// SPDX-License-Identifier: MIT
pragma solidity >0.5.0 <0.8.0;
pragma experimental ABIEncoderV2;

/* Library Imports */
import { Lib_CrossDomainUtils } from "../../libraries/bridge/Lib_CrossDomainUtils.sol";
import { Lib_DefaultValues } from "../../libraries/constants/Lib_DefaultValues.sol";
import { Lib_PredeployAddresses } from "../../libraries/constants/Lib_PredeployAddresses.sol";

/* Interface Imports */
import { IL2CrossDomainMessenger } from "./IL2CrossDomainMessenger.sol";
import { iOVM_L1MessageSender } from "../predeploys/iOVM_L1MessageSender.sol";
import { iOVM_L2ToL1MessagePasser } from "../predeploys/iOVM_L2ToL1MessagePasser.sol";

/* External Imports */
import { ReentrancyGuard } from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

/* External Imports */
import { ReentrancyGuard } from "@openzeppelin/contracts/utils/ReentrancyGuard.sol";

/**
 * @title L2CrossDomainMessenger
 * @dev The L2 Cross Domain Messenger contract sends messages from L2 to L1, and is the entry point
 * for L2 messages sent via the L1 Cross Domain Messenger.
 *
*/
contract L2CrossDomainMessenger is
    IL2CrossDomainMessenger,
    ReentrancyGuard
{

    /*************
     * Variables *
     *************/

    mapping (bytes32 => bool) public relayedMessages;
    mapping (bytes32 => bool) public successfulMessages;
    mapping (bytes32 => bool) public sentMessages;
    uint256 public messageNonce;
    address internal xDomainMsgSender = Lib_DefaultValues.DEFAULT_XDOMAIN_SENDER;
    address public l1CrossDomainMessenger;

    /***************
     * Constructor *
     ***************/

    constructor(
        address _l1CrossDomainMessenger
    )
        ReentrancyGuard()
    {
        l1CrossDomainMessenger = _l1CrossDomainMessenger;
    }

    /********************
     * Public Functions *
     ********************/

    function xDomainMessageSender()
        public
        override
        view
        returns (
            address
        )
    {
        require(xDomainMsgSender != Lib_DefaultValues.DEFAULT_XDOMAIN_SENDER, "xDomainMessageSender is not set");
        return xDomainMsgSender;
    }

    /**
     * Sends a cross domain message to the target messenger.
     * @param _target Target contract address.
     * @param _message Message to send to the target.
     * @param _gasLimit Gas limit for the provided message.
     */
    function sendMessage(
        address _target,
        bytes memory _message,
        uint32 _gasLimit
    )
        override
        public
    {
        bytes memory xDomainCalldata = Lib_CrossDomainUtils.encodeXDomainCalldata(
            _target,
            msg.sender,
            _message,
            messageNonce
        );

        sentMessages[keccak256(xDomainCalldata)] = true;

        _sendXDomainMessage(xDomainCalldata, _gasLimit);
        emit SentMessage(_target, msg.sender, _message, messageNonce, _gasLimit);

        messageNonce += 1;
    }

    /**
     * Relays a cross domain message to a contract.
     * @inheritdoc IL2CrossDomainMessenger
     */
    function relayMessage(
        address _target,
        address _sender,
        bytes memory _message,
        uint256 _messageNonce
    )
        override
        nonReentrant
        public
    {
        require(
            _verifyXDomainMessage() == true,
            "Provided message could not be verified."
        );

        bytes memory xDomainCalldata = Lib_CrossDomainUtils.encodeXDomainCalldata(
            _target,
            _sender,
            _message,
            _messageNonce
        );

        bytes32 xDomainCalldataHash = keccak256(xDomainCalldata);

        require(
            successfulMessages[xDomainCalldataHash] == false,
            "Provided message has already been received."
        );

        // Prevent calls to OVM_L2ToL1MessagePasser, which would enable
        // an attacker to maliciously craft the _message to spoof
        // a call from any L2 account.
        if (_target == Lib_PredeployAddresses.L2_TO_L1_MESSAGE_PASSER) {
            // Write to the successfulMessages mapping and return immediately.
            successfulMessages[xDomainCalldataHash] = true;
            return;
        }

        xDomainMsgSender = _sender;
        (bool success, ) = _target.call(_message);
        xDomainMsgSender = Lib_DefaultValues.DEFAULT_XDOMAIN_SENDER;

        // Mark the message as received if the call was successful. Ensures that a message can be
        // relayed multiple times in the case that the call reverted.
        if (success == true) {
            successfulMessages[xDomainCalldataHash] = true;
            emit RelayedMessage(xDomainCalldataHash);
        } else {
            emit FailedRelayedMessage(xDomainCalldataHash);
        }

        // Store an identifier that can be used to prove that the given message was relayed by some
        // user. Gives us an easy way to pay relayers for their work.
        bytes32 relayId = keccak256(
            abi.encodePacked(
                xDomainCalldata,
                msg.sender,
                block.number
            )
        );

        relayedMessages[relayId] = true;
    }


    /**********************
     * Internal Functions *
     **********************/

    /**
     * Verifies that a received cross domain message is valid.
     * @return _valid Whether or not the message is valid.
     */
    function _verifyXDomainMessage()
        internal
        view
        returns (
            bool _valid
        )
    {
        return (
            iOVM_L1MessageSender(
                Lib_PredeployAddresses.L1_MESSAGE_SENDER
            ).getL1MessageSender() == l1CrossDomainMessenger
        );
    }

    /**
     * Sends a cross domain message.
     * @param _message Message to send.
     * param _gasLimit Gas limit for the provided message.
     */
    function _sendXDomainMessage(
        bytes memory _message,
        uint256 // _gasLimit
    )
        internal
    {
        iOVM_L2ToL1MessagePasser(
            Lib_PredeployAddresses.L2_TO_L1_MESSAGE_PASSER
        ).passMessageToL1(_message);
    }
}
