{-# LANGUAGE DeriveAnyClass #-}
{-# LANGUAGE StandaloneKindSignatures #-}
{-# LANGUAGE UndecidableInstances #-}

-- | The 'Transform' typeclass with various types and helper functions
-- for evaluating transformations.
module Hasura.RQL.DDL.Webhook.Transform.Class
  ( -- * Transformation Interface and Utilities
    Transform (..),

    -- ** Error Context
    TransformErrorBundle (..),
    throwErrorBundle,

    -- ** Request Transformation Context
    RequestTransformCtx (..),
    ResponseTransformCtx (..),
    mkReqTransformCtx,

    -- * Templating
    TemplatingEngine (..),
    Template (..),
    Version (..),
    runRequestTemplateTransform,
    validateRequestTemplateTransform,
    validateRequestTemplateTransform',

    -- * Unescaped
    UnescapedTemplate (..),
    wrapUnescapedTemplate,
    runUnescapedRequestTemplateTransform,
    runUnescapedRequestTemplateTransform',
    runUnescapedResponseTemplateTransform,
    runUnescapedResponseTemplateTransform',
    validateRequestUnescapedTemplateTransform,
    validateRequestUnescapedTemplateTransform',
  )
where

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

import Control.Arrow (left)
import Control.Lens (bimap, view)
import Data.Aeson (FromJSON, FromJSONKey, ToJSON, ToJSONKey)
import Data.Aeson qualified as J
import Data.Aeson.Kriti.Functions as KFunc
import Data.ByteString (ByteString)
import Data.ByteString.Builder (toLazyByteString)
import Data.ByteString.Builder.Scientific (scientificBuilder)
import Data.ByteString.Lazy qualified as LBS
import Data.HashMap.Strict qualified as M
import Data.Kind (Constraint, Type)
import Data.Text.Encoding (encodeUtf8)
import Data.Text.Encoding qualified as TE
import Data.Validation (Validation, fromEither)
import Hasura.Incremental (Cacheable)
import Hasura.Prelude
import Hasura.Session (SessionVariables)
import Kriti.Error qualified as Kriti (CustomFunctionError (..), serialize)
import Kriti.Parser qualified as Kriti (parser)
import Network.HTTP.Client.Transformable qualified as HTTP

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

-- | 'Transform' describes how to reify a defunctionalized transformation for
-- a particular request field.
type Transform :: Type -> Constraint
class Transform a where
  -- | The associated type 'TransformFn a' is the defunctionalized version
  -- of some transformation that should be applied to a given request field.
  --
  -- In most cases it is some variation on a piece of template text describing
  -- the transformation.
  data TransformFn a :: Type

  -- | 'transform' is a function which takes 'TransformFn' of @a@ and reifies
  -- it into a function of the form:
  --
  -- @
  --   ReqTransformCtx -> a -> m a
  -- @
  transform ::
    MonadError TransformErrorBundle m =>
    TransformFn a ->
    RequestTransformCtx ->
    a ->
    m a

  -- | Validate a 'TransformFn' of @a@.
  validate ::
    TemplatingEngine ->
    TransformFn a ->
    Validation TransformErrorBundle ()

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

-- | We use collect all transformation failures as a '[J.Value]'.
newtype TransformErrorBundle = TransformErrorBundle
  { tebMessages :: [J.Value]
  }
  deriving stock (Eq, Generic, Show)
  deriving newtype (Monoid, Semigroup, FromJSON, ToJSON)
  deriving anyclass (Cacheable, NFData)

-- | A helper function for serializing transformation errors to JSON.
throwErrorBundle ::
  MonadError TransformErrorBundle m =>
  Text ->
  Maybe J.Value ->
  m a
throwErrorBundle msg val = do
  let requiredCtx =
        [ "error_code" J..= ("TransformationError" :: Text),
          "message" J..= msg
        ]
      optionalCtx =
        [ ("value" J..=) <$> val
        ]
      err = J.object (requiredCtx <> catMaybes optionalCtx)
  throwError $ TransformErrorBundle [err]

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

-- | Common context that is made available to all request transformations.
data RequestTransformCtx = RequestTransformCtx
  { rtcBaseUrl :: Maybe J.Value,
    rtcBody :: J.Value,
    rtcSessionVariables :: J.Value,
    rtcQueryParams :: Maybe J.Value,
    rtcEngine :: TemplatingEngine,
    rtcFunctions :: M.HashMap Text (J.Value -> Either Kriti.CustomFunctionError J.Value)
  }

instance ToJSON RequestTransformCtx where
  toJSON RequestTransformCtx {..} =
    let required =
          [ "body" J..= rtcBody,
            "session_variables" J..= rtcSessionVariables
          ]
        optional =
          [ ("base_url" J..=) <$> rtcBaseUrl,
            ("query_params" J..=) <$> rtcQueryParams
          ]
     in J.object (required <> catMaybes optional)

