{.push raises: [Defect].}

import
  typetraits, tables,
  stew/[results, objects, endians2, io2],
  serialization, chronicles, snappy,
  eth/db/[kvstore, kvstore_sqlite3],
  ./spec/[datatypes, digest, crypto, state_transition, signatures],
  ./ssz/[ssz_serialization, merkleization],
  merkle_minimal, filepath

type
  DbSeq*[T] = object
    insertStmt: SqliteStmt[openArray[byte], void]
    selectStmt: SqliteStmt[int64, seq[byte]]
    recordCount: int64

  DbMap*[K, V] = object
    db: SqStoreRef
    keyspace: int

  DepositsSeq = DbSeq[DepositData]
  ImmutableValidatorDataSeq = seq[ImmutableValidatorData]
  ValidatorKeyToIndexMap = Table[ValidatorPubKey, ValidatorIndex]

  DepositsMerkleizer* = SszMerkleizer[depositContractLimit]

  BeaconChainDB* = ref object
    ## Database storing resolved blocks and states - resolved blocks are such
    ## blocks that form a chain back to the tail block.
    ##
    ## We assume that the database backend is working / not corrupt - as such,
    ## we will raise a Defect any time there is an issue. This should be
    ## revisited in the future, when/if the calling code safely can handle
    ## corruption of this kind.
    ##
    ## We do however make an effort not to crash on invalid data inside the
    ## database - this may have a number of "natural" causes such as switching
    ## between different versions of the client and accidentally using an old
    ## database.
    backend: KvStoreRef
    preset: RuntimePreset

    deposits*: DepositsSeq
    immutableValidatorData*: ImmutableValidatorDataSeq
    validatorKeyToIndex*: ValidatorKeyToIndexMap

    finalizedEth1DepositsMerkleizer*: DepositsMerkleizer
      ## A merkleizer keeping track of the `deposit_root` value obtained from
      ## Eth1 after finalizing blocks with ETH1_FOLLOW_DISTANCE confirmations.
      ## The value is used when voting for Eth1 heads.

    finalizedEth2DepositsMerkleizer*: DepositsMerkleizer
      ## A separate merkleizer which is advanced when the Eth2 chain finalizes.
      ## It will lag behind the "eth1 merkleizer". We use to produce merkle
      ## proofs for deposits when they are added to Eth2 blocks.

  Keyspaces* = enum
    defaultKeyspace = "kvstore"
    validatorIndexFromPubKey

  DbKeyKind = enum
    kHashToState
    kHashToBlock
    kHeadBlock
      ## Pointer to the most recent block selected by the fork choice
    kTailBlock
      ## Pointer to the earliest finalized block - this is the genesis block when
      ## the chain starts, but might advance as the database gets pruned
      ## TODO: determine how aggressively the database should be pruned. For a
      ##       healthy network sync, we probably need to store blocks at least
      ##       past the weak subjectivity period.
    kBlockSlotStateRoot
      ## BlockSlot -> state_root mapping
    kGenesisBlockRoot
      ## Immutable reference to the network genesis state
      ## (needed for satisfying requests to the beacon node API).
    kEth1PersistedTo
      ## The latest ETH1 block hash which satisfied the follow distance and
      ## had its deposits persisted to disk.
    kFinalizedEth1DepositsMarkleizer
      ## A merkleizer used to compute the `deposit_root` of all finalized
      ## deposits (i.e. deposits confirmed by ETH1_FOLLOW_DISTANCE blocks)
    kFinalizedEth2DepositsMarkleizer
      ## A merkleizer used for computing merkle proofs of deposits added
      ## to Eth2 blocks (it may lag behind the finalized deposits merkleizer).
    kHashToBlockSummary
      ## Cache of beacon block summaries - during startup when we construct the
      ## chain dag, loading full blocks takes a lot of time - the block
      ## summary contains a minimal snapshot of what's needed to instanciate
      ## the BlockRef tree.

