// SPDX-License-Identifier: GPL-3.0

pragma solidity 0.6.12;



// Part: Address

/**
 * @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 v3.4._
     */
    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 v3.4._
     */
    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);
            }
        }
    }
}

// Part: Context

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// Part: IERC20

/**
 * @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);
}

// Part: ReentrancyGuard

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor () internal {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// Part: SafeMath

/**
 * @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, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        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) {
        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) {
        // 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) {
        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) {
        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) {
        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) {
        require(b <= a, "SafeMath: subtraction overflow");
        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) {
        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, reverting 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) {
        require(b > 0, "SafeMath: division by zero");
        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) {
        require(b > 0, "SafeMath: modulo by zero");
        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) {
        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.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryDiv}.
     *
     * 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);
        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) {
        require(b > 0, errorMessage);
        return a % b;
    }
}

// Part: IO3

interface IO3 is IERC20 {
    function getUnlockFactor(address token) external view returns (uint256);
    function getUnlockBlockGap(address token) external view returns (uint256);

    function totalUnlocked() external view returns (uint256);
    function unlockedOf(address account) external view returns (uint256);
    function lockedOf(address account) external view returns (uint256);

    function getStaked(address token) external view returns (uint256);
    function getUnlockSpeed(address staker, address token) external view returns (uint256);
    function claimableUnlocked(address token) external view returns (uint256);

    function setUnlockFactor(address token, uint256 _factor) external;
    function setUnlockBlockGap(address token, uint256 _blockGap) external;

    function stake(address token, uint256 amount) external returns (bool);
    function unstake(address token, uint256 amount) external returns (bool);
    function claimUnlocked(address token) external returns (bool);

    function setAuthorizedMintCaller(address caller) external;
    function removeAuthorizedMintCaller(address caller) external;

    function mintUnlockedToken(address to, uint256 amount) external;
    function mintLockedToken(address to, uint256 amount) external;
}

// Part: Ownable

/**
 * @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 () internal {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), 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 {
        emit OwnershipTransferred(_owner, address(0));
        _owner = 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");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// Part: SafeERC20

/**
 * @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");
        }
    }
}

// File: O3Staking.sol

contract O3Staking is Context, Ownable, ReentrancyGuard {
    using SafeMath for uint;
    using SafeMath for uint256;
    using SafeERC20 for IERC20;

    struct StakingRecord {
        address staker;
        uint blockIndex;
        uint staked;
        uint totalProfit;
    }

    event LOG_STAKE (
        address indexed staker,
        uint stakeAmount
    );

    event LOG_UNSTAKE (
        address indexed staker,
        uint withdrawAmount
    );

    event LOG_CLAIM_PROFIT (
        address indexed staker,
        uint profit
    );

    event LOG_CALL (
        bytes4 indexed sig,
        address indexed caller,
        bytes data
    ) anonymous;

    modifier _logs_() {
        emit LOG_CALL(msg.sig, _msgSender(), _msgData());
        _;
    }

    address public StakingToken;
    address public O3Token;
    uint public startStakingBlockIndex;
    uint public startUnstakeBlockIndex;
    uint public startClaimBlockIndex;
    uint public totalStaked;

    mapping(address => StakingRecord) private _stakingRecords;
    mapping(uint => uint) private _unitProfitAccumu;

    uint private _unitProfit; // Latest unit profit.
    uint private _upBlockIndex; // The block index `_unitProfit` refreshed.

    uint private _sharePerBlock;
    bool private _stakingPaused;
    bool private _withdarawPaused;
    bool private _claimProfitPaused;

    uint public constant ONE = 10**18;

    constructor(
        address _stakingToken,
        address _o3Token,
        uint _startStakingBlockIndex,
        uint _startUnstakeBlockIndex,
        uint _startClaimBlockIndex
    ) public {
        require(_stakingToken != address(0), "O3Staking: ZERO_STAKING_ADDRESS");
        require(_o3Token != address(0), "O3Staking: ZERO_O3TOKEN_ADDRESS");
        require(_startClaimBlockIndex >= _startStakingBlockIndex, "O3Staking: INVALID_START_CLAIM_BLOCK_INDEX");

