter = 395 days;
    
    // Uniswap v2 Router
    IUniswapV2Router public uniswapV2Router = IUniswapV2Router(0x7a250d5630B4cF539739dF2C5dAcb4c659F2488D);
    
    // ========================= END CONTRACT VARIABLES ==============================
    
    address public feeRecipientAddress;
    
    uint public totalClaimedRewards = 0;
    uint public totalClaimedReferralFee = 0;
    
    uint public immutable contractStartTime;
    bool public isEmergency = false;
    
    // Contracts are not allowed to deposit, claim or withdraw
    modifier noContractsAllowed() {
        require(!(address(msg.sender).isContract()) && tx.origin == msg.sender, "No Contracts Allowed!");
        _;
    }
    
    modifier notDuringEmergency() {
        require(!isEmergency, "Cannot execute during emergency!");
        _;
    }
    
    
    EnumerableSet.AddressSet private holders;
    
    mapping (address => uint) public depositedTokens;
    mapping (address => uint) public stakingTime;
    mapping (address => uint) public lastClaimedTime;
    mapping (address => uint) public totalEarnedTokens;
    
    mapping (address => uint) public rewardsPendingClaim;
    
    mapping (address => address) public referrals;
    mapping (address => uint) public totalReferralFeeEarned;
    
    mapping (address => EnumerableSet.AddressSet) private activeReferredAddressesOfUser;
    mapping (address => EnumerableSet.AddressSet) private totalReferredAddressesOfUser;
    
    mapping (address => bool) public isTrustedDepositContract;
    
    uint public adminClaimableTime;

    constructor(
        address _uniswapV2RouterAddress,
        address _feeRecipientAddress,
        
        address trustedDepositTokenAddress,
        address trustedRewardTokenAddress,
        
        uint referralFeeRateX100,
        uint stakingFeeRateX100,
        uint unstakingFeeRateX100,
        
        uint rewardRateX100,
        uint rewardInterval,
        
        uint lockupTime

        ) public {
            
        setUniswapV2Router(IUniswapV2Router(_uniswapV2RouterAddress));
        setFeeRecipientAddress(_feeRecipientAddress);
        
        setStakingFeeRateX100(stakingFeeRateX100);
        setUnstakingFeeRateX100(unstakingFeeRateX100);
        setReferralFeeRateX100(referralFeeRateX100);
        
        require(trustedDepositTokenAddress != address(0), "Invalid deposit token address!");
        require(trustedRewardTokenAddress != address(0), "Invalid reward token address!");
        
        TRUSTED_DEPOSIT_TOKEN_ADDRESS = trustedDepositTokenAddress;
        TRUSTED_REWARD_TOKEN_ADDRESS = trustedRewardTokenAddress;
        
        REWARD_RATE_X_100 = rewardRateX100;
        REWARD_INTERVAL = rewardInterval;
        require(REWARD_INTERVAL <= 365 days, "Contract must expire in less than 365 days!");
        
        setLockupTime(lockupTime);
        
        contractStartTime = now;
        
        //require(adminCanClaimAfter <= 395 days, "Admin Claimable Time should be less than 395 days!");
        adminClaimableTime = now.add(adminCanClaimAfter);
        
    }
    function setFeeRecipientAddress(address newFeeRecipientAddress) public onlyOwner {
        require(newFeeRecipientAddress != address(0), "Invalid address!");
        feeRecipientAddress = newFeeRecipientAddress;
        emit FeeRecipientAddressChanged(feeRecipientAddress);
    }

    //function setBuybackContractAddress(address trustedBuybackContractAddress) external onlyOwner {
    //    require(trustedBuybackContractAddress != address(0), "Invalid address!");
    //    TRUSTED_BUYBACK_CONTRACT_ADDRESS = trustedBuybackContractAddress;
    //    emit BuybackContractChanged(TRUSTED_BUYBACK_CONTRACT_ADDRESS);
    //}
    
