Cryo Explorer Ethereum Mainnet

// 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);
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (security/Pausable.sol)

pragma solidity ^0.8.0;

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

/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        _requireNotPaused();
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        _requirePaused();
        _;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Throws if the contract is paused.
     */
    function _requireNotPaused() internal view virtual {
        require(!paused(), "Pausable: paused");
    }

    /**
     * @dev Throws if the contract is not paused.
     */
    function _requirePaused() internal view virtual {
        require(paused(), "Pausable: not paused");
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

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

pragma solidity ^0.8.0;

/**
 * @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() {
        _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 making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

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

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

    /**
     * @dev Returns true if the reentrancy guard is currently set to "entered", which indicates there is a
     * `nonReentrant` function in the call stack.
     */
    function _reentrancyGuardEntered() internal view returns (bool) {
        return _status == _ENTERED;
    }
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/extensions/IERC20Permit.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 Permit extension allowing approvals to be made via signatures, as defined in
 * https://eips.ethereum.org/EIPS/eip-2612[EIP-2612].
 *
 * Adds the {permit} method, which can be used to change an account's ERC20 allowance (see {IERC20-allowance}) by
 * presenting a message signed by the account. By not relying on {IERC20-approve}, the token holder account doesn't
 * need to send a transaction, and thus is not required to hold Ether at all.
 */
interface IERC20Permit {
    /**
     * @dev Sets `value` as the allowance of `spender` over ``owner``'s tokens,
     * given ``owner``'s signed approval.
     *
     * IMPORTANT: The same issues {IERC20-approve} has related to transaction
     * ordering also apply here.
     *
     * Emits an {Approval} event.
     *
     * Requirements:
     *
     * - `spender` cannot be the zero address.
     * - `deadline` must be a timestamp in the future.
     * - `v`, `r` and `s` must be a valid `secp256k1` signature from `owner`
     * over the EIP712-formatted function arguments.
     * - the signature must use ``owner``'s current nonce (see {nonces}).
     *
     * For more information on the signature format, see the
     * https://eips.ethereum.org/EIPS/eip-2612#specification[relevant EIP
     * section].
     */
    function permit(
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) external;

    /**
     * @dev Returns the current nonce for `owner`. This value must be
     * included whenever a signature is generated for {permit}.
     *
     * Every successful call to {permit} increases ``owner``'s nonce by one. This
     * prevents a signature from being used multiple times.
     */
    function nonces(address owner) external view returns (uint256);

    /**
     * @dev Returns the domain separator used in the encoding of the signature for {permit}, as defined by {EIP712}.
     */
    // solhint-disable-next-line func-name-mixedcase
    function DOMAIN_SEPARATOR() external view returns (bytes32);
}

// 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);
}

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.9.0) (token/ERC20/utils/SafeERC20.sol)

pragma solidity ^0.8.0;

import "../IERC20.sol";
import "../extensions/IERC20Permit.sol";
import "../../../utils/Address.sol";

/**
 * @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 Address for address;

    /**
     * @dev Transfer `value` amount of `token` from the calling contract to `to`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    /**
     * @dev Transfer `value` amount of `token` from `from` to `to`, spending the approval given by `from` to the
     * calling contract. If `token` returns no value, non-reverting calls are assumed to be successful.
     */
    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'
        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));
    }

    /**
     * @dev Increase the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 oldAllowance = token.allowance(address(this), spender);
        _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance + value));
    }

    /**
     * @dev Decrease the calling contract's allowance toward `spender` by `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful.
     */
    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        unchecked {
            uint256 oldAllowance = token.allowance(address(this), spender);
            require(oldAllowance >= value, "SafeERC20: decreased allowance below zero");
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, oldAllowance - value));
        }
    }

    /**
     * @dev Set the calling contract's allowance toward `spender` to `value`. If `token` returns no value,
     * non-reverting calls are assumed to be successful. Compatible with tokens that require the approval to be set to
     * 0 before setting it to a non-zero value.
     */
    function forceApprove(IERC20 token, address spender, uint256 value) internal {
        bytes memory approvalCall = abi.encodeWithSelector(token.approve.selector, spender, value);

        if (!_callOptionalReturnBool(token, approvalCall)) {
            _callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, 0));
            _callOptionalReturn(token, approvalCall);
        }
    }

