Contract Source Code:
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.10;
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/token/ERC721/utils/ERC721Holder.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/security/Pausable.sol";
import "../shared/interfaces/RealmsToken.sol";
import "../shared/interfaces/LordsToken.sol";
contract Journey is ERC721Holder, Ownable, ReentrancyGuard, Pausable {
event StakeRealms(uint256[] tokenIds, address player);
event UnStakeRealms(uint256[] tokenIds, address player);
mapping(address => uint256) epochClaimed;
mapping(uint256 => address) ownership;
mapping(address => mapping(uint256 => uint256)) public realmsStaked;
LordsToken lordsToken;
RealmsToken realmsToken;
// contracts
address bridge;
// consts
uint256 lordsPerRealm;
uint256 genesis;
uint256 epoch;
uint256 finalAge;
constructor(
uint256 _lordsPerRealm,
uint256 _epoch,
address _realmsAddress,
address _lordsToken
) {
genesis = block.timestamp;
lordsPerRealm = _lordsPerRealm;
epoch = _epoch;
lordsToken = LordsToken(_lordsToken);
realmsToken = RealmsToken(_realmsAddress);
}
/**
* @notice Set's Lords Issuance in gwei per staked realm
*/
function lordsIssuance(uint256 _new) external onlyOwner {
lordsPerRealm = _new * 10**18; // converted into decimals
}
function updateRealmsAddress(address _newRealms) external onlyOwner {
realmsToken = RealmsToken(_newRealms);
}
function updateLordsAddress(address _newLords) external onlyOwner {
lordsToken = LordsToken(_newLords);
}
function updateEpochLength(uint256 _newEpoch) external onlyOwner {
epoch = _newEpoch;
}
function setBridge(address _newBridge) external onlyOwner {
bridge = _newBridge;
}
function pause() external onlyOwner {
_pause();
}
function unpause() external onlyOwner {
_unpause();
}
function setFinalAge(uint256 _finalAge) external onlyOwner {
finalAge = _finalAge;
}
/**
* @notice Set's epoch to epoch * 1 hour.
*/
function _epochNum() internal view returns (uint256) {
if (finalAge != 0) {
return finalAge;
} else {
return (block.timestamp - genesis) / (epoch * 3600); // hours
}
// return 5;
}
/**
* @notice Boards the Ship (Stakes). Sets ownership of Token to Staker. Transfers NFT to Contract. Set's epoch date, Set's number of Realms staked in the Epoch.
* @param _tokenIds Ids of Realms
*/
function boardShip(uint256[] memory _tokenIds)
external
whenNotPaused
nonReentrant
{
for (uint256 i = 0; i < _tokenIds.length; i++) {
require(
realmsToken.ownerOf(_tokenIds[i]) == msg.sender,
"NOT_OWNER"
);
ownership[_tokenIds[i]] = msg.sender;
realmsToken.safeTransferFrom(
msg.sender,
address(this),
_tokenIds[i]
);
}
if (getNumberRealms(msg.sender) == 0) {
epochClaimed[msg.sender] = _epochNum();
}
realmsStaked[msg.sender][_epochNum()] += uint256(_tokenIds.length);
emit StakeRealms(_tokenIds, msg.sender);
}
function exitShip(uint256[] memory _tokenIds)
external
whenNotPaused
nonReentrant
{
_exitShip(_tokenIds);
}
/**
* @notice Exits Ship, and transfers all Realms back to owner. Claims any lords available.
* @param _tokenIds Ids of Realms
*/
function _exitShip(uint256[] memory _tokenIds) internal {
if (lordsAvailable(msg.sender) != 0) {
_claimLords();
}
for (uint256 i = 0; i < _tokenIds.length; i++) {
require(ownership[_tokenIds[i]] == msg.sender, "NOT_OWNER");
ownership[_tokenIds[i]] = address(0);
realmsToken.safeTransferFrom(
address(this),
msg.sender,
_tokenIds[i]
);
}
// remove last in first
if (_epochNum() == 0) {
realmsStaked[msg.sender][_epochNum()] -= _tokenIds.length;
} else {
uint256 realmsInPrevious = realmsStaked[msg.sender][
_epochNum() - 1
];
uint256 realmsInCurrent = realmsStaked[msg.sender][_epochNum()];
if (realmsInPrevious > _tokenIds.length) {
realmsStaked[msg.sender][_epochNum() - 1] -= _tokenIds.length;
} else if (realmsInCurrent == _tokenIds.length) {
realmsStaked[msg.sender][_epochNum()] -= _tokenIds.length;
} else if (realmsInPrevious <= _tokenIds.length) {
// remove oldest first
uint256 oldestFirst = (_tokenIds.length - realmsInPrevious);
realmsStaked[msg.sender][_epochNum() - 1] -= (_tokenIds.length -
oldestFirst);
realmsStaked[msg.sender][_epochNum()] -= oldestFirst;
}
}
emit UnStakeRealms(_tokenIds, msg.sender);
}
/**
* @notice Claims all available Lords for Owner.
