// SPDX-License-Identifier: MIT
pragma solidity =0.8.21;
pragma experimental ABIEncoderV2;

/**
 * @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;
    }
}

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

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing 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);
    }
}

/**
 * @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);
}

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the substraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @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 a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

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

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * 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) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}

/** 
 * @dev a library for sorting leaderboard
 * https://gist.github.com/taobun/198cb6b2d620f687cacf665a791375cc
 */
contract School is Ownable {
    mapping(address => uint256) public scores;
    mapping(address => address) _nextStudents;
    uint256 public listSize;
    address constant GUARD = address(1);

    constructor() {
        _nextStudents[GUARD] = GUARD;
    }

    function addStudent(address student, uint256 score) public onlyOwner {
        require(_nextStudents[student] == address(0), "addStudent");
        address index = _findIndex(score);
        scores[student] = score;
        _nextStudents[student] = _nextStudents[index];
        _nextStudents[index] = student;
        listSize++;
    }

    function increaseScore(address student, uint256 score) public onlyOwner {
        updateScore(student, scores[student] + score);
    }

    function reduceScore(address student, uint256 score) public onlyOwner {
        updateScore(student, scores[student] - score);
    }

    function updateScore(address student, uint256 newScore) public onlyOwner {
        require(_nextStudents[student] != address(0), "updateScore");
        address prevStudent = _findPrevStudent(student);
        address nextStudent = _nextStudents[student];
        if(_verifyIndex(prevStudent, newScore, nextStudent)){
            scores[student] = newScore;
        } else {
            removeStudent(student);
            addStudent(student, newScore);
        }
    }

    function removeStudent(address student) public onlyOwner {
        require(_nextStudents[student] != address(0), "removeStudent");
        address prevStudent = _findPrevStudent(student);
        _nextStudents[prevStudent] = _nextStudents[student];
        _nextStudents[student] = address(0);
        scores[student] = 0;
        listSize--;
    }

    function getTop(uint256 k) public view returns(address[] memory) {
        require(k <= listSize);
        address[] memory studentLists = new address[](k);
        address currentAddress = _nextStudents[GUARD];
        for(uint256 i = 0; i < k; ++i) {
            studentLists[i] = currentAddress;
            currentAddress = _nextStudents[currentAddress];
        }
        return studentLists;
    }

    function _verifyIndex(address prevStudent, uint256 newValue, address nextStudent)
        internal
        view
        returns(bool)
    {
        return (prevStudent == GUARD || scores[prevStudent] >= newValue) && 
            (nextStudent == GUARD || newValue > scores[nextStudent]);
    }

    function _findIndex(uint256 newValue) internal view returns(address) {
        address candidateAddress = GUARD;
        while(true) {
            if(_verifyIndex(candidateAddress, newValue, _nextStudents[candidateAddress]))
                return candidateAddress;
            candidateAddress = _nextStudents[candidateAddress];
        }
        return address(0);
    }

    function _isPrevStudent(address student, address prevStudent) internal view returns(bool) {
        return _nextStudents[prevStudent] == student;
    }

    function _findPrevStudent(address student) internal view returns(address) {
        address currentAddress = GUARD;
        while(_nextStudents[currentAddress] != GUARD) {
            if(_isPrevStudent(student, currentAddress))
                return currentAddress;
            currentAddress = _nextStudents[currentAddress];
        }
        return address(0);
    }
}

/**
 * @dev Contract module which provides a staking mechanism
 */
contract EFOLIOStake is Context, Ownable {
    using SafeMath for uint256;

    mapping(address => uint256) public staked;
    uint256 public stakedLength = 0;
    mapping(address => uint256) public lastClaim;

    uint256 public startSessionTime;
    uint256 public endSessionTime;

