{-# LANGUAGE TemplateHaskell #-}

module Hasura.Backends.MySQL.Meta
  ( getMetadata,
  )
where

import Control.Exception (throw)
import Data.ByteString.Char8 qualified as B8
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.Sequence.NonEmpty qualified as NESeq
import Data.String (fromString)
import Database.MySQL.Base (Connection)
import Database.MySQL.Base.Types (Field (..))
import Database.MySQL.Simple (Only (Only), query)
import Database.MySQL.Simple.QueryResults (QueryResults (..), convertError)
import Database.MySQL.Simple.Result (Result, ResultError (..), convert)
import Hasura.Backends.MySQL.Instances.Types ()
import Hasura.Backends.MySQL.Types
import Hasura.Prelude
import Hasura.RQL.Types.Column
import Hasura.RQL.Types.Common
import Hasura.RQL.Types.Table
import Hasura.SQL.Backend
import Language.GraphQL.Draft.Syntax qualified as G

getMetadata :: ConnSourceConfig -> Connection -> IO (DBTablesMetadata 'MySQL)
getMetadata ConnSourceConfig {_cscDatabase} scConnection = do
  let sql = $(makeRelativeToProject "src-rsr/mysql_table_metadata.sql" >>= embedFile)
  results :: [InformationSchema] <- query scConnection (fromString . B8.unpack $ sql) (Only _cscDatabase)
  pure (mkMetadata results)

mkMetadata :: [InformationSchema] -> DBTablesMetadata 'MySQL
mkMetadata = foldr mergeMetadata HM.empty

mergeMetadata :: InformationSchema -> DBTablesMetadata 'MySQL -> DBTablesMetadata 'MySQL
mergeMetadata InformationSchema {..} =
  HM.insertWith
    mergeDBTableMetadata
    (TableName {name = isTableName, schema = pure isTableSchema})
    $ DBTableMetadata
      { _ptmiOid = OID 0,
        _ptmiColumns =
          [ RawColumnInfo
              { rciName = Column isColumnName,
                rciPosition = fromIntegral isOrdinalPosition,
                rciType = parseMySQLScalarType isColumnType, -- TODO: This needs to become more precise by considering Field length and character-set
                rciIsNullable = isIsNullable == "YES", -- ref: https://dev.mysql.com/doc/refman/8.0/en/information-schema-columns-table.html
                rciDescription = Just $ G.Description isColumnComment,
                rciMutability = ColumnMutability {_cmIsInsertable = True, _cmIsUpdatable = True}
              }
          ],
        _ptmiPrimaryKey =
          if isColumnKey == PRI
            then
              Just $
                PrimaryKey
                  ( Constraint
                      (ConstraintName $ fromMaybe "" isConstraintName)
                      (OID $ fromIntegral $ fromMaybe 0 isConstraintOrdinalPosition)
                  )
                  (NESeq.singleton (Column isColumnName))
            else Nothing,
        _ptmiUniqueConstraints =
          if isColumnKey == UNI
            then
              HS.singleton
                ( UniqueConstraint
                    { _ucConstraint =
                        Constraint
                          (ConstraintName $ fromMaybe "" isConstraintName)
                          (OID $ fromIntegral $ fromMaybe 0 isConstraintOrdinalPosition),
                      _ucColumns = HS.singleton (Column isColumnName)
                    }
                )
            else HS.empty,
        _ptmiForeignKeys =
          if isColumnKey == MUL
            then
              HS.singleton
                ( ForeignKeyMetadata
                    ( ForeignKey
                        ( Constraint
                            (ConstraintName $ fromMaybe "" isConstraintName)
                            (OID $ fromIntegral $ fromMaybe 0 isConstraintOrdinalPosition)
                        )
                        ( TableName
                            { name = (fromMaybe "" isReferencedTableName),
                              schema = isReferencedTableSchema
                            }
                        )
                        ( NEHashMap.singleton
                            (Column isColumnName)
                            (Column $ fromMaybe "" isReferencedColumnName)
                        )
                    )
                )
            else HS.empty,
        _ptmiViewInfo = Nothing,
        _ptmiDescription = Nothing,
        _ptmiExtraTableMetadata = (),
        _ptmiCustomObjectTypes = mempty
      }

