module Database.Persist.Sql.Util
    ( parseEntityValues
    , entityColumnNames
    , keyAndEntityColumnNames
    , entityColumnCount
    , isIdField
    , hasCompositeKey
    , hasCompositePrimaryKey
    , hasNaturalKey
    , dbIdColumns
    , dbIdColumnsEsc
    , dbColumns
    , updateFieldDef
    , updatePersistValue
    , mkUpdateText
    , mkUpdateText'
    , commaSeparated
    , parenWrapped
    , mkInsertValues
    , mkInsertPlaceholders
    ) where

import qualified Data.Maybe as Maybe
import Data.Monoid ((<>))
import Data.Text (Text, pack)
import qualified Data.Text as T

import Database.Persist (
    Entity(Entity), EntityDef, EntityField, HaskellName(HaskellName)
  , PersistEntity(..), PersistValue
  , keyFromValues, fromPersistValues, fieldDB, entityId, entityPrimary
  , entityFields, entityKeyFields, fieldHaskell, compositeFields, persistFieldDef
  , keyAndEntityFields, toPersistValue, DBName, Update(..), PersistUpdate(..)
  , FieldDef(..)
  )
import Database.Persist.Sql.Types (Sql, SqlBackend, connEscapeName)

entityColumnNames :: EntityDef -> SqlBackend -> [Sql]
entityColumnNames ent conn =
     (if hasCompositeKey ent
      then [] else [connEscapeName conn $ fieldDB (entityId ent)])
  <> map (connEscapeName conn . fieldDB) (entityFields ent)

keyAndEntityColumnNames :: EntityDef -> SqlBackend -> [Sql]
keyAndEntityColumnNames ent conn = map (connEscapeName conn . fieldDB) (keyAndEntityFields ent)

entityColumnCount :: EntityDef -> Int
entityColumnCount e = length (entityFields e)
                    + if hasCompositeKey e then 0 else 1

{-# DEPRECATED hasCompositeKey "hasCompositeKey is misleading - it returns True if the entity is defined with the Primary keyword. See issue #685 for discussion. \n If you want the same behavior, use 'hasNaturalKey'. If you want to know if the key has multiple fields, use 'hasCompositePrimaryKey'. This function will be removed in the next major version." #-}
-- | Deprecated as of 2.11. See 'hasNaturalKey' or 'hasCompositePrimaryKey'
-- for replacements.
hasCompositeKey :: EntityDef -> Bool
hasCompositeKey = Maybe.isJust . entityPrimary

-- | Returns 'True' if the entity has a natural key defined with the
-- Primary keyword.
--
-- A natural key is a key that is inherent to the record, and is part of
-- the actual Haskell record. The opposite of a natural key is a "surrogate
-- key", which is not part of the normal domain object. Automatically
-- generated ID columns are the most common surrogate ID, while an email
-- address is a common natural key.
--
-- @
-- User
--     email String
--     name String
--     Primary email
--
-- Person
--     Id   UUID
--     name String
--
-- Follower
--     name String
-- @
--
-- Given these entity definitions, @User@ would return 'True', because the
-- @Primary@ keyword sets the @email@ column to be the primary key. The
-- generated Haskell type would look like this:
--
-- @
-- data User = User
--     { userEmail :: String
--     , userName :: String
--     }
-- @
--
-- @Person@ would be false. While the @Id@ syntax allows you to define
-- a custom ID type for an entity, the @Id@ column is a surrogate key.
--
-- The same is true for @Follower@. The automatically generated
-- autoincremented integer primary key is a surrogate key.
--
-- There's nothing preventing you from defining a @Primary@ definition that
-- refers to a surrogate key. This is totally fine.
--
-- @since 2.11.0
hasNaturalKey :: EntityDef -> Bool
hasNaturalKey =
    Maybe.isJust . entityPrimary

-- | Returns 'True' if the provided entity has a custom composite primary
-- key. Composite keys have multiple fields in them.
--
-- @
-- User
--     email String
--     name String
--     Primary userId
--
-- Profile
--     personId PersonId
--     email    String
--     Primary personId email
--
-- Person
--     Id   UUID
--     name String
--
-- Follower
--     name String
-- @
--
-- Given these entity definitions, only @Profile@ would return 'True',
-- because it is the only entity with multiple columns in the primary key.
-- @User@ has a single column natural key. @Person@ has a custom single
-- column surrogate key defined with @Id@. And @Follower@ has a default
-- single column surrogate key.
--
-- @since 2.11.0
hasCompositePrimaryKey :: EntityDef -> Bool
hasCompositePrimaryKey ed =
    case entityPrimary ed of
        Just cdef ->
            case compositeFields cdef of
                (_ : _ : _) ->
                    True
                _ ->
                    False
        Nothing ->
            False

