Context.hs

{-# LANGUAGE BangPatterns #-}

module Json.Context
  ( Context (..)

    -- * Encoding
  , builderUtf8

    -- * Conversion
  , toPath
  ) where

import Data.Bytes.Builder (Builder)
import Data.Text.Short (ShortText)
import Json.Path (Path)

import qualified Json.Path as Path

{- | A finger into a json value indicating where a parser is
currently operating. When a parser focuses on a key-value
pair in a map, it adds 'Key' constructor to the context, and
when it focuses on an element of an array, it adds an 'Index'
constructor. Like all zipper-like data structures, it is, in
a sense, reversed, which makes it cheap to construct while
parsing.
-}
data Context
  = Top
  | Key !ShortText !Context
  | Index !Int !Context
  deriving (Eq, Show)

{- | Reverse the context, converting it to a 'Path'.
For example, toPath performs this conversion:

> 12.bar.foo.Top ==> foo.bar.12.Nil
-}
toPath :: Context -> Path
toPath = go Path.Nil
 where
  go !acc Top = acc
  go !acc (Key k xs) = go (Path.Key k acc) xs
  go !acc (Index i xs) = go (Path.Index i acc) xs

{- | Convert 'Context' to textual representation using UTF-8 as the encoding
scheme. This reverses the context to present it in the expected order.
-}
builderUtf8 :: Context -> Builder
builderUtf8 ctx0 = Path.builderUtf8 (toPath ctx0)