Types.hs

{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE PolyKinds #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}

{-|
  Module      : Database.PostgreSQL.Entity.Types
  Copyright   : © Clément Delafargue, 2018
                  Théophile Choutri, 2021
  License     : MIT
  Maintainer  : theophile@choutri.eu
  Stability   : stable

  Types and classes
-}
module Database.PostgreSQL.Entity.Types
  ( -- * The /Entity/ Typeclass
    Entity (..)

    -- * Associated Types
  , Field
  , field
  , fieldName
  , fieldType
  , UpdateRow (..)
  , SortKeyword (..)

    -- * Generics
  , Options (..)
  , defaultEntityOptions

    -- * DerivingVia Options
  , GenericEntity (..)
  , EntityOptions (..)
  , PrimaryKey
  , Schema
  , TableName
  , FieldModifiers
  , TextModifier (..)
  , StripPrefix
  , CamelTo
  , CamelToSnake
  , CamelToKebab
  )
where

import Data.Char
import Data.Kind
import Data.Maybe
import Data.Proxy
import Data.Text (Text)
import qualified Data.Text as T
import Data.Text.Display (Display, ShowInstance (..))
import qualified Data.Text.Manipulate as T
import Data.Vector (Vector)
import qualified Data.Vector as V
import qualified Data.Vector as Vector
import Database.PostgreSQL.Entity.Internal.QQ (field)
import Database.PostgreSQL.Entity.Internal.Unsafe (Field (Field))
import Database.PostgreSQL.Simple.ToRow (ToRow (..))
import GHC.Generics
import GHC.TypeLits

{-| An 'Entity' stores the following information about the structure of a database table:

 * Its name
 * Its primary key
 * The fields it contains

 == Example

 > data ExampleEntity = E
 >   { key    :: Key
 >   , field1 :: Int
 >   , field2 :: Bool
 >   }
 >   deriving stock (Eq, Show, Generic)
 >   deriving anyclass (FromRow, ToRow)
 >   deriving Entity
 >      via (GenericEntity '[TableName "entities"] ExampleEntity)

 When using the functions provided by this library, you will sometimes need to be explicit about the Entity you are
 referring to.

 @since 0.0.1.0
-}
class Entity e where
  -- | The name of the table in the PostgreSQL database.
  tableName :: Text
  default tableName :: (GetTableName (Rep e)) => Text
  tableName = getTableName @(Rep e) defaultEntityOptions

  -- | The name of the schema; will be appended to the table name: schema."tablename"
  schema :: Maybe Text
  schema = Nothing

  -- | The name of the primary key for the table.
  primaryKey :: Field
  default primaryKey :: (GetFields (Rep e)) => Field
  primaryKey = newPrimaryKey
    where
      primMod = primaryKeyModifiers defaultEntityOptions
      fs = getField @(Rep e) defaultEntityOptions
      newPrimaryKey =
        case Vector.find (\(Field name _type) -> name == primMod name) fs of
          Nothing -> Field (primMod "") Nothing
          Just f -> f

  -- | The fields of the table.
  fields :: Vector Field
  default fields :: (GetFields (Rep e)) => Vector Field
  fields = getField @(Rep e) defaultEntityOptions

-- The sub-class that fetches the table name
class GetTableName (e :: Type -> Type) where
  getTableName :: Options -> Text

instance (TypeError ('Text "You can't derive Entity for a void type")) => GetTableName V1 where
  getTableName _opts = error "You can't derive Entity for a void type"

instance (TypeError ('Text "You can't derive Entity for a unit type")) => GetTableName U1 where
  getTableName _opts = error "You can't derive Entity for a unit type"

instance (TypeError ('Text "You can't derive Entity for a sum type")) => GetTableName (e :+: f) where
  getTableName _opts = error "You can't derive Entity for a sum type"

