module Hasura.Backends.Postgres.DDL.Source
  ( ToMetadataFetchQuery
  , fetchPgScalars
  , fetchTableMetadata
  , fetchFunctionMetadata
  , initCatalogForSource
  , postDropSourceHook
  , resolveDatabaseMetadata
  , resolveSourceConfig
  ) where

import           Hasura.Prelude

import qualified Data.HashMap.Strict                         as Map
import qualified Data.List.NonEmpty                          as NE
import qualified Database.PG.Query                           as Q
import qualified Language.Haskell.TH.Lib                     as TH
import qualified Language.Haskell.TH.Syntax                  as TH

import           Control.Monad.Trans.Control                 (MonadBaseControl)
import           Data.FileEmbed                              (makeRelativeToProject)
import           Data.Time.Clock                             (UTCTime)

import           Hasura.Backends.Postgres.Connection
import           Hasura.Backends.Postgres.DDL.Source.Version
import           Hasura.Backends.Postgres.SQL.Types
import           Hasura.Base.Error
import           Hasura.RQL.Types.Backend
import           Hasura.RQL.Types.Common
import           Hasura.RQL.Types.EventTrigger               (RecreateEventTriggers (..))
import           Hasura.RQL.Types.Function
import           Hasura.RQL.Types.Source
import           Hasura.RQL.Types.Table
import           Hasura.SQL.Backend
import           Hasura.Server.Migrate.Internal
import           Hasura.Server.Types                         (MaintenanceMode (..))


-- | We differentiate the handling of metadata between Citus and Vanilla
-- Postgres because Citus imposes limitations on the types of joins that it
-- permits, which then limits the types of relations that we can track.
class ToMetadataFetchQuery (pgKind :: PostgresKind) where
    tableMetadata :: Q.Query

instance ToMetadataFetchQuery 'Vanilla where
    tableMetadata = $(makeRelativeToProject "src-rsr/pg_table_metadata.sql" >>= Q.sqlFromFile)

instance ToMetadataFetchQuery 'Citus where
    tableMetadata = $(makeRelativeToProject "src-rsr/citus_table_metadata.sql" >>= Q.sqlFromFile)

resolveSourceConfig
  :: (MonadIO m, MonadResolveSource m)
  => SourceName -> PostgresConnConfiguration -> m (Either QErr (SourceConfig ('Postgres pgKind)))
resolveSourceConfig name config = runExceptT do
  sourceResolver <- getSourceResolver
  liftEitherM $ liftIO $ sourceResolver name config

resolveDatabaseMetadata
  :: forall pgKind m
   . (Backend ('Postgres pgKind), ToMetadataFetchQuery pgKind, MonadIO m, MonadBaseControl IO m)
  => SourceConfig ('Postgres pgKind) -> m (Either QErr (ResolvedSource ('Postgres pgKind)))
resolveDatabaseMetadata sourceConfig = runExceptT do
  (tablesMeta, functionsMeta, pgScalars) <- runLazyTx (_pscExecCtx sourceConfig) Q.ReadOnly $ do
    tablesMeta    <- fetchTableMetadata
    functionsMeta <- fetchFunctionMetadata
    pgScalars     <- fetchPgScalars
    pure (tablesMeta, functionsMeta, pgScalars)
  pure $ ResolvedSource sourceConfig tablesMeta functionsMeta pgScalars

-- | Initialise catalog tables for a source, including those required by the event delivery subsystem.
initCatalogForSource
  :: forall m . MonadTx m => MaintenanceMode -> UTCTime -> m RecreateEventTriggers
initCatalogForSource maintenanceMode migrationTime = do
  hdbCatalogExist <- doesSchemaExist "hdb_catalog"
  eventLogTableExist <- doesTableExist "hdb_catalog" "event_log"
  sourceVersionTableExist <- doesTableExist "hdb_catalog" "hdb_source_catalog_version"
     -- when maintenance mode is enabled, don't perform any migrations
  if | maintenanceMode == MaintenanceModeEnabled -> pure RETDoNothing
     -- Fresh database
     | not hdbCatalogExist -> liftTx do
        Q.unitQE defaultTxErrorHandler "CREATE SCHEMA hdb_catalog" () False
        enablePgcryptoExtension
        initPgSourceCatalog
        return RETDoNothing
     -- Only 'hdb_catalog' schema defined
     | not sourceVersionTableExist && not eventLogTableExist -> do
        liftTx initPgSourceCatalog
        return RETDoNothing
     -- Source is initialised by pre multisource support servers
     | not sourceVersionTableExist && eventLogTableExist -> do
       -- Update the Source Catalog to v43 to include the new migration
       -- changes. Skipping this step will result in errors.
        currMetadataCatalogVersion <- liftTx getCatalogVersion
        -- we migrate to the 43 version, which is the migration where
        -- metadata separation is introduced
        migrateTo43MetadataCatalog currMetadataCatalogVersion
        liftTx createVersionTable
        -- Migrate the catalog from initial version i.e '1'
        migrateSourceCatalogFrom "1"
        return RETRecreate
     | otherwise -> migrateSourceCatalog >> return RETRecreate
  where
    initPgSourceCatalog = do
      () <- Q.multiQE defaultTxErrorHandler $(makeRelativeToProject "src-rsr/init_pg_source.sql" >>= Q.sqlFromFile)
      setSourceCatalogVersion