  BeaconBlockSummary* = object
    slot*: Slot
    parent_root*: Eth2Digest

const
  maxDecompressedDbRecordSize = 16*1024*1024

# Subkeys essentially create "tables" within the key-value store by prefixing
# each entry with a table id

func subkey(kind: DbKeyKind): array[1, byte] =
  result[0] = byte ord(kind)

func subkey[N: static int](kind: DbKeyKind, key: array[N, byte]):
    array[N + 1, byte] =
  result[0] = byte ord(kind)
  result[1 .. ^1] = key

func subkey(kind: type BeaconState, key: Eth2Digest): auto =
  subkey(kHashToState, key.data)

func subkey(kind: type SignedBeaconBlock, key: Eth2Digest): auto =
  subkey(kHashToBlock, key.data)

func subkey(kind: type BeaconBlockSummary, key: Eth2Digest): auto =
  subkey(kHashToBlockSummary, key.data)

func subkey(root: Eth2Digest, slot: Slot): array[40, byte] =
  var ret: array[40, byte]
  # big endian to get a naturally ascending order on slots in sorted indices
  ret[0..<8] = toBytesBE(slot.uint64)
  # .. but 7 bytes should be enough for slots - in return, we get a nicely
  # rounded key length
  ret[0] = byte ord(kBlockSlotStateRoot)
  ret[8..<40] = root.data

  ret

template panic =
  # TODO: Could we recover from a corrupted database?
  #       Review all usages.
  raiseAssert "The database should not be corrupted"

proc init*[T](Seq: type DbSeq[T], db: SqStoreRef, name: string): Seq =
  db.exec("""
    CREATE TABLE IF NOT EXISTS """ & name & """(
       id INTEGER PRIMARY KEY,
       value BLOB
    );
  """).expect "working database"

  let
    insertStmt = db.prepareStmt(
      "INSERT INTO " & name & "(value) VALUES (?);",
      openArray[byte], void).expect("this is a valid statement")

    selectStmt = db.prepareStmt(
      "SELECT value FROM " & name & " WHERE id = ?;",
      int64, seq[byte]).expect("this is a valid statement")

    countStmt = db.prepareStmt(
      "SELECT COUNT(*) FROM " & name & ";",
      NoParams, int64).expect("this is a valid statement")

  var recordCount = int64 0
  let countQueryRes = countStmt.exec do (res: int64):
    recordCount = res

  let found = countQueryRes.expect("working database")
  if not found: panic()

  Seq(insertStmt: insertStmt,
      selectStmt: selectStmt,
      recordCount: recordCount)

proc add*[T](s: var DbSeq[T], val: T) =
  var bytes = SSZ.encode(val)
  s.insertStmt.exec(bytes).expect "working database"
  inc s.recordCount

template len*[T](s: DbSeq[T]): uint64 =
  s.recordCount.uint64

proc get*[T](s: DbSeq[T], idx: uint64): T =
  # This is used only locally
  let resultAddr = addr result

  let queryRes = s.selectStmt.exec(int64(idx) + 1) do (recordBytes: seq[byte]):
    try:
      resultAddr[] = decode(SSZ, recordBytes, T)
    except SerializationError:
      panic()

  let found = queryRes.expect("working database")
  if not found: panic()

proc createMap*(db: SqStoreRef, keyspace: int;
                K, V: distinct type): DbMap[K, V] =
  DbMap[K, V](db: db, keyspace: keyspace)

proc insert*[K, V](m: var DbMap[K, V], key: K, value: V) =
  m.db.put(m.keyspace, SSZ.encode key, SSZ.encode value).expect("working database")

proc contains*[K, V](m: DbMap[K, V], key: K): bool =
  contains(m.db, SSZ.encode key).expect("working database")

template insert*[K, V](t: var Table[K, V], key: K, value: V) =
  add(t, key, value)