instance (TypeError ('Text "You can't derive an Entity for a type constructor's field")) => GetTableName (K1 i c) where
  getTableName _opts = error "You can't derive Entity for a type constructor's field"

instance (TypeError ('Text "You don't have to derive GetTableName for a product type")) => GetTableName (e :*: f) where
  getTableName _opts = error "You don't have to derive GetTableName for a product type"

instance GetTableName e => GetTableName (M1 C _1 e) where
  getTableName opts = getTableName @e opts

instance GetTableName e => GetTableName (M1 S _1 e) where
  getTableName opts = getTableName @e opts

instance
  (KnownSymbol name)
  => GetTableName (M1 D ('MetaData name _1 _2 _3) e)
  where
  getTableName Options{tableNameModifiers, fieldModifiers} = tableNameModifiers $ fieldModifiers $ T.pack $ symbolVal (Proxy :: Proxy name)

-- The sub-class that fetches the table fields
class GetFields (e :: Type -> Type) where
  getField :: Options -> Vector Field

instance (TypeError ('Text "You can't derive Entity for a void type")) => GetFields V1 where
  getField _opts = error "You can't derive Entity for a void type"

instance (TypeError ('Text "You can't derive Entity for a unit type")) => GetFields U1 where
  getField _opts = error "You can't derive Entity for a unit type"

instance (TypeError ('Text "You can't derive Entity for a sum type")) => GetFields (e :+: f) where
  getField _opts = error "You can't derive Entity for a sum type"

instance (TypeError ('Text "You can't derive Entity for a a type constructor's field")) => GetFields (K1 i c) where
  getField _opts = error "You can't derive Entity for a type constructor's field"

instance (GetFields e, GetFields f) => GetFields (e :*: f) where
  getField opts = getField @e opts <> getField @f opts

instance GetFields e => GetFields (M1 C _1 e) where
  getField opts = getField @e opts

instance GetFields e => GetFields (M1 D ('MetaData _1 _2 _3 _4) e) where
  getField opts = getField @e opts

instance (KnownSymbol name) => GetFields (M1 S ('MetaSel ('Just name) _1 _2 _3) _4) where
  getField Options{fieldModifiers} = V.singleton $ Field fieldName' Nothing
    where
      fieldName' = fieldModifiers $ T.pack $ symbolVal (Proxy @name)

-- Deriving Via machinery

newtype GenericEntity t e = GenericEntity {getGenericEntity :: e}

instance (EntityOptions t, GetTableName (Rep e), GetFields (Rep e)) => Entity (GenericEntity t e) where
  tableName = getTableName @(Rep e) (entityOptions @t)

  schema = schemaModifier (entityOptions @t)

  primaryKey = newPrimaryKey
    where
      primMod = primaryKeyModifiers (entityOptions @t)
      fs = getField @(Rep e) (entityOptions @t)
      newPrimaryKey =
        case Vector.find (\(Field name _type) -> name == primMod name) fs of
          Nothing -> Field (primMod "") Nothing
          Just f -> f

  fields = getField @(Rep e) (entityOptions @t)

-- | Term-level options
data Options = Options
  { tableNameModifiers :: Text -> Text
  , schemaModifier :: Maybe Text
  , primaryKeyModifiers :: Text -> Text
  , fieldModifiers :: Text -> Text
  }

defaultEntityOptions :: Options
defaultEntityOptions =
  Options
    { tableNameModifiers = T.toSnake
    , schemaModifier = Nothing
    , primaryKeyModifiers = T.toSnake
    , fieldModifiers = T.toSnake
    }

