// SPDX-License-Identifier:MIT
pragma solidity ^0.6.2;

/**
 * a contract must implement this interface in order to support relayed transaction.
 * It is better to inherit the BaseRelayRecipient as its implementation.
 */
abstract contract IRelayRecipient {

    /**
     * return if the forwarder is trusted to forward relayed transactions to us.
     * the forwarder is required to verify the sender's signature, and verify
     * the call is not a replay.
     */
    function isTrustedForwarder(address forwarder) public virtual view returns(bool);

    /**
     * return the sender of this call.
     * if the call came through our trusted forwarder, then the real sender is appended as the last 20 bytes
     * of the msg.data.
     * otherwise, return `msg.sender`
     * should be used in the contract anywhere instead of msg.sender
     */
    function _msgSender() internal virtual view returns (address payable);

    /**
     * return the msg.data of this call.
     * if the call came through our trusted forwarder, then the real sender was appended as the last 20 bytes
     * of the msg.data - so this method will strip those 20 bytes off.
     * otherwise, return `msg.data`
     * should be used in the contract instead of msg.data, where the difference matters (e.g. when explicitly
     * signing or hashing the
     */
    function _msgData() internal virtual view returns (bytes memory);

    function versionRecipient() external virtual view returns (string memory);
}