    /**
     * @dev Use a ERC-2612 signature to set the `owner` approval toward `spender` on `token`.
     * Revert on invalid signature.
     */
    function safePermit(
        IERC20Permit token,
        address owner,
        address spender,
        uint256 value,
        uint256 deadline,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal {
        uint256 nonceBefore = token.nonces(owner);
        token.permit(owner, spender, value, deadline, v, r, s);
        uint256 nonceAfter = token.nonces(owner);
        require(nonceAfter == nonceBefore + 1, "SafeERC20: permit did not succeed");
    }

    /**
     * @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");
        require(returndata.length == 0 || abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
    }

    /**
     * @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).
     *
     * This is a variant of {_callOptionalReturn} that silents catches all reverts and returns a bool instead.
     */
    function _callOptionalReturnBool(IERC20 token, bytes memory data) private returns (bool) {
        // 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 cannot use {Address-functionCall} here since this should return false
        // and not revert is the subcall reverts.

        (bool success, bytes memory returndata) = address(token).call(data);
        return
            success && (returndata.length == 0 || abi.decode(returndata, (bool))) && Address.isContract(address(token));
    }
}

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

pragma solidity ^0.8.1;

/**
 * @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
     *
     * Furthermore, `isContract` will also return true if the target contract within
     * the same transaction is already scheduled for destruction by `SELFDESTRUCT`,
     * which only has an effect at the end of a transaction.
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 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://consensys.net/diligence/blog/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/v0.8.0/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");

        (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 functionCallWithValue(target, data, 0, "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");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, 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) {
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // 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
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

// 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;
    }
}

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.17;

/**
 * @title NRDCStaking
 * @author 
 * @notice A tier-based staking contract for an ERC20 token (NRDC).
 *         - Multiple tiers, each with its own minimum stake amount, lock duration, APR, etc.
 *         - Users can create multiple stakes, each belonging to a specific tier.
 *         - Rewards are distributed linearly based on APR and time staked.
 *         - The contract must hold or be replenished with enough NRDC to pay out rewards, unless NRDC is mintable.
 * @dev 
 *      **Security**:
 *        - Uses OpenZeppelin's ReentrancyGuard, Ownable, Pausable, SafeERC20 for safe token handling.
 *      **Key Points**:
 *        - `tier.stakers` now tracks *unique* stakers in that tier. 
 *        - An optional `emergencyUnstake()` function is included for early withdrawal with a penalty (owner-configurable).
 *        - Admin can add/modify tiers, pause/unpause the contract, adjust penalty, etc.
 *      **Disclaimer**: 
 *        - This code is provided as-is for educational purposes. 
 *        - Always test and/or audit before deploying for real funds.
 */

import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/security/Pausable.sol";

contract NRDCStaking is ReentrancyGuard, Ownable, Pausable {
    using SafeERC20 for IERC20;

    // ----------------------------------------
    // State Variables
    // ----------------------------------------

    /// @notice The ERC20 token to be staked (NRDC).
    IERC20 public immutable nrdcToken;

    /**
     * @notice Represents a single staking tier.
     * @param minAmount The minimum amount of NRDC required to stake in this tier.
     * @param lockDuration The lock time (in seconds) before a user can unstake.
     * @param apr The annual percentage rate (e.g., 15 means 15% APR).
     * @param totalStaked How many tokens are currently staked in this tier (sum of all users' stakes).
     * @param stakers How many unique addresses currently have an active stake in this tier.
     * @param isActive Whether users can stake into this tier.
     */
    struct StakingTier {
        uint256 minAmount;    
        uint256 lockDuration; 
        uint256 apr;          
        uint256 totalStaked;  
        uint256 stakers;      
        bool isActive;        
    }

    /**
     * @notice Stores details of an individual stake by a user.
     * @dev `active` indicates if the stake is still locked/ongoing (not unstaked).
     */
    struct StakeInfo {
        uint256 amount;
        uint256 startTimestamp;
        uint256 lastClaim;
        uint256 tierIndex;
        bool active;
    }

    /// @dev Array of all staking tiers. Tiers are identified by index (0, 1, 2, etc.).
    StakingTier[] public tiers;

    /// @dev userStakes[user] => array of stakes the user has created.
    mapping(address => StakeInfo[]) public userStakes;

    /**
     * @dev Tracks whether a user has any *active* stake in a given tier.
     *      - This is used to accurately increment/decrement `tier.stakers`
     *        only when a user goes from zero -> one active stake,
     *        or from one -> zero active stakes, in a given tier.
     */
    mapping(uint256 => mapping(address => uint256)) private _userActiveStakesInTier;