-- | A smart constructor for constructing the 'RequestTransformCtx'
--
-- XXX: This function makes internal usage of 'TE.decodeUtf8', which throws an
-- impure exception when the supplied 'ByteString' cannot be decoded into valid
-- UTF8 text!
mkReqTransformCtx ::
  Text ->
  Maybe SessionVariables ->
  TemplatingEngine ->
  HTTP.Request ->
  RequestTransformCtx
mkReqTransformCtx url sessionVars rtcEngine reqData =
  let rtcBaseUrl = Just $ J.toJSON url
      rtcBody =
        let mBody = view HTTP.body reqData >>= J.decode @J.Value
         in fromMaybe J.Null mBody
      rtcSessionVariables = J.toJSON sessionVars
      rtcQueryParams =
        let queryParams =
              view HTTP.queryParams reqData & fmap \(key, val) ->
                (TE.decodeUtf8 key, fmap TE.decodeUtf8 val)
         in Just $ J.toJSON queryParams
   in RequestTransformCtx
        { rtcBaseUrl,
          rtcBody,
          rtcSessionVariables,
          rtcQueryParams,
          rtcEngine,
          rtcFunctions = KFunc.sessionFunctions sessionVars
        }

-- | Common context that is made available to all response transformations.
data ResponseTransformCtx = ResponseTransformCtx
  { responseTransformBody :: J.Value,
    responseTransformReqCtx :: J.Value,
    responseTransformFunctions :: M.HashMap Text (J.Value -> Either Kriti.CustomFunctionError J.Value),
    responseTransformEngine :: TemplatingEngine
  }

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

-- | Available templating engines.
data TemplatingEngine
  = Kriti
  deriving stock (Bounded, Enum, Eq, Generic, Show)
  deriving anyclass (Cacheable, NFData)

-- XXX(jkachmar): We need roundtrip tests for these instances.
instance FromJSON TemplatingEngine where
  parseJSON =
    J.genericParseJSON
      J.defaultOptions
        { J.tagSingleConstructors = True
        }

-- XXX(jkachmar): We need roundtrip tests for these instances.
instance ToJSON TemplatingEngine where
  toJSON =
    J.genericToJSON
      J.defaultOptions
        { J.tagSingleConstructors = True
        }

  toEncoding =
    J.genericToEncoding
      J.defaultOptions
        { J.tagSingleConstructors = True
        }

-- | Textual transformation template.
newtype Template = Template
  { unTemplate :: Text
  }
  deriving stock (Eq, Generic, Ord, Show)
  deriving newtype (Hashable, FromJSONKey, ToJSONKey)
  deriving anyclass (Cacheable, NFData)

instance J.FromJSON Template where
  parseJSON = J.withText "Template" (pure . Template)

instance J.ToJSON Template where
  toJSON = J.String . coerce

-- | A helper function for executing transformations from a 'Template'
-- and a 'RequestTransformCtx'.
--
-- NOTE: This and all related funtions are hard-coded to Kriti at the
-- moment. When we add additional template engines this function will
-- need to take a 'TemplatingEngine' parameter.
runRequestTemplateTransform ::
  Template ->
  RequestTransformCtx ->
  Either TransformErrorBundle J.Value
runRequestTemplateTransform template RequestTransformCtx {rtcEngine = Kriti, ..} =
  let context =
        [ ("$body", rtcBody),
          ("$session_variables", rtcSessionVariables)
        ]
          <> catMaybes
            [ ("$query_params",) <$> rtcQueryParams,
              ("$base_url",) <$> rtcBaseUrl
            ]
      eResult = KFunc.runKritiWith (unTemplate $ template) context rtcFunctions
   in eResult & left \kritiErr ->
        let renderedErr = J.toJSON kritiErr
         in TransformErrorBundle [renderedErr]

-- TODO: Should this live in 'Hasura.RQL.DDL.Webhook.Transform.Validation'?
validateRequestTemplateTransform ::
  TemplatingEngine ->
  Template ->
  Either TransformErrorBundle ()
validateRequestTemplateTransform Kriti (Template template) =
  bimap packBundle (const ()) $ Kriti.parser $ TE.encodeUtf8 template
  where
    packBundle = TransformErrorBundle . pure . J.toJSON . Kriti.serialize

validateRequestTemplateTransform' ::
  TemplatingEngine ->
  Template ->
  Validation TransformErrorBundle ()
validateRequestTemplateTransform' engine =
  fromEither . validateRequestTemplateTransform engine

-- | A helper function for executing transformations from a 'Template'
-- and a 'ResponseTransformCtx'.
--
-- NOTE: This and all related funtions are hard-coded to Kriti at the
-- moment. When we add additional template engines this function will
-- need to take a 'TemplatingEngine' parameter.
runResponseTemplateTransform ::
  Template ->
  ResponseTransformCtx ->
  Either TransformErrorBundle J.Value
runResponseTemplateTransform template ResponseTransformCtx {responseTransformEngine = Kriti, ..} =
  let context = [("$body", responseTransformBody), ("$request", responseTransformReqCtx)]
      eResult = KFunc.runKritiWith (unTemplate $ template) context responseTransformFunctions
   in eResult & left \kritiErr ->
        let renderedErr = J.toJSON kritiErr
         in TransformErrorBundle [renderedErr]

