nimbus-eth2/beacon_chain/spec/validator.nim

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

# Helpers and functions pertaining to managing the validator set

import
  options,
  eth_common,
  ./crypto, ./datatypes, ./digest, ./helpers

func min_empty_validator_index(validators: seq[ValidatorRecord], current_slot: uint64): Option[int] =
  for i, v in validators:
      if v.balance == 0 and v.last_status_change_slot + DELETION_PERIOD.uint64 <= current_slot:
          return some(i)

func get_new_validators*(current_validators: seq[ValidatorRecord],
                         fork_data: ForkData,
                         pubkey: ValidatorPubKey,
                         deposit: uint64,
                         proof_of_possession: seq[byte],
                         withdrawal_credentials: Eth2Digest,
                         randao_commitment: Eth2Digest,
                         status: ValidatorStatusCodes,
                         current_slot: uint64
                         ): tuple[validators: seq[ValidatorRecord], index: int] =
  # TODO Spec candidate: inefficient API
  #
  # Check that validator really did register
  # let signed_message = signed_message = bytes32(pubkey) + withdrawal_credentials + randao_commitment
  # assert BLSVerify(pub=pubkey,
  #                  msg=hash(signed_message),
  #                  sig=proof_of_possession,
  # domain=get_domain(
  #     fork_data,
  #     current_slot,
  #     DOMAIN_DEPOSIT
  # ))

  var new_validators = current_validators

  for index, val in new_validators.mpairs():
    if val.pubkey == pubkey:
      # assert deposit_size >= MIN_TOPUP_SIZE
      # assert val.status != WITHDRAWN
      # assert val.withdrawal_credentials == withdrawal_credentials

      val.balance.inc(deposit.int)
      return (new_validators, index)

  # new validator
  let
    rec = ValidatorRecord(
      pubkey: pubkey,
      withdrawal_credentials: withdrawal_credentials,
      randao_commitment: randao_commitment,
      randao_skips: 0,
      balance: deposit,
      status: status,
      last_status_change_slot: current_slot,
      exit_seq: 0
    )

  let index = min_empty_validator_index(new_validators, current_slot)
  if index.isNone:
    new_validators.add(rec)
    (new_validators, len(new_validators) - 1)
  else:
    new_validators[index.get()] = rec
    (new_validators, index.get())

func get_active_validator_indices*(validators: openArray[ValidatorRecord]): seq[Uint24] =
  ## Select the active validators
  for idx, val in validators:
    if val.status == ACTIVE or val.status == PENDING_EXIT:
      result.add idx.Uint24

func get_new_shuffling*(seed: Eth2Digest,
                        validators: openArray[ValidatorRecord],
                        crosslinking_start_shard: int
                        ): array[EPOCH_LENGTH, seq[ShardAndCommittee]] =
  ## Split up validators into groups at the start of every epoch,
  ## determining at what height they can make attestations and what shard they are making crosslinks for
  ## Implementation should do the following: http://vitalik.ca/files/ShuffleAndAssign.png

  let
    active_validators = get_active_validator_indices(validators)
    committees_per_slot = clamp(
      len(active_validators) div EPOCH_LENGTH div TARGET_COMMITTEE_SIZE,
      1, SHARD_COUNT div EPOCH_LENGTH)
    # Shuffle with seed
    shuffled_active_validator_indices = shuffle(active_validators, seed)
    # Split the shuffled list into cycle_length pieces
    validators_per_slot = split(shuffled_active_validator_indices, EPOCH_LENGTH)

  assert validators_per_slot.len() == EPOCH_LENGTH # what split should do..

  for slot, slot_indices in validators_per_slot:
    let
      shard_indices = split(slot_indices, committees_per_slot)
      shard_id_start = crosslinking_start_shard + slot * committees_per_slot

    var committees = newSeq[ShardAndCommittee](shard_indices.len)
    for shard_position, indices in shard_indices:
      committees[shard_position].shard =
        uint64(shard_id_start + shard_position) mod SHARD_COUNT
      committees[shard_position].committee = indices

    result[slot] = committees