    function setStakingFeeRateX100(uint _newStakingFeeRateX100) public onlyOwner {
        require(_newStakingFeeRateX100 < 100e2, "New Staking fee too much!");
        STAKING_FEE_RATE_X_100 = _newStakingFeeRateX100;
        emit StakingFeeChanged(STAKING_FEE_RATE_X_100);
    }
    function setUnstakingFeeRateX100(uint _newUnstakingFeeRateX100) public onlyOwner {
        require(_newUnstakingFeeRateX100 < 100e2, "New Unstaking fee too much!");
        UNSTAKING_FEE_RATE_X_100 = _newUnstakingFeeRateX100;
        emit UnstakingFeeChanged(UNSTAKING_FEE_RATE_X_100);
    }
    function setReferralFeeRateX100(uint _newReferralFeeRateX100) public onlyOwner {
        require(_newReferralFeeRateX100 < 100e2, "Too much referral fee!");
        REFERRAL_FEE_RATE_X_100 = _newReferralFeeRateX100;
        emit ReferralFeeChanged(REFERRAL_FEE_RATE_X_100);
    }
    function setUniswapV2Router(IUniswapV2Router _newUniswapV2Router) public onlyOwner {
        require(address(_newUniswapV2Router) != address(0), "Invalid router!");
        uniswapV2Router = _newUniswapV2Router;
        emit UniswapV2RouterChanged(address(uniswapV2Router));
    }
    function setLockupTime(uint _newLockupTime) public onlyOwner {
        require(_newLockupTime <= 90 days, "Lockup Time too long!");
        LOCKUP_TIME = _newLockupTime;
        emit LockupTimeChanged(LOCKUP_TIME);
    }
    function addTrustedDepositContractAddress(address _address) external onlyOwner {
        isTrustedDepositContract[_address] = true;
        emit TrustedDepositContractAdded(_address);
    }
    function removeTrustedDepositContractAddress(address _address) external onlyOwner {
        isTrustedDepositContract[_address] = false;
        emit TrustedDepositContractRemoved(_address);
    }
    
    modifier onlyTrustedDepositContract() {
        require(isTrustedDepositContract[msg.sender], "Not trusted deposit contract!");
        _;
    }
    
    function setContractVariables(
        uint lockupTime,
        uint referralFeeRateX100, 
        uint stakingFeeRateX100, 
        uint unstakingFeeRateX100, 
        address router,
        address _feeRecipientAddress
    ) external onlyOwner {
        setLockupTime(lockupTime);
        setReferralFeeRateX100(referralFeeRateX100);
        setStakingFeeRateX100(stakingFeeRateX100);
        setUnstakingFeeRateX100(unstakingFeeRateX100);
        setUniswapV2Router(IUniswapV2Router(router));
        setFeeRecipientAddress(_feeRecipientAddress);
    }
    
    function declareEmergency() external onlyOwner notDuringEmergency {
        isEmergency = true;
        adminClaimableTime = now.add(EMERGENCY_WAIT_TIME);
        LOCKUP_TIME = 0;
        
        emit EmergencyDeclared(owner);
    }
    
    function doSwap(address fromToken, address toToken, uint fromTokenAmount, uint amountOutMin, uint deadline) 
        private returns (uint _toTokenReceived) {
            
        if (fromToken == toToken) {
            return fromTokenAmount;
        }
            
        IERC20(fromToken).safeApprove(address(uniswapV2Router), 0);
        IERC20(fromToken).safeApprove(address(uniswapV2Router), fromTokenAmount);
        
        uint oldToTokenBalance = IERC20(toToken).balanceOf(address(this));
        
        address[] memory path;
        
        if (fromToken == uniswapV2Router.WETH() || toToken == uniswapV2Router.WETH()) {
            path = new address[](2);
            path[0] = fromToken;
            path[1] = toToken;
        } else {
            path = new address[](3);
            path[0] = fromToken;
            path[1] = uniswapV2Router.WETH();
            path[2] = toToken;
        }
        
        uniswapV2Router.swapExactTokensForTokens(fromTokenAmount, amountOutMin, path, address(this), deadline);
        
        uint newToTokenBalance = IERC20(toToken).balanceOf(address(this));
        uint toTokenReceived = newToTokenBalance.sub(oldToTokenBalance);
        return toTokenReceived;
    }
    
    function updateAccount(address account, uint _amountOutMin_referralFee, uint _deadline) private {
        uint pendingDivs = getPendingDivs(account);
        if (pendingDivs > 0) {
            uint referralFee = pendingDivs.mul(REFERRAL_FEE_RATE_X_100).div(100e2);
            uint pendingDivsAfterFee = pendingDivs.sub(referralFee);
            
            bool success = transferReferralFeeIfPossible(referrals[account], referralFee, _amountOutMin_referralFee, _deadline);
            
            uint amount = pendingDivs;
            if (success) {
                amount = pendingDivsAfterFee;
            }
            
            rewardsPendingClaim[account] = rewardsPendingClaim[account].add(amount);
            totalEarnedTokens[account] = totalEarnedTokens[account].add(amount);
            
            totalClaimedRewards = totalClaimedRewards.add(amount);
            
        }
        lastClaimedTime[account] = now;
    }
    
    function transferReferralFeeIfPossible(address account, uint amount, uint _amountOutMin_referralFee, uint _deadline) private returns (bool) {
        if (account != address(0) && amount > 0) {
            
