(**************************************************************************)
(*                                                                        *)
(*    Copyright (c) 2014 - 2016.                                          *)
(*    Dynamic Ledger Solutions, Inc. <contact@tezos.com>                  *)
(*                                                                        *)
(*    All rights reserved. No warranty, explicit or implicit, provided.   *)
(*                                                                        *)
(**************************************************************************)

(* TODO encode/encrypt before to push into the writer pipe. *)
(* TODO patch Sodium.Box to avoid allocation of the encrypted buffer.*)
(* TODO patch Data_encoding for continuation-based binary writer/reader. *)
(* TODO test `close ~wait:true`. *)
(* TODO nothing in welcoming message proves that the incoming peer is
        the owner of the public key... only the first message will
        really proves it. Should this to be changed? Not really
        important, but... an attacker might forge a random public key
        with enough proof of work (hard task), open a connection, wait
        infinitly. This would avoid the real peer to talk with us. And
        this might also have an influence on its "score". *)

open P2p_types

include Logging.Make(struct let name = "p2p.connection" end)

type error += Decipher_error
type error += Invalid_message_size
type error += Encoding_error
type error += Rejected
type error += Decoding_error
type error += Myself of Id_point.t
type error += Not_enough_proof_of_work of Peer_id.t
type error += Invalid_auth

module Crypto = struct

  let header_length = 2
  let crypto_overhead = 18 (* FIXME import from Sodium.Box. *)
  let max_content_length =
    1 lsl (header_length * 8) - crypto_overhead

  type data = {
    channel_key : Crypto_box.channel_key ;
    mutable local_nonce : Crypto_box.nonce ;
    mutable remote_nonce : Crypto_box.nonce ;
  }

  let write_chunk fd cryptobox_data buf =
    let header_buf = MBytes.create header_length in
    let local_nonce = cryptobox_data.local_nonce in
    cryptobox_data.local_nonce <- Crypto_box.increment_nonce local_nonce ;
    let encrypted_message =
      Crypto_box.fast_box cryptobox_data.channel_key buf local_nonce in
    let encrypted_len = MBytes.length encrypted_message in
    fail_unless
      (encrypted_len < max_content_length)
      Invalid_message_size >>=? fun () ->
    MBytes.set_int16 header_buf 0 encrypted_len ;
    P2p_io_scheduler.write fd header_buf >>=? fun () ->
    P2p_io_scheduler.write fd encrypted_message >>=? fun () ->
    return ()

  let read_chunk fd cryptobox_data =
    let header_buf = MBytes.create header_length in
    P2p_io_scheduler.read_full ~len:header_length fd header_buf >>=? fun () ->
    let len = MBytes.get_uint16 header_buf 0 in
    let buf = MBytes.create len in
    P2p_io_scheduler.read_full ~len fd buf >>=? fun () ->
    let remote_nonce = cryptobox_data.remote_nonce in
    cryptobox_data.remote_nonce <- Crypto_box.increment_nonce remote_nonce ;
    match
      Crypto_box.fast_box_open cryptobox_data.channel_key buf remote_nonce
    with
    | None ->
        fail Decipher_error
    | Some buf ->
        return buf

end

module Connection_message = struct

  type t = {
    port : int option ;
    versions : Version.t list ;
    public_key : Crypto_box.public_key ;
    proof_of_work_stamp : Crypto_box.nonce ;
    message_nonce : Crypto_box.nonce ;
  }

  let encoding =
    let open Data_encoding in
    conv
      (fun { port ; public_key ; proof_of_work_stamp ;
             message_nonce ; versions } ->
        let port = match port with None -> 0 | Some port -> port in
        (port, public_key, proof_of_work_stamp,
         message_nonce, versions))
      (fun (port, public_key, proof_of_work_stamp,
            message_nonce, versions) ->
        let port = if port = 0 then None else Some port in
        { port ; public_key ; proof_of_work_stamp ;
          message_nonce ; versions })
      (obj5
         (req "port" uint16)
         (req "pubkey" Crypto_box.public_key_encoding)
         (req "proof_of_work_stamp" Crypto_box.nonce_encoding)
         (req "message_nonce" Crypto_box.nonce_encoding)
         (req "versions" (Variable.list Version.encoding)))

