# nimbus-eth1
# 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.

## Aristo DB -- a Patricia Trie with labeled edges
## ===============================================
##
## These data structures allow to overlay the *Patricia Trie* with *Merkel
## Trie* hashes. See the `README.md` in the `aristo` folder for documentation.
##
## Some semantic explanations;
##
## * HashKey, NodeRef etc. refer to the standard/legacy `Merkle Patricia Tree`
## * VertexID, VertexRef, etc. refer to the `Aristo Trie`
##
{.push raises: [].}

import
  std/[hashes, sets, tables],
  eth/common,
  results,
  ./aristo_constants,
  ./aristo_desc/[desc_error, desc_identifiers, desc_structural]

from ./aristo_desc/desc_backend
  import BackendRef

# Not auto-exporting backend
export
  aristo_constants, desc_error, desc_identifiers, desc_structural

type
  AristoTxRef* = ref object
    ## Transaction descriptor
    db*: AristoDbRef                  ## Database descriptor
    parent*: AristoTxRef              ## Previous transaction
    txUid*: uint                      ## Unique ID among transactions
    level*: int                       ## Stack index for this transaction

  DudesRef = ref object
    case rwOk: bool
    of true:
      roDudes: HashSet[AristoDbRef]   ## Read-only peers
    else:
      rwDb: AristoDbRef               ## Link to writable descriptor

  AristoDbRef* = ref AristoDbObj
  AristoDbObj* = object
    ## Three tier database object supporting distributed instances.
    top*: LayerRef                    ## Database working layer, mutable
    stack*: seq[LayerRef]             ## Stashed immutable parent layers
    roFilter*: FilterRef              ## Apply read filter (locks writing)
    backend*: BackendRef              ## Backend database (may well be `nil`)

    txRef*: AristoTxRef               ## Latest active transaction
    txUidGen*: uint                   ## Tx-relative unique number generator
    dudes: DudesRef                   ## Related DB descriptors

    # Debugging data below, might go away in future
    xMap*: Table[HashLabel,VertexID]  ## For pretty printing, extends `pAmk`

  AristoDbAction* = proc(db: AristoDbRef) {.gcsafe, raises: [CatchableError].}
    ## Generic call back function/closure.

# ------------------------------------------------------------------------------
# Public helpers
# ------------------------------------------------------------------------------

func getOrVoid*[W](tab: Table[W,VertexRef]; w: W): VertexRef =
  tab.getOrDefault(w, VertexRef(nil))

func getOrVoid*[W](tab: Table[W,HashLabel]; w: W): HashLabel =
  tab.getOrDefault(w, VOID_HASH_LABEL)

func getOrVoid*[W](tab: Table[W,HashKey]; w: W): HashKey =
  tab.getOrDefault(w, VOID_HASH_KEY)

func getOrVoid*[W](tab: Table[W,VertexID]; w: W): VertexID =
  tab.getOrDefault(w, VertexID(0))

# --------

func isValid*(vtx: VertexRef): bool =
  vtx != VertexRef(nil) 

func isValid*(nd: NodeRef): bool =
  nd != NodeRef(nil)

func isValid*(pld: PayloadRef): bool =
  pld != PayloadRef(nil)

func isValid*(filter: FilterRef): bool =
  filter != FilterRef(nil)

func isValid*(key: HashKey): bool =
  key != VOID_HASH_KEY

func isValid*(lbl: HashLabel): bool =
  lbl != VOID_HASH_LABEL

func isValid*(vid: VertexID): bool =
  vid != VertexID(0)

func isValid*(qid: QueueID): bool =
  qid != QueueID(0)

func isValid*(fid: FilterID): bool =
  fid != FilterID(0)

# ------------------------------------------------------------------------------
# Public functions, miscellaneous
# ------------------------------------------------------------------------------

# Hash set helper
func hash*(db: AristoDbRef): Hash =
  ## Table/KeyedQueue/HashSet mixin
  cast[pointer](db).hash

# Note that the below `init()` function cannot go into `desc_identifiers` as
# this would result in a circular import.
func init*(key: var HashKey; data: openArray[byte]): bool =
  ## Import argument `data` into `key` which must have length either `32`, or
  ## `0`. The latter case is equivalent to an all zero byte array of size `32`.
  if data.len == 32:
    (addr key.ByteArray32[0]).copyMem(unsafeAddr data[0], data.len)
    return true
  if data.len == 0:
    key = VOID_HASH_KEY
    return true