            // swap to DYP here
            uint platformTokenReceived = doSwap(TRUSTED_REWARD_TOKEN_ADDRESS, TRUSTED_DEPOSIT_TOKEN_ADDRESS, amount, _amountOutMin_referralFee, _deadline);
            
            totalReferralFeeEarned[account] = totalReferralFeeEarned[account].add(platformTokenReceived);
            IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransfer(account, platformTokenReceived);
            totalClaimedReferralFee = totalClaimedReferralFee.add(platformTokenReceived);
            emit ReferralFeeTransferred(account, platformTokenReceived);
            return true;
        }
        return false;
    }
    
    function getPendingDivs(address _holder) public view returns (uint) {
        if (!holders.contains(_holder)) return 0;
        if (depositedTokens[_holder] == 0) return 0;
        
        uint timeDiff;
        uint stakingEndTime = contractStartTime.add(REWARD_INTERVAL);
        uint _now = now;
        if (_now > stakingEndTime) {
            _now = stakingEndTime;
        }
        
        if (lastClaimedTime[_holder] >= _now) {
            timeDiff = 0;
        } else {
            timeDiff = _now.sub(lastClaimedTime[_holder]);
        }

        uint stakedAmount = depositedTokens[_holder];
        
        uint pendingDivs = stakedAmount
                            .mul(REWARD_RATE_X_100)
                            .mul(timeDiff)
                            .div(REWARD_INTERVAL)
                            .div(1e4);
            
        return pendingDivs;
    }
    
    function getTotalPendingDivs(address _holder) external view returns (uint) {
        uint pending = getPendingDivs(_holder);
        uint awaitingClaim = rewardsPendingClaim[_holder];
        return pending.add(awaitingClaim);
    }
    
    function getNumberOfHolders() external view returns (uint) {
        return holders.length();
    }
    
    function getNumberOfReferredStakers(address referrer) external view returns (uint _activeStakers, uint _totalStakers) {
        _activeStakers = activeReferredAddressesOfUser[referrer].length();
        _totalStakers = totalReferredAddressesOfUser[referrer].length();
    }
    
    function getReferredStaker(address account, uint i) external view returns (address _staker, uint _totalEarned) {
        _staker = totalReferredAddressesOfUser[account].at(i);
        _totalEarned = totalEarnedTokens[_staker];
    }
    function getActiveReferredStaker(address account, uint i) external view returns (address _staker, uint _totalEarned) {
        _staker = activeReferredAddressesOfUser[account].at(i);
        _totalEarned = totalEarnedTokens[_staker];
    }
    
    function depositByContract(address account, uint amount, uint _amountOutMin_stakingReferralFee, uint _deadline) external onlyTrustedDepositContract {
        require(amount > 0, "Amount must not be 0!");
        require(account != address(0), "Invalid account!");
        IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransferFrom(msg.sender, address(this), amount);
        
        updateAccount(account, _amountOutMin_stakingReferralFee, _deadline);
        
        depositedTokens[account] = depositedTokens[account].add(amount);
        
        holders.add(account);
    
        stakingTime[account] = now;
        emit Stake(account, amount);
    }
    
    function stake(uint amountToStake, address referrer, uint _amountOutMin_referralFee, uint _deadline) external noContractsAllowed notDuringEmergency {
        require(amountToStake > 0, "Cannot deposit 0 Tokens");
        IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransferFrom(msg.sender, address(this), amountToStake);
        
        updateAccount(msg.sender, _amountOutMin_referralFee, _deadline);
        
        uint fee = amountToStake.mul(STAKING_FEE_RATE_X_100).div(1e4);
        uint amountAfterFee = amountToStake.sub(fee);
        if (fee > 0) {
            IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransfer(feeRecipientAddress, fee);
        }
        
        //uint _75Percent = amountAfterFee.mul(75e2).div(100e2);

        //uint contractDepositAmount = doSwap(TRUSTED_DEPOSIT_TOKEN_ADDRESS, TRUSTED_REWARD_TOKEN_ADDRESS, _75Percent, _amountOutMin_75Percent, _deadline);

        //IERC20(TRUSTED_REWARD_TOKEN_ADDRESS).safeApprove(TRUSTED_BUYBACK_CONTRACT_ADDRESS, 0);
        //IERC20(TRUSTED_REWARD_TOKEN_ADDRESS).safeApprove(TRUSTED_BUYBACK_CONTRACT_ADDRESS, contractDepositAmount);
        //BuybackContract(TRUSTED_BUYBACK_CONTRACT_ADDRESS).depositByContract(msg.sender, contractDepositAmount);
        