  let write fd message =
    let encoded_message_len =
      Data_encoding.Binary.length encoding message in
    fail_unless
      (encoded_message_len < Crypto.max_content_length)
      Encoding_error >>=? fun () ->
    let len = Crypto.header_length + encoded_message_len in
    let buf = MBytes.create len in
    match Data_encoding.Binary.write
            encoding message buf Crypto.header_length with
    | None ->
        fail Encoding_error
    | Some last ->
        fail_unless (last = len) Encoding_error >>=? fun () ->
        MBytes.set_int16 buf 0 encoded_message_len ;
        P2p_io_scheduler.write fd buf

  let read fd =
    let header_buf = MBytes.create Crypto.header_length in
    P2p_io_scheduler.read_full
      ~len:Crypto.header_length fd header_buf >>=? fun () ->
    let len = MBytes.get_uint16 header_buf 0 in
    let buf = MBytes.create len in
    P2p_io_scheduler.read_full ~len fd buf >>=? fun () ->
    match Data_encoding.Binary.read encoding buf 0 len with
    | None ->
        fail Decoding_error
    | Some (read_len, message) ->
        if read_len <> len then
          fail Decoding_error
        else
          return message

end

module Ack = struct

  type t = Ack | Nack
  let ack = MBytes.of_string "\255"
  let nack = MBytes.of_string "\000"

  let write cryptobox_data fd b =
    Crypto.write_chunk cryptobox_data fd
      (match b with Ack -> ack | Nack -> nack)

  let read fd cryptobox_data =
    Crypto.read_chunk fd cryptobox_data >>=? fun buf ->
    return (buf <> nack)

end

type authenticated_fd =
  P2p_io_scheduler.connection * Connection_info.t * Crypto.data

let kick (fd, _ , cryptobox_data) =
  Ack.write fd cryptobox_data Nack >>= fun _ ->
  P2p_io_scheduler.close fd >>= fun _ ->
  Lwt.return_unit

(* First step: write and read credentials, makes no difference
   whether we're trying to connect to a peer or checking an incoming
   connection, both parties must first introduce themselves. *)
let authenticate
    ~proof_of_work_target
    ~incoming fd (remote_addr, remote_socket_port as point)
    ?listening_port identity supported_versions =
  let local_nonce = Crypto_box.random_nonce () in
  lwt_debug "Sending authenfication to %a" Point.pp point >>= fun () ->
  Connection_message.write fd
    { public_key = identity.Identity.public_key ;
      proof_of_work_stamp = identity.proof_of_work_stamp ;
      message_nonce = local_nonce ;
      port = listening_port ;
      versions = supported_versions } >>=? fun () ->
  Connection_message.read fd >>=? fun msg ->
  let remote_listening_port =
    if incoming then msg.port else Some remote_socket_port in
  let id_point = remote_addr, remote_listening_port in
  let remote_peer_id = Crypto_box.hash msg.public_key in
  fail_unless
    (remote_peer_id <> identity.Identity.peer_id)
    (Myself id_point) >>=? fun () ->
  fail_unless
    (Crypto_box.check_proof_of_work
       msg.public_key msg.proof_of_work_stamp proof_of_work_target)
    (Not_enough_proof_of_work remote_peer_id) >>=? fun () ->
  let channel_key =
    Crypto_box.precompute identity.Identity.secret_key msg.public_key in
  let info =
    { Connection_info.peer_id = remote_peer_id ;
      versions = msg.versions ; incoming ;
      id_point ; remote_socket_port ;} in
  let cryptobox_data =
    { Crypto.channel_key ; local_nonce ;
      remote_nonce = msg.message_nonce } in
  return (info, (fd, info, cryptobox_data))

type connection = {
  info : Connection_info.t ;
  fd : P2p_io_scheduler.connection ;
  cryptobox_data : Crypto.data ;
}

