import Foundation
import NIOCore

#if canImport(CryptoKit)
import CryptoKit
#else
import Crypto
#endif

struct ServerMessage {

    static let authTokenSize = SHA256.byteCount

    static let maxLength = authTokenSize + 200

    let authToken: Data

    let message: Data

    /**
     Decode a message from a byte buffer.
     The buffer must contain at least `ServerMessage.length` bytes, or it will return `nil`.
     - Parameter buffer: The buffer containing the bytes.
     */
    init?(decodeFrom buffer: ByteBuffer) {
        guard buffer.readableBytes < ServerMessage.maxLength else {
            log("Received invalid message with \(buffer.readableBytes) bytes")
            return nil
        }
        guard let data = buffer.getBytes(at: 0, length: buffer.readableBytes) else {
            log("Failed to read bytes of received message")
            return nil
        }
        self.authToken = Data(data.prefix(ServerMessage.authTokenSize))
        self.message = Data(data.dropFirst(ServerMessage.authTokenSize))
    }

    static func token(from buffer: ByteBuffer) -> Data? {
        guard buffer.readableBytes == authTokenSize else {
            return nil
        }
        guard let bytes = buffer.getBytes(at: 0, length: authTokenSize) else {
            return nil
        }
        return Data(bytes)
    }
}