-- TODO: Make sure transaction closed in all error cases
-- TODO: Don't allow writing non-contiguous events
module Vere.Log (
  init,
  shutdown,
  -- we don't export write; you use the queue
  readEvents,
  latestEventNumber,
  readLogIdentity,
  writeLogIdentity
) where

import ClassyPrelude hiding (init)
import Control.Lens hiding ((<|))

import Data.Noun
import Data.Noun.Atom
import Data.Noun.Jam
import Data.Noun.Pill
import Data.Void
import Database.LMDB.Raw
import Foreign.Ptr
import Foreign.Marshal.Alloc
import Vere.Pier.Types

import Control.Lens     ((^.))
import Foreign.Storable (peek, poke, sizeOf)

import qualified Data.ByteString.Unsafe as BU
import qualified Data.ByteString        as B
import qualified Data.Vector            as V
import qualified Data.Vector.Mutable    as MV

--------------------------------------------------------------------------------

-- TODO: Handle throws on the async
init :: FilePath -> TQueue (Writ [Effect]) -> (Writ [Effect] -> STM ())
     -> IO LogState
init dir inp cb = do
  env <- mdb_env_create
  mdb_env_set_maxdbs env 3
  mdb_env_set_mapsize env (40 * 1024 * 1024 * 1024)
  mdb_env_open env dir []
  writer <- persistThread env inp cb
  pure (LogState env inp cb writer)

-- TODO: properly handle shutdowns during write
shutdown :: LogState -> IO ()
shutdown s = do
  void $ waitCancel (writer s)
  mdb_env_close (env s)

waitCancel :: Async a -> IO (Either SomeException a)
waitCancel async = cancel async >> waitCatch async

--------------------------------------------------------------------------------

{-
    Read one or more items from a TQueue, only blocking on the first item.
-}
readQueue :: TQueue a -> STM (NonNull [a])
readQueue q =
    readTQueue q >>= go . singleton
  where
    go acc =
      tryReadTQueue q >>= \case
        Nothing   -> pure (reverse acc)
        Just item -> go (item <| acc)

byteStringAsMdbVal :: ByteString -> (MDB_val -> IO a) -> IO a
byteStringAsMdbVal bs k =
  BU.unsafeUseAsCStringLen bs \(ptr,sz) ->
    k (MDB_val (fromIntegral sz) (castPtr ptr))

mdbValToAtom :: MDB_val -> IO Atom
mdbValToAtom (MDB_val sz ptr) = do
  bs <- BU.unsafePackCStringLen (castPtr ptr, fromIntegral sz)
  pure (bs ^. from (pill . pillBS))

maybeErr :: Maybe a -> String -> IO a
maybeErr (Just x) _   = pure x
maybeErr Nothing  msg = error msg

mdbValToNoun :: MDB_val -> IO Noun
mdbValToNoun (MDB_val sz ptr) = do
  bs <- BU.unsafePackCStringLen (castPtr ptr, fromIntegral sz)
  let res = (bs ^? from pillBS . from pill . _Cue)
  maybeErr res "mdb bad cue"

putRaw :: MDB_WriteFlags -> MDB_txn -> MDB_dbi -> MDB_val -> MDB_val -> IO ()
putRaw flags txn db key val =
  mdb_put flags txn db key val >>= \case
    True  -> pure ()
    False -> error "mdb bad put"

putNoun :: MDB_WriteFlags -> MDB_txn -> MDB_dbi -> ByteString -> Noun -> IO ()
putNoun flags txn db key val =
  byteStringAsMdbVal key $ \mKey ->
  byteStringAsMdbVal (val ^. re _CueBytes) $ \mVal ->
  putRaw flags txn db mKey mVal

putJam :: MDB_WriteFlags -> MDB_txn -> MDB_dbi -> Word64 -> Jam -> IO ()
putJam flags txn db id (Jam atom) = do
  withWord64AsMDBval id $ \idVal -> do
    let !bs = atom ^. pill . pillBS
    byteStringAsMdbVal bs $ \mVal -> do
      putRaw flags txn db idVal mVal

get :: MDB_txn -> MDB_dbi -> ByteString -> IO Noun
get txn db key =
  byteStringAsMdbVal key \mKey ->
  mdb_get txn db mKey >>= maybe (error "mdb bad get") mdbValToNoun

mdbValToWord64 :: MDB_val -> IO Word64
mdbValToWord64 (MDB_val sz ptr) = do
  assertErr (sz == 8) "wrong size in mdbValToWord64"
  peek (castPtr ptr)

withWord64AsMDBval :: Word64 -> (MDB_val -> IO a) -> IO a
withWord64AsMDBval w cb = do
  withWordPtr w $ \p ->
    cb (MDB_val (fromIntegral (sizeOf w)) (castPtr p))