    /// @dev If you allow an early exit, you can define an emergency penalty.
    ///      e.g., 10 => 10% penalty on the staked principal returned (or reward).
    uint256 public emergencyPenaltyPercent;

    // ----------------------------------------
    // Events
    // ----------------------------------------

    event Staked(address indexed user, uint256 tierIndex, uint256 amount);
    event Unstaked(address indexed user, uint256 stakeIndex, uint256 amount);
    event RewardClaimed(address indexed user, uint256 stakeIndex, uint256 reward);
    event TierModified(uint256 indexed tierIndex, uint256 newApr, uint256 newMinAmount, uint256 newDuration, bool newActive);
    event EmergencyWithdraw(address indexed user, uint256 stakeIndex, uint256 returnedAmount, uint256 penaltyAmount);
    event EmergencyPenaltyUpdated(uint256 oldPenalty, uint256 newPenalty);

    // ----------------------------------------
    // Constructor
    // ----------------------------------------

    /**
     * @param _nrdcToken The address of the NRDC ERC20 token.
     * @dev Initializes a few sample tiers for demonstration purposes.
     */
    constructor(address _nrdcToken) {
        require(_nrdcToken != address(0), "Invalid token address");
        nrdcToken = IERC20(_nrdcToken);

        // Example tiers (can be modified or removed as needed):
        tiers.push(StakingTier({
            minAmount: 1000 ether,      // e.g., 1000 NRDC
            lockDuration: 7 days,       // 7 days
            apr: 1,                     // 1%
            totalStaked: 0,
            stakers: 0,
            isActive: true
        }));

        tiers.push(StakingTier({
            minAmount: 2500 ether,      // 2,500 NRDC
            lockDuration: 30 days,      // 30 days
            apr: 4,                     // 4%
            totalStaked: 0,
            stakers: 0,
            isActive: true
        }));

        tiers.push(StakingTier({
            minAmount: 5000 ether,      // 5,000 NRDC
            lockDuration: 90 days,      // 90 days
            apr: 8,                     // 8%
            totalStaked: 0,
            stakers: 0,
            isActive: true
        }));

        tiers.push(StakingTier({
            minAmount: 10000 ether,     // 10,000 NRDC
            lockDuration: 180 days,     // 180 days
            apr: 12,                    // 12%
            totalStaked: 0,
            stakers: 0,
            isActive: true
        }));

        tiers.push(StakingTier({
            minAmount: 25000 ether,     // 25,000 NRDC
            lockDuration: 365 days,     // 365 days
            apr: 15,                    // 15%
            totalStaked: 0,
            stakers: 0,
            isActive: true
        }));
    }

    // ----------------------------------------
    // External/Public Functions
    // ----------------------------------------

    /**
     * @notice Stake NRDC tokens into a specific tier.
     * @dev Caller must have approved this contract to spend `_amount` of NRDC beforehand.
     * @param _tierIndex The index of the tier (0-based).
     * @param _amount The amount of NRDC tokens to stake.
     */
    function stake(uint256 _tierIndex, uint256 _amount) external nonReentrant whenNotPaused {
        require(_tierIndex < tiers.length, "Invalid tier index");
        StakingTier storage tier = tiers[_tierIndex];
        require(tier.isActive, "Tier is inactive");
        require(_amount >= tier.minAmount, "Below min stake");

        // Transfer tokens from user to this contract
        nrdcToken.safeTransferFrom(msg.sender, address(this), _amount);

        // Create and store stake info
        userStakes[msg.sender].push(StakeInfo({
            amount: _amount,
            startTimestamp: block.timestamp,
            lastClaim: block.timestamp,
            tierIndex: _tierIndex,
            active: true
        }));

        // Update tier stats
        tier.totalStaked += _amount;

        // If user previously had no active stake in this tier, increment stakers
        if (_userActiveStakesInTier[_tierIndex][msg.sender] == 0) {
            tier.stakers += 1;
        }
        _userActiveStakesInTier[_tierIndex][msg.sender] += 1;

        emit Staked(msg.sender, _tierIndex, _amount);
    }

    /**
     * @notice Claim the rewards accrued by a specific stake.
     * @dev Reward is calculated since the user's `lastClaim`.
     * @param _stakeIndex The index in `userStakes[msg.sender]`.
     */
    function claim(uint256 _stakeIndex) public nonReentrant whenNotPaused {
        StakeInfo storage stakeData = _getActiveStake(msg.sender, _stakeIndex);

        uint256 reward = calculateReward(msg.sender, _stakeIndex);
        require(reward > 0, "No reward to claim");

