# Copyright (c) 2018-2023 Status Research & Development GmbH
# Licensed and distributed under either of
#   * MIT license (license terms in the root directory or at https://opensource.org/licenses/MIT).
#   * Apache v2 license (license terms in the root directory or at https://www.apache.org/licenses/LICENSE-2.0).
# at your option. This file may not be copied, modified, or distributed except according to those terms.

{.push raises: [].}

import
  chronos, chronicles, presto/client,
  "."/[rest_types, eth2_rest_serialization, rest_common]

proc getValidatorsActivity*(epoch: Epoch,
                            body: seq[ValidatorIndex]
                           ): RestPlainResponse {.
     rest, endpoint: "/nimbus/v1/validator/activity/{epoch}",
     meth: MethodPost.}

proc getTimesyncInifo*(body: RestNimbusTimestamp1): RestPlainResponse {.
     rest, endpoint: "/nimbus/v1/timesync", meth: MethodPost.}

proc getTimeOffset*(client: RestClientRef,
                    delay: Duration): Future[int64] {.async.} =
  let
    timestamp1 = getTimestamp()
    data = RestNimbusTimestamp1(timestamp1: timestamp1)
    resp = await client.getTimesyncInifo(data)
    timestamp4 = getTimestamp()

  return
    case resp.status
    of 200:
      if resp.contentType.isNone() or
         isWildCard(resp.contentType.get().mediaType) or
         resp.contentType.get().mediaType != ApplicationJsonMediaType:
        raise newException(RestError, "Missing or incorrect Content-Type")

      let stamps = decodeBytes(RestNimbusTimestamp2, resp.data,
                               resp.contentType).valueOr:
        raise newException(RestError, $error)

      trace "Time offset data",
            timestamp1 = timestamp1,
            timestamp2 = stamps.timestamp2,
            timestamp3 = stamps.timestamp3,
            timestamp4 = timestamp4,
            delay14 = delay.nanoseconds,
            delay23 = stamps.delay

      # t1 - time when we sent request.
      # t2 - time when remote server received request.
      # t3 - time when remote server sent response.
      # t4 - time when we received response.
      # delay14 = validator client processing delay.
      # delay23 = beacon node processing delay.
      #
      # Round-trip network delay `delta` = (t4 - t1) - (t3 - t2)
      # but with delays this will be:
      # `delta` = (t4 - t1 + delay14) - (t3 - t2 + delay23)
      # Estimated server time is t3 + (delta div 2)
      # Estimated clock skew `theta` = t3 + (delta div 2) - t4
      let
        delay14 = delay.nanoseconds
        delay23 = int64(stamps.delay)
        offset = (int64(stamps.timestamp2) - int64(timestamp1) +
                  int64(stamps.timestamp3) - int64(timestamp4) +
                  delay14 - delay23) div 2
      offset
    else:
      let error = decodeBytes(RestErrorMessage, resp.data,
                              resp.contentType).valueOr:
        let msg = "Incorrect response error format (" & $resp.status &
                  ") [" & $error & "]"
        raise (ref RestResponseError)(msg: msg, status: resp.status)
      let msg = "Error response (" & $resp.status & ") [" & error.message & "]"
      raise (ref RestResponseError)(
        msg: msg, status: error.code, message: error.message)