# ------------------------------------------------------------------------------
# Public functions, `dude` related
# ------------------------------------------------------------------------------

func isCentre*(db: AristoDbRef): bool =
  ## This function returns `true` is the argument `db` is the centre (see
  ## comments on `reCentre()` for details.)
  ##
  db.dudes.isNil or db.dudes.rwOk

func getCentre*(db: AristoDbRef): AristoDbRef =
  ## Get the centre descriptor among all other descriptors accessing the same
  ## backend database (see comments on `reCentre()` for details.)
  ##
  if db.dudes.isNil or db.dudes.rwOk:
    db
  else:
    db.dudes.rwDb

proc reCentre*(db: AristoDbRef) =
  ## Re-focus the `db` argument descriptor so that it becomes the centre.
  ## Nothing is done if the `db` descriptor is the centre, already.
  ##
  ## With several descriptors accessing the same backend database there is a
  ## single one that has write permission for the backend (regardless whether
  ## there is a backend, at all.) The descriptor entity with write permission
  ## is called *the centre*.
  ##
  ## After invoking `reCentre()`, the argument database `db` can only be
  ## destructed by `finish()` which also destructs all other descriptors
  ## accessing the same backend database. Descriptors where `isCentre()`
  ## returns `false` must be single destructed with `forget()`.
  ##
  if not db.isCentre:
    let parent = db.dudes.rwDb

    # Steal dudes list from parent, make the rw-parent a read-only dude
    db.dudes = parent.dudes
    parent.dudes = DudesRef(rwOk: false, rwDb: db)

    # Exclude self
    db.dudes.roDudes.excl db

    # Update dudes
    for w in db.dudes.roDudes:
      # Let all other dudes refer to this one
      w.dudes.rwDb = db

    # Update dudes list (parent was alredy updated)
    db.dudes.roDudes.incl parent


proc fork*(
    db: AristoDbRef;
    rawToplayer = false;
      ): Result[AristoDbRef,AristoError] =
  ## This function creates a new empty descriptor accessing the same backend
  ## (if any) database as the argument `db`. This new descriptor joins the
  ## list of descriptors accessing the same backend database.
  ##
  ## After use, any unused non centre descriptor should be destructed via
  ## `forget()`. Not doing so will not only hold memory ressources but might
  ## also cost computing ressources for maintaining and updating backend
  ## filters when writing to the backend database .
  ##
  ## If the argument `rawToplayer` is set `true` the function will provide an
  ## uninitalised and inconsistent (!) top layer. This setting avoids some
  ## database lookup for cases where the top layer is redefined anyway.
  ##
  let clone = AristoDbRef(
    top:      LayerRef(),
    backend:  db.backend)

  if not rawToplayer:
    let rc = clone.backend.getIdgFn()
    if rc.isOk:
      clone.top.vGen = rc.value
    elif rc.error != GetIdgNotFound:
      return err(rc.error)

  # Update dudes list
  if db.dudes.isNil:
    clone.dudes = DudesRef(rwOk: false, rwDb: db)
    db.dudes = DudesRef(rwOk: true, roDudes: [clone].toHashSet)
  else:
    let parent = if db.dudes.rwOk: db else: db.dudes.rwDb
    clone.dudes = DudesRef(rwOk: false, rwDb: parent)
    parent.dudes.roDudes.incl clone

  ok clone

iterator forked*(db: AristoDbRef): AristoDbRef =
  ## Interate over all non centre descriptors (see comments on `reCentre()`
  ## for details.)
  if not db.dudes.isNil:
    for dude in db.getCentre.dudes.roDudes.items:
      yield dude

func nForked*(db: AristoDbRef): int =
  ## Returns the number of non centre descriptors (see comments on `reCentre()`
  ## for details.) This function is a fast version of `db.forked.toSeq.len`.
  let parent = db.getCentre
  if not parent.dudes.isNil:
    return db.getCentre.dudes.roDudes.len


proc forget*(db: AristoDbRef): Result[void,AristoError] =
  ## Destruct the non centre argument `db` descriptor (see comments on
  ## `reCentre()` for details.)
  ##
  ## A non centre descriptor should always be destructed after use (see also
  ## comments on `fork()`.)
  ##
  if db.isCentre:
    return err(NotAllowedOnCentre)

  # Unlink argument `db`
  let parent = db.dudes.rwDb
  if parent.dudes.roDudes.len < 2:
    parent.dudes = DudesRef(nil)
  else:
    db.dudes.rwDb.dudes.roDudes.excl db

  # Clear descriptor so it would not do harm if used wrongly
  db[] = AristoDbObj(top: LayerRef())
  ok()

proc forgetOthers*(db: AristoDbRef): Result[void,AristoError] =
  ## For the centre argument `db` descriptor (see comments on `reCentre()`
  ## for details), destruct all other descriptors accessing the same backend.
  ##
  if not db.isCentre:
    return err(MustBeOnCentre)

  if not db.dudes.isNil:
    for dude in db.dudes.roDudes.items:
      dude[] = AristoDbObj(top: LayerRef())

    db.dudes = DudesRef(nil)
  ok()

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