    createVersionTable = do
      () <- Q.multiQE defaultTxErrorHandler
        [Q.sql|
           CREATE TABLE hdb_catalog.hdb_source_catalog_version(
             version TEXT NOT NULL,
             upgraded_on TIMESTAMPTZ NOT NULL
           );

           CREATE UNIQUE INDEX hdb_source_catalog_version_one_row
           ON hdb_catalog.hdb_source_catalog_version((version IS NOT NULL));
        |]
      pure ()

    migrateTo43MetadataCatalog prevVersion = do
      let neededMigrations = dropWhile ((/= prevVersion) . fst) upMigrationsUntil43
      case NE.nonEmpty neededMigrations of
        Just nonEmptyNeededMigrations -> do
          -- Migrations aren't empty. We need to update the catalog version after migrations
          traverse_ snd nonEmptyNeededMigrations
          setCatalogVersion "43" migrationTime
        Nothing ->
          -- No migrations exists, implies the database is migrated to latest metadata catalog version
          pure ()

-- NOTE (rakesh):
-- Down migrations for postgres sources is not supported in this PR. We need an
-- exhaustive discussion to make a call as I think, as of now, it is not
-- trivial. For metadata catalog migrations, we have a separate downgrade
-- command in the graphql-engine exe.
--
-- I can think of two ways:
--
--  - Just like downgrade, we need to have a new command path for downgrading
--  pg sources (command design should support other backends too,
--  graphql-engine source-downgrade postgres --to-catalog-version 1 --
--  downgrade all available pg sources to 1)
--  - Have an online documentation with necessary SQLs to help users to
--  downgrade pg sources themselves. Improve error message by referring the URL
--  to the documentation.

migrateSourceCatalog :: MonadTx m => m ()
migrateSourceCatalog =
  getSourceCatalogVersion >>= migrateSourceCatalogFrom

migrateSourceCatalogFrom :: (MonadTx m) => Text -> m ()
migrateSourceCatalogFrom prevVersion
  | prevVersion == latestSourceCatalogVersionText = pure ()
  | [] <- neededMigrations =
      throw400 NotSupported $
        "Expected source catalog version <= "
        <> latestSourceCatalogVersionText
        <> ", but the current version is " <> prevVersion
  | otherwise = do
      traverse_ snd neededMigrations
      setSourceCatalogVersion
  where
    neededMigrations =
      dropWhile ((/= prevVersion) . fst) sourceMigrations

sourceMigrations :: (MonadTx m) => [(Text, m ())]
sourceMigrations =
  $(let migrationFromFile from =
          let to = from + 1
              path = "src-rsr/pg_source_migrations/" <> show from <> "_to_" <> show to <> ".sql"
          in [| runTx $(makeRelativeToProject path >>= Q.sqlFromFile) |]

        migrationsFromFile = map $ \(from :: Integer) ->
          [| ($(TH.lift $ tshow from), $(migrationFromFile from)) |]

    in TH.listE $ migrationsFromFile [1..(latestSourceCatalogVersion - 1)]
   )

-- Upgrade the hdb_catalog schema to v43 (Metadata catalog)
upMigrationsUntil43 :: MonadTx m => [(Text, m ())]
upMigrationsUntil43 =
    $(let migrationFromFile from to =
            let path = "src-rsr/migrations/" <> from <> "_to_" <> to <> ".sql"
             in [| runTx $(makeRelativeToProject path >>= Q.sqlFromFile) |]

          migrationsFromFile = map $ \(to :: Integer) ->
            let from = to - 1
            in [| ( $(TH.lift $ tshow from)
                  , $(migrationFromFile (show from) (show to))
                  ) |]
      in TH.listE
        -- version 0.8 is the only non-integral catalog version
        $  [| ("0.8", $(migrationFromFile "08" "1")) |]
        :  migrationsFromFile [2..3]
        ++ [| ("3", from3To4) |]
        :  migrationsFromFile [5..43]
     )