*/
function claimLords() external whenNotPaused nonReentrant {
_claimLords();
}
function _claimLords() internal {
uint256 totalClaimable;
uint256 totalRealms;
require(_epochNum() > 1, "GENESIS_epochNum");
// loop over epochs, sum up total claimable staked lords per epoch
for (uint256 i = epochClaimed[msg.sender]; i < _epochNum(); i++) {
totalRealms += realmsStaked[msg.sender][i];
totalClaimable +=
realmsStaked[msg.sender][i] *
((_epochNum() - 1) - i);
}
// set totalRealms staked in latest epoch - 1 so loop doesn't have to iterate again
realmsStaked[msg.sender][_epochNum() - 1] = totalRealms;
// set epoch claimed to current - 1
epochClaimed[msg.sender] = _epochNum() - 1;
require(totalClaimable > 0, "NOTHING_TO_CLAIM");
// available lords * total realms staked per period
uint256 lords = lordsPerRealm * totalClaimable;
lordsToken.approve(address(this), lords);
lordsToken.transferFrom(address(this), msg.sender, lords);
}
/**
* @notice Lords available for the player.
*/
function lordsAvailable(address _player)
public
view
returns (uint256 lords)
{
uint256 totalClaimable;
if (_epochNum() > 1) {
for (uint256 i = epochClaimed[_player]; i < _epochNum(); i++) {
totalClaimable +=
realmsStaked[_player][i] *
((_epochNum() - 1) - i);
}
lords = lordsPerRealm * totalClaimable;
} else {
lords = 0;
}
}
/**
* @notice Called only by future Bridge contract to withdraw the Realms
* @param _tokenIds Ids of Realms
*/
function bridgeWithdraw(address _player, uint256[] memory _tokenIds)
public
onlyBridge
{
for (uint256 i = 0; i < _tokenIds.length; i++) {
ownership[_tokenIds[i]] = address(0);
realmsToken.safeTransferFrom(address(this), _player, _tokenIds[i]);
}
emit UnStakeRealms(_tokenIds, _player);
}
function withdrawAllLords(address _destination) public onlyOwner {
uint256 balance = lordsToken.balanceOf(address(this));
lordsToken.approve(address(this), balance);
lordsToken.transferFrom(address(this), _destination, balance);
}
modifier onlyBridge() {
require(msg.sender == bridge, "NOT_THE_BRIDGE");
_;
}
function checkOwner(uint256 _tokenId) public view returns (address) {
return ownership[_tokenId];
}
function getEpoch() public view returns (uint256) {
return _epochNum();
}
function getLordsAddress() public view returns (address) {
return address(lordsToken);
}
function getRealmsAddress() public view returns (address) {
return address(realmsToken);
}
function getEpochLength() public view returns (uint256) {
return epoch;
}
function getLordsIssurance() public view returns (uint256) {
return lordsPerRealm;
}
function getTimeUntilEpoch() public view returns (uint256) {
return (epoch * 3600 * (getEpoch() + 1)) - (block.timestamp - genesis);
}
function getFinalAge() public view returns (uint256) {
return finalAge;
}
function getNumberRealms(address _player) public view returns (uint256) {
uint256 totalRealms;
if (_epochNum() >= 1) {
for (uint256 i = epochClaimed[_player]; i <= _epochNum(); i++) {
totalRealms += realmsStaked[_player][i];
}
return totalRealms;
} else {
return realmsStaked[_player][0];
}
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (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 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);
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/utils/ERC721Holder.sol)
pragma solidity ^0.8.0;
import "../IERC721Receiver.sol";
/**
* @dev Implementation of the {IERC721Receiver} interface.
*
* Accepts all token transfers.
* Make sure the contract is able to use its token with {IERC721-safeTransferFrom}, {IERC721-approve} or {IERC721-setApprovalForAll}.
*/
contract ERC721Holder is IERC721Receiver {
/**
* @dev See {IERC721Receiver-onERC721Received}.
*
* Always returns `IERC721Receiver.onERC721Received.selector`.
*/
function onERC721Received(
address,
address,
uint256,
bytes memory
) public virtual override returns (bytes4) {
return this.onERC721Received.selector;
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (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() {
// 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;
}
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (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 Returns true if the contract is paused, and false otherwise.
*/
function paused() public view virtual returns (bool) {
return _paused;
}
/**
* @dev Modifier to make a function callable only when the contract is not paused.
*
* Requirements:
*
* - The contract must not be paused.
*/
modifier whenNotPaused() {
require(!paused(), "Pausable: paused");
_;
}
/**
* @dev Modifier to make a function callable only when the contract is paused.
*
* Requirements:
*
* - The contract must be paused.
*/
modifier whenPaused() {
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
pragma solidity ^0.8.2;
import "@openzeppelin/contracts/token/ERC721/extensions/IERC721Enumerable.sol";
/**
* @dev Required interface of an ERC721 compliant contract.
