nim-codex/codex/slots/sampler/sampler.nim

## Nim-Codex
## Copyright (c) 2023 Status Research & Development GmbH
## Licensed under either of
##  * Apache License, version 2.0, ([LICENSE-APACHE](LICENSE-APACHE))
##  * MIT license ([LICENSE-MIT](LICENSE-MIT))
## at your option.
## This file may not be copied, modified, or distributed except according to
## those terms.

import std/sugar

import pkg/chronos
import pkg/questionable
import pkg/questionable/results
import pkg/stew/arrayops

import ../../logutils
import ../../market
import ../../blocktype as bt
import ../../merkletree
import ../../manifest
import ../../stores

import ../converters
import ../builder
import ../types
import ./utils

logScope:
  topics = "codex datasampler"

type
  DataSampler*[T, H] = ref object of RootObj
    index: Natural
    blockStore: BlockStore
    builder: SlotsBuilder[T, H]

func getCell*[T, H](
  self: DataSampler[T, H],
  blkBytes: seq[byte],
  blkCellIdx: Natural): seq[H] =

  let
    cellSize = self.builder.cellSize.uint64
    dataStart = cellSize * blkCellIdx.uint64
    dataEnd = dataStart + cellSize

  doAssert (dataEnd - dataStart) == cellSize, "Invalid cell size"

  blkBytes[dataStart ..< dataEnd].elements(H).toSeq()

proc getSample*[T, H](
  self: DataSampler[T, H],
  cellIdx: int,
  slotTreeCid: Cid,
  slotRoot: H): Future[?!Sample[H]] {.async.} =

  let
    cellsPerBlock = self.builder.numBlockCells
    blkCellIdx    = cellIdx.toCellInBlk(cellsPerBlock) # block cell index
    blkSlotIdx    = cellIdx.toBlkInSlot(cellsPerBlock) # slot tree index
    origBlockIdx  = self.builder.slotIndicies(self.index)[blkSlotIdx]  # convert to original dataset block index

  logScope:
    cellIdx       = cellIdx
    blkSlotIdx    = blkSlotIdx
    blkCellIdx    = blkCellIdx
    origBlockIdx  = origBlockIdx

  trace "Retrieving sample from block tree"
  let
    (_, proof) = (await self.blockStore.getCidAndProof(
      slotTreeCid, blkSlotIdx.Natural)).valueOr:
      return failure("Failed to get slot tree CID and proof")

    slotProof = proof.toVerifiableProof().valueOr:
      return failure("Failed to get verifiable proof")

    (bytes, blkTree) = (await self.builder.buildBlockTree(
      origBlockIdx, blkSlotIdx)).valueOr:
      return failure("Failed to build block tree")

    cellData = self.getCell(bytes, blkCellIdx)
    cellProof = blkTree.getProof(blkCellIdx).valueOr:
      return failure("Failed to get proof from block tree")

  success Sample[H](
    cellData: cellData,
    merklePaths: (cellProof.path & slotProof.path))

proc getProofInput*[T, H](
  self: DataSampler[T, H],
  entropy: ProofChallenge,
  nSamples: Natural): Future[?!ProofInputs[H]] {.async.} =
  ## Generate proofs as input to the proving circuit.
  ##

  let
    entropy = H.fromBytes(
      array[31, byte].initCopyFrom(entropy[0..30])) # truncate to 31 bytes, otherwise it _might_ be greater than mod

    verifyTree = self.builder.verifyTree.toFailure.valueOr:
      return failure("Failed to get verify tree")

    slotProof = verifyTree.getProof(self.index).valueOr:
      return failure("Failed to get slot proof")

    datasetRoot = verifyTree.root().valueOr:
      return failure("Failed to get dataset root")

    slotTreeCid = self.builder.manifest.slotRoots[self.index]
    slotRoot    = self.builder.slotRoots[self.index]
    cellIdxs    = entropy.cellIndices(
      slotRoot,
      self.builder.numSlotCells,
      nSamples)

  logScope:
    cells = cellIdxs

  trace "Collecting input for proof"
  let samples = collect(newSeq):
    for cellIdx in cellIdxs:
      (await self.getSample(cellIdx, slotTreeCid, slotRoot)).valueOr:
        return failure("Failed to get sample")

  success ProofInputs[H](
    entropy: entropy,
    datasetRoot: datasetRoot,
    slotProof: slotProof.path,
    nSlotsPerDataSet: self.builder.numSlots,
    nCellsPerSlot: self.builder.numSlotCells,
    slotRoot: slotRoot,
    slotIndex: self.index,
    samples: samples)

proc new*[T, H](
    _: type DataSampler[T, H],
    index: Natural,
    blockStore: BlockStore,
    builder: SlotsBuilder[T, H]): ?!DataSampler[T, H] =

  if index > builder.slotRoots.high:
    error "Slot index is out of range"
    return failure("Slot index is out of range")

  if not builder.verifiable:
    return failure("Cannot instantiate DataSampler for non-verifiable builder")

  success DataSampler[T, H](
    index: index,
    blockStore: blockStore,
    builder: builder)