-- | Fetch Postgres metadata of all user tables
fetchTableMetadata
  :: forall pgKind m
   . (Backend ('Postgres pgKind), ToMetadataFetchQuery pgKind, MonadTx m)
  => m (DBTablesMetadata ('Postgres pgKind))
fetchTableMetadata = do
  results <- liftTx $ Q.withQE defaultTxErrorHandler
             (tableMetadata @pgKind) () True
  pure $ Map.fromList $ flip map results $
    \(schema, table, Q.AltJ info) -> (QualifiedObject schema table, info)

-- | Fetch Postgres metadata for all user functions
fetchFunctionMetadata :: (MonadTx m) => m (DBFunctionsMetadata ('Postgres pgKind))
fetchFunctionMetadata = do
  results <- liftTx $ Q.withQE defaultTxErrorHandler
             $(makeRelativeToProject "src-rsr/pg_function_metadata.sql" >>= Q.sqlFromFile) () True
  pure $ Map.fromList $ flip map results $
    \(schema, table, Q.AltJ infos) -> (QualifiedObject schema table, infos)

-- | Fetch all scalar types from Postgres
fetchPgScalars :: MonadTx m => m (HashSet PGScalarType)
fetchPgScalars =
  liftTx $ Q.getAltJ . runIdentity . Q.getRow
  <$> Q.withQE defaultTxErrorHandler
  [Q.sql|
    SELECT coalesce(json_agg(typname), '[]')
    FROM pg_catalog.pg_type where typtype = 'b'
   |] () True

-- | Clean source database after dropping in metadata
postDropSourceHook
  :: (MonadIO m, MonadError QErr m, MonadBaseControl IO m)
  => PGSourceConfig -> m ()
postDropSourceHook sourceConfig = do
  -- Clean traces of Hasura in source database
  --
  -- There are three type of database we have to consider here, which we
  -- refer to as types 1, 2, and 3 below:
  --   1. default postgres source (no separate metadata database)
  --   In this case, we want to drop nothing.
  --
  --   2. dedicated metadata database
  --   In this case, we want to only drop source-related tables ("event_log",
  --   "hdb_source_catalog_version", etc), leaving the rest of the schema intact.
  --
  --   3. non-default postgres source (necessarily without metadata tables)
  --   In this case, we want to drop the entire "hdb_catalog" schema.
  liftEitherM $ runPgSourceWriteTx sourceConfig $ do
    hdbMetadataTableExist <- doesTableExist "hdb_catalog" "hdb_metadata"
    eventLogTableExist <- doesTableExist "hdb_catalog" "event_log"
    if
       -- If "hdb_metadata" and "event_log" tables are found in the "hdb_catalog" schema,
       -- then this implies the source is being used as the default postgres source, i.e.
       -- this is a default postgres source (type 1 above).
       -- In this case we don't drop anything in the catalog schema.
      | hdbMetadataTableExist && eventLogTableExist -> pure ()
       -- However, it is possible that the above condition is not met for a default
       -- postgres source. This will happen if no event triggers have been defined,
       -- because we initialise event catalog tables only when required (i.e. when
       -- a trigger is defined).
       --
       -- This could lead to a possible problem where "hdb_metadata" exists, "event_log"
       -- does not exist, but the _other_ source-related tables exist. In that case, we
       -- would end up dropping them here, which would go against our requirements above.
       -- However, observe that these tables are always all created or destroyed together,
       -- in single transactions where we run setup/teardown SQL files, so this condition
       -- is guaranteed to not take place.
       --
       -- So if only "hdb_metadata" exists, we have one of two possible cases:
       --   * this is a metadata database (type 2) and we can drop all source-related tables
       --   * this is a default database (type 1) which has no source-related tables (because
       --     it has no "event_log" table, it cannot have the others, because of the previous
       --     argument)
       --
       -- It should be clear that we can now safely issue DROP IF EXISTS statements for
       -- all source-related tables now according to the spec above. The IF EXISTS lets us
       -- handle both cases uniformly, doing nothing in the second case, and for metadata
       -- databases, we drop only source-related tables from the database's "hdb_catalog" schema.
       | hdbMetadataTableExist -> Q.multiQE
         defaultTxErrorHandler $(makeRelativeToProject "src-rsr/drop_pg_source.sql" >>= Q.sqlFromFile)
       -- Otherwise, we have a non-default postgres source, which has no metadata tables.
       -- We drop the entire "hdb_catalog" schema as discussed above.
       | otherwise -> dropHdbCatalogSchema

  -- Destory postgres source connection
  liftIO $ _pecDestroyConn $ _pscExecCtx sourceConfig

  -- Run other drop hooks configured at source creation time
  liftIO $ _pscPostDropHook sourceConfig