*/
interface RealmsToken is IERC721Enumerable {
}
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.2;
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
interface LordsToken is IERC20 {
function mint(address to, uint256 amount) external;
function getAgeDistribution(uint256 _age) external view returns (uint256);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (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
// OpenZeppelin Contracts v4.4.0 (token/ERC721/IERC721Receiver.sol)
pragma solidity ^0.8.0;
/**
* @title ERC721 token receiver interface
* @dev Interface for any contract that wants to support safeTransfers
* from ERC721 asset contracts.
*/
interface IERC721Receiver {
/**
* @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
* by `operator` from `from`, this function is called.
*
* It must return its Solidity selector to confirm the token transfer.
* If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
*
* The selector can be obtained in Solidity with `IERC721.onERC721Received.selector`.
*/
function onERC721Received(
address operator,
address from,
uint256 tokenId,
bytes calldata data
) external returns (bytes4);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/extensions/IERC721Enumerable.sol)
pragma solidity ^0.8.0;
import "../IERC721.sol";
/**
* @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
* @dev See https://eips.ethereum.org/EIPS/eip-721
*/
interface IERC721Enumerable is IERC721 {
/**
* @dev Returns the total amount of tokens stored by the contract.
*/
function totalSupply() external view returns (uint256);
/**
* @dev Returns a token ID owned by `owner` at a given `index` of its token list.
* Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
*/
function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);
/**
* @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
* Use along with {totalSupply} to enumerate all tokens.
*/
function tokenByIndex(uint256 index) external view returns (uint256);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC721/IERC721.sol)
pragma solidity ^0.8.0;
import "../../utils/introspection/IERC165.sol";
/**
* @dev Required interface of an ERC721 compliant contract.
*/
interface IERC721 is IERC165 {
/**
* @dev Emitted when `tokenId` token is transferred from `from` to `to`.
*/
event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);
/**
* @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
*/
event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);
/**
* @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
*/
event ApprovalForAll(address indexed owner, address indexed operator, bool approved);
/**
* @dev Returns the number of tokens in ``owner``'s account.
*/
function balanceOf(address owner) external view returns (uint256 balance);
/**
* @dev Returns the owner of the `tokenId` token.
*
* Requirements:
*
* - `tokenId` must exist.
*/
function ownerOf(uint256 tokenId) external view returns (address owner);
/**
* @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
* are aware of the ERC721 protocol to prevent tokens from being forever locked.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must exist and be owned by `from`.
* - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
* - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
*
* Emits a {Transfer} event.
*/
function safeTransferFrom(
address from,
address to,
uint256 tokenId
) external;
/**
* @dev Transfers `tokenId` token from `from` to `to`.
*
* WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must be owned by `from`.
* - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
*
* Emits a {Transfer} event.
*/
function transferFrom(
address from,
address to,
uint256 tokenId
) external;
/**
* @dev Gives permission to `to` to transfer `tokenId` token to another account.
* The approval is cleared when the token is transferred.
*
* Only a single account can be approved at a time, so approving the zero address clears previous approvals.
*
* Requirements:
*
* - The caller must own the token or be an approved operator.
* - `tokenId` must exist.
*
* Emits an {Approval} event.
*/
function approve(address to, uint256 tokenId) external;
/**
* @dev Returns the account approved for `tokenId` token.
*
* Requirements:
*
* - `tokenId` must exist.
*/
function getApproved(uint256 tokenId) external view returns (address operator);
/**
* @dev Approve or remove `operator` as an operator for the caller.
* Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
*
* Requirements:
*
* - The `operator` cannot be the caller.
*
* Emits an {ApprovalForAll} event.
*/
function setApprovalForAll(address operator, bool _approved) external;
/**
* @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
*
* See {setApprovalForAll}
*/
function isApprovedForAll(address owner, address operator) external view returns (bool);
/**
* @dev Safely transfers `tokenId` token from `from` to `to`.
*
* Requirements:
*
* - `from` cannot be the zero address.
* - `to` cannot be the zero address.
* - `tokenId` token must exist and be owned by `from`.
* - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
* - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
*
* Emits a {Transfer} event.
*/
function safeTransferFrom(
address from,
address to,
uint256 tokenId,
bytes calldata data
) external;
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (utils/introspection/IERC165.sol)
pragma solidity ^0.8.0;
/**
* @dev Interface of the ERC165 standard, as defined in the
* https://eips.ethereum.org/EIPS/eip-165[EIP].
*
* Implementers can declare support of contract interfaces, which can then be
* queried by others ({ERC165Checker}).
*
* For an implementation, see {ERC165}.
*/
interface IERC165 {
/**
* @dev Returns true if this contract implements the interface defined by
* `interfaceId`. See the corresponding
* https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
* to learn more about how these ids are created.
*
* This function call must use less than 30 000 gas.
*/
function supportsInterface(bytes4 interfaceId) external view returns (bool);
}
// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.0 (token/ERC20/IERC20.sol)
pragma solidity ^0.8.0;
/**
* @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);
}