import std/os
import std/times

import pkg/chronos
import pkg/questionable
import pkg/questionable/results
import pkg/sqlite3_abi
import pkg/stew/byteutils
from pkg/stew/results as stewResults import isErr
import pkg/upraises

import ./datastore
import ./sqlitedsdb

export datastore, sqlitedsdb

push: {.upraises: [].}

type
  SQLiteDatastore* = ref object of Datastore
    readOnly: bool
    db: SQLiteDsDB

proc path*(self: SQLiteDatastore): string =
  self.db.dbPath

proc `readOnly=`*(self: SQLiteDatastore): bool
  {.error: "readOnly should not be assigned".}

proc timestamp*(t = epochTime()): int64 =
  (t * 1_000_000).int64

method contains*(self: SQLiteDatastore, key: Key): Future[?!bool] {.async.} =
  var
    exists = false

  proc onData(s: RawStmtPtr) =
    exists = sqlite3_column_int64(s, ContainsStmtExistsCol.cint).bool

  let
    queryRes = self.db.containsStmt.query((key.id), onData)

  if queryRes.isErr: return queryRes
  return success exists

method delete*(self: SQLiteDatastore, key: Key): Future[?!void] {.async.} =
  return self.db.deleteStmt.exec((key.id))

method get*(self: SQLiteDatastore, key: Key): Future[?!seq[byte]] {.async.} =
  # see comment in ./filesystem_datastore re: finer control of memory
  # allocation in `method get`, could apply here as well if bytes were read
  # incrementally with `sqlite3_blob_read`

  var
    bytes: seq[byte]

  let
    dataCol = self.db.getDataCol

  proc onData(s: RawStmtPtr) =
    bytes = dataCol()

  let
    queryRes = self.db.getStmt.query((key.id), onData)

  if queryRes.isErr:
    return failure queryRes.error.msg

  return success bytes

method put*(self: SQLiteDatastore, key: Key, data: seq[byte]): Future[?!void] {.async.} =
  return self.db.putStmt.exec((key.id, @data, timestamp()))

iterator query*(
  self: SQLiteDatastore,
  query: Query): Future[QueryResponse] =

  let
    queryStmt = QueryStmt.prepare(
      self.db.env, QueryStmtStr).expect("should not fail")

    s = RawStmtPtr(queryStmt)

  defer:
    discard sqlite3_reset(s)
    discard sqlite3_clear_bindings(s)
    s.dispose

  let
    v = sqlite3_bind_text(s, 1.cint, query.key.id.cstring, -1.cint,
      SQLITE_TRANSIENT_GCSAFE)

  if not (v == SQLITE_OK):
    raise (ref Defect)(msg: $sqlite3_errstr(v))

  while true:
    let
      v = sqlite3_step(s)

    case v
    of SQLITE_ROW:
      let
        key = Key.init($sqlite3_column_text_not_null(
          s, QueryStmtIdCol)).expect("should not fail")

        blob = sqlite3_column_blob(s, QueryStmtDataCol)

      # detect out-of-memory error
      # see the conversion table and final paragraph of:
      # https://www.sqlite.org/c3ref/column_blob.html
      # see also https://www.sqlite.org/rescode.html

      # the "data" column can be NULL so in order to detect an out-of-memory
      # error it is necessary to check that the result is a null pointer and
      # that the result code is an error code
      if blob.isNil:
        let
          v = sqlite3_errcode(sqlite3_db_handle(s))

        if not (v in [SQLITE_OK, SQLITE_ROW, SQLITE_DONE]):
          raise (ref Defect)(msg: $sqlite3_errstr(v))

      let
        dataLen = sqlite3_column_bytes(s, QueryStmtDataCol)
        dataBytes = cast[ptr UncheckedArray[byte]](blob)
        data = @(toOpenArray(dataBytes, 0, dataLen - 1))
        fut = newFuture[QueryResponse]()

      fut.complete((key, data))
      yield fut
    of SQLITE_DONE:
      break
    else:
      raise (ref Defect)(msg: $sqlite3_errstr(v))

proc new*(
  T: type SQLiteDatastore,
  path: string,
  readOnly = false): ?!T =

  let
    flags =
      if readOnly: SQLITE_OPEN_READONLY
      else: SQLITE_OPEN_READWRITE or SQLITE_OPEN_CREATE

  success T(
    db: ? SQLIteDsDb.open(path, flags),
    readOnly: readOnly)

proc new*(
  T: type SQLiteDatastore,
  db: SQLIteDsDb): ?!T =

  success T(
    db: db,
    readOnly: db.readOnly)