proc produceDerivedData(deposit: DepositData,
                        preset: RuntimePreset,
                        validators: var ImmutableValidatorDataSeq,
                        validatorKeyToIndex: var ValidatorKeyToIndexMap,
                        finalizedEth1DepositsMerkleizer: var DepositsMerkleizer) =
  let htr = hash_tree_root(deposit)
  finalizedEth1DepositsMerkleizer.addChunk htr.data

  if verify_deposit_signature(preset, deposit):
    let pubkey = deposit.pubkey
    if pubkey notin validatorKeyToIndex:
      let idx = ValidatorIndex validators.len
      validators.add ImmutableValidatorData(
        pubkey: pubkey,
        withdrawal_credentials: deposit.withdrawal_credentials)
      validatorKeyToIndex.insert(pubkey, idx)

proc processDeposit*(db: BeaconChainDB, newDeposit: DepositData) =
  db.deposits.add newDeposit

  produceDerivedData(
    newDeposit,
    db.preset,
    db.immutableValidatorData,
    db.validatorKeyToIndex,
    db.finalizedEth1DepositsMerkleizer)

proc init*(T: type BeaconChainDB,
           preset: RuntimePreset,
           dir: string,
           inMemory = false): BeaconChainDB =
  if inMemory:
    # TODO
    # The inMemory store shuold offer the complete functionality
    # of the database-backed one (i.e. tracking of deposits and validators)
    T(backend: kvStore MemStoreRef.init(),
      preset: preset,
      finalizedEth1DepositsMerkleizer: init DepositsMerkleizer,
      finalizedEth2DepositsMerkleizer: init DepositsMerkleizer)
  else:
    let s = secureCreatePath(dir)
    doAssert s.isOk # TODO Handle this in a better way

    let sqliteStore = SqStoreRef.init(dir, "nbc", Keyspaces).expect(
      "working database")

    var
      immutableValidatorData = newSeq[ImmutableValidatorData]()
      validatorKeyToIndex = initTable[ValidatorPubKey, ValidatorIndex]()
      depositsSeq = DbSeq[DepositData].init(sqliteStore, "deposits")
      finalizedEth1DepositsMerkleizer = init DepositsMerkleizer
      finalizedEth2DepositsMerkleizer = init DepositsMerkleizer

    for i in 0 ..< depositsSeq.len:
      produceDerivedData(
        depositsSeq.get(i),
        preset,
        immutableValidatorData,
        validatorKeyToIndex,
        finalizedEth1DepositsMerkleizer)

    T(backend: kvStore sqliteStore,
      preset: preset,
      deposits: depositsSeq,
      immutableValidatorData: immutableValidatorData,
      validatorKeyToIndex: validatorKeyToIndex,
      finalizedEth1DepositsMerkleizer: finalizedEth1DepositsMerkleizer,
      finalizedEth2DepositsMerkleizer: finalizedEth2DepositsMerkleizer)

proc advanceTo*(merkleizer: var DepositsMerkleizer,
                db: BeaconChainDB,
                deposit_index: uint64) =
  for i in merkleizer.totalChunks ..< depositIndex:
    merkleizer.addChunk hash_tree_root(db.deposits.get(i)).data

proc snappyEncode(inp: openArray[byte]): seq[byte] =
  try:
    snappy.encode(inp)
  except CatchableError as err:
    raiseAssert err.msg

proc put(db: BeaconChainDB, key: openArray[byte], v: Eth2Digest) =
  db.backend.put(key, v.data).expect("working database")

proc put(db: BeaconChainDB, key: openArray[byte], v: auto) =
  db.backend.put(key, snappyEncode(SSZ.encode(v))).expect("working database")

proc get(db: BeaconChainDB, key: openArray[byte], T: type Eth2Digest): Opt[T] =
  var res: Opt[T]
  proc decode(data: openArray[byte]) =
    if data.len == 32:
      res.ok Eth2Digest(data: toArray(32, data))
    else:
      # If the data can't be deserialized, it could be because it's from a
      # version of the software that uses a different SSZ encoding
      warn "Unable to deserialize data, old database?",
       typ = name(T), dataLen = data.len
      discard

  discard db.backend.get(key, decode).expect("working database")

  res

type GetResult = enum
  found
  notFound
  corrupted

proc get[T](db: BeaconChainDB, key: openArray[byte], output: var T): GetResult =
  var status = GetResult.notFound

