{-# LANGUAGE AllowAmbiguousTypes #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE GADTs #-}
{-# LANGUAGE NoImplicitPrelude #-}

-- |
-- Module      : Data.Morpheus.Types.SelectionTree
-- Description : A simple interface for Morpheus internal Selection Set's representation.
module Data.Morpheus.Types.SelectionTree where

import Data.Morpheus.Internal.Utils (elems, keyOf)
import Data.Morpheus.Types.Internal.AST
  ( FieldName (..),
    Selection (..),
    Selection (selectionContent),
    SelectionContent (SelectionField, SelectionSet, UnionSelection),
    UnionTag (..),
    VALID,
  )
import Data.Text (unpack)
import Relude

-- | The 'SelectionTree' instance is a simple interface for interacting
-- with morpheus's internal AST while keeping the ability to safely change the concrete
-- representation of the AST.
-- The set of operation is very limited on purpose.
class SelectionTree nodeType where
  -- | leaf test: is the list of children empty?
  isLeaf :: nodeType -> Bool

  -- | Get the children
  getChildrenList :: nodeType -> [nodeType]

  -- | get a node's name
  getName :: IsString name => nodeType -> name

instance SelectionTree (Selection VALID) where
  isLeaf node = case selectionContent node of
    SelectionField -> True
    _ -> False

  getChildrenList node = case selectionContent node of
    SelectionField -> mempty
    (SelectionSet deeperSel) -> elems deeperSel
    (UnionSelection sel) ->
      concatMap
        (elems . unionTagSelection)
        (elems sel)

  getName =
    fromString
      . unpack
      . readName
      . keyOf