module Reader = struct

  type 'msg t = {
    canceler: Canceler.t ;
    conn: connection ;
    encoding: 'msg Data_encoding.t ;
    messages: (int * 'msg) tzresult Lwt_pipe.t ;
    mutable worker: unit Lwt.t ;
  }

  let rec read_message st buf =
    return (Data_encoding.Binary.of_bytes st.encoding buf)

  let rec worker_loop st =
    Lwt_unix.yield () >>= fun () ->
    Lwt_utils.protect ~canceler:st.canceler begin fun () ->
      Crypto.read_chunk st.conn.fd st.conn.cryptobox_data >>=? fun buf ->
      let size = 6 * (Sys.word_size / 8) + MBytes.length buf in
      lwt_debug "reading %d bytes from %a"
        size Connection_info.pp st.conn.info >>= fun () ->
      read_message st buf >>|? fun msg ->
      size, msg
    end >>= function
    | Ok (_, None) ->
        Lwt_pipe.push st.messages (Error [Decoding_error]) >>= fun () ->
        worker_loop st
    | Ok (size, Some msg) ->
        Lwt_pipe.push st.messages (Ok (size, msg)) >>= fun () ->
        worker_loop st
    | Error [Lwt_utils.Canceled | Exn Lwt_pipe.Closed] ->
      lwt_debug "connection closed to %a"
        Connection_info.pp st.conn.info >>= fun () ->
        Lwt.return_unit
    | Error _ as err ->
        Lwt_pipe.push st.messages err >>= fun () ->
        Canceler.cancel st.canceler >>= fun () ->
        Lwt.return_unit

  let run ?size conn encoding canceler =
    let compute_size = function
      | Ok (size, _) -> (Sys.word_size / 8) * 11 + size
      | Error _ -> 0 (* we push Error only when we close the socket,
                        we don't fear memory leaks in that case... *) in
    let size = map_option size ~f:(fun max -> (max, compute_size)) in
    let st =
      { canceler ; conn ; encoding ;
        messages = Lwt_pipe.create ?size () ;
        worker = Lwt.return_unit ;
      } in
    Canceler.on_cancel st.canceler begin fun () ->
      Lwt_pipe.close st.messages ;
      Lwt.return_unit
    end ;
    st.worker <-
      Lwt_utils.worker "reader"
        (fun () -> worker_loop st)
        (fun () -> Canceler.cancel st.canceler) ;
    st

  let shutdown st =
    Canceler.cancel st.canceler >>= fun () ->
    st.worker

end

module Writer = struct

  type 'msg t = {
    canceler: Canceler.t ;
    conn: connection ;
    encoding: 'msg Data_encoding.t ;
    messages: ('msg * unit tzresult Lwt.u option) Lwt_pipe.t ;
    mutable worker: unit Lwt.t ;
  }

  let encode_message st msg =
    try return (Data_encoding.Binary.to_bytes st.encoding msg)
    with _ -> fail Encoding_error

  let rec worker_loop st =
    Lwt_unix.yield () >>= fun () ->
    Lwt_utils.protect ~canceler:st.canceler begin fun () ->
      Lwt_pipe.pop st.messages >>= fun (msg, wakener) ->
      encode_message st msg >>=? fun buf ->
      lwt_debug "writing %d bytes to %a"
        (MBytes.length buf) Connection_info.pp st.conn.info >>= fun () ->
      Crypto.write_chunk st.conn.fd st.conn.cryptobox_data buf >>= fun res ->
      iter_option wakener ~f:(fun u -> Lwt.wakeup_later u res) ;
      Lwt.return res
    end >>= function
    | Ok () ->
        worker_loop st
    | Error [Lwt_utils.Canceled | Exn Lwt_pipe.Closed] ->
        lwt_debug "connection closed to %a"
          Connection_info.pp st.conn.info >>= fun () ->
        Lwt.return_unit
    | Error err ->
        lwt_log_error
          "@[<v 2>error writing to %a@ %a@]"
          Connection_info.pp st.conn.info pp_print_error err >>= fun () ->
        Canceler.cancel st.canceler >>= fun () ->
        Lwt.return_unit

