{- |
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.Base.Error
import           Hasura.EncJSON
import           Hasura.RQL.Types
import           Hasura.SQL.Tag
import           Hasura.Session


newtype TrackFunction b = TrackFunction { tfName :: FunctionName 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 b m
   . (CacheRM m, QErrM m, Backend b)
  => SourceName
  -> FunctionName b
  -> m ()
trackFunctionP1 sourceName qf = do
  rawSchemaCache <- askSchemaCache
  unless (isJust $ AB.unpackAnyBackend @b =<< Map.lookup sourceName (scSources rawSchemaCache)) $
    throw400 NotExists $ sourceName <<> " is not a known " <> reify (backendTag @b) <<> " source"
  when (isJust $ unsafeFunctionInfo @b sourceName qf $ scSources rawSchemaCache) $
    throw400 AlreadyTracked $ "function already tracked : " <>> qf
  let qt = functionToTable @b 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 @b qf)
    $ MetadataModifier
    $ metaSources.ix sourceName.toSourceMetadata.(smFunctions @b)
      %~ OMap.insert qf (FunctionMetadata qf config mempty)
  pure successMsg

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

runTrackFunc
  :: forall b m
   . (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 @b defaultSource qf
  trackFunctionP2 @b defaultSource qf emptyFunctionConfig

-- | JSON API payload for v2 of 'track_function':
--
-- https://hasura.io/docs/latest/graphql/core/api-reference/schema-metadata-api/custom-functions.html#track-function-v2
data TrackFunctionV2 (b :: BackendType) = TrackFunctionV2
  { _tfv2Source        :: !SourceName
  , _tfv2Function      :: !(FunctionName b)
  , _tfv2Configuration :: !FunctionConfig
  }

instance Backend b => FromJSON (TrackFunctionV2 b) where
  parseJSON = withObject "track function" $ \o ->
    TrackFunctionV2
    <$> o .:? "source" .!= defaultSource
    <*> o .: "function"
    <*> o .:? "configuration" .!= emptyFunctionConfig

runTrackFunctionV2
  :: forall b m
   . (BackendMetadata b, QErrM m, CacheRWM m, MetadataM m)
  => TrackFunctionV2 b
  -> m EncJSON
runTrackFunctionV2 (TrackFunctionV2 source qf config) = do
  trackFunctionP1 @b source qf
  trackFunctionP2 @b 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
  }

instance (Backend b) => FromJSON (UnTrackFunction b) where
  -- Following was the previous implementation, which while seems to be correct,
  -- has an unexpected behaviour. In the case when @source@ key is present but
  -- @function@ key is absent, it would silently coerce it into a @default@
  -- source. The culprint being the _alternative_ operator, which silently fails
  -- the first parse. This note exists so that we don't try to simplify using
  -- the _alternative_ pattern here.
  -- Previous implementation :-
  -- Consider the following JSON -
  --  {
  --    "source": "custom_source",
  --    "schema": "public",
  --    "name": "my_function"
  --  }
  -- it silently fails parsing the source here because @function@ key is not
  -- present, and proceeds to parse using @withoutSource@ as default source. Now
  -- this is surprising for the user, because they mention @source@ key
  -- explicitly. A better behaviour is to explicitly look for @function@ key if
  -- a @source@ key is present.
  -- >>
  -- parseJSON v = withSource <|> withoutSource
  --   where
  --     withoutSource = UnTrackFunction <$> parseJSON v <*> pure defaultSource
  --     withSource = flip (withObject "UnTrackFunction") v \o -> do
  --                  UnTrackFunction <$> o .: "function"
  --                                  <*> o .:? "source" .!= defaultSource
  parseJSON v = flip (withObject "UnTrackFunction") v $ \o -> do
    source <- o .:? "source"
    case source of
      Just src -> flip UnTrackFunction src <$> o .: "function"
      Nothing  -> UnTrackFunction <$> parseJSON v <*> pure defaultSource


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

dropFunctionInMetadata
  :: forall b
   . (BackendMetadata b)
  => SourceName
  -> FunctionName b
  -> MetadataModifier
dropFunctionInMetadata source function = MetadataModifier $
  metaSources.ix source.toSourceMetadata.(smFunctions @b) %~ 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 FunctionPermissionArgument b = FunctionPermissionArgument
  { _afpFunction :: !(FunctionName b)
  , _afpSource   :: !SourceName
  , _afpRole     :: !RoleName
  }

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

runCreateFunctionPermission
  :: forall b m
   . ( CacheRWM m
     , MonadError QErr m
     , MetadataM m
     , BackendMetadata b
     )
  => FunctionPermissionArgument b
  -> m EncJSON
runCreateFunctionPermission (FunctionPermissionArgument functionName source role) = do
  sourceCache <- scSources <$> askSchemaCache
  functionInfo <- askFunctionInfo @b 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 @b functionName role))
    $ MetadataModifier
    $ metaSources.ix
        source.toSourceMetadata.(smFunctions @b).ix functionName.fmPermissions
    %~ (:) (FunctionPermissionMetadata role)
  pure successMsg

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

runDropFunctionPermission
  :: forall m b
   . ( CacheRWM m
     , MonadError QErr m
     , MetadataM m
     , BackendMetadata b
     )
  => FunctionPermissionArgument b
  -> m EncJSON
runDropFunctionPermission (FunctionPermissionArgument functionName source role) = do
  functionInfo <- askFunctionInfo @b 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 @b functionName role)
    $ dropFunctionPermissionInMetadata @b source functionName role
  pure successMsg