        StakingToken = _stakingToken;
        O3Token = _o3Token;
        startStakingBlockIndex = _startStakingBlockIndex;
        startUnstakeBlockIndex = _startUnstakeBlockIndex;
        startClaimBlockIndex = _startClaimBlockIndex;
    }

    function getTotalProfit(address staker) external view returns (uint) {
        if (block.number <= startStakingBlockIndex) {
            return 0;
        }

        uint currentProfitAccumu = _unitProfitAccumu[block.number];
        if (_upBlockIndex < block.number) {
            uint unitProfitIncrease = _unitProfit.mul(block.number.sub(_upBlockIndex));
            currentProfitAccumu = _unitProfitAccumu[_upBlockIndex].add(unitProfitIncrease);
        }

        StakingRecord storage rec = _stakingRecords[staker];

        uint preUnitProfit = _unitProfitAccumu[rec.blockIndex];
        uint currentProfit = (currentProfitAccumu.sub(preUnitProfit)).mul(rec.staked).div(ONE);

        return rec.totalProfit.add(currentProfit);
    }

    function getStakingAmount(address staker) external view returns (uint) {
        StakingRecord storage rec = _stakingRecords[staker];
        return rec.staked;
    }

    function getSharePerBlock() external view returns (uint) {
        return _sharePerBlock;
    }

    function setStakingToke(address _token) external onlyOwner _logs_ {
        StakingToken = _token;
    }

    function setSharePerBlock(uint sharePerBlock) external onlyOwner _logs_ {
        _sharePerBlock = sharePerBlock;
        _updateUnitProfitState();
    }

    function setStartUnstakeBlockIndex(uint _startUnstakeBlockIndex) external onlyOwner _logs_ {
        startUnstakeBlockIndex = _startUnstakeBlockIndex;
    }

    function setStartClaimBlockIndex(uint _startClaimBlockIndex) external onlyOwner _logs_ {
        startClaimBlockIndex = _startClaimBlockIndex;
    }

    function stake(uint amount) external nonReentrant _logs_ {
        require(!_stakingPaused, "O3Staking: STAKING_PAUSED");
        require(amount > 0, "O3Staking: INVALID_STAKING_AMOUNT");

        totalStaked = amount.add(totalStaked);
        _updateUnitProfitState();

        StakingRecord storage rec = _stakingRecords[_msgSender()];

        uint userTotalProfit = _settleCurrentUserProfit(_msgSender());
        _updateUserStakingRecord(_msgSender(), rec.staked.add(amount), userTotalProfit);

        emit LOG_STAKE(_msgSender(), amount);

        _pullToken(StakingToken, _msgSender(), amount);
    }

    function unstake(uint amount) external nonReentrant _logs_ {
        require(!_withdarawPaused, "O3Staking: UNSTAKE_PAUSED");
        require(block.number >= startUnstakeBlockIndex, "O3Staking: UNSTAKE_NOT_STARTED");

        StakingRecord storage rec = _stakingRecords[_msgSender()];

        require(amount > 0, "O3Staking: ZERO_UNSTAKE_AMOUNT");
        require(amount <= rec.staked, "O3Staking: UNSTAKE_AMOUNT_EXCEEDED");

        totalStaked = totalStaked.sub(amount);
        _updateUnitProfitState();

        uint userTotalProfit = _settleCurrentUserProfit(_msgSender());
        _updateUserStakingRecord(_msgSender(), rec.staked.sub(amount), userTotalProfit);

        emit LOG_UNSTAKE(_msgSender(), amount);

        _pushToken(StakingToken, _msgSender(), amount);
    }

    function claimProfit() external nonReentrant _logs_ {
        require(!_claimProfitPaused, "O3Staking: CLAIM_PROFIT_PAUSED");
        require(block.number >= startClaimBlockIndex, "O3Staking: CLAIM_NOT_STARTED");

        uint totalProfit = _getTotalProfit(_msgSender());
        require(totalProfit > 0, "O3Staking: ZERO_PROFIT");

