{-# LANGUAGE TemplateHaskell #-}

-- | Metadata related types, functions and helpers.
--
-- Provides a single function which loads the MSSQL database metadata.
-- See the file at src-rsr/mssql/mssql_table_metadata.sql for the SQL we use to build
-- this metadata.
-- See 'Hasura.RQL.Types.Table.DBTableMetadata' for the Haskell type we use forall
-- storing this metadata.
module Hasura.Backends.MSSQL.Meta
  ( loadDBMetadata,
  )
where

import Data.Aeson as Aeson
import Data.ByteString.UTF8 qualified as BSUTF8
import Data.FileEmbed (embedFile, makeRelativeToProject)
import Data.HashMap.Strict qualified as HM
import Data.HashMap.Strict.NonEmpty qualified as NEHashMap
import Data.HashSet qualified as HS
import Data.String
import Data.Text qualified as T
import Data.Text.Encoding qualified as T
import Database.MSSQL.Transaction qualified as Tx
import Database.ODBC.SQLServer qualified as ODBC
import Hasura.Backends.MSSQL.Instances.Types ()
import Hasura.Backends.MSSQL.SQL.Error
import Hasura.Backends.MSSQL.Types.Internal
import Hasura.Base.Error
import Hasura.Prelude
import Hasura.RQL.Types.Column
import Hasura.RQL.Types.Common (OID (..))
import Hasura.RQL.Types.Table
import Hasura.SQL.Backend

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

-- * Loader

loadDBMetadata :: (MonadIO m) => Tx.TxET QErr m (DBTablesMetadata 'MSSQL)
loadDBMetadata = do
  let queryBytes = $(makeRelativeToProject "src-rsr/mssql/mssql_table_metadata.sql" >>= embedFile)
      odbcQuery :: ODBC.Query = fromString . BSUTF8.toString $ queryBytes
  sysTablesText <- runIdentity <$> Tx.singleRowQueryE defaultMSSQLTxErrorHandler odbcQuery
  case Aeson.eitherDecodeStrict (T.encodeUtf8 sysTablesText) of
    Left e -> throw500 $ T.pack $ "error loading sql server database schema: " <> e
    Right sysTables -> pure $ HM.fromList $ map transformTable sysTables

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

-- * Local types

data SysTable = SysTable
  { staName :: Text,
    staObjectId :: Int,
    staJoinedSysColumn :: [SysColumn],
    staJoinedSysSchema :: SysSchema,
    staJoinedSysPrimaryKey :: Maybe SysPrimaryKey
  }
  deriving (Show, Generic)

instance FromJSON SysTable where
  parseJSON = genericParseJSON hasuraJSON

newtype SysPrimaryKeyColumn = SysPrimaryKeyColumn
  {spkcName :: Text}
  deriving (Show, Generic)

instance FromJSON SysPrimaryKeyColumn where
  parseJSON = genericParseJSON hasuraJSON

data SysPrimaryKey = SysPrimaryKey
  { spkName :: Text,
    spkIndexId :: Int,
    spkColumns :: NESeq SysPrimaryKeyColumn
  }
  deriving (Show, Generic)

instance FromJSON SysPrimaryKey where
  parseJSON = genericParseJSON hasuraJSON

data SysSchema = SysSchema
  { ssName :: Text,
    ssSchemaId :: Int
  }
  deriving (Show, Generic)

instance FromJSON SysSchema where
  parseJSON = genericParseJSON hasuraJSON

data SysColumn = SysColumn
  { scName :: Text,
    scColumnId :: Int,
    scUserTypeId :: Int,
    scIsNullable :: Bool,
    scIsIdentity :: Bool,
    scIsComputed :: Bool,
    scJoinedSysType :: SysType,
    scJoinedForeignKeyColumns :: [SysForeignKeyColumn]
  }
  deriving (Show, Generic)

instance FromJSON SysColumn where
  parseJSON = genericParseJSON hasuraJSON

data SysType = SysType
  { styName :: Text,
    stySchemaId :: Int,
    styUserTypeId :: Int
  }
  deriving (Show, Generic)

