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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (access/Ownable.sol)

pragma solidity ^0.8.0;

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

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby disabling any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @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);

    /**
     * @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 `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, 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 `from` to `to` 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 from, address to, uint256 amount) external returns (bool);
}

// File: @openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC20/extensions/IERC20Metadata.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";

/**
 * @dev Interface for the optional metadata functions from the ERC20 standard.
 *
 * _Available since v4.1._
 */
interface IERC20Metadata is IERC20 {
    /**
     * @dev Returns the name of the token.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the symbol of the token.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the decimals places of the token.
     */
    function decimals() external view returns (uint8);
}

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



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

/**
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with 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) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}

// File: src/Kong/Interfaces.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";

interface ITreasury {
	function mint(address to_, uint256 amount_) external;

	function TOKEN() external view returns (address);

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

interface IDistributor {
	function distribute() external;

	function nextRewardAt(uint256 _rate) external view returns (uint256);

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

interface IStaking {
	function stake(address _to, uint256 _amount) external;

	function unstake(address _to, uint256 _amount, bool _rebase) external;

	function rebase() external;

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

interface ITOKEN is IERC20Metadata {
	function mint(address to_, uint256 amount_) external;

	function burnFrom(address account_, uint256 amount_) external;

	function burn(uint256 amount_) external;

	function uniswapV2Pair() external view returns (address);
}

interface IsStakingProtocol is IERC20 {
	function rebase(uint256 amount_, uint epoch_) external returns (uint256);

	function circulatingSupply() external view returns (uint256);

	function gonsForBalance(uint amount) external view returns (uint);

	function balanceForGons(uint gons) external view returns (uint);

	function index() external view returns (uint);
}

// File: src/Kong/Staking.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

/*



(Website) https://xxx.xxx
(Telegram) https://t.me/xxx
(Twitter) https://twitter.com/xxx

*/

import "./Interfaces.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract Staking is Ownable, IStaking {
	/// EVENTS ///

	event DistributorSet(address distributor);

	/// DATA STRUCTURES ///

	struct Epoch {
		uint256 length; // in seconds
		uint256 number; // since inception
		uint256 end; // timestamp
		uint256 distribute; // amount
	}

	/// STATE VARIABLES ///

	/// @notice TOKEN address
	IERC20 public immutable TOKEN;
	/// @notice sTOKEN address
	IsStakingProtocol public immutable sTOKEN;

	/// @notice Current epoch details
	Epoch public epoch;

	/// @notice Distributor address
	IDistributor public distributor;

	/// CONSTRUCTOR ///

	/// @param _TOKEN                   Address of TOKEN
	/// @param _sTOKEN                  Address of sTOKEN
	/// @param _epochLength            Epoch length
	/// @param _secondsTillFirstEpoch  Seconds till first epoch starts
	constructor(address _TOKEN, address _sTOKEN, uint256 _epochLength, uint256 _secondsTillFirstEpoch) {
		require(_TOKEN != address(0), "Zero address: TOKEN");
		TOKEN = IERC20(_TOKEN);
		require(_sTOKEN != address(0), "Zero address");
		sTOKEN = IsStakingProtocol(_sTOKEN);

		epoch = Epoch({length: _epochLength, number: 0, end: block.timestamp + _secondsTillFirstEpoch, distribute: 0});
	}

	/// MUTATIVE FUNCTIONS ///

	/// @notice stake TOKEN
	/// @param _to address
	/// @param _amount uint
	function stake(address _to, uint256 _amount) external {
		rebase();
		TOKEN.transferFrom(msg.sender, address(this), _amount);
		sTOKEN.transfer(_to, _amount);
	}

	/// @notice redeem sTOKEN for TOKEN
	/// @param _to address
	/// @param _amount uint
	function unstake(address _to, uint256 _amount, bool _rebase) external {
		if (_rebase) rebase();
		sTOKEN.transferFrom(msg.sender, address(this), _amount);
		require(_amount <= TOKEN.balanceOf(address(this)), "Insufficient TOKEN balance in contract");
		TOKEN.transfer(_to, _amount);
	}

	///@notice Trigger rebase if epoch over
	function rebase() public {
		if (epoch.end <= block.timestamp) {
			sTOKEN.rebase(epoch.distribute, epoch.number);

			epoch.end = epoch.end + epoch.length;
			epoch.number++;

			if (address(distributor) != address(0)) {
				distributor.distribute();
			}

			uint256 balance = TOKEN.balanceOf(address(this));
			uint256 staked = sTOKEN.circulatingSupply();

			if (balance <= staked) {
				epoch.distribute = 0;
			} else {
				epoch.distribute = balance - staked;
			}
		}
	}

	/// INTERNAL FUNCTIONS ///

	/// @notice         Send sTOKEN upon staking
	/// @param _to      Address of where sending sTOKEN
	/// @param _amount  Amount of sTOKEN to send
	/// @return _sent   Amount of sTOKEN sent
	function _send(address _to, uint256 _amount) internal returns (uint256 _sent) {
		sTOKEN.transfer(_to, _amount); // send as sTOKEN (equal unit as TOKEN)
		return _amount;
	}

	/// VIEW FUNCTIONS ///

	/// @notice         Returns the sTOKEN index, which tracks rebase growth
	/// @return index_  Index of sTOKEN
	function index() public view returns (uint256 index_) {
		return sTOKEN.index();
	}

	/// @notice           Returns econds until the next epoch begins
	/// @return seconds_  Till next epoch
	function secondsToNextEpoch() external view returns (uint256 seconds_) {
		return epoch.end - block.timestamp;
	}

	/// MANAGERIAL FUNCTIONS ///

	/// @notice              Sets the contract address for LP staking
	/// @param _distributor  Distributor Address
	function setDistributor(address _distributor) external onlyOwner {
		distributor = IDistributor(_distributor);
		emit DistributorSet(_distributor);
	}
}