// SPDX-License-Identifier: MIT
pragma solidity ^0.8.13;

contract HeartbeatCapabilityRegistry {
    struct Entry {
        address agent;
        bytes32 endpoint;
        uint64 expiration;
    }

    mapping(bytes4 => Entry) private entries;

    event CapabilityRegistered(bytes4 indexed capability, address indexed agent, bytes32 endpoint, uint256 expiration);
    event CapabilityRemoved(bytes4 indexed capability, address indexed agent);

    error BadExpiry();
    error NotAgent();
    error NotRemovable();
    error NotActive();

    function set(bytes4 capability, bytes32 endpoint, uint256 expiration) external {
        if (!(expiration > block.timestamp && expiration <= block.timestamp + 90 days)) revert BadExpiry();

        Entry storage entry = entries[capability];
        if (!(entry.agent == address(0) || entry.expiration <= block.timestamp || entry.agent == msg.sender)) revert NotAgent();

        entry.agent = msg.sender;
        entry.endpoint = endpoint;
        entry.expiration = uint64(expiration);

        emit CapabilityRegistered(capability, msg.sender, endpoint, expiration);
    }

    function remove(bytes4 capability) external {
        Entry storage entry = entries[capability];
        if (!(entry.agent != address(0) && entry.expiration <= block.timestamp)) revert NotRemovable();

        emit CapabilityRemoved(capability, entry.agent);
        delete entries[capability];
    }

    function get(bytes4 capability) external view returns (address agent, bytes32 endpoint, uint256 expiration) {
        Entry storage entry = entries[capability];
        if (!(entry.expiration > block.timestamp)) revert NotActive();
        return (entry.agent, entry.endpoint, uint256(entry.expiration));
    }
}