openzeppelin-contracts/contracts/governance/extensions/GovernorVotesQuorumFraction.sol

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v5.0.0) (governance/extensions/GovernorVotesQuorumFraction.sol)

pragma solidity ^0.8.20;

import {GovernorVotes} from "./GovernorVotes.sol";
import {Math} from "../../utils/math/Math.sol";
import {SafeCast} from "../../utils/math/SafeCast.sol";
import {Checkpoints} from "../../utils/structs/Checkpoints.sol";

/**
 * @dev Extension of {Governor} for voting weight extraction from an {ERC20Votes} token and a quorum expressed as a
 * fraction of the total supply.
 */
abstract contract GovernorVotesQuorumFraction is GovernorVotes {
    using Checkpoints for Checkpoints.Trace208;

    Checkpoints.Trace208 private _quorumNumeratorHistory;

    event QuorumNumeratorUpdated(uint256 oldQuorumNumerator, uint256 newQuorumNumerator);

    /**
     * @dev The quorum set is not a valid fraction.
     */
    error GovernorInvalidQuorumFraction(uint256 quorumNumerator, uint256 quorumDenominator);

    /**
     * @dev Initialize quorum as a fraction of the token's total supply.
     *
     * The fraction is specified as `numerator / denominator`. By default the denominator is 100, so quorum is
     * specified as a percent: a numerator of 10 corresponds to quorum being 10% of total supply. The denominator can be
     * customized by overriding {quorumDenominator}.
     */
    constructor(uint256 quorumNumeratorValue) {
        _updateQuorumNumerator(quorumNumeratorValue);
    }

    /**
     * @dev Returns the current quorum numerator. See {quorumDenominator}.
     */
    function quorumNumerator() public view virtual returns (uint256) {
        return _quorumNumeratorHistory.latest();
    }

    /**
     * @dev Returns the quorum numerator at a specific timepoint. See {quorumDenominator}.
     */
    function quorumNumerator(uint256 timepoint) public view virtual returns (uint256) {
        return _optimisticUpperLookupRecent(_quorumNumeratorHistory, timepoint);
    }

    /**
     * @dev Returns the quorum denominator. Defaults to 100, but may be overridden.
     */
    function quorumDenominator() public view virtual returns (uint256) {
        return 100;
    }

    /**
     * @dev Returns the quorum for a timepoint, in terms of number of votes: `supply * numerator / denominator`.
     */
    function quorum(uint256 timepoint) public view virtual override returns (uint256) {
        return Math.mulDiv(token().getPastTotalSupply(timepoint), quorumNumerator(timepoint), quorumDenominator());
    }

    /**
     * @dev Changes the quorum numerator.
     *
     * Emits a {QuorumNumeratorUpdated} event.
     *
     * Requirements:
     *
     * - Must be called through a governance proposal.
     * - New numerator must be smaller or equal to the denominator.
     */
    function updateQuorumNumerator(uint256 newQuorumNumerator) external virtual onlyGovernance {
        _updateQuorumNumerator(newQuorumNumerator);
    }

    /**
     * @dev Changes the quorum numerator.
     *
     * Emits a {QuorumNumeratorUpdated} event.
     *
     * Requirements:
     *
     * - New numerator must be smaller or equal to the denominator.
     */
    function _updateQuorumNumerator(uint256 newQuorumNumerator) internal virtual {
        uint256 denominator = quorumDenominator();
        if (newQuorumNumerator > denominator) {
            revert GovernorInvalidQuorumFraction(newQuorumNumerator, denominator);
        }

        uint256 oldQuorumNumerator = quorumNumerator();
        _quorumNumeratorHistory.push(clock(), SafeCast.toUint208(newQuorumNumerator));

        emit QuorumNumeratorUpdated(oldQuorumNumerator, newQuorumNumerator);
    }

    /**
     * @dev Returns the numerator at a specific timepoint.
     */
    function _optimisticUpperLookupRecent(
        Checkpoints.Trace208 storage ckpts,
        uint256 timepoint
    ) internal view returns (uint256) {
        // If trace is empty, key and value are both equal to 0.
        // In that case `key <= timepoint` is true, and it is ok to return 0.
        (, uint48 key, uint208 value) = ckpts.latestCheckpoint();
        return key <= timepoint ? value : ckpts.upperLookupRecent(SafeCast.toUint48(timepoint));
    }
}