// SPDX-License-Identifier: MIT
pragma solidity 0.8.30;

/// @notice Self-reported public activity intervals. No rewards or proof of real work.
contract ChronyxIntervals {
    struct Interval { bytes32 topic; uint64 startedAt; uint64 endedAt; }
    mapping(address => uint256) public intervalCount;
    mapping(address => uint256) public activeInterval;
    mapping(address => mapping(uint256 => Interval)) public intervals;
    event IntervalStarted(address indexed account, uint256 indexed id, bytes32 topic, uint64 startedAt);
    event IntervalEnded(address indexed account, uint256 indexed id, uint64 endedAt);
    error EmptyTopic(); error AlreadyActive(); error NoActiveInterval(); error StaleInterval();
    function start(bytes32 topic) external returns (uint256 id) {
        if (topic == bytes32(0)) revert EmptyTopic();
        if (activeInterval[msg.sender] != 0) revert AlreadyActive();
        id = ++intervalCount[msg.sender];
        uint64 timestamp = uint64(block.timestamp);
        intervals[msg.sender][id] = Interval(topic, timestamp, 0);
        activeInterval[msg.sender] = id;
        emit IntervalStarted(msg.sender, id, topic, timestamp);
    }
    function end(uint256 expectedId) external {
        uint256 id = activeInterval[msg.sender];
        if (id == 0) revert NoActiveInterval();
        if (id != expectedId) revert StaleInterval();
        uint64 timestamp = uint64(block.timestamp);
        intervals[msg.sender][id].endedAt = timestamp;
        activeInterval[msg.sender] = 0;
        emit IntervalEnded(msg.sender, id, timestamp);
    }
}