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Votes.sol
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Votes.sol
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// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (governance/utils/Votes.sol)
pragma solidity ^0.8.0;
import { Checkpoints } from "@openzeppelin/contracts/utils/Checkpoints.sol";
/**
* @dev This is a base abstract contract that tracks voting units, which are a measure of voting power that can be
* transferred, and provides a system of vote delegation, where an account can delegate its voting units to a sort of
* "representative" that will pool delegated voting units from different accounts and can then use it to vote in
* decisions. In fact, voting units _must_ be delegated in order to count as actual votes, and an account has to
* delegate those votes to itself if it wishes to participate in decisions and does not have a trusted representative.
*
* This contract is often combined with a token contract such that voting units correspond to token units. For an
* example, see {ERC721Votes}.
*
* The full history of delegate votes is tracked on-chain so that governance protocols can consider votes as distributed
* at a particular block number to protect against flash loans and double voting. The opt-in delegate system makes the
* cost of this history tracking optional.
*
* When using this module the derived contract must implement {_getVotingUnits} (for example, make it return
* {ERC721-balanceOf}), and can use {_transferVotingUnits} to track a change in the distribution of those units (in the
* previous example, it would be included in {ERC721-_beforeTokenTransfer}).
*
* _Available since v4.5._
*/
abstract contract Votes {
using Checkpoints for Checkpoints.History;
error SIGNATURE_EXPIRED();
error BLOCK_NOT_YET_MINED();
error INVALID();
/**
* @dev Emitted when an account changes their delegate.
*/
event DelegateChanged(address indexed delegator, address indexed fromDelegate, address indexed toDelegate);
/**
* @dev Emitted when a token transfer or delegate change results in changes to a delegate's number of votes.
*/
event DelegateVotesChanged(address indexed delegate, uint256 previousBalance, uint256 newBalance);
mapping(address => address) private _delegation;
mapping(address => Checkpoints.History) private _delegateCheckpoints;
Checkpoints.History private _totalCheckpoints;
/**
* @dev Returns the current amount of votes that `account` has.
*/
function getVotes(address account) public view virtual returns (uint256) {
return _delegateCheckpoints[account].latest();
}
/**
* @dev Returns the amount of votes that `account` had at the end of a past block (`blockNumber`).
*
* Requirements:
*
* - `blockNumber` must have been already mined
*/
function getPastVotes(address account, uint256 blockNumber) public view virtual returns (uint256) {
return _delegateCheckpoints[account].getAtBlock(blockNumber);
}
/**
* @dev Returns the total supply of votes available at the end of a past block (`blockNumber`).
*
* NOTE: This value is the sum of all available votes, which is not necessarily the sum of all delegated votes.
* Votes that have not been delegated are still part of total supply, even though they would not participate in a
* vote.
*
* Requirements:
*
* - `blockNumber` must have been already mined
*/
function getPastTotalSupply(uint256 blockNumber) public view virtual returns (uint256) {
if (blockNumber >= block.number) revert BLOCK_NOT_YET_MINED();
return _totalCheckpoints.getAtBlock(blockNumber);
}
/**
* @dev Returns the current total supply of votes.
*/
function _getTotalSupply() internal view virtual returns (uint256) {
return _totalCheckpoints.latest();
}
/**
* @dev Returns the delegate that `account` has chosen.
*/
function delegates(address account) public view virtual returns (address) {
return _delegation[account];
}
/**
* @dev Delegates votes from the sender to `delegatee`.
*/
function delegate(address delegatee) public virtual {
_delegate(msg.sender, delegatee);
}
/**
* @dev Delegate all of `account`'s voting units to `delegatee`.
*
* Emits events {DelegateChanged} and {DelegateVotesChanged}.
*/
function _delegate(address account, address delegatee) internal virtual {
address oldDelegate = delegates(account);
_delegation[account] = delegatee;
emit DelegateChanged(account, oldDelegate, delegatee);
_moveDelegateVotes(oldDelegate, delegatee, _getVotingUnits(account));
}
/**
* @dev Transfers, mints, or burns voting units. To register a mint, `from` should be zero. To register a burn, `to`
* should be zero. Total supply of voting units will be adjusted with mints and burns.
*/
function _transferVotingUnits(address from, address to, uint256 amount) internal virtual {
if (from == address(0)) {
_totalCheckpoints.push(_add, amount);
}
if (to == address(0)) {
_totalCheckpoints.push(_subtract, amount);
}
_moveDelegateVotes(delegates(from), delegates(to), amount);
}
/**
* @dev Moves delegated votes from one delegate to another.
*/
function _moveDelegateVotes(address from, address to, uint256 amount) private {
if (from != to && amount > 0) {
if (from != address(0)) {
(uint256 oldValue, uint256 newValue) = _delegateCheckpoints[from].push(_subtract, amount);
emit DelegateVotesChanged(from, oldValue, newValue);
}
if (to != address(0)) {
(uint256 oldValue, uint256 newValue) = _delegateCheckpoints[to].push(_add, amount);
emit DelegateVotesChanged(to, oldValue, newValue);
}
}
}
function _add(uint256 a, uint256 b) internal pure returns (uint256) {
return a + b;
}
function _subtract(uint256 a, uint256 b) internal pure returns (uint256) {
return a - b;
}
/**
* @dev Must return the voting units held by an account.
*/
function _getVotingUnits(address) internal view virtual returns (uint256);
}