module Hasura.RQL.DDL.Schema.Cache.Dependencies
  ( resolveDependencies
  ) where

import           Hasura.Prelude

import qualified Data.HashMap.Strict.Extended       as M
import qualified Data.HashSet                       as HS

import           Control.Arrow.Extended
import           Control.Lens                       hiding ((.=))
import           Data.Aeson
import           Data.List                          (nub)
import           Data.Monoid                        (First)

import           Hasura.RQL.DDL.Schema.Cache.Common
import           Hasura.RQL.Types
import           Hasura.SQL.Types

-- | Processes collected 'CIDependency' values into a 'DepMap', performing integrity checking to
-- ensure the dependencies actually exist. If a dependency is missing, its transitive dependents are
-- removed from the cache, and 'InconsistentMetadata's are returned.
resolveDependencies
  :: (ArrowKleisli m arr, QErrM m)
  => ( BuildOutputs
     , [(MetadataObject, SchemaObjId, SchemaDependency)]
     ) `arr` (BuildOutputs, [InconsistentMetadata], DepMap)
resolveDependencies = arrM \(cache, dependencies) -> do
  let dependencyMap = dependencies
        & M.groupOn (view _2)
        & fmap (map \(metadataObject, _, schemaDependency) -> (metadataObject, schemaDependency))
  performIteration 0 cache [] dependencyMap

-- Processes dependencies using an iterative process that alternates between two steps:
--
--   1. First, pruneDanglingDependents searches for any dependencies that do not exist in the
--      current cache and removes their dependents from the dependency map, returning an
--      InconsistentMetadata for each dependent that was removed. This step does not change
--      the schema cache in any way.
--
--   2. Second, deleteMetadataObject drops the pruned dependent objects from the cache. It does
--      not alter (or consult) the dependency map, so transitive dependents are /not/ removed.
--
-- By iterating the above process until pruneDanglingDependents does not discover any new
-- inconsistencies, all missing dependencies will eventually be removed, and since dependency
-- graphs between schema objects are unlikely to be very deep, it will usually terminate in just
-- a few iterations.
performIteration
  :: (QErrM m)
  => Int
  -> BuildOutputs
  -> [InconsistentMetadata]
  -> HashMap SchemaObjId [(MetadataObject, SchemaDependency)]
  -> m (BuildOutputs, [InconsistentMetadata], DepMap)
performIteration iterationNumber cache inconsistencies dependencies = do
  let (newInconsistencies, prunedDependencies) = pruneDanglingDependents cache dependencies
  case newInconsistencies of
    [] -> pure (cache, inconsistencies, HS.fromList . map snd <$> prunedDependencies)
    _ | iterationNumber < 100 -> do
          let inconsistentIds = nub $ concatMap imObjectIds newInconsistencies
              prunedCache = foldl' (flip deleteMetadataObject) cache inconsistentIds
              allInconsistencies = inconsistencies <> newInconsistencies
          performIteration (iterationNumber + 1) prunedCache allInconsistencies prunedDependencies
      | otherwise ->
          -- Running for 100 iterations without terminating is (hopefully) enormously unlikely
          -- unless we did something very wrong, so halt the process and abort with some
          -- debugging information.
          throwError (err500 Unexpected "schema dependency resolution failed to terminate")
            { qeInternal = Just $ object
                [ "inconsistent_objects" .= object
                  [ "old" .= inconsistencies
                  , "new" .= newInconsistencies ]
                , "pruned_dependencies" .= (map snd <$> prunedDependencies) ] }

