Add simple load and store methods for Metadata

src/Mima/Vm/Storage.hs

@@ -0,0 +1,39 @@
+module Mima.Vm.Storage
+  (
+  -- * Methods for loading/storing Metadata
+    loadMetadata
+  , saveMetadata
+  -- * Test methods
+  , roundTripFile
+  ) where
+
+import           Data.Aeson
+import           Data.Aeson.Encode.Pretty
+import qualified Data.ByteString.Lazy     as BSL
+import qualified Data.Text                as T
+import           Mima.Run
+import           Mima.Vm.Metadata
+
+-- | Loads 'Metadata' from a given file path
+loadMetadata :: FilePath -> Run Metadata
+loadMetadata path = do
+  file <- readFileBS path
+  let decoded = eitherDecode (BSL.fromStrict file) :: Either String Metadata
+  case decoded of
+    Left msg       -> throw (T.pack msg)
+    Right metadata -> pure metadata
+
+-- | Stores prettified 'Metadata' in a given file.
+saveMetadata :: FilePath -> Metadata -> Run ()
+saveMetadata path metadata = writeFileBS path (BSL.toStrict (encodePretty metadata))
+
+-- | A garbage test method that resds the input file, parses it and writes the
+--   prettified result back in the output file.
+--
+-- Can be used with the example file:
+--
+-- > roundTripFile "test/files/SimpleMetadataFile.json" "/tmp/test.json"
+roundTripFile :: FilePath -- ^ The input file
+              -> FilePath -- ^ The output file
+              -> Run ()
+roundTripFile input output = loadMetadata input >>= saveMetadata output