{-# LANGUAGE DeriveAnyClass #-}

module Hasura.GraphQL.Execute.Remote
  ( buildExecStepRemote,
    getVariableDefinitionAndValue,
    resolveRemoteVariable,
    resolveRemoteField,
    runVariableCache,
  )
where

import Data.Aeson qualified as J
import Data.HashMap.Strict qualified as HashMap
import Data.HashSet qualified as Set
import Data.Text qualified as T
import Data.Text.Extended
import Hasura.Base.Error
import Hasura.GraphQL.Execute.Backend
import Hasura.GraphQL.Execute.RemoteJoin.Types (RemoteJoins)
import Hasura.GraphQL.Parser
import Hasura.GraphQL.Transport.HTTP.Protocol
import Hasura.GraphQL.Transport.HTTP.Protocol qualified as GH
import Hasura.Prelude
import Hasura.RQL.IR.RemoteSchema qualified as IR
import Hasura.RQL.Types.Relationships.Remote
import Hasura.RQL.Types.ResultCustomization
import Hasura.RemoteSchema.SchemaCache
import Hasura.Session
import Language.GraphQL.Draft.Syntax qualified as G

getVariableDefinitionAndValue :: Variable -> (G.VariableDefinition, (G.Name, J.Value))
getVariableDefinitionAndValue var@(Variable varInfo gType varValue) =
  (varDefn, (varName, varJSONValue))
  where
    varName = getName var

    varDefn = G.VariableDefinition varName gType defaultVal

    defaultVal =
      case varInfo of
        VIRequired _ -> Nothing
        VIOptional _ val -> Just val

    varJSONValue =
      case varValue of
        JSONValue v -> v
        GraphQLValue val -> graphQLValueToJSON val

unresolveVariables ::
  forall fragments.
  (Functor fragments) =>
  G.SelectionSet fragments Variable ->
  G.SelectionSet fragments G.Name
unresolveVariables =
  fmap (fmap (getName . vInfo))

collectVariables ::
  forall fragments var.
  (Foldable fragments, Hashable var) =>
  G.SelectionSet fragments var ->
  Set.HashSet var
collectVariables =
  Set.unions . fmap (foldMap Set.singleton)

buildExecStepRemote ::
  RemoteSchemaInfo ->
  ResultCustomizer ->
  G.OperationType ->
  IR.GraphQLField Void Variable ->
  Maybe RemoteJoins ->
  Maybe OperationName ->
  ExecutionStep
buildExecStepRemote remoteSchemaInfo resultCustomizer tp rootField remoteJoins operationName =
  let selSet = [G.SelectionField $ IR.convertGraphQLField rootField]
      unresolvedSelSet = unresolveVariables selSet
      allVars = map getVariableDefinitionAndValue $ Set.toList $ collectVariables selSet
      varValues = HashMap.fromList $ map snd allVars
      varValsM = bool (Just varValues) Nothing $ HashMap.null varValues
      varDefs = map fst allVars
      _grQuery = G.TypedOperationDefinition tp (_unOperationName <$> operationName) varDefs [] unresolvedSelSet
      _grVariables = varValsM
      _grOperationName = operationName
   in ExecStepRemote remoteSchemaInfo resultCustomizer GH.GQLReq {..} remoteJoins

-- | Association between keys uniquely identifying some remote JSON variable and
-- an 'Int' identifier that will be used to construct a valid variable name to
-- be used in a GraphQL query.
newtype RemoteJSONVariableMap
  = RemoteJSONVariableMap (HashMap RemoteJSONVariableKey Int)
  deriving newtype (Eq, Monoid, Semigroup)

-- | A unique identifier for some remote JSON variable whose name will need to
-- be substituted when constructing a GraphQL query.
--
-- For a detailed explanation of this behavior, see the following comment:
-- https://github.com/hasura/graphql-engine/issues/7170#issuecomment-880838970
data RemoteJSONVariableKey = RemoteJSONVariableKey !G.GType !J.Value
  deriving stock (Eq, Generic)
  deriving anyclass (Hashable)