--------------------------------------------------------------------------------

withWordPtr :: Word64 -> (Ptr Word64 -> IO a) -> IO a
withWordPtr w cb = do
  allocaBytes (sizeOf w) (\p -> poke p w >> cb p)

-- TODO: We need to be able to send back an exception to the main thread on an
-- exception on the persistence thread.
persistThread :: MDB_env
              -> TQueue (Writ [Effect])
              -> (Writ [Effect] -> STM ())
              -> IO (Async ())
persistThread env inputQueue onPersist = asyncBound $
  forever do
    writs <- atomically $ readQueue inputQueue
    writeEvents writs
    atomically $ traverse_ onPersist writs
  where
    writeEvents writs = do
      txn <- mdb_txn_begin env Nothing False
      db  <- mdb_dbi_open txn (Just "EVENTS") [MDB_CREATE, MDB_INTEGERKEY]

      let flags = compileWriteFlags [MDB_NOOVERWRITE]

      for_ writs $ \w -> do
        putJam flags txn db (eventId w) (event w)

      mdb_txn_commit txn

deriving instance Show MDB_val

-- TODO: This will read len items and will error if there are less than that
-- available. This differs from the current pier.c's expectations.
readEvents :: LogState -> Word64 -> Word64 -> IO (V.Vector (Word64,Atom))
readEvents (LogState env _ _ _) first len =
  withWordPtr first $ \pIdx ->
  withKVPtrs (MDB_val 8 (castPtr pIdx)) (MDB_val 0 nullPtr) $ \pKey pVal ->
  do
    txn <- mdb_txn_begin env Nothing True
    db  <- mdb_dbi_open txn (Just "EVENTS") [MDB_CREATE, MDB_INTEGERKEY]
    cur <- mdb_cursor_open txn db

    found <- mdb_cursor_get MDB_SET_KEY cur pKey pVal
    assertErr found "mdb could not read initial event of sequence"

    vec <- V.generateM (int len) \i -> do
      key <- peek pKey >>= mdbValToWord64
      val <- peek pVal >>= mdbValToAtom

      let idx = first + (fromIntegral i)

      assertErr (key == idx) ("missing event in database " <> (show idx))

      when (i + 1 /= (int len)) do
        found <- mdb_cursor_get MDB_NEXT cur pKey pVal
        assertErr found "lmdb: next event not found"

      pure (idx, val)

    mdb_cursor_close cur
    mdb_txn_abort txn

    pure vec

int :: Word64 -> Int
int = fromIntegral

assertErr :: Bool -> String -> IO ()
assertErr True  _ = pure ()
assertErr False m = error m

latestEventNumber :: LogState -> IO Word64
latestEventNumber (LogState env _ _ _) =
  do
    txn <- mdb_txn_begin env Nothing True
    db  <- mdb_dbi_open txn (Just "EVENTS") [MDB_CREATE, MDB_INTEGERKEY]
    cur <- mdb_cursor_open txn db
    res <- fetch txn db cur
    mdb_cursor_close cur
    mdb_txn_abort txn
    pure res
  where
    key = MDB_val 0 nullPtr
    val = MDB_val 0 nullPtr
    fetch txn db cur =
      withKVPtrs key val $ \pKey pVal ->
        mdb_cursor_get MDB_LAST cur pKey pVal >>= \case
          False -> pure 0
          True -> peek pKey >>= mdbValToWord64

--------------------------------------------------------------------------------

readLogIdentity :: LogState -> IO LogIdentity
readLogIdentity (LogState env _ _ _) = do
  txn <- mdb_txn_begin env Nothing True
  db  <- mdb_dbi_open txn (Just "META") []
  who <- get txn db "who"
  is_fake <- get txn db "is-fake"
  life <- get txn db "life"
  mdb_txn_abort txn
  pure (LogIdentity who is_fake life)

writeLogIdentity :: LogState -> LogIdentity -> IO ()
writeLogIdentity (LogState env _ _ _) LogIdentity{..} = do
  txn <- mdb_txn_begin env Nothing False
  db  <- mdb_dbi_open txn (Just "META") [MDB_CREATE]
  let flags = compileWriteFlags []
  putNoun flags txn db "who" who
  putNoun flags txn db "is-fake" is_fake
  putNoun flags txn db "life" life
  mdb_txn_commit txn
  pure ()