instance FromJSON SysType where
  parseJSON = genericParseJSON hasuraJSON

data SysForeignKeyColumn = SysForeignKeyColumn
  { sfkcConstraintObjectId :: Int,
    sfkcConstraintColumnId :: Int,
    sfkcParentObjectId :: Int,
    sfkcParentColumnId :: Int,
    sfkcReferencedObjectId :: Int,
    sfkcReferencedColumnId :: Int,
    sfkcJoinedReferencedTableName :: Text,
    sfkcJoinedReferencedColumnName :: Text,
    sfkcJoinedReferencedSysSchema :: SysSchema
  }
  deriving (Show, Generic)

instance FromJSON SysForeignKeyColumn where
  parseJSON = genericParseJSON hasuraJSON

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

-- * Transform

transformTable :: SysTable -> (TableName, DBTableMetadata 'MSSQL)
transformTable tableInfo =
  let schemaName = SchemaName $ ssName $ staJoinedSysSchema tableInfo
      tableName = TableName (staName tableInfo) schemaName
      tableOID = OID $ staObjectId tableInfo
      (columns, foreignKeys) = unzip $ transformColumn <$> staJoinedSysColumn tableInfo
      foreignKeysMetadata = HS.fromList $ map ForeignKeyMetadata $ coalesceKeys $ concat foreignKeys
      primaryKey = transformPrimaryKey <$> staJoinedSysPrimaryKey tableInfo
      identityColumns =
        map (ColumnName . scName) $
          filter scIsIdentity $
            staJoinedSysColumn tableInfo
   in ( tableName,
        DBTableMetadata
          tableOID
          columns
          primaryKey
          HS.empty -- no unique constraints?
          foreignKeysMetadata
          Nothing -- no views, only tables
          Nothing -- no description
          identityColumns
      )

transformColumn ::
  SysColumn ->
  (RawColumnInfo 'MSSQL, [ForeignKey 'MSSQL])
transformColumn sysCol =
  let rciName = ColumnName $ scName sysCol
      rciPosition = scColumnId sysCol

      rciIsNullable = scIsNullable sysCol
      rciDescription = Nothing
      rciType = parseScalarType $ styName $ scJoinedSysType sysCol
      foreignKeys =
        scJoinedForeignKeyColumns sysCol <&> \foreignKeyColumn ->
          let _fkConstraint = Constraint (ConstraintName "fk_mssql") $ OID $ sfkcConstraintObjectId foreignKeyColumn

              schemaName = SchemaName $ ssName $ sfkcJoinedReferencedSysSchema foreignKeyColumn
              _fkForeignTable = TableName (sfkcJoinedReferencedTableName foreignKeyColumn) schemaName
              _fkColumnMapping = NEHashMap.singleton rciName $ ColumnName $ sfkcJoinedReferencedColumnName foreignKeyColumn
           in ForeignKey {..}

      colIsImmutable = scIsComputed sysCol || scIsIdentity sysCol
      rciMutability = ColumnMutability {_cmIsInsertable = not colIsImmutable, _cmIsUpdatable = not colIsImmutable}
   in (RawColumnInfo {..}, foreignKeys)

transformPrimaryKey :: SysPrimaryKey -> PrimaryKey 'MSSQL (Column 'MSSQL)
transformPrimaryKey (SysPrimaryKey {..}) =
  let constraint = Constraint (ConstraintName spkName) $ OID spkIndexId
      columns = (ColumnName . spkcName) <$> spkColumns
   in PrimaryKey constraint columns

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

-- * Helpers

coalesceKeys :: [ForeignKey 'MSSQL] -> [ForeignKey 'MSSQL]
coalesceKeys = HM.elems . foldl' coalesce HM.empty
  where
    coalesce mapping fk@(ForeignKey constraint tableName _) = HM.insertWith combine (constraint, tableName) fk mapping
    combine oldFK newFK = oldFK {_fkColumnMapping = (NEHashMap.union `on` _fkColumnMapping) oldFK newFK}