dbIdColumns :: SqlBackend -> EntityDef -> [Text]
dbIdColumns conn = dbIdColumnsEsc (connEscapeName conn)

dbIdColumnsEsc :: (DBName -> Text) -> EntityDef -> [Text]
dbIdColumnsEsc esc t = map (esc . fieldDB) $ entityKeyFields t

dbColumns :: SqlBackend -> EntityDef -> [Text]
dbColumns conn t = case entityPrimary t of
    Just _  -> flds
    Nothing -> escapeDB (entityId t) : flds
  where
    escapeDB = connEscapeName conn . fieldDB
    flds = map escapeDB (entityFields t)

parseEntityValues :: PersistEntity record
                  => EntityDef -> [PersistValue] -> Either Text (Entity record)
parseEntityValues t vals =
    case entityPrimary t of
      Just pdef ->
            let pks = map fieldHaskell $ compositeFields pdef
                keyvals = map snd . filter ((`elem` pks) . fst)
                        $ zip (map fieldHaskell $ entityFields t) vals
            in fromPersistValuesComposite' keyvals vals
      Nothing -> fromPersistValues' vals
  where
    fromPersistValues' (kpv:xs) = -- oracle returns Double
        case fromPersistValues xs of
            Left e -> Left e
            Right xs' ->
                case keyFromValues [kpv] of
                    Left _ -> error $ "fromPersistValues': keyFromValues failed on " ++ show kpv
                    Right k -> Right (Entity k xs')


    fromPersistValues' xs = Left $ pack ("error in fromPersistValues' xs=" ++ show xs)

    fromPersistValuesComposite' keyvals xs =
        case fromPersistValues xs of
            Left e -> Left e
            Right xs' -> case keyFromValues keyvals of
                Left _ -> error "fromPersistValuesComposite': keyFromValues failed"
                Right key -> Right (Entity key xs')


isIdField :: PersistEntity record => EntityField record typ -> Bool
isIdField f = fieldHaskell (persistFieldDef f) == HaskellName "Id"

-- | Gets the 'FieldDef' for an 'Update'.
updateFieldDef :: PersistEntity v => Update v -> FieldDef
updateFieldDef (Update f _ _) = persistFieldDef f
updateFieldDef BackendUpdate {} = error "updateFieldDef: did not expect BackendUpdate"

updatePersistValue :: Update v -> PersistValue
updatePersistValue (Update _ v _) = toPersistValue v
updatePersistValue (BackendUpdate{}) =
    error "updatePersistValue: did not expect BackendUpdate"

commaSeparated :: [Text] -> Text
commaSeparated = T.intercalate ", "

mkUpdateText :: PersistEntity record => SqlBackend -> Update record -> Text
mkUpdateText conn = mkUpdateText' (connEscapeName conn) id

mkUpdateText' :: PersistEntity record => (DBName -> Text) -> (Text -> Text) -> Update record -> Text
mkUpdateText' escapeName refColumn x =
  case updateUpdate x of
    Assign -> n <> "=?"
    Add -> T.concat [n, "=", refColumn n, "+?"]
    Subtract -> T.concat [n, "=", refColumn n, "-?"]
    Multiply -> T.concat [n, "=", refColumn n, "*?"]
    Divide -> T.concat [n, "=", refColumn n, "/?"]
    BackendSpecificUpdate up ->
      error . T.unpack $ "mkUpdateText: BackendSpecificUpdate " <> up <> " not supported"
  where
    n = escapeName . fieldDB . updateFieldDef $ x

parenWrapped :: Text -> Text
parenWrapped t = T.concat ["(", t, ")"]

-- | Make a list 'PersistValue' suitable for detabase inserts. Pairs nicely
-- with the function 'mkInsertPlaceholders'.
--
-- Does not include generated columns.
--
-- @since 2.11.0.0
mkInsertValues
    :: PersistEntity rec
    => rec
    -> [PersistValue]
mkInsertValues entity =
    Maybe.catMaybes
        . zipWith redactGeneratedCol (entityFields . entityDef $ Just entity)
        . map toPersistValue
        $ toPersistFields entity
  where
    redactGeneratedCol fd pv = case fieldGenerated fd of
        Nothing ->
            Just pv
        Just _ ->
            Nothing

-- | Returns a list of escaped field names and @"?"@ placeholder values for
-- performing inserts. This does not include generated columns.
--
-- Does not include generated columns.
--
-- @since 2.11.0.0
mkInsertPlaceholders
    :: EntityDef
    -> (DBName -> Text)
    -- ^ An `escape` function
    -> [(Text, Text)]
mkInsertPlaceholders ed escape =
    Maybe.mapMaybe redactGeneratedCol (entityFields ed)
  where
    redactGeneratedCol fd = case fieldGenerated fd of
        Nothing ->
            Just (escape (fieldDB fd), "?")
        Just _ ->
            Nothing