        //uint remainingAmount = amountAfterFee.sub(_75Percent);
        
        depositedTokens[msg.sender] = depositedTokens[msg.sender].add(amountAfterFee);
        
        holders.add(msg.sender);
        
        if (referrals[msg.sender] == address(0)) {
            referrals[msg.sender] = referrer;
        }
        
        totalReferredAddressesOfUser[referrals[msg.sender]].add(msg.sender);
        activeReferredAddressesOfUser[referrals[msg.sender]].add(msg.sender);
        
        stakingTime[msg.sender] = now;
        emit Stake(msg.sender, amountAfterFee);
    }
    
    function unstake(uint amountToWithdraw, uint _amountOutMin_referralFee, uint _deadline) external noContractsAllowed {
        require(depositedTokens[msg.sender] >= amountToWithdraw, "Invalid amount to withdraw");
        
        require(now.sub(stakingTime[msg.sender]) > LOCKUP_TIME, "You recently staked, please wait before withdrawing.");
        
        updateAccount(msg.sender, _amountOutMin_referralFee, _deadline);
        
        uint fee = amountToWithdraw.mul(UNSTAKING_FEE_RATE_X_100).div(1e4);
        uint amountAfterFee = amountToWithdraw.sub(fee);
        if (fee > 0) {
            IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransfer(feeRecipientAddress, fee);
        }
        IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransfer(msg.sender, amountAfterFee);
        
        depositedTokens[msg.sender] = depositedTokens[msg.sender].sub(amountToWithdraw);
        
        if (holders.contains(msg.sender) && depositedTokens[msg.sender] == 0) {
            holders.remove(msg.sender);
            activeReferredAddressesOfUser[referrals[msg.sender]].remove(msg.sender);
        }
        
        emit Unstake(msg.sender, amountToWithdraw);
    }
    
    function claim(uint _amountOutMin_referralFee, uint _amountOutMin_claim, uint _deadline) external noContractsAllowed notDuringEmergency {
        updateAccount(msg.sender, _amountOutMin_referralFee, _deadline);
        uint amount = rewardsPendingClaim[msg.sender];
        if (amount > 0) {
            rewardsPendingClaim[msg.sender] = 0;
            
            // swap to DYP here
            uint platformTokenReceived = doSwap(TRUSTED_REWARD_TOKEN_ADDRESS, TRUSTED_DEPOSIT_TOKEN_ADDRESS, amount, _amountOutMin_claim, _deadline);
            
            IERC20(TRUSTED_DEPOSIT_TOKEN_ADDRESS).safeTransfer(msg.sender, platformTokenReceived);  
            emit RewardsTransferred(msg.sender, platformTokenReceived);
        }
    }
    
    function reInvest(uint _amountOutMin_referralFee, uint _amountOutMin_reinvest, uint _deadline) external noContractsAllowed notDuringEmergency {
        updateAccount(msg.sender, _amountOutMin_referralFee, _deadline);
        uint amount = rewardsPendingClaim[msg.sender];
        if (amount > 0) {
            rewardsPendingClaim[msg.sender] = 0;
            
            // swap to DYP here
            uint platformTokenReceived = doSwap(TRUSTED_REWARD_TOKEN_ADDRESS, TRUSTED_DEPOSIT_TOKEN_ADDRESS, amount, _amountOutMin_reinvest, _deadline);
            
            // re-invest here
            depositedTokens[msg.sender] = depositedTokens[msg.sender].add(platformTokenReceived);
            
            // no lock time reset for reinvest
            // stakingTime[msg.sender] = now;
            emit Reinvest(msg.sender, platformTokenReceived);
        }
    }
    
    function getStakersList(uint startIndex, uint endIndex) 
        public 
        view 
        returns (address[] memory stakers, 
            uint[] memory stakingTimestamps, 
            uint[] memory lastClaimedTimeStamps,
            uint[] memory stakedTokens) {
        require (startIndex < endIndex);
        
        uint length = endIndex.sub(startIndex);
        address[] memory _stakers = new address[](length);
        uint[] memory _stakingTimestamps = new uint[](length);
        uint[] memory _lastClaimedTimeStamps = new uint[](length);
        uint[] memory _stakedTokens = new uint[](length);
        
        for (uint i = startIndex; i < endIndex; i = i.add(1)) {
            address staker = holders.at(i);
            uint listIndex = i.sub(startIndex);
            _stakers[listIndex] = staker;
            _stakingTimestamps[listIndex] = stakingTime[staker];
            _lastClaimedTimeStamps[listIndex] = lastClaimedTime[staker];
            _stakedTokens[listIndex] = depositedTokens[staker];
        }
        
        return (_stakers, _stakingTimestamps, _lastClaimedTimeStamps, _stakedTokens);
    }
    
    // admin can claim any tokens left in the contract after it expires or during emergency
    function claimAnyToken(address token, address recipient, uint amount) external onlyOwner {
        require(recipient != address(0), "Invalid Recipient");
        require(now > adminClaimableTime, "Contract not expired yet!");
        if (token == address(0)) {
            address payable _recipient = payable(recipient);
            _recipient.transfer(amount);
            return;
        }
        IERC20(token).safeTransfer(recipient, amount);
    }
}