# Nimbus
# Copyright (c) 2021 Status Research & Development GmbH
# Licensed under either of
#  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
#    http://www.apache.org/licenses/LICENSE-2.0)
#  * MIT license ([LICENSE-MIT](LICENSE-MIT) or
#    http://opensource.org/licenses/MIT)
# at your option. This file may not be copied, modified, or distributed
# except according to those terms.

## This module fetches the Ethereum account state trie from network peers by
## traversing leaves of the trie in leaf path order, making network requests
## using the `snap` protocol.

import
  std/sequtils,
  chronos,
  eth/[common, p2p, trie/trie_defs],
  stew/interval_set,
  "../../.."/[protocol, protocol/trace_config],
  "../.."/[constants, range_desc, worker_desc],
  ./com_error

{.push raises: [Defect].}

logScope:
  topics = "snap-fetch"

type
  GetAccountRange* = object
    data*: PackedAccountRange             ## Re-packed reply data
    withStorage*: seq[AccountSlotsHeader] ## Accounts with non-idle storage root

# ------------------------------------------------------------------------------
# Private functions
# ------------------------------------------------------------------------------

proc getAccountRangeReq(
    buddy: SnapBuddyRef;
    root: Hash256;
    iv: NodeTagRange;
    pivot: string;
      ): Future[Result[Option[SnapAccountRange],void]] {.async.} =
  let
    peer = buddy.peer
  try:
    let reply = await peer.getAccountRange(
      root, iv.minPt.to(Hash256), iv.maxPt.to(Hash256), fetchRequestBytesLimit)
    return ok(reply)
  except CatchableError as e:
    trace trSnapRecvError & "waiting for GetAccountRange reply", peer, pivot,
      error=e.msg
    return err()

# ------------------------------------------------------------------------------
# Public functions
# ------------------------------------------------------------------------------

proc getAccountRange*(
    buddy: SnapBuddyRef;
    stateRoot: Hash256;         ## Current DB base (see `pivot` for logging)
    iv: NodeTagRange;           ## Range to be fetched
    pivot: string;              ## For logging, instead of `stateRoot`
      ): Future[Result[GetAccountRange,ComError]] {.async.} =
  ## Fetch data using the `snap#` protocol, returns the range covered.
  let
    peer = buddy.peer
  if trSnapTracePacketsOk:
    trace trSnapSendSending & "GetAccountRange", peer, pivot, accRange=iv

  var dd = block:
    let rc = await buddy.getAccountRangeReq(stateRoot, iv, pivot)
    if rc.isErr:
      return err(ComNetworkProblem)
    if rc.value.isNone:
      trace trSnapRecvTimeoutWaiting & "for AccountRange", peer, pivot
      return err(ComResponseTimeout)
    let snAccRange = rc.value.get
    GetAccountRange(
      data:        PackedAccountRange(
        proof:     snAccRange.proof,
        accounts:  snAccRange.accounts
          # Re-pack accounts data
          .mapIt(PackedAccount(
            accKey:  it.accHash.to(NodeKey),
            accBlob: it.accBody.encode))),
      withStorage: snAccRange.accounts
        # Collect accounts with non-empty storage
        .filterIt(it.accBody.storageRoot != emptyRlpHash).mapIt(
          AccountSlotsHeader(
            accKey:      it.accHash.to(NodeKey),
            storageRoot: it.accBody.storageRoot)))
  let
    nAccounts = dd.data.accounts.len
    nProof = dd.data.proof.len

  if nAccounts == 0:
    # github.com/ethereum/devp2p/blob/master/caps/snap.md#getaccountrange-0x00:
    # Notes:
    # * Nodes must always respond to the query.
    # * If the node does not have the state for the requested state root, it
    #   must return an empty reply. It is the responsibility of the caller to
    #   query an state not older than 128 blocks.
    # * The responding node is allowed to return less data than requested (own
    #   QoS limits), but the node must return at least one account. If no
    #   accounts exist between startingHash and limitHash, then the first (if
    #   any) account after limitHash must be provided.
    if nProof == 0:
      # Maybe try another peer
      trace trSnapRecvReceived & "empty AccountRange", peer, pivot,
        nAccounts, nProof, accRange="n/a", reqRange=iv
      return err(ComNoAccountsForStateRoot)

    # So there is no data and a proof.
    trace trSnapRecvReceived & "terminal AccountRange", peer, pivot, nAccounts,
      nProof, accRange=NodeTagRange.new(iv.minPt, high(NodeTag)), reqRange=iv
    return ok(dd)

  let (accMinPt, accMaxPt) = (
    dd.data.accounts[0].accKey.to(NodeTag),
    dd.data.accounts[^1].accKey.to(NodeTag))

  if accMinPt < iv.minPt:
    # Not allowed
    trace trSnapRecvProtocolViolation & "min too small in AccountRange", peer,
      pivot, nAccounts, nProof, accRange=NodeTagRange.new(accMinPt, accMaxPt),
      reqRange=iv
    return err(ComAccountsMinTooSmall)

  if iv.maxPt < accMaxPt:
    # github.com/ethereum/devp2p/blob/master/caps/snap.md#getaccountrange-0x00:
    # Notes:
    # * [..]
    # * [..]
    # * [..] If no accounts exist between startingHash and limitHash, then the
    #   first (if any) account after limitHash must be provided.
    if 1 < nAccounts:
      # Geth always seems to allow the last account to be larger than the
      # limit (seen with Geth/v1.10.18-unstable-4b309c70-20220517.)
      if iv.maxPt < dd.data.accounts[^2].accKey.to(NodeTag):
        # The second largest should not excceed the top one requested.
        trace trSnapRecvProtocolViolation & "AccountRange top exceeded", peer,
          pivot, nAccounts, nProof,
          accRange=NodeTagRange.new(iv.minPt, accMaxPt), reqRange=iv
        return err(ComAccountsMaxTooLarge)

  trace trSnapRecvReceived & "AccountRange", peer, pivot, nAccounts, nProof,
    accRange=NodeTagRange.new(accMinPt, accMaxPt), reqRange=iv

  return ok(dd)

# ------------------------------------------------------------------------------
# End
# ------------------------------------------------------------------------------