    IERC20 public token;
    School public school;

    bool public leaderboardEnabled = true;
    uint256 public stakeWindowDuration = 1 days;
    uint256 public rewardWindowDuration = 1 days;

    uint256 public totalStaked;
    uint256 public endTotalStaked;
    uint256 public totalReward;

    event SessionStarted(uint256 timestamp);
    event SessionEnded(uint256 timestamp);
    event Staked(address indexed account, uint256 amount);
    event ClaimedReward(address indexed account, uint256 value);
    event Unstaked(address indexed account, uint256 amount);
    
    constructor(address tokenAddr) {
        token = IERC20(tokenAddr);
        school = new School();
    }

    function enableLeaderboard(bool enabled) external onlyOwner {
        leaderboardEnabled = enabled;
    }

    function updateStakeWindowDuration(uint256 duration) external onlyOwner {
        stakeWindowDuration = duration * (1 days);
    }

    function updateRewardWindowDuration(uint256 duration) external onlyOwner {
        rewardWindowDuration = duration * (1 days);
    }

    function startSession() external onlyOwner {
        require(startSessionTime == 0, "session is running");

        (bool sent, ) = owner().call{value: address(this).balance}("");
        require(sent, "transfer remained ETH failed");

        startSessionTime = block.timestamp;
        endSessionTime = 0;

        totalReward = 0;
        endTotalStaked = 0;

        emit SessionStarted(startSessionTime);
    }

    function endSession() external payable onlyOwner {
        require(endSessionTime == 0, "no session");
        
        startSessionTime = 0;
        endSessionTime = block.timestamp;

        totalReward = msg.value;
        endTotalStaked = totalStaked;

        emit SessionEnded(endSessionTime);
    }

    function stake(uint256 amount) external {
        require(amount > 0, "zero stake");
        address sender = _msgSender();
        require(sender != owner(), "owner, it's you?");
        require(
            block.timestamp <= startSessionTime + stakeWindowDuration || 
            (block.timestamp <= endSessionTime + rewardWindowDuration && lastClaim[sender] > endSessionTime), 
            "you late, wait for next session"
        );

        staked[sender] += amount;
        totalStaked += amount;

        if (leaderboardEnabled) {
            try school.increaseScore(sender, amount) {
            } catch {
                school.addStudent(sender, amount);
                stakedLength++;
            }
        }

        token.transferFrom(sender, address(this), amount);
        
        emit Staked(sender, amount);
    }

    function claimReward() external {
        require(endSessionTime > 0, "reward window is not open");
        require(block.timestamp <= endSessionTime + rewardWindowDuration, "you missed this reward, maybe another time");
        address sender = _msgSender();
        require(lastClaim[sender] < endSessionTime, "double claim");

        lastClaim[sender] = block.timestamp;
        uint256 stakedAmount = staked[sender];
        require(stakedAmount > 0, "reward is only for stakers");

        // uint256 value = (totalReward * ((stakedAmount * 1e18) / endTotalStaked)) / 1e18;
        uint256 value = totalReward.mul((stakedAmount * 1e18).div(endTotalStaked)).div(1e18);
        (bool sent, ) = _msgSender().call{value: value}("");
        require(sent, "transfer reward failed");

        emit ClaimedReward(_msgSender(), value);
    }

    function unstake(uint256 amount) external {
        require(amount > 0, "zero unstake");
        address sender = _msgSender();
        require(
            block.timestamp <= startSessionTime + stakeWindowDuration || 
            (block.timestamp <= endSessionTime + rewardWindowDuration && lastClaim[sender] > endSessionTime) ||
            (endSessionTime > 0 && block.timestamp > endSessionTime + rewardWindowDuration), 
            "session is started, wait till end"
        );
        uint256 senderStaked = staked[sender];
        require(senderStaked >= amount, "amount exceeds staked");
        unchecked {
            staked[sender] = senderStaked - amount;
            totalStaked = totalStaked - amount;
        }

        if (leaderboardEnabled) {
            if (staked[sender] == 0) {
                school.removeStudent(sender);
                stakedLength--;
            } else {
                school.reduceScore(sender, amount);
            }
        }

        token.transfer(sender, amount);

        emit Staked(_msgSender(), amount);
    }

    function getTop(uint256 k) public view returns(address[] memory) {
        return school.getTop(k);
    }

    function claimRemainedReward() external onlyOwner {
        require(block.timestamp > endSessionTime + rewardWindowDuration, "reward window is still open");

        (bool sent, ) = owner().call{value: address(this).balance}("");
        require(sent, "transfer remained ETH failed");
    }
}

{
  "compilationTarget": {
    "contracts/estake.sol": "EFOLIOStake"
  },
  "evmVersion": "shanghai",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs"
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}