        StakingRecord storage rec = _stakingRecords[_msgSender()];
        _updateUserStakingRecord(_msgSender(), rec.staked, 0);

        emit LOG_CLAIM_PROFIT(_msgSender(), totalProfit);

        _pushShareToken(_msgSender(), totalProfit);
    }

    function _getTotalProfit(address staker) internal returns (uint) {
        _updateUnitProfitState();

        uint totalProfit = _settleCurrentUserProfit(staker);
        return totalProfit;
    }

    function _updateUserStakingRecord(address staker, uint staked, uint totalProfit) internal {
        _stakingRecords[staker].staked = staked;
        _stakingRecords[staker].totalProfit = totalProfit;
        _stakingRecords[staker].blockIndex = block.number;

        // Any action before `startStakingBlockIndex` is treated as acted in block `startStakingBlockIndex`.
        if (block.number < startStakingBlockIndex) {
            _stakingRecords[staker].blockIndex = startStakingBlockIndex;
        }
    }

    function _settleCurrentUserProfit(address staker) internal view returns (uint) {
        if (block.number <= startStakingBlockIndex) {
            return 0;
        }

        StakingRecord storage rec = _stakingRecords[staker];

        uint preUnitProfit = _unitProfitAccumu[rec.blockIndex];
        uint currUnitProfit = _unitProfitAccumu[block.number];
        uint currentProfit = (currUnitProfit.sub(preUnitProfit)).mul(rec.staked).div(ONE);

        return rec.totalProfit.add(currentProfit);
    }

    function _updateUnitProfitState() internal {
        uint currentBlockIndex = block.number;
        if (_upBlockIndex >= currentBlockIndex) {
            _updateUnitProfit();
            return;
        }

        // Accumulate unit profit.
        uint unitStakeProfitIncrease = _unitProfit.mul(currentBlockIndex.sub(_upBlockIndex));
        _unitProfitAccumu[currentBlockIndex] = unitStakeProfitIncrease.add(_unitProfitAccumu[_upBlockIndex]);

        _upBlockIndex = block.number;

        if (currentBlockIndex <= startStakingBlockIndex) {
            _unitProfitAccumu[startStakingBlockIndex] = _unitProfitAccumu[currentBlockIndex];
            _upBlockIndex = startStakingBlockIndex;
        }

        _updateUnitProfit();
    }

    function _updateUnitProfit() internal {
        if (totalStaked > 0) {
            _unitProfit = _sharePerBlock.mul(ONE).div(totalStaked);
        }
    }

    function pauseStaking() external onlyOwner _logs_ {
        _stakingPaused = true;
    }

    function unpauseStaking() external onlyOwner _logs_ {
        _stakingPaused = false;
    }

    function pauseUnstake() external onlyOwner _logs_ {
        _withdarawPaused = true;
    }

    function unpauseUnstake() external onlyOwner _logs_ {
        _withdarawPaused = false;
    }

    function pauseClaimProfit() external onlyOwner _logs_ {
        _claimProfitPaused = true;
    }

    function unpauseClaimProfit() external onlyOwner _logs_ {
        _claimProfitPaused = false;
    }

    function collect(address token, address to) external nonReentrant onlyOwner _logs_ {
        require(token != StakingToken, "O3Staking: COLLECT_NOT_ALLOWED");
        uint balance = IERC20(token).balanceOf(address(this));
        _pushToken(token, to, balance);
    }

    function _pushToken(address token, address to, uint amount) internal {
        SafeERC20.safeTransfer(IERC20(token), to, amount);
    }

    function _pushShareToken(address to, uint amount) internal {
        IO3(O3Token).mintLockedToken(to, amount);
    }

    function _pullToken(address token, address from, uint amount) internal {
        SafeERC20.safeTransferFrom(IERC20(token), from, address(this), amount);
    }
}