-- | Resolves a `RemoteSchemaVariable` into a GraphQL `Variable`.
--
-- A `RemoteSchemaVariable` can either be a query variable (i.e. a variable
-- provided in the query) or it can be a `SessionPresetVariable` (in which case
-- we look up the value of the session variable and coerce it into the
-- appropriate type and then construct the GraphQL 'Variable').
--
-- NOTE: The session variable preset is a hard preset (i.e. if the session
-- variable doesn't exist, an error will be thrown).
--
-- The name of the GraphQL variable generated will be a GraphQL-ized version of
-- the session variable (i.e. '-' will be replaced with '_'), since session
-- variables are not valid GraphQL names.
--
-- Additionally, we need to handle partially traversed JSON values; likewise, we
-- create a new variable out of thin air.
--
-- For example, considering the following schema for a role:
--
--   input UserName {
--     firstName : String! @preset(value:"Foo")
--     lastName  : String!
--   }
--
--   type Query {
--     user(
--       user_id:   Int! @preset(value:"x-hasura-user-id")
--       user_name: UserName!
--     ): User
--   }
--
-- and the incoming query to the graphql-engine is:
--
--   query($foo: UserName!) {
--     user(user_name: $foo) { id name }
--   }
--
-- with variables:
--
--   { "foo": {"lastName": "Bar"} }
--
--
-- After resolving the session argument presets, the query that will be sent to
-- the remote server will be:
--
-- query ($x_hasura_user_id: Int!, $hasura_json_var_1: String!) {
--   user (user_id: $x_hasura_user_id, user_name: {firstName: "Foo", lastName: $hasura_json_var_1}) {
--     id
--     name
--   }
-- }
resolveRemoteVariable ::
  (MonadError QErr m) =>
  UserInfo ->
  RemoteSchemaVariable ->
  StateT RemoteJSONVariableMap m Variable
resolveRemoteVariable userInfo = \case
  SessionPresetVariable sessionVar typeName presetInfo -> do
    sessionVarVal <-
      onNothing (getSessionVariableValue sessionVar $ _uiSession userInfo)
        $ throw400 NotFound
        $ sessionVar
        <<> " session variable expected, but not found"
    varName <-
      sessionVariableToGraphQLName sessionVar
        `onNothing` throw500 ("'" <> sessionVariableToText sessionVar <> "' cannot be made into a valid GraphQL name")
    coercedValue <-
      case presetInfo of
        SessionArgumentPresetScalar ->
          case G.unName typeName of
            "Int" ->
              case readMaybe $ T.unpack sessionVarVal of
                Nothing -> throw400 CoercionError $ sessionVarVal <<> " cannot be coerced into an Int value"
                Just i -> pure $ G.VInt i
            "Boolean" ->
              if
                | sessionVarVal `elem` ["true", "false"] ->
                    pure $ G.VBoolean $ "true" == sessionVarVal
                | otherwise ->
                    throw400 CoercionError $ sessionVarVal <<> " cannot be coerced into a Boolean value"
            "Float" ->
              case readMaybe $ T.unpack sessionVarVal of
                Nothing ->
                  throw400 CoercionError $ sessionVarVal <<> " cannot be coerced into a Float value"
                Just i -> pure $ G.VFloat i
            -- The `String`,`ID` and the default case all use the same code. But,
            -- it will be better to not merge all of them into the default case
            -- because it will be helpful to know how all the built-in scalars
            -- are handled
            "String" -> pure $ G.VString sessionVarVal
            "ID" -> pure $ G.VString sessionVarVal
            -- When we encounter a custom scalar, we just pass it as a string
            _ -> pure $ G.VString sessionVarVal
        SessionArgumentPresetEnum enumVals -> do
          sessionVarEnumVal <-
            G.EnumValue
              <$> onNothing
                (G.mkName sessionVarVal)
                (throw400 CoercionError $ sessionVarVal <<> " is not a valid GraphQL name")
          case sessionVarEnumVal `Set.member` enumVals of
            True -> pure $ G.VEnum sessionVarEnumVal
            False -> throw400 CoercionError $ sessionVarEnumVal <<> " is not one of the valid enum values"
    -- nullability is false, because we treat presets as hard presets
    let variableGType = G.TypeNamed (G.Nullability False) typeName
    pure $ Variable (VIRequired varName) variableGType (GraphQLValue coercedValue)
  RemoteJSONValue gtype jsonValue -> do
    let key = RemoteJSONVariableKey gtype jsonValue
    varMap <- gets coerce
    index <-
      HashMap.lookup key varMap `onNothing` do
        let i = HashMap.size varMap + 1
        put . coerce $ HashMap.insert key i varMap
        pure i
    -- This should never fail.
    let varText = "hasura_json_var_" <> tshow index
    varName <-
      G.mkName varText
        `onNothing` throw500 ("'" <> varText <> "' is not a valid GraphQL name")
    pure $ Variable (VIRequired varName) gtype $ JSONValue jsonValue
  QueryVariable variable -> pure variable

-- | TODO: Documentation.
resolveRemoteField ::
  (MonadError QErr m) =>
  UserInfo ->
  IR.RemoteSchemaRootField r RemoteSchemaVariable ->
  StateT RemoteJSONVariableMap m (IR.RemoteSchemaRootField r Variable)
resolveRemoteField userInfo = traverse (resolveRemoteVariable userInfo)

-- | TODO: Documentation.
runVariableCache ::
  (Monad m) =>
  StateT RemoteJSONVariableMap m a ->
  m a
runVariableCache = flip evalStateT mempty