        // Update lastClaim to now
        stakeData.lastClaim = block.timestamp;

        // Transfer reward from contract to user
        // (Ensure the contract is funded with enough NRDC, or mint if you control supply.)
        nrdcToken.safeTransfer(msg.sender, reward);

        emit RewardClaimed(msg.sender, _stakeIndex, reward);
    }

    /**
     * @notice Unstake your tokens (and auto-claim any pending rewards) after the lock period.
     * @param _stakeIndex The index in `userStakes[msg.sender]`.
     */
    function unstake(uint256 _stakeIndex) external nonReentrant whenNotPaused {
        StakeInfo storage stakeData = _getActiveStake(msg.sender, _stakeIndex);
        StakingTier storage tier = tiers[stakeData.tierIndex];

        // Ensure lock period is over
        require(
            block.timestamp >= stakeData.startTimestamp + tier.lockDuration,
            "Lock period not over"
        );

        // 1. Claim any pending rewards
        uint256 reward = calculateReward(msg.sender, _stakeIndex);
        if (reward > 0) {
            stakeData.lastClaim = block.timestamp;
            nrdcToken.safeTransfer(msg.sender, reward);
            emit RewardClaimed(msg.sender, _stakeIndex, reward);
        }

        // 2. Return staked principal
        uint256 stakedAmount = stakeData.amount;
        stakeData.active = false;
        stakeData.amount = 0;
        tier.totalStaked -= stakedAmount;

        // Adjust stakers count if user has no other active stake in this tier
        _userActiveStakesInTier[stakeData.tierIndex][msg.sender] -= 1;
        if (_userActiveStakesInTier[stakeData.tierIndex][msg.sender] == 0) {
            tier.stakers -= 1;
        }

        nrdcToken.safeTransfer(msg.sender, stakedAmount);

        emit Unstaked(msg.sender, _stakeIndex, stakedAmount);
    }

    /**
     * @notice Emergency unstake (with a penalty) before the lock duration.
     * @dev If you'd rather not allow early exits, you can remove/disable this function.
     *      The penalty is taken from the user's principal (or you could apply it to rewards, 
     *      but here we do principal for simplicity). It's sent to the contract owner or
     *      burned, depending on your token economics.
     * @param _stakeIndex The index in `userStakes[msg.sender]`.
     */
    function emergencyUnstake(uint256 _stakeIndex) external nonReentrant whenNotPaused {
        require(emergencyPenaltyPercent > 0, "Emergency withdraw not allowed");
        StakeInfo storage stakeData = _getActiveStake(msg.sender, _stakeIndex);
        StakingTier storage tier = tiers[stakeData.tierIndex];

        // 1. Calculate *unclaimed* reward and do NOT pay it out. (Or pay partial if you prefer.)
        //    Typically, you might forfeit all or partial rewards if exiting early.
        //    We'll assume user forfeits all rewards in an emergency exit:
        //    so we skip `claim()` or reward transfer.

        // 2. Apply penalty to principal
        uint256 stakedAmount = stakeData.amount;
        uint256 penalty = (stakedAmount * emergencyPenaltyPercent) / 100;
        uint256 amountToReturn = stakedAmount - penalty;

        // 3. Update internal state
        stakeData.active = false;
        stakeData.amount = 0;
        tier.totalStaked -= stakedAmount;
        
        // Adjust stakers count if user now has zero active stakes in this tier
        _userActiveStakesInTier[stakeData.tierIndex][msg.sender] -= 1;
        if (_userActiveStakesInTier[stakeData.tierIndex][msg.sender] == 0) {
            tier.stakers -= 1;
        }

        // 4. Transfer penalty & principal
        //    For example, the penalty can be kept in the contract or sent to the owner:
        if (penalty > 0) {
            // e.g., send to owner or burn if your NRDC supports burn
            nrdcToken.safeTransfer(owner(), penalty);
        }

        // Return the rest to the user
        nrdcToken.safeTransfer(msg.sender, amountToReturn);

        emit EmergencyWithdraw(msg.sender, _stakeIndex, amountToReturn, penalty);
    }

    /**
     * @notice Calculates the pending reward for a specific stake.
     * @param _user The user address.
     * @param _stakeIndex The index in `userStakes[_user]`.
     * @return reward The amount of NRDC reward currently accrued but not yet claimed.
     */
    function calculateReward(address _user, uint256 _stakeIndex) public view returns (uint256) {
        StakeInfo memory stakeData = _getActiveStakeMemory(_user, _stakeIndex);
        if (!stakeData.active) {
            return 0;
        }

