/*
TODO:
    - add arguments to methods
*/

/**
 * The [ProtocolTranslator] interface provides methods that coincide 1:1 with each request type in the 9P protocol.
 * Every method that can fail, that is, every request that can receive a response with `Rerror` type instead of the same
 * type as itself, returns a non-null `String` that contains the error message received in the response.
 *
 * Tags are supposed to be managed internally by the class that provides the implementation.
 *
 * When compared to 9P's formal message descriptions, like those which can be read in Plan 9's manual pages, some of the
 * methods might lack parameters. Those which can be inferred from the existing parameters are purposefully omitted. An
 * example is [walk], which omits `nwname` because it can be obtained by calculating the size of `wname`.
 *
 * Trivia: comments for each method are taken from each message type's manual page in section 5.
 */
interface ProtocolTranslator {
    /**
     * Negotiate protocol version.
     *
     * This must be the first message sent on the 9P connection and no other requests can be issued until a response has
     * been received.
     *
     * @param msize The maximum length, in bytes, that the client will ever generate or expect to receive in a single
     *              9P message.
     * @param version Should be "9P2000", which is the only defined value.
     * @return a possible error.
     */
    fun version(msize: UInt, version: String): String?

    /**
     * Perform authentication.
     */
    fun auth(afid: UInt, uname: String, aname: String)

    /**
     * Abort a message.
     */
    fun flush()

    /**
     * Establish a connection.
     */
    fun attach()

    /**
     * Descend a directory hierarchy.
     *
     * @param fid The existing FID. It must represent a directory.
     * @param newfid The proposed FID, which is going to be associated with the result of walking the hierarchy. It must
     * be not in use, unless it is the same as [fid].
     * @param wname The successive path name elements which describe the file to walk to.
     * @return a possible error.
     */
    fun walk(fid: UInt, newfid: UInt, wname: List<String>): String?

    /**
     * Prepare an FID for I/O on an existing file.
     */
    fun open(path: String)

    /**
     * Prepare an FID for I/O on a new file.
     */
    fun create(path: String)

    /**
     * Transfer data from file. Due to the negotiated maximum size of 9P messages, called `msize`, one is supposed to
     * call this method multiple times, unless the content is smaller than `msize`.
     *
     * @return A pair of: (1) an optional error message and (2) the content read with the call just made. If the string
     * is not null, an error occurred and the array is going to be empty.
     */
    fun read(fid: UInt, offset: ULong, count: UInt): Pair<String?, Array<UByte>>

    /**
     * Transfer data to file. Due to the negotiated maximum size of 9P messages, called `msize`, one is supposed to
     * call this method multiple times, unless the content is smaller than `msize`.
     *
     * @param fid The FID to write to.
     * @param offset The distance between the beginning of the file and the first written byte.
     * @param data The raw bytes that are going to be written.
     * @return A pair of: (1) an optional error message and (2) the amount of bytes written with the call just made. If
     * the string is not null, an error occurred and the amount of written bytes is going to be zero.
     */
    fun write(fid: UInt, offset: ULong, count: UInt, data: Iterable<UByte>): Pair<String?, UInt>

    /**
     * Forget about an FID.
     */
    fun clunk(path: String)

    /**
     * Remove a file from a server.
     */
    fun remove(path: String)

    /**
     * Inquire file attributes.
     */
    fun stat(path: String)

    /**
     * Change file attributes.
     */
    fun wstat(path: String)
}