# nimbus-eth1
# Copyright (c) 2023-2024 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.

{.push raises: [].}

import
  eth/common,
  results,
  "."/[aristo_desc, aristo_get, aristo_serialise]

proc putKeyAtLevel(
    db: AristoDbRef, rvid: RootedVertexID, key: HashKey, level: int
): Result[void, AristoError] =
  ## Store a hash key in the given layer or directly to the underlying database
  ## which helps ensure that memory usage is proportional to the pending change
  ## set (vertex data may have been committed to disk without computing the
  ## corresponding hash!)
  if level == -2:
    let be = db.backend
    doAssert be != nil, "source data is from the backend"
    # TODO long-running batch here?
    let writeBatch = ?be.putBegFn()
    be.putKeyFn(writeBatch, rvid, key)
    ?be.putEndFn writeBatch
    ok()
  else:
    db.deltaAtLevel(level).kMap[rvid] = key
    ok()

func maxLevel(cur, other: int): int =
  # Compare two levels and return the topmost in the stack, taking into account
  # the odd reversal of order around the zero point
  if cur < 0:
    max(cur, other) # >= 0 is always more topmost than <0
  elif other < 0:
    cur
  else:
    min(cur, other) # Here the order is reversed and 0 is the top layer

proc computeKeyImpl(
    db: AristoDbRef;                  # Database, top layer
    rvid: RootedVertexID;             # Vertex to convert
      ): Result[(HashKey, int), AristoError] =
  ## Compute the key for an arbitrary vertex ID. If successful, the length of
  ## the resulting key might be smaller than 32. If it is used as a root vertex
  ## state/hash, it must be converted to a `Hash256` (using (`.to(Hash256)`) as
  ## in `db.computeKey(rvid).value.to(Hash256)` which always results in a
  ## 32 byte value.

  db.getKeyRc(rvid).isErrOr:
    # Value cached either in layers or database
    return ok value
  let (vtx, vl) = ? db.getVtxRc rvid

  # Top-most level of all the verticies this hash compution depends on
  var level = vl

  # TODO this is the same code as when serializing NodeRef, without the NodeRef
  var writer = initRlpWriter()

  case vtx.vType:
  of Leaf:
    writer.startList(2)
    writer.append(vtx.lPfx.toHexPrefix(isLeaf = true))

    case vtx.lData.pType
    of AccountData:
      let
        stoID = vtx.lData.stoID
        skey =
          if stoID.isValid:
            let (skey, sl) = ?db.computeKeyImpl((stoID, stoID))
            level = maxLevel(level, sl)
            skey
          else:
            VOID_HASH_KEY

      writer.append(encode Account(
        nonce:       vtx.lData.account.nonce,
        balance:     vtx.lData.account.balance,
        storageRoot: skey.to(Hash256),
        codeHash:    vtx.lData.account.codeHash)
      )
    of RawData:
      writer.append(vtx.lData.rawBlob)
    of StoData:
      # TODO avoid memory allocation when encoding storage data
      writer.append(rlp.encode(vtx.lData.stoData))

  of Branch:
    template writeBranch(w: var RlpWriter) =
      w.startList(17)
      for n in 0..15:
        let vid = vtx.bVid[n]
        if vid.isValid:
          let (bkey, bl) = ?db.computeKeyImpl((rvid.root, vid))
          level = maxLevel(level, bl)
          w.append(bkey)
        else:
          w.append(VOID_HASH_KEY)
      w.append EmptyBlob
    if vtx.ePfx.len > 0: # Extension node
      var bwriter = initRlpWriter()
      writeBranch(bwriter)

      writer.startList(2)
      writer.append(vtx.ePfx.toHexPrefix(isleaf = false))
      writer.append(bwriter.finish().digestTo(HashKey))
    else:
      writeBranch(writer)

  let h = writer.finish().digestTo(HashKey)

  # Cache the hash int the same storage layer as the the top-most value that it
  # depends on (recursively) - this could be an ephemeral in-memory layer or the
  # underlying database backend - typically, values closer to the root are more
  # likely to live in an in-memory layer since any leaf change will lead to the
  # root key also changing while leaves that have never been hashed will see
  # their hash being saved directly to the backend.
  ? db.putKeyAtLevel(rvid, h, level)

  ok (h, level)

proc computeKey*(
    db: AristoDbRef;                  # Database, top layer
    rvid: RootedVertexID;             # Vertex to convert
      ): Result[HashKey, AristoError] =
  ok (?computeKeyImpl(db, rvid))[0]

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# End
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