        StakingTier memory tier = tiers[stakeData.tierIndex];
        uint256 timeDiff = block.timestamp - stakeData.lastClaim;

        // yearlyReward = amount * (apr / 100)
        // reward = yearlyReward * (timeDiff / 365 days)
        uint256 yearlyReward = (stakeData.amount * tier.apr) / 100;
        uint256 reward = (yearlyReward * timeDiff) / (365 days);

        return reward;
    }

    // ----------------------------------------
    // Owner/Admin Functions
    // ----------------------------------------

    /**
     * @notice Owner can modify any existing tier (e.g., update APR, min stake, lock duration, active status).
     */
    function modifyTier(
        uint256 _tierIndex,
        uint256 _minAmount,
        uint256 _lockDuration,
        uint256 _apr,
        bool _isActive
    ) external onlyOwner {
        require(_tierIndex < tiers.length, "Invalid tier index");
        require(_apr <= 100, "APR too high");
        
        StakingTier storage tier = tiers[_tierIndex];
        tier.minAmount = _minAmount;
        tier.lockDuration = _lockDuration;
        tier.apr = _apr;
        tier.isActive = _isActive;

        emit TierModified(_tierIndex, _apr, _minAmount, _lockDuration, _isActive);
    }

    /**
     * @notice Owner can add a brand new tier.
     */
    function addTier(
        uint256 _minAmount,
        uint256 _lockDuration,
        uint256 _apr,
        bool _isActive
    ) external onlyOwner {
        require(_apr <= 100, "APR too high");

        tiers.push(StakingTier({
            minAmount: _minAmount,
            lockDuration: _lockDuration,
            apr: _apr,
            totalStaked: 0,
            stakers: 0,
            isActive: _isActive
        }));

        emit TierModified(tiers.length - 1, _apr, _minAmount, _lockDuration, _isActive);
    }

    /**
     * @notice Owner can set the emergency penalty percent for early withdrawals (0% means disabled).
     */
    function setEmergencyPenaltyPercent(uint256 _penalty) external onlyOwner {
        require(_penalty <= 50, "Penalty cannot exceed 50%");
        uint256 old = emergencyPenaltyPercent;
        emergencyPenaltyPercent = _penalty;
        emit EmergencyPenaltyUpdated(old, _penalty);
    }

    /**
     * @notice Owner can pause the contract (disables stake/unstake/claim).
     */
    function pause() external onlyOwner {
        _pause();
    }

    /**
     * @notice Owner can unpause the contract.
     */
    function unpause() external onlyOwner {
        _unpause();
    }

    /**
     * @notice Optional: Owner can withdraw NRDC tokens from the contract 
     *         (e.g., if over-funded or to collect penalty fees).
     */
    function ownerWithdrawNRDC(uint256 _amount) external onlyOwner {
        require(_amount > 0, "Invalid amount");
        nrdcToken.safeTransfer(msg.sender, _amount);
    }

    // ----------------------------------------
    // View / Helper Functions
    // ----------------------------------------

    /**
     * @dev Returns how many tiers exist.
     */
    function getTiersCount() external view returns (uint256) {
        return tiers.length;
    }

    /**
     * @dev Returns how many stakes a user has in total.
     */
    function getUserStakeCount(address _user) external view returns (uint256) {
        return userStakes[_user].length;
    }

    /**
     * @dev Safely fetches an active stake from storage.
     *      Reverts if the stake index is out of range or if stake is inactive.
     */
    function _getActiveStake(address _user, uint256 _stakeIndex)
        internal
        view
        returns (StakeInfo storage)
    {
        require(_stakeIndex < userStakes[_user].length, "Invalid stake index");
        StakeInfo storage stakeData = userStakes[_user][_stakeIndex];
        require(stakeData.active, "Stake not active");
        return stakeData;
    }

    /**
     * @dev Same as `_getActiveStake` but returns a memory copy (for read-only operations).
     */
    function _getActiveStakeMemory(address _user, uint256 _stakeIndex)
        internal
        view
        returns (StakeInfo memory)
    {
        require(_stakeIndex < userStakes[_user].length, "Invalid stake index");
        StakeInfo memory stakeData = userStakes[_user][_stakeIndex];
        require(stakeData.active, "Stake not active");
        return stakeData;
    }
}