-- | Helper functions for generating the schema of database tables
module Hasura.GraphQL.Schema.Table
  ( getTableGQLName
  , tableSelectColumnsEnum
  , tableUpdateColumnsEnum
  , tablePermissions
  , tableSelectPermissions
  , tableSelectFields
  , tableColumns
  , tableSelectColumns
  , tableUpdateColumns
  ) where

import           Hasura.Prelude

import qualified Data.HashMap.Strict           as Map
import qualified Data.HashSet                  as Set
import qualified Language.GraphQL.Draft.Syntax as G

import           Data.Text.Extended

import qualified Hasura.GraphQL.Parser         as P

import           Hasura.GraphQL.Parser         (Kind (..), Parser)
import           Hasura.GraphQL.Parser.Class
import           Hasura.GraphQL.Schema.Backend
import           Hasura.RQL.DML.Internal       (getRolePermInfo)
import           Hasura.RQL.Types

-- | Helper function to get the table GraphQL name. A table may have a
-- custom name configured with it. When the custom name exists, the GraphQL nodes
-- that are generated according to the custom name. For example: Let's say,
-- we have a table called `users address`, the name of the table is not GraphQL
-- compliant so we configure the table with a GraphQL compliant name,
-- say `users_address`
-- The generated top-level nodes of this table will be like `users_address`,
-- `insert_users_address` etc
getTableGQLName
  :: forall b r m. (Backend b, MonadTableInfo r m)
  => TableName b
  -> m G.Name
getTableGQLName tableName = do
  -- FIXME: pass tableInfo along to avoid unecessary cache lookups
  tableInfo <- askTableInfo @b tableName
  let tableCustomName = _tcCustomName . _tciCustomConfig . _tiCoreInfo $ tableInfo
  tableCustomName
    `onNothing` tableGraphQLName @b tableName
    `onLeft`    throwError

-- | Table select columns enum
--
-- Parser for an enum type that matches the columns of the given
-- table. Used as a parameter for "distinct", among others. Maps to
-- the table_select_column object.
--
-- Return Nothing if there's no column the current user has "select"
-- permissions for.
tableSelectColumnsEnum
  :: forall m n r b
   . (BackendSchema b, MonadSchema n m, MonadRole r m, MonadTableInfo r m)
  => TableName b
  -> SelPermInfo b
  -> m (Maybe (Parser 'Both n (Column b)))
tableSelectColumnsEnum table selectPermissions = do
  tableGQLName <- getTableGQLName @b table
  columns      <- tableSelectColumns table selectPermissions
  let enumName    = tableGQLName <> $$(G.litName "_select_column")
      description = Just $ G.Description $
        "select columns of table " <>> table
  pure $ P.enum enumName description <$> nonEmpty
    [ ( define $ pgiName column
      , pgiColumn column
      )
    | column <- columns
    ]
  where
    define name =
      P.mkDefinition name (Just $ G.Description "column name") P.EnumValueInfo

-- | Table update columns enum
--
-- Parser for an enum type that matches the columns of the given
-- table. Used for conflict resolution in "insert" mutations, among
-- others. Maps to the table_update_column object.
--
-- If there's no column for which the current user has "update"
-- permissions, this functions returns an enum that only contains a
-- placeholder, so as to still allow this type to exist in the schema.
tableUpdateColumnsEnum
  :: forall m n r b
   . (BackendSchema b, MonadSchema n m, MonadRole r m, MonadTableInfo r m)
  => TableName b
  -> UpdPermInfo b
  -> m (Parser 'Both n (Maybe (Column b)))
tableUpdateColumnsEnum table updatePermissions = do
  tableGQLName <- getTableGQLName @b table
  columns      <- tableUpdateColumns table updatePermissions
  let enumName   = tableGQLName <> $$(G.litName "_update_column")
      enumDesc   = Just $ G.Description $ "update columns of table " <>> table
      altDesc    = Just $ G.Description $ "placeholder for update columns of table " <> table <<> " (current role has no relevant permissions)"
      enumValues = do
        column <- columns
        pure (define $ pgiName column, Just $ pgiColumn column)
  pure $ case nonEmpty enumValues of
    Just values -> P.enum enumName enumDesc values
    Nothing     -> P.enum enumName altDesc $ pure (placeholder, Nothing)
  where
    define name = P.mkDefinition name (Just $ G.Description "column name") P.EnumValueInfo
    placeholder = P.mkDefinition $$(G.litName "_PLACEHOLDER") (Just $ G.Description "placeholder (do not use)") P.EnumValueInfo

tablePermissions
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => TableName b
  -> m (Maybe (RolePermInfo b))
tablePermissions table = do
  roleName  <- askRoleName
  tableInfo <- askTableInfo table
  pure $ getRolePermInfo roleName tableInfo

tableSelectPermissions
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => TableName b
  -> m (Maybe (SelPermInfo b))
tableSelectPermissions table = (_permSel =<<) <$> tablePermissions table

tableSelectFields
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => TableName b
  -> SelPermInfo b
  -> m [FieldInfo b]
tableSelectFields table permissions = do
  tableFields <- _tciFieldInfoMap . _tiCoreInfo <$> askTableInfo table
  filterM canBeSelected $ Map.elems tableFields
  where
    canBeSelected (FIColumn columnInfo) =
      pure $ Map.member (pgiColumn columnInfo) (spiCols permissions)
    canBeSelected (FIRelationship relationshipInfo) =
      isJust <$> tableSelectPermissions @_ @_ @_ @b (riRTable relationshipInfo)
    canBeSelected (FIComputedField computedFieldInfo) =
      case _cfiReturnType computedFieldInfo of
        CFRScalar _ ->
          pure $ Map.member (_cfiName computedFieldInfo) $ spiScalarComputedFields permissions
        CFRSetofTable tableName ->
          isJust <$> tableSelectPermissions @_ @_ @_ @b tableName
    canBeSelected (FIRemoteRelationship _) = pure True

tableColumns
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m)
  => TableName b
  -> m [ColumnInfo b]
tableColumns table =
  mapMaybe columnInfo . Map.elems . _tciFieldInfoMap . _tiCoreInfo <$> askTableInfo table
  where
    columnInfo (FIColumn ci) = Just ci
    columnInfo _             = Nothing

tableSelectColumns
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m, MonadRole r m)
  => TableName b
  -> SelPermInfo b
  -> m [ColumnInfo b]
tableSelectColumns table permissions =
  mapMaybe columnInfo <$> tableSelectFields table permissions
  where
    columnInfo (FIColumn ci) = Just ci
    columnInfo _             = Nothing

tableUpdateColumns
  :: forall m n r b. (Backend b, MonadSchema n m, MonadTableInfo r m)
  => TableName b
  -> UpdPermInfo b
  -> m [ColumnInfo b]
tableUpdateColumns table permissions = do
  tableFields <- _tciFieldInfoMap . _tiCoreInfo <$> askTableInfo table
  pure $ mapMaybe isUpdatable $ Map.elems tableFields
  where
    isUpdatable (FIColumn columnInfo) =
      if Set.member (pgiColumn columnInfo) (upiCols permissions)
         && not (Map.member (pgiColumn columnInfo) (upiSet permissions))
      then Just columnInfo
      else Nothing
    isUpdatable _ = Nothing