  # TODO address is needed because there's no way to express lifetimes in nim
  #      we'll use unsafeAddr to find the code later
  var outputPtr = unsafeAddr output # callback is local, ptr wont escape
  proc decode(data: openArray[byte]) =
    try:
      let decompressed = snappy.decode(data, maxDecompressedDbRecordSize)
      if decompressed.len > 0:
        outputPtr[] = SSZ.decode(decompressed, T, updateRoot = false)
        status = GetResult.found
      else:
        warn "Corrupt snappy record found in database", typ = name(T)
        status = GetResult.corrupted
    except SerializationError as e:
      # If the data can't be deserialized, it could be because it's from a
      # version of the software that uses a different SSZ encoding
      warn "Unable to deserialize data, old database?",
        err = e.msg, typ = name(T), dataLen = data.len
      status = GetResult.corrupted

  discard db.backend.get(key, decode).expect("working database")

  status

proc close*(db: BeaconChainDB) =
  discard db.backend.close()

func toBeaconBlockSummary(v: SomeBeaconBlock): BeaconBlockSummary =
  BeaconBlockSummary(
    slot: v.slot,
    parent_root: v.parent_root,
  )

proc putBlock*(db: BeaconChainDB, value: SignedBeaconBlock) =
  db.put(subkey(type value, value.root), value)
  db.put(subkey(BeaconBlockSummary, value.root), value.message.toBeaconBlockSummary())
proc putBlock*(db: BeaconChainDB, value: TrustedSignedBeaconBlock) =
  db.put(subkey(SignedBeaconBlock, value.root), value)
  db.put(subkey(BeaconBlockSummary, value.root), value.message.toBeaconBlockSummary())

proc putState*(db: BeaconChainDB, key: Eth2Digest, value: BeaconState) =
  # TODO prune old states - this is less easy than it seems as we never know
  #      when or if a particular state will become finalized.

  db.put(subkey(type value, key), value)

proc putState*(db: BeaconChainDB, value: BeaconState) =
  db.putState(hash_tree_root(value), value)

proc putStateRoot*(db: BeaconChainDB, root: Eth2Digest, slot: Slot,
    value: Eth2Digest) =
  db.put(subkey(root, slot), value)

proc delBlock*(db: BeaconChainDB, key: Eth2Digest) =
  db.backend.del(subkey(SignedBeaconBlock, key)).expect("working database")
  db.backend.del(subkey(BeaconBlockSummary, key)).expect("working database")

proc delState*(db: BeaconChainDB, key: Eth2Digest) =
  db.backend.del(subkey(BeaconState, key)).expect("working database")

proc delStateRoot*(db: BeaconChainDB, root: Eth2Digest, slot: Slot) =
  db.backend.del(subkey(root, slot)).expect("working database")

proc putHeadBlock*(db: BeaconChainDB, key: Eth2Digest) =
  db.put(subkey(kHeadBlock), key)

proc putTailBlock*(db: BeaconChainDB, key: Eth2Digest) =
  db.put(subkey(kTailBlock), key)

proc putGenesisBlockRoot*(db: BeaconChainDB, key: Eth2Digest) =
  db.put(subkey(kGenesisBlockRoot), key)

proc putEth1PersistedTo*(db: BeaconChainDB, key: Eth1Data) =
  db.put(subkey(kEth1PersistedTo), key)

proc getBlock*(db: BeaconChainDB, key: Eth2Digest): Opt[TrustedSignedBeaconBlock] =
  # We only store blocks that we trust in the database
  result.ok(TrustedSignedBeaconBlock())
  if db.get(subkey(SignedBeaconBlock, key), result.get) != GetResult.found:
    result.err()
  else:
    # set root after deserializing (so it doesn't get zeroed)
    result.get().root = key

