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

/// @notice Publisher attestations to offchain swarm snapshots, not execution proofs.
/// @dev Stores hashes only. No token custody, fee collection or spending functions.
contract SwarmCheckpoints {
    address public immutable publisher;
    mapping(bytes32 => bool) public recorded;
    uint256 public checkpointCount;
    event CheckpointRecorded(bytes32 indexed digest, bytes32 indexed engineHash, uint32 seed, uint32 population, uint64 steps, uint256 sequence);
    error Unauthorized();
    error InvalidCheckpoint();
    error AlreadyRecorded();
    constructor(address publisher_) {
        if (publisher_ == address(0)) revert InvalidCheckpoint();
        publisher = publisher_;
    }
    function record(bytes32 digest, bytes32 engineHash, uint32 seed, uint32 population, uint64 steps) external {
        if (msg.sender != publisher) revert Unauthorized();
        if (digest == bytes32(0) || engineHash == bytes32(0) || (population != 64 && population != 128 && population != 256 && population != 512)) revert InvalidCheckpoint();
        if (recorded[digest]) revert AlreadyRecorded();
        recorded[digest] = true;
        emit CheckpointRecorded(digest, engineHash, seed, population, steps, ++checkpointCount);
    }
}