-- | Type-level options for Deriving Via
class EntityOptions xs where
  entityOptions :: Options

instance EntityOptions '[] where
  entityOptions = defaultEntityOptions

instance (GetName name, EntityOptions xs) => EntityOptions (TableName name ': xs) where
  entityOptions = (entityOptions @xs){tableNameModifiers = const (getName @name)}

instance (GetName name, EntityOptions xs) => EntityOptions (PrimaryKey name ': xs) where
  entityOptions = (entityOptions @xs){primaryKeyModifiers = const (getName @name)}

instance (TextModifier mods, EntityOptions xs) => EntityOptions (FieldModifiers mods ': xs) where
  entityOptions = (entityOptions @xs){fieldModifiers = getTextModifier @mods}

instance (GetName name, EntityOptions xs) => EntityOptions (Schema name ': xs) where
  entityOptions = (entityOptions @xs){schemaModifier = Just $ getName @name}

data TableName (t :: Symbol)

data PrimaryKey (t :: Symbol)

data Schema (t :: Symbol)

-- | Contains a list of 'TextModifiers' modifiers
data FieldModifiers ms

-- | 'TextModifier' to remove a certain prefix from the fields
data StripPrefix (prefix :: Symbol)

-- | 'FieldModifier' taking a separator Char when transforming from CamelCase.
data CamelTo (separator :: Symbol)

-- | CamelCase to snake_case
type CamelToSnake = CamelTo "_"

-- | CamelCase to kebab-case
type CamelToKebab = CamelTo "-"

{-| The modifiers that you can apply to the fields:

 * 'StripPrefix'
 * 'CamelTo', and its variations
   * 'CamelToSnake'
   * 'CamelToKebab'
-}
class TextModifier t where
  getTextModifier :: Text -> Text

--  No modifier
instance TextModifier '[] where
  getTextModifier = id

-- How we can have multiple modifiers chained
instance (TextModifier x, TextModifier xs) => TextModifier (x ': xs) where
  getTextModifier = getTextModifier @xs . getTextModifier @x

instance (KnownSymbol prefix) => TextModifier (StripPrefix prefix) where
  getTextModifier fld = fromMaybe fld (T.stripPrefix prefixToStrip fld)
    where
      prefixToStrip = T.pack $ symbolVal (Proxy @prefix)

instance (KnownSymbol separator, NonEmptyText separator) => TextModifier (CamelTo separator) where
  getTextModifier fld = T.pack $ camelTo2 char (T.unpack fld)
    where
      char :: Char
      char = head $ symbolVal (Proxy @separator)
      camelTo2 :: Char -> String -> String
      camelTo2 c text = map toLower . go2 $ go1 text
        where
          go1 "" = ""
          go1 (x : u : l : xs) | isUpper u && isLower l = x : c : u : l : go1 xs
          go1 (x : xs) = x : go1 xs
          go2 "" = ""
          go2 (l : u : xs) | isLower l && isUpper u = l : c : u : go2 xs
          go2 (x : xs) = x : go2 xs

class GetName name where
  getName :: Text

instance (KnownSymbol name, NonEmptyText name) => GetName name where
  getName = T.pack (symbolVal (Proxy @name))

type family NonEmptyText (xs :: Symbol) :: Constraint where
  NonEmptyText "" = TypeError ('Text "User-provided string cannot be empty!")
  NonEmptyText _ = ()

{-| Get the name of a field.

 @since 0.1.0.0
-}
fieldName :: Field -> Text
fieldName (Field name _) = name

{-| Get the type of a field, if any.

 @since 0.1.0.0
-}
fieldType :: Field -> Maybe Text
fieldType (Field _ typ) = typ

{-| Wrapper used by the update function in order to have the primary key as the last parameter passed,
 since it appears in the WHERE clause.

 @since 0.0.1.0
-}
newtype UpdateRow a = UpdateRow {getUpdate :: a}
  deriving stock (Eq, Show)
  deriving newtype (Entity)

instance ToRow a => ToRow (UpdateRow a) where
  toRow = (drop <> take) 1 . toRow . getUpdate

{-|
 @since 0.0.2.0
-}
data SortKeyword = ASC | DESC
  deriving stock (Eq, Show)
  deriving
    (Display)
    via ShowInstance SortKeyword