{- |
Description: Create/delete SQL functions to/from Hasura metadata.
-}

module Hasura.RQL.DDL.Schema.Function where

import           Hasura.Prelude

import qualified Data.HashMap.Strict        as Map
import qualified Data.HashMap.Strict.InsOrd as OMap

import           Data.Aeson
import           Data.Text.Extended

import qualified Hasura.SQL.AnyBackend      as AB

import           Hasura.EncJSON
import           Hasura.RQL.Types
import           Hasura.Session

newtype TrackFunction b
  = TrackFunction
  { tfName :: FunctionName b }
deriving instance (Backend b) => Show (TrackFunction b)
deriving instance (Backend b) => Eq (TrackFunction b)
deriving instance (Backend b) => FromJSON (TrackFunction b)
deriving instance (Backend b) => ToJSON (TrackFunction b)

-- | Track function, Phase 1:
-- Validate function tracking operation. Fails if function is already being
-- tracked, or if a table with the same name is being tracked.
trackFunctionP1
  :: forall m b
   . (CacheRM m, QErrM m, Backend b)
  => SourceName -> FunctionName b -> m ()
trackFunctionP1 sourceName qf = do
  rawSchemaCache <- askSchemaCache
  when (isJust $ unsafeFunctionInfo @b sourceName qf $ scSources rawSchemaCache) $
    throw400 AlreadyTracked $ "function already tracked : " <>> qf
  let qt = functionToTable qf
  when (isJust $ unsafeTableInfo @b sourceName qt $ scSources rawSchemaCache) $
    throw400 NotSupported $ "table with name " <> qf <<> " already exists"

trackFunctionP2
  :: forall b m
   . (MonadError QErr m, CacheRWM m, MetadataM m, BackendMetadata b)
  => SourceName -> FunctionName b -> FunctionConfig -> m EncJSON
trackFunctionP2 sourceName qf config = do
  buildSchemaCacheFor
    (MOSourceObjId sourceName $ AB.mkAnyBackend $ SMOFunction qf)
    $ MetadataModifier
    $ metaSources.ix sourceName.toSourceMetadata.smFunctions
      %~ OMap.insert qf (FunctionMetadata qf config mempty)
  pure successMsg

handleMultipleFunctions :: (QErrM m, Backend b) => FunctionName b -> [a] -> m a
handleMultipleFunctions qf = \case
  []      ->
    throw400 NotExists $ "no such function exists in postgres : " <>> qf
  [fi] -> return fi
  _       ->
    throw400 NotSupported $
    "function " <> qf <<> " is overloaded. Overloaded functions are not supported"

runTrackFunc
  :: (MonadError QErr m, CacheRWM m, MetadataM m, BackendMetadata b)
  => TrackFunction b -> m EncJSON
runTrackFunc (TrackFunction qf)= do
  -- v1 track_function lacks a means to take extra arguments
  trackFunctionP1 defaultSource qf
  trackFunctionP2 defaultSource qf emptyFunctionConfig

runTrackFunctionV2
  :: (QErrM m, CacheRWM m, MetadataM m)
  => TrackFunctionV2 -> m EncJSON
runTrackFunctionV2 (TrackFunctionV2 source qf config) = do
  trackFunctionP1 source qf
  trackFunctionP2 source qf config

-- | JSON API payload for 'untrack_function':
--
-- https://hasura.io/docs/latest/graphql/core/api-reference/schema-metadata-api/custom-functions.html#untrack-function
data UnTrackFunction b
  = UnTrackFunction
  { _utfFunction :: !(FunctionName b)
  , _utfSource   :: !SourceName
  } deriving (Generic)
deriving instance (Backend b) => Show (UnTrackFunction b)
deriving instance (Backend b) => Eq (UnTrackFunction b)
instance (Backend b) => ToJSON (UnTrackFunction b) where
  toJSON = genericToJSON hasuraJSON

instance (Backend b) => FromJSON (UnTrackFunction b) where
  parseJSON v = withSource <|> withoutSource
    where
      withoutSource = UnTrackFunction <$> parseJSON v <*> pure defaultSource
      withSource = flip (withObject "UnTrackFunction") v \o ->
                   UnTrackFunction <$> o .: "function"
                                   <*> o .:? "source" .!= defaultSource

askFunctionInfo
  :: forall m b
   . (CacheRM m, MonadError QErr m, Backend b)
  => SourceName -> FunctionName b -> m (FunctionInfo b)
askFunctionInfo source functionName = do
  sourceCache <- scSources <$> askSchemaCache
  unsafeFunctionInfo @b source functionName sourceCache
    `onNothing` throw400 NotExists ("function " <> functionName <<> " not found in the cache")

runUntrackFunc
  :: (CacheRWM m, MonadError QErr m, MetadataM m, BackendMetadata b)
  => UnTrackFunction b -> m EncJSON
runUntrackFunc (UnTrackFunction functionName sourceName) = do
  void $ askFunctionInfo sourceName functionName
  withNewInconsistentObjsCheck
    $ buildSchemaCache
    $ dropFunctionInMetadata defaultSource functionName
  pure successMsg

dropFunctionInMetadata :: (BackendMetadata b) => SourceName -> FunctionName b -> MetadataModifier
dropFunctionInMetadata source function = MetadataModifier $
  metaSources.ix source.toSourceMetadata.smFunctions %~ OMap.delete function

