Add simple load and store methods for Metadata

package.yaml

@@ -9,12 +9,13 @@ description: Please see the README on GitHub at <https://github.com/Garmelon/mim
 github: Garmelon/mima-tools
 
 extra-source-files:
-- README.md
+  - README.md
 
 dependencies:
   - base >= 4.7 && < 5
   - OddWord >= 1.0 && < 1.1
   - aeson
+  - aeson-pretty
   - bytestring
   - containers
   - text

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

test/files/SimpleMetadataFile.json

@@ -0,0 +1,13 @@
+{
+  "global": {
+    "some-data": "some value"
+  },
+  "local": [
+    {
+      "at": 20,
+      "info": {
+        "src-line": 200
+      }
+    }
+  ]
+}