// SPDX-License-Identifier: MIT
// https://github.com/fx-portal/contracts/blob/main/contracts/tunnel/FxBaseChildTunnel.sol
pragma solidity 0.8.24;

// IFxMessageProcessor represents interface to process message
interface IFxMessageProcessor {
    function processMessageFromRoot(uint256 stateId, address rootMessageSender, bytes calldata data) external;
}

///@dev Polygon-side abstract contract of the bidirectional Polygon/Ethereum bridge
abstract contract FxBaseChildTunnel is IFxMessageProcessor {
    // MessageTunnel on L1 will get data from this event
    event MessageSent(bytes message);

    // fx child
    address public fxChild;

    // fx root tunnel
    address public fxRootTunnel;

    constructor(address _fxChild) {
        fxChild = _fxChild;
    }

    // Sender must be fxRootTunnel in case of ERC20 tunnel
    modifier validateSender(address sender) {
        require(sender == fxRootTunnel, "FxBaseChildTunnel: INVALID_SENDER_FROM_ROOT");
        _;
    }

    // set fxRootTunnel if not set already
    function setFxRootTunnel(address _fxRootTunnel) public virtual {
        require(fxRootTunnel == address(0x0), "FxBaseChildTunnel: ROOT_TUNNEL_ALREADY_SET");
        fxRootTunnel = _fxRootTunnel;
    }

    function processMessageFromRoot(uint256 stateId, address rootMessageSender, bytes calldata data) external override {
        require(msg.sender == fxChild, "FxBaseChildTunnel: INVALID_SENDER");
        _processMessageFromRoot(stateId, rootMessageSender, data);
    }

    /// @notice Emit message that can be received on Root Tunnel
    /// @dev Call the internal function when need to emit message
    /// @param message bytes message that will be sent to Root Tunnel
    /// some message examples -
    ///   abi.encode(tokenId);
    ///   abi.encode(tokenId, tokenMetadata);
    ///   abi.encode(messageType, messageData);
    function _sendMessageToRoot(bytes memory message) internal {
        emit MessageSent(message);
    }

    /// @notice Process message received from Root Tunnel
    /// @dev function needs to be implemented to handle message as per requirement
    /// This is called by onStateReceive function.
    /// Since it is called via a system call, any event will not be emitted during its execution.
    /// @param stateId unique state id
    /// @param sender root message sender
    /// @param message bytes message that was sent from Root Tunnel
    function _processMessageFromRoot(uint256 stateId, address sender, bytes memory message) internal virtual;
}