{-# LANGUAGE CPP #-}
module Data.GraphQL.Execute where

#if !MIN_VERSION_base(4,8,0)
import Control.Applicative ((<$>), pure)
import Data.Traversable (traverse)
#endif
import Control.Applicative (Alternative, empty)
import Data.Foldable (fold)
import Data.Maybe (catMaybes)

import qualified Data.Aeson as Aeson
import qualified Data.HashMap.Strict as HashMap
import qualified Data.Text as T

import Data.GraphQL.AST
import Data.GraphQL.Schema (Resolver, Schema(..))
import qualified Data.GraphQL.Schema as Schema

execute :: (Alternative m, Monad m) => Schema m -> Schema.Subs -> Document -> m Aeson.Value
execute (Schema resolv) f doc = selectionSet f resolv =<< query doc

query :: Alternative f => Document -> f SelectionSet
query (Document [DefinitionOperation (Query (Node _varDefs _ _ sels))]) =
  pure sels
query  _ = empty

selectionSet :: Alternative f => Schema.Subs -> Resolver f -> SelectionSet -> f Aeson.Value
selectionSet f resolv = fmap (Aeson.Object . fold) . traverse (selection f resolv)

selection :: Alternative f => Schema.Subs -> Resolver f -> Selection -> f Aeson.Object
selection f resolv (SelectionField field@(Field alias name _ _ _)) =
    fmap (HashMap.singleton aliasOrName) $ Aeson.toJSON <$> resolv (fieldToInput f field)
  where
    aliasOrName = if T.null alias then name else alias
selection _ _ _ = empty

-- * AST/Schema conversions

argument :: Schema.Subs -> Argument -> Maybe Schema.Argument
argument f (Argument n (ValueVariable (Variable v))) =
    maybe Nothing (\v' -> Just (n, v')) $ f v
argument _ (Argument n (ValueInt v)) =
    Just (n, Schema.ScalarInt $ fromIntegral v)
argument _ (Argument n (ValueString (StringValue v))) =
    Just (n, Schema.ScalarString v)
argument _ _ = error "argument: not implemented yet"

fieldToInput :: Schema.Subs -> Field -> Schema.Input
fieldToInput f (Field _ n as _ sels) =
    Schema.InputField n (catMaybes $ argument f <$> as)
                        (fieldToInput f . selectionToField <$> sels)

selectionToField :: Selection -> Field
selectionToField (SelectionField x) = x
selectionToField _ = error "selectionField: not implemented yet"