hyperlane-monorepo/solidity/optics-core/contracts/Queue.sol

// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity >=0.6.11;

// ============ Internal Imports ============
import {QueueLib} from "../libs/Queue.sol";
// ============ External Imports ============
import {Initializable} from "@openzeppelin/contracts-upgradeable/proxy/Initializable.sol";

/**
 * @title QueueManager
 * @author Celo Labs Inc.
 * @notice Contains a queue instance and
 * exposes view functions for the queue.
 **/
contract QueueManager is Initializable {
    // ============ Libraries ============

    using QueueLib for QueueLib.Queue;
    QueueLib.Queue internal queue;

    // ============ Upgrade Gap ============

    // gap for upgrade safety
    uint256[49] private __GAP;

    // ============ Initializer ============

    function __QueueManager_initialize() internal initializer {
        queue.initialize();
    }

    // ============ Public Functions ============

    /**
     * @notice Returns number of elements in queue
     */
    function queueLength() external view returns (uint256) {
        return queue.length();
    }

    /**
     * @notice Returns TRUE iff `_item` is in the queue
     */
    function queueContains(bytes32 _item) external view returns (bool) {
        return queue.contains(_item);
    }

    /**
     * @notice Returns last item enqueued to the queue
     */
    function queueEnd() external view returns (bytes32) {
        return queue.lastItem();
    }
}