decoding-nested-json-fragment.purs

module X where

import Prelude
import Data.Foreign (F)
import Data.Foreign.Class (class IsForeign, readJSON, readProp)
import Data.Foreign.Index (prop)
import Control.Monad.Eff.Console (logShow)
import Data.Either (Either(..))

-- { repo(owner: “tom”, name: “holborn”)
--   { commit(ref: “master“) { target blob(path: “README.md”) { contents date } } } }
type DateTime = Int


data BrowseFragment = BrowseFragment
  { repo ::
       { commit ::
            { target :: String
            , blob :: { contents :: String, date :: DateTime }
            }
       }
  }

-- manually constructed fragment:
fragment = BrowseFragment { repo: { commit: { target: "master", blob: { contents: "main = print 10", date: 2016 } } } }

-- reading a fragment from JSON
instance isForeignBrowseFragment :: IsForeign BrowseFragment where
  read value = do
    repo <- prop "repo" value
    commit <- prop "commit" repo
    target <- readProp "target" commit
    blob <- prop "blob" commit
    contents <- readProp "contents" blob
    date <- readProp "date" blob
    pure (BrowseFragment { repo: { commit: { target: target, blob: { contents, date }}}})


testJSON = """{ "repo": { "commit": { "target": "master", "blob": { "contents": "main = print 10", "date": 2016 } } } }"""

test = case (readJSON testJSON :: F BrowseFragment) of
  Right r -> do
    logShow "Ok"
  Left err -> do
    logShow "no"