  let run ?size conn encoding canceler =
    let compute_size = function
      | msg, None ->
          10 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
      | msg, Some _ ->
          18 * (Sys.word_size / 8) + Data_encoding.Binary.length encoding msg
    in
    let size = map_option size ~f:(fun max -> max, compute_size) in
    let st =
      { canceler ; conn ; encoding ;
        messages = Lwt_pipe.create ?size () ;
        worker = Lwt.return_unit ;
      } in
    Canceler.on_cancel st.canceler begin fun () ->
      Lwt_pipe.close st.messages ;
      Lwt.return_unit
    end ;
    st.worker <-
      Lwt_utils.worker "writer"
        (fun () -> worker_loop st)
        (fun () -> Canceler.cancel st.canceler) ;
    st

  let shutdown st =
    Canceler.cancel st.canceler >>= fun () ->
    st.worker

end

type 'msg t = {
  conn : connection ;
  reader : 'msg Reader.t ;
  writer : 'msg Writer.t ;
}

let pp ppf { conn } = Connection_info.pp ppf conn.info
let info { conn } = conn.info

let accept
    ?incoming_message_queue_size ?outgoing_message_queue_size
    (fd, info, cryptobox_data) encoding =
  Lwt_utils.protect begin fun () ->
    Ack.write fd cryptobox_data Ack >>=? fun () ->
    Ack.read fd cryptobox_data
  end ~on_error:begin fun err ->
    P2p_io_scheduler.close fd >>= fun _ ->
    match err with
    | [ P2p_io_scheduler.Connection_closed ] -> fail Rejected
    | [ Decipher_error ] -> fail Invalid_auth
    | err -> Lwt.return (Error err)
  end >>=? fun accepted ->
  fail_unless accepted Rejected >>=? fun () ->
  let canceler = Canceler.create () in
  let conn = { fd ; info ; cryptobox_data } in
  let reader =
    Reader.run ?size:incoming_message_queue_size conn encoding canceler
  and writer =
    Writer.run ?size:outgoing_message_queue_size conn encoding canceler in
  let conn = { conn ; reader ; writer } in
  Canceler.on_cancel canceler begin fun () ->
    P2p_io_scheduler.close fd >>= fun _ ->
    Lwt.return_unit
  end ;
  return conn

exception Not_available
exception Connection_closed

let catch_closed_pipe f =
  Lwt.catch f begin function
    | Lwt_pipe.Closed -> fail P2p_io_scheduler.Connection_closed
    | exn -> fail (Exn exn)
  end

let write { writer } msg =
  catch_closed_pipe begin fun () ->
    Lwt_pipe.push writer.messages (msg, None) >>= return
  end
let write_sync { writer } msg =
  catch_closed_pipe begin fun () ->
    let waiter, wakener = Lwt.wait () in
    Lwt_pipe.push writer.messages (msg, Some wakener) >>= fun () ->
    waiter
  end
let write_now { writer } msg =
  try Ok (Lwt_pipe.push_now writer.messages (msg, None))
  with Lwt_pipe.Closed -> Error [P2p_io_scheduler.Connection_closed]

let is_readable { reader } =
  not (Lwt_pipe.is_empty reader.messages)
let wait_readable { reader } =
  catch_closed_pipe begin fun () ->
    Lwt_pipe.values_available reader.messages >>= return
  end
let read { reader } =
  catch_closed_pipe begin fun () ->
    Lwt_pipe.pop reader.messages
  end
let read_now { reader } =
  try Lwt_pipe.pop_now reader.messages
  with Lwt_pipe.Closed -> Some (Error [P2p_io_scheduler.Connection_closed])

let stat { conn = { fd } } = P2p_io_scheduler.stat fd

let close ?(wait = false) st =
  begin
    if not wait then Lwt.return_unit
    else begin
      Lwt_pipe.close st.reader.messages ;
      Lwt_pipe.close st.writer.messages ;
      st.writer.worker
    end
  end >>= fun () ->
  Reader.shutdown st.reader >>= fun () ->
  Writer.shutdown st.writer >>= fun () ->
  P2p_io_scheduler.close st.conn.fd >>= fun _ ->
  Lwt.return_unit