# 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.

import
  std/[options, tables],
  results,
  ".."/[aristo_desc, aristo_desc/desc_backend],
  "."/[filter_merge, journal_scheduler]

type
  JournalOpsMod* = object
    ## Database journal instructions for storing or deleting filters.
    put*: seq[(QueueID,FilterRef)]
    scd*: QidSchedRef

  JournalOpsFetch* = object
    ## Database journal instructions for merge-fetching slots.
    fil*: FilterRef
    del*: JournalOpsMod

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

template getFilterOrReturn(be: BackendRef; qid: QueueID): FilterRef =
  let rc = be.getFilFn qid
  if rc.isErr:
    return err(rc.error)
  rc.value

template joinFiltersOrReturn(upper, lower: FilterRef): FilterRef =
  let rc = upper.merge lower
  if rc.isErr:
    return err(rc.error[1])
  rc.value

template getNextFidOrReturn(be: BackendRef; fid: Option[FilterID]): FilterID =
  ## Get next free filter ID, or exit function using this wrapper
  var nxtFid = fid.get(otherwise = FilterID(1))

  let qid = be.journal[0]
  if qid.isValid:
    let rc = be.getFilFn qid
    if rc.isErr:
      # Must exist when `qid` exists
      return err(rc.error)
    elif fid.isNone:
      # Stepwise increase is the default
      nxtFid = rc.value.fid + 1
    elif nxtFid <= rc.value.fid:
      # The bespoke filter IDs must be greater than the existing ones
      return err(FilQuBespokeFidTooSmall)

  nxtFid

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

proc journalOpsPushSlot*(
    be: BackendRef;                              # Database backend
    filter: FilterRef;                           # Filter to store
    fid: Option[FilterID];                       # Next filter ID (if any)
      ): Result[JournalOpsMod,AristoError] =
  ## Calculate backend instructions for storing the arguent `filter` on the
  ## argument backend `be`.
  ##
  ## The journal is not modified by this function.
  ##
  if be.journal.isNil:
    return err(FilQuSchedDisabled)

  # Calculate filter table queue update by slot addresses
  let
    qTop = be.journal[0]
    upd = be.journal.addItem

  # Update journal filters and calculate database update
  var
    instr = JournalOpsMod(scd: upd.journal)
    dbClear: seq[QueueID]
    hold: seq[FilterRef]
    saved = false

  # make sure that filter matches top entry (if any)
  if qTop.isValid:
    let top = be.getFilterOrReturn qTop
    if filter.trg != top.src:
      return err(FilTrgTopSrcMismatch)

  for act in upd.exec:
    case act.op:
    of Oops:
      return err(FilExecOops)

    of SaveQid:
      if saved:
        return err(FilExecDublicateSave)
      instr.put.add (act.qid, filter)
      saved = true

    of DelQid:
      instr.put.add (act.qid, FilterRef(nil))

    of HoldQid:
      # Push filter
      dbClear.add act.qid
      hold.add be.getFilterOrReturn act.qid

      # Merge additional journal filters into top filter
      for w in act.qid+1 .. act.xid:
        dbClear.add w
        let lower = be.getFilterOrReturn w
        hold[^1] = hold[^1].joinFiltersOrReturn lower

    of DequQid:
      if hold.len == 0:
        return err(FilExecStackUnderflow)
      var lower = hold.pop
      while 0 < hold.len:
        let upper = hold.pop
        lower = upper.joinFiltersOrReturn lower
      instr.put.add (act.qid, lower)
      for qid in dbClear:
        instr.put.add (qid, FilterRef(nil))
      dbClear.setLen(0)

  if not saved:
    return err(FilExecSaveMissing)

  # Set next filter ID
  filter.fid = be.getNextFidOrReturn fid

  ok instr


proc journalOpsFetchSlots*(
    be: BackendRef;                              # Database backend
    backSteps: int;                              # Backstep this many filters
      ): Result[JournalOpsFetch,AristoError] =
  ## This function returns the single filter obtained by squash merging the
  ## topmost `backSteps` filters on the backend journal fifo. Also, backend
  ## instructions are calculated and returned for deleting the extracted
  ## journal slots.
  ##
  ## The journal is not modified by this function.
  ##
  if be.journal.isNil:
    return err(FilQuSchedDisabled)
  if backSteps <= 0:
    return err(FilBackStepsExpected)

  # Get instructions
  let fetch = be.journal.fetchItems backSteps
  var instr = JournalOpsFetch(del: JournalOpsMod(scd: fetch.journal))

  # Follow `HoldQid` instructions and combine journal filters for sub-queues
  # and push intermediate results on the `hold` stack
  var hold: seq[FilterRef]
  for act in fetch.exec:
    if act.op != HoldQid:
      return err(FilExecHoldExpected)

    hold.add be.getFilterOrReturn act.qid
    instr.del.put.add (act.qid,FilterRef(nil))

    for qid in act.qid+1 .. act.xid:
      let lower = be.getFilterOrReturn qid
      instr.del.put.add (qid,FilterRef(nil))

      hold[^1] = hold[^1].joinFiltersOrReturn lower

  # Resolve `hold` stack
  if hold.len == 0:
    return err(FilExecStackUnderflow)

  var upper = hold.pop
  while 0 < hold.len:
    let lower = hold.pop

    upper = upper.joinFiltersOrReturn lower

  instr.fil = upper
  ok instr


proc journalOpsDeleteSlots*(
    be: BackendRef;                              # Database backend
    backSteps: int;                              # Backstep this many filters
      ): Result[JournalOpsMod,AristoError] =
  ## Calculate backend instructions for deleting the most recent `backSteps`
  ## slots on the journal. This is basically the deletion calculator part
  ## from `journalOpsFetchSlots()`.
  ##
  ## The journal is not modified by this function.
  ##
  if be.journal.isNil:
    return err(FilQuSchedDisabled)
  if backSteps <= 0:
    return err(FilBackStepsExpected)

  # Get instructions
  let fetch = be.journal.fetchItems backSteps
  var instr = JournalOpsMod(scd: fetch.journal)

  # Follow `HoldQid` instructions for producing the list of entries that
  # need to be deleted
  for act in fetch.exec:
    if act.op != HoldQid:
      return err(FilExecHoldExpected)
    for qid in act.qid .. act.xid:
      instr.put.add (qid,FilterRef(nil))

  ok instr

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