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

contract CapabilityIndex {
    mapping(bytes32 => bool) private _supported;

    event SelectorSet(address indexed agent, bytes4 indexed selector, bool supported);

    function setSelector(bytes4 selector, bool supported) external {
        bytes32 key = _key(msg.sender, selector);
        _supported[key] = supported;
        emit SelectorSet(msg.sender, selector, supported);
    }

    function isSupported(address agent, bytes4 selector) external view returns (bool) {
        return _supported[_key(agent, selector)];
    }

    function _key(address agent, bytes4 selector) private pure returns (bytes32) {
        return bytes32((uint256(uint160(agent)) << 32) | uint32(selector));
    }
}