pruneDanglingDependents
  :: BuildOutputs
  -> HashMap SchemaObjId [(MetadataObject, SchemaDependency)]
  -> ([InconsistentMetadata], HashMap SchemaObjId [(MetadataObject, SchemaDependency)])
pruneDanglingDependents cache = fmap (M.filter (not . null)) . traverse do
  partitionEithers . map \(metadataObject, dependency) -> case resolveDependency dependency of
    Right ()          -> Right (metadataObject, dependency)
    Left errorMessage -> Left (InconsistentObject errorMessage metadataObject)
  where
    resolveDependency :: SchemaDependency -> Either Text ()
    resolveDependency (SchemaDependency objectId _) = case objectId of
      SOTable tableName -> void $ resolveTable tableName
      SOFunction functionName -> unless (functionName `M.member` _boFunctions cache) $
        Left $ "function " <> functionName <<> " is not tracked"
      SORemoteSchema remoteSchemaName -> unless (remoteSchemaName `M.member` _boRemoteSchemas cache) $
        Left $ "remote schema " <> remoteSchemaName <<> " is not found"
      SOTableObj tableName tableObjectId -> do
        tableInfo <- resolveTable tableName
        case tableObjectId of
          TOCol columnName ->
            void $ resolveField tableInfo (fromPGCol columnName) _FIColumn "column"
          TORel relName ->
            void $ resolveField tableInfo (fromRel relName) _FIRelationship "relationship"
          TOComputedField fieldName ->
            void $ resolveField tableInfo (fromComputedField fieldName) _FIComputedField "computed field"
          TORemoteRel fieldName ->
            void $ resolveField tableInfo (fromRemoteRelationship fieldName) _FIRemoteRelationship "remote relationship"
          TOForeignKey constraintName -> do
            let foreignKeys = _tciForeignKeys $ _tiCoreInfo tableInfo
            unless (isJust $ find ((== constraintName) . _cName . _fkConstraint) foreignKeys) $
              Left $ "no foreign key constraint named " <> constraintName <<> " is "
                <> "defined for table " <>> tableName
          TOPerm roleName permType -> withPermType permType \accessor -> do
            let permLens = permAccToLens accessor
            unless (has (tiRolePermInfoMap.ix roleName.permLens._Just) tableInfo) $
              Left $ "no " <> permTypeToCode permType <> " permission defined on table "
                <> tableName <<> " for role " <>> roleName
          TOTrigger triggerName ->
            unless (M.member triggerName (_tiEventTriggerInfoMap tableInfo)) $ Left $
              "no event trigger named " <> triggerName <<> " is defined for table " <>> tableName

    resolveTable tableName = M.lookup tableName (_boTables cache) `onNothing`
      Left ("table " <> tableName <<> " is not tracked")

    resolveField :: TableInfo -> FieldName -> Getting (First a) FieldInfo a -> Text -> Either Text a
    resolveField tableInfo fieldName fieldType fieldTypeName = do
      let coreInfo = _tiCoreInfo tableInfo
          tableName = _tciName coreInfo
      fieldInfo <- M.lookup fieldName (_tciFieldInfoMap coreInfo) `onNothing` Left
        ("table " <> tableName <<> " has no field named " <>> fieldName)
      (fieldInfo ^? fieldType) `onNothing` Left
        ("field " <> fieldName <<> "of table " <> tableName <<> " is not a " <> fieldTypeName)

deleteMetadataObject :: MetadataObjId -> BuildOutputs -> BuildOutputs
deleteMetadataObject objectId = case objectId of
  MOTable        name -> boTables        %~ M.delete name
  MOFunction     name -> boFunctions     %~ M.delete name
  MORemoteSchema name -> boRemoteSchemas %~ M.delete name
  MOCronTrigger name  -> boCronTriggers %~ M.delete name
  MOTableObj tableName tableObjectId -> boTables.ix tableName %~ case tableObjectId of
    MTORel           name _    -> tiCoreInfo.tciFieldInfoMap %~ M.delete (fromRel name)
    MTOComputedField name      -> tiCoreInfo.tciFieldInfoMap %~ M.delete (fromComputedField name)
    MTORemoteRelationship name -> tiCoreInfo.tciFieldInfoMap %~ M.delete (fromRemoteRelationship name)
    MTOPerm roleName permType -> withPermType permType \accessor ->
      tiRolePermInfoMap.ix roleName.permAccToLens accessor .~ Nothing
    MTOTrigger name -> tiEventTriggerInfoMap %~ M.delete name
  MOCustomTypes                -> boCustomTypes %~ const (NonObjectTypeMap mempty, mempty)
  MOAction           name      -> boActions %~ M.delete name
  MOActionPermission name role -> boActions.ix name.aiPermissions %~ M.delete role