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

-- | 'RequestTransform' Versioning
data Version
  = V1
  | V2
  deriving stock (Eq, Generic, Show)
  deriving anyclass (Cacheable, Hashable, NFData)

instance J.FromJSON Version where
  parseJSON v = do
    version :: Int <- J.parseJSON v
    case version of
      1 -> pure V1
      2 -> pure V2
      i -> fail $ "expected 1 or 2, encountered " ++ show i

instance J.ToJSON Version where
  toJSON = \case
    V1 -> J.toJSON @Int 1
    V2 -> J.toJSON @Int 2

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

-- | Validated textual transformation template /for string
-- interpolation only/.
--
-- This is necessary due to Kriti not distinguishing between string
-- literals and string templates.
newtype UnescapedTemplate = UnescapedTemplate
  { getUnescapedTemplate :: Text
  }
  deriving stock (Eq, Generic, Ord, Show)
  deriving newtype (Hashable, FromJSONKey, ToJSONKey)
  deriving anyclass (Cacheable, NFData)

instance J.FromJSON UnescapedTemplate where
  parseJSON = J.withText "Template" (pure . UnescapedTemplate)

instance J.ToJSON UnescapedTemplate where
  toJSON = J.String . coerce

-- | Wrap an 'UnescapedTemplate' with escaped double quotes.
wrapUnescapedTemplate :: UnescapedTemplate -> Template
wrapUnescapedTemplate (UnescapedTemplate txt) = Template $ "\"" <> txt <> "\""

-- | A helper function for executing Kriti transformations from a
-- 'UnescapedTemplate' and a 'RequestTrasformCtx'.
--
-- The difference from 'runRequestTemplateTransform' is that this
-- function will wrap the template text in double quotes before
-- running Kriti.
runUnescapedRequestTemplateTransform ::
  RequestTransformCtx ->
  UnescapedTemplate ->
  Either TransformErrorBundle ByteString
runUnescapedRequestTemplateTransform context unescapedTemplate = do
  result <-
    runRequestTemplateTransform
      (wrapUnescapedTemplate unescapedTemplate)
      context
  encodeScalar result

-- | Run a Kriti transformation with an unescaped template in
-- 'Validation' instead of 'Either'.
runUnescapedRequestTemplateTransform' ::
  RequestTransformCtx ->
  UnescapedTemplate ->
  Validation TransformErrorBundle ByteString
runUnescapedRequestTemplateTransform' context unescapedTemplate =
  fromEither $
    runUnescapedRequestTemplateTransform context unescapedTemplate

-- TODO: Should this live in 'Hasura.RQL.DDL.Webhook.Transform.Validation'?
validateRequestUnescapedTemplateTransform ::
  TemplatingEngine ->
  UnescapedTemplate ->
  Either TransformErrorBundle ()
validateRequestUnescapedTemplateTransform engine =
  validateRequestTemplateTransform engine . wrapUnescapedTemplate

validateRequestUnescapedTemplateTransform' ::
  TemplatingEngine ->
  UnescapedTemplate ->
  Validation TransformErrorBundle ()
validateRequestUnescapedTemplateTransform' engine =
  fromEither . validateRequestUnescapedTemplateTransform engine

-- | Run an 'UnescapedTemplate' with a 'ResponseTransformCtx'.
runUnescapedResponseTemplateTransform ::
  ResponseTransformCtx ->
  UnescapedTemplate ->
  Either TransformErrorBundle ByteString
runUnescapedResponseTemplateTransform context unescapedTemplate = do
  result <- runResponseTemplateTransform (wrapUnescapedTemplate unescapedTemplate) context
  encodeScalar result

-- | Run an 'UnescapedTemplate' with a 'ResponseTransformCtx' in 'Validation'.
runUnescapedResponseTemplateTransform' ::
  ResponseTransformCtx ->
  UnescapedTemplate ->
  Validation TransformErrorBundle ByteString
runUnescapedResponseTemplateTransform' context unescapedTemplate =
  fromEither $
    runUnescapedResponseTemplateTransform context unescapedTemplate

-------------------------------------------------------------------------------
-- Utility functions.

-- | Encode a JSON Scalar Value as a 'ByteString'.
-- If a non-Scalar value is provided, will return a 'TrnasformErrorBundle'
encodeScalar ::
  MonadError TransformErrorBundle m =>
  J.Value ->
  m ByteString
encodeScalar = \case
  J.String str -> pure $ encodeUtf8 str
  J.Number num ->
    pure . LBS.toStrict . toLazyByteString $ scientificBuilder num
  J.Bool True -> pure "true"
  J.Bool False -> pure "false"
  val ->
    throwErrorBundle "Template must produce a String, Number, or Boolean value" (Just val)