// SPDX-License-Identifier: MIT OR Apache-2.0
pragma solidity ^0.8.13;

/// @title IVerifier
/// @author The Warp Team <contact@warp.inc>
/// @notice Interface for a cross-chain message verifier.
/// @dev The verifier is responsible for verifying the authenticity of a
///      message. It contains any necessary logic and state to authenticate
///      messages. The Verifier is called by the Inbox contract before
///      delivering a message to the handler. The address of the Verifier is
///      passed to the Handler with the message. The handler may then check
///      that the Verifier is trusted before processing messages.
interface IVerifier {
    /// @notice A statement that has been verified by a Verifier. Contains a
    ///         message field that SHOULD contain a serialized `Message`.
    /// @dev The fields are as follows:
    ///      - emitterChainId - The ID of the chain that emitted the statement.
    ///      - emitterAddress - The address that emitted the statement.
    ///      - message - The body of the statement, which SHOULD contain a
    ///                  serialized message.
    struct VerifiedStatement {
        uint16 emitterChainId;
        bytes32 emitterAddress;
        bytes message;
    }

    /// @notice Verify a witnessed statement, returning the statement it
    ///         contains  if the witness is valid, and contains a validly
    ///         formatted statement, and reverting otherwise.
    /// @dev    This function may unpack the statement according to any
    ///         arbitrary logic and/or state. Application developers must
    ///         evaluate the safety and trustworthiness of a particular
    ///         verifier.
    /// @dev    MUST revert if statement is not valid.
    /// @param  witnessedStatement - The statement to verify.
    /// @return statement The statement contained in the witnessed statement.
    function verify(bytes memory witnessedStatement) external view returns (VerifiedStatement memory statement);
}