{- Note [Function Permissions]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Before we started supporting tracking volatile functions, permissions
for a function was inferred from the target table of the function.
The rationale behind this is that a stable/immutable function does not
modify the database and the data returned by the function is filtered using
the permissions that are specified precisely for that data.
Now consider mutable/volatile functions, we can't automatically infer whether or
not these functions should be exposed for the sole reason that they can modify
the database. This necessitates a permission system for functions.
So, we introduce a new API `pg_create_function_permission` which will
explicitly grant permission to a function to a role. For creating a
function permission, the role must have select permissions configured
for the target table.
Since, this is a breaking change, we enable it only when the graphql-engine
is started with
`--infer-function-permissions`/HASURA_GRAPHQL_INFER_FUNCTION_PERMISSIONS set
to false (by default, it's set to true).
-}

data CreateFunctionPermission b
  = CreateFunctionPermission
  { _afpFunction :: !(FunctionName b)
  , _afpSource   :: !SourceName
  , _afpRole     :: !RoleName
  } deriving (Generic)
deriving instance (Backend b) => Show (CreateFunctionPermission b)
deriving instance (Backend b) => Eq (CreateFunctionPermission b)
instance (Backend b) => ToJSON (CreateFunctionPermission b) where
  toJSON = genericToJSON hasuraJSON

instance (Backend b) => FromJSON (CreateFunctionPermission b) where
  parseJSON v =
    flip (withObject "CreateFunctionPermission") v $ \o ->
      CreateFunctionPermission
      <$> o .: "function"
      <*> o .:? "source" .!= defaultSource
      <*> o .: "role"

runCreateFunctionPermission
  :: forall m b
   . ( CacheRWM m
     , MonadError QErr m
     , MetadataM m
     , BackendMetadata b
     )
  => CreateFunctionPermission b
  -> m EncJSON
runCreateFunctionPermission (CreateFunctionPermission functionName source role) = do
  sourceCache <- scSources <$> askSchemaCache
  functionInfo <- askFunctionInfo source functionName
  when (role `elem` _fiPermissions functionInfo) $
    throw400 AlreadyExists $
    "permission of role "
    <> role <<> " already exists for function " <> functionName <<> " in source: " <>> source
  functionTableInfo <-
    unsafeTableInfo @b source (_fiReturnType functionInfo) sourceCache
    `onNothing` throw400 NotExists ("function's return table " <> _fiReturnType functionInfo <<> " not found in the cache")
  unless (role `Map.member` _tiRolePermInfoMap functionTableInfo) $
    throw400 NotSupported $
    "function permission can only be added when the function's return table "
    <> _fiReturnType functionInfo <<>  " has select permission configured for role: " <>> role
  buildSchemaCacheFor
    (MOSourceObjId source
      $ AB.mkAnyBackend (SMOFunctionPermission functionName role))
    $ MetadataModifier
    $ metaSources.ix
        source.toSourceMetadata.smFunctions.ix
        functionName.fmPermissions
    %~ (:) (FunctionPermissionMetadata role)
  pure successMsg

dropFunctionPermissionInMetadata
  :: (BackendMetadata b)
  => SourceName -> FunctionName b -> RoleName -> MetadataModifier
dropFunctionPermissionInMetadata source function role = MetadataModifier $
  metaSources.ix source.toSourceMetadata.smFunctions.ix function.fmPermissions %~ filter ((/=) role . _fpmRole)

type DropFunctionPermission = CreateFunctionPermission

runDropFunctionPermission
  :: forall m b
   . ( CacheRWM m
     , MonadError QErr m
     , MetadataM m
     , BackendMetadata b
     )
  => DropFunctionPermission b
  -> m EncJSON
runDropFunctionPermission (CreateFunctionPermission functionName source role) = do
  functionInfo <- askFunctionInfo source functionName
  unless (role `elem` _fiPermissions functionInfo) $
    throw400 NotExists $
    "permission of role "
    <> role <<> " does not exist for function " <> functionName <<> " in source: " <>> source
  buildSchemaCacheFor
    (MOSourceObjId source
      $ AB.mkAnyBackend
      $ SMOFunctionPermission functionName role)
    $ dropFunctionPermissionInMetadata source functionName role
  pure successMsg