# beacon_chain
# Copyright (c) 2022 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.

when (NimMajor, NimMinor) < (1, 4):
  {.push raises: [Defect].}
else:
  {.push raises: [].}

import std/macros
import metrics
import ../beacon_node

from eth/async_utils import awaitWithTimeout
from ../spec/datatypes/bellatrix import SignedBeaconBlock
from ../spec/mev/rest_bellatrix_mev_calls import submitBlindedBlock

const
  BUILDER_BLOCK_SUBMISSION_DELAY_TOLERANCE = 4.seconds

declareCounter beacon_block_builder_proposed,
  "Number of beacon chain blocks produced using an external block builder"

func getFieldNames*(x: typedesc[auto]): seq[string] {.compileTime.} =
  var res: seq[string]
  for name, _ in fieldPairs(default(x)):
    res.add name
  res

macro copyFields*(
    dst: untyped, src: untyped, fieldNames: static[seq[string]]): untyped =
  result = newStmtList()
  for name in fieldNames:
    if name notin [
        # These fields are the ones which vary between the blinded and
        # unblinded objects, and can't simply be copied.
        "transactions_root", "execution_payload",
        "execution_payload_header", "body"]:
      # TODO use stew/assign2
      result.add newAssignment(
        newDotExpr(dst, ident(name)), newDotExpr(src, ident(name)))

proc unblindAndRouteBlockMEV*(
    node: BeaconNode, blindedBlock: SignedBlindedBeaconBlock):
    Future[Result[Opt[BlockRef], string]] {.async.} =
  # By time submitBlindedBlock is called, must already have done slashing
  # protection check
  let unblindedPayload =
    try:
      awaitWithTimeout(
          node.payloadBuilderRestClient.submitBlindedBlock(blindedBlock),
          BUILDER_BLOCK_SUBMISSION_DELAY_TOLERANCE):
        return err("Submitting blinded block timed out")
      # From here on, including error paths, disallow local EL production by
      # returning Opt.some, regardless of whether on head or newBlock.
    except RestDecodingError as exc:
      return err("REST decoding error submitting blinded block: " & exc.msg)
    except CatchableError as exc:
      return err("exception in submitBlindedBlock: " & exc.msg)

  const httpOk = 200
  if unblindedPayload.status == httpOk:
    if  hash_tree_root(
          blindedBlock.message.body.execution_payload_header) !=
        hash_tree_root(unblindedPayload.data.data):
      debug "unblindAndRouteBlockMEV: unblinded payload doesn't match blinded payload",
        blindedPayload =
          blindedBlock.message.body.execution_payload_header
    else:
      # Signature provided is consistent with unblinded execution payload,
      # so construct full beacon block
      # https://github.com/ethereum/builder-specs/blob/v0.2.0/specs/validator.md#block-proposal
      var signedBlock = bellatrix.SignedBeaconBlock(
        signature: blindedBlock.signature)
      copyFields(
        signedBlock.message, blindedBlock.message,
        getFieldNames(typeof(signedBlock.message)))
      copyFields(
        signedBlock.message.body, blindedBlock.message.body,
        getFieldNames(typeof(signedBlock.message.body)))
      signedBlock.message.body.execution_payload = unblindedPayload.data.data

      signedBlock.root = hash_tree_root(signedBlock.message)

      doAssert signedBlock.root == hash_tree_root(blindedBlock.message)

      debug "unblindAndRouteBlockMEV: proposing unblinded block",
        blck = shortLog(signedBlock)

      let newBlockRef =
        (await node.router.routeSignedBeaconBlock(signedBlock)).valueOr:
          # submitBlindedBlock has run, so don't allow fallback to run
          return err("routeSignedBeaconBlock error") # Errors logged in router

      if newBlockRef.isSome:
        beacon_block_builder_proposed.inc()
        notice "Block proposed (MEV)",
          blockRoot = shortLog(signedBlock.root), blck = shortLog(signedBlock),
          signature = shortLog(signedBlock.signature)

      return ok newBlockRef
  else:
    debug "unblindAndRouteBlockMEV: submitBlindedBlock failed",
      blindedBlock, payloadStatus = unblindedPayload.status

  # https://github.com/ethereum/builder-specs/blob/v0.2.0/specs/validator.md#proposer-slashing
  # This means if a validator publishes a signature for a
  # `BlindedBeaconBlock` (via a dissemination of a
  # `SignedBlindedBeaconBlock`) then the validator **MUST** not use the
  # local build process as a fallback, even in the event of some failure
  # with the external buildernetwork.
  return err("unblindAndRouteBlockMEV error")