// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.8.0) (crosschain/arbitrum/LibArbitrumL2.sol)

pragma solidity ^0.8.4;

import {IArbSys as ArbitrumL2_Bridge} from "../../vendor/arbitrum/IArbSys.sol";
import "../errors.sol";

/**
 * @dev Primitives for cross-chain aware contracts for
 * https://arbitrum.io/[Arbitrum].
 *
 * This version should only be used on L2 to process cross-chain messages
 * originating from L1. For the other side, use {LibArbitrumL1}.
 *
 * WARNING: There is currently a bug in Arbitrum that causes this contract to
 * fail to detect cross-chain calls when deployed behind a proxy. This will be
 * fixed when the network is upgraded to Arbitrum Nitro, currently scheduled for
 * August 31st 2022.
 */
library LibArbitrumL2 {
    /**
     * @dev Returns whether the current function call is the result of a
     * cross-chain message relayed by `arbsys`.
     */
    address public constant ARBSYS = 0x0000000000000000000000000000000000000064;

    function isCrossChain(address arbsys) internal view returns (bool) {
        return ArbitrumL2_Bridge(arbsys).wasMyCallersAddressAliased();
    }

    /**
     * @dev Returns the address of the sender that triggered the current
     * cross-chain message through `arbsys`.
     *
     * NOTE: {isCrossChain} should be checked before trying to recover the
     * sender, as it will revert with `NotCrossChainCall` if the current
     * function call is not the result of a cross-chain message.
     */
    function crossChainSender(address arbsys) internal view returns (address) {
        if (!isCrossChain(arbsys)) revert NotCrossChainCall();

        return ArbitrumL2_Bridge(arbsys).myCallersAddressWithoutAliasing();
    }
}