proc getBlockSummary*(db: BeaconChainDB, key: Eth2Digest): Opt[BeaconBlockSummary] =
  # We only store blocks that we trust in the database
  result.ok(BeaconBlockSummary())
  if db.get(subkey(BeaconBlockSummary, key), result.get) != GetResult.found:
    result.err()

proc getState*(
    db: BeaconChainDB, key: Eth2Digest, output: var BeaconState,
    rollback: RollbackProc): bool =
  ## Load state into `output` - BeaconState is large so we want to avoid
  ## re-allocating it if possible
  ## Return `true` iff the entry was found in the database and `output` was
  ## overwritten.
  ## Rollback will be called only if output was partially written - if it was
  ## not found at all, rollback will not be called
  # TODO rollback is needed to deal with bug - use `noRollback` to ignore:
  #      https://github.com/nim-lang/Nim/issues/14126
  # TODO RVO is inefficient for large objects:
  #      https://github.com/nim-lang/Nim/issues/13879
  case db.get(subkey(BeaconState, key), output)
  of GetResult.found:
    true
  of GetResult.notFound:
    false
  of GetResult.corrupted:
    rollback(output)
    false

proc getStateRoot*(db: BeaconChainDB,
                   root: Eth2Digest,
                   slot: Slot): Opt[Eth2Digest] =
  db.get(subkey(root, slot), Eth2Digest)

proc getHeadBlock*(db: BeaconChainDB): Opt[Eth2Digest] =
  db.get(subkey(kHeadBlock), Eth2Digest)

proc getTailBlock*(db: BeaconChainDB): Opt[Eth2Digest] =
  db.get(subkey(kTailBlock), Eth2Digest)

proc getGenesisBlockRoot*(db: BeaconChainDB): Eth2Digest =
  db.get(subkey(kGenesisBlockRoot), Eth2Digest).expect(
    "The database must be seeded with the genesis state")

proc getEth1PersistedTo*(db: BeaconChainDB): Opt[Eth1Data] =
  result.ok(Eth1Data())
  if db.get(subkey(kEth1PersistedTo), result.get) != GetResult.found:
    result.err()

proc containsBlock*(db: BeaconChainDB, key: Eth2Digest): bool =
  db.backend.contains(subkey(SignedBeaconBlock, key)).expect("working database")

proc containsState*(db: BeaconChainDB, key: Eth2Digest): bool =
  db.backend.contains(subkey(BeaconState, key)).expect("working database")

iterator getAncestors*(db: BeaconChainDB, root: Eth2Digest):
    TrustedSignedBeaconBlock =
  ## Load a chain of ancestors for blck - returns a list of blocks with the
  ## oldest block last (blck will be at result[0]).
  ##
  ## The search will go on until the ancestor cannot be found.

  var
    res: TrustedSignedBeaconBlock
    root = root
  while db.get(subkey(SignedBeaconBlock, root), res) == GetResult.found:
    res.root = root
    yield res
    root = res.message.parent_root

iterator getAncestorSummaries*(db: BeaconChainDB, root: Eth2Digest):
    tuple[root: Eth2Digest, summary: BeaconBlockSummary] =
  ## Load a chain of ancestors for blck - returns a list of blocks with the
  ## oldest block last (blck will be at result[0]).
  ##
  ## The search will go on until the ancestor cannot be found.

  var
    res: tuple[root: Eth2Digest, summary: BeaconBlockSummary]
    tmp: TrustedSignedBeaconBlock
    root = root

  while true:
    if db.get(subkey(BeaconBlockSummary, root), res.summary) == GetResult.found:
      res.root = root
      yield res
    elif db.get(subkey(SignedBeaconBlock, root), tmp) == GetResult.found:
      res.summary = tmp.message.toBeaconBlockSummary()
      db.put(subkey(BeaconBlockSummary, root), res.summary)
      res.root = root
      yield res
    else:
      break

    root = res.summary.parent_root