mergeDBTableMetadata :: DBTableMetadata 'MySQL -> DBTableMetadata 'MySQL -> DBTableMetadata 'MySQL
mergeDBTableMetadata new existing =
  DBTableMetadata
    { _ptmiOid = OID 0,
      _ptmiColumns = _ptmiColumns existing <> _ptmiColumns new,
      _ptmiPrimaryKey = _ptmiPrimaryKey existing <|> _ptmiPrimaryKey new, -- Only one column can be a PRIMARY KEY, so this is just a courtesy choice.
      _ptmiUniqueConstraints = _ptmiUniqueConstraints existing <> _ptmiUniqueConstraints new, -- union
      _ptmiForeignKeys = _ptmiForeignKeys existing <> _ptmiForeignKeys new, -- union
      _ptmiViewInfo = _ptmiViewInfo existing <|> _ptmiViewInfo new,
      _ptmiDescription = _ptmiDescription existing <|> _ptmiDescription new,
      _ptmiExtraTableMetadata = (),
      _ptmiCustomObjectTypes = mempty
    }

data InformationSchema = InformationSchema
  { isTableSchema :: Text,
    isTableName :: Text,
    isColumnName :: Text,
    isOrdinalPosition :: Word,
    isColumnDefault :: Maybe Text,
    isIsNullable :: Text,
    isDataType :: Maybe Text,
    isColumnType :: Text,
    isColumnKey :: InformationSchemaColumnKey,
    isColumnComment :: Text,
    isConstraintName :: Maybe Text,
    isConstraintOrdinalPosition :: Maybe Word,
    isPositionInUniqueConstraint :: Maybe Word,
    isReferencedTableSchema :: Maybe Text,
    isReferencedTableName :: Maybe Text,
    isReferencedColumnName :: Maybe Text
  }
  deriving (Show, Eq, Generic)

instance QueryResults InformationSchema where
  convertResults
    [ fisTableSchema,
      fisTableName,
      fisColumnName,
      fisOrdinalPosition,
      fisColumnDefault,
      fisIsNullable,
      fisDataType,
      fisColumnType,
      fisColumnKey,
      fisColumnComment,
      fisConstraintName,
      fisConstraintOrdinalPosition,
      fisPositionInUniqueConstraint,
      fisReferencedTableSchema,
      fisReferencedTableName,
      fisReferencedColumnName
      ]
    [ visTableSchema,
      visTableName,
      visColumnName,
      visOrdinalPosition,
      visColumnDefault,
      visIsNullable,
      visDataType,
      visColumnType,
      visColumnKey,
      visColumnComment,
      visConstraintName,
      visConstraintOrdinalPosition,
      visPositionInUniqueConstraint,
      visReferencedTableSchema,
      visReferencedTableName,
      visReferencedColumnName
      ] =
      InformationSchema
        (convert fisTableSchema visTableSchema)
        (convert fisTableName visTableName)
        (convert fisColumnName visColumnName)
        (convert fisOrdinalPosition visOrdinalPosition)
        (convert fisColumnDefault visColumnDefault)
        (convert fisIsNullable visIsNullable)
        (convert fisDataType visDataType)
        (convert fisColumnType visColumnType)
        (convert fisColumnKey visColumnKey)
        (convert fisColumnComment visColumnComment)
        (convert fisConstraintName visConstraintName)
        (convert fisConstraintOrdinalPosition visConstraintOrdinalPosition)
        (convert fisPositionInUniqueConstraint visPositionInUniqueConstraint)
        (convert fisReferencedTableSchema visReferencedTableSchema)
        (convert fisReferencedTableName visReferencedTableName)
        (convert fisReferencedColumnName visReferencedColumnName)
  convertResults fs vs = convertError fs vs 16

data InformationSchemaColumnKey
  = PRI
  | UNI
  | MUL
  | -- | This field isn't NULLable and uses empty strings, by the looks of it.
    BLANK
  deriving (Show, Read, Eq, Generic)

instance Result InformationSchemaColumnKey where
  convert f mbs =
    case mbs of
      Nothing ->
        throw $
          UnexpectedNull
            (show $ fieldType f)
            "InformationSchemaColumnKey"
            (B8.unpack $ fieldName f)
            "COLUMN_KEY in INFORMATION_SCHEMA cannot be NULL"
      Just bs -> case bs of
        -- Could have used 'readMaybe' here, but we need the specific errors.
        "PRI" -> PRI -- primary key
        "UNI" -> UNI -- unique key
        "MUL" -> MUL -- foreign key (`MUL`tiple allowed, non-unique key)
        "" -> BLANK
        x ->
          throw $
            ConversionFailed
              (show $ fieldType f)
              "InformationSchemaColumnKey"
              (B8.unpack $ fieldName f)
              ("COLUMN_KEY in INFORMATION_SCHEMA has value extraneous to the expected ENUM: " <> B8.unpack x)