3 files changed, 149 insertions, 30 deletions
diff --git a/src/Conftrack/Source.hs b/src/Conftrack/Source.hs
index df6f82c..ecfa20d 100644
--- a/src/Conftrack/Source.hs
+++ b/src/Conftrack/Source.hs
@@ -3,44 +3,21 @@
 {-# LANGUAGE ImpredicativeTypes #-}
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}
-{-# LANGUAGE OverloadedStrings #-}
 
-module Conftrack.Source (ConfigSource(..), SomeSource(..), Trivial(..)) where
+module Conftrack.Source (ConfigSource(..), SomeSource(..)) where
 
-import Conftrack.Value (Key, Value(..), ConfigError(..), Origin)
+import Conftrack.Value (Key, Value(..), ConfigError(..))
 
-import Control.Monad.State (get, modify, StateT (..), MonadState (..))
-import Data.Map.Strict (Map)
-import qualified Data.Map.Strict as M
-import Data.Function ((&))
+import Control.Monad.State (StateT (..))
 import Data.Text (Text)
-import qualified Data.Text as T
 
 
 class ConfigSource s where
-  type ConfigState s
-  fetchValue :: Key ->  s -> StateT (ConfigState s) IO (Either ConfigError (Value, Text))
-  leftovers ::  s -> StateT (ConfigState s) IO (Maybe [Key])
+  type SourceState s
+  fetchValue :: Key -> s -> StateT (SourceState s) IO (Either ConfigError (Value, Text))
+  leftovers :: s -> StateT (SourceState s) IO (Maybe [Key])
 
 data SomeSource = forall source. ConfigSource source
-   => SomeSource (source, ConfigState source)
+   => SomeSource (source, SourceState source)
 
 
-newtype Trivial = Trivial (Map Key Value)
-
-instance ConfigSource Trivial where
-  type ConfigState Trivial = [Key]
-  fetchValue key (Trivial tree) = do
-    case M.lookup key tree of
-      Nothing -> pure $ Left NotPresent
-      Just val -> do
-        modify (key :)
-        pure $ Right (val, "Trivial source with keys "<> T.pack (show (M.keys tree)))
-
-  leftovers (Trivial tree) = do
-    used <- get
-
-    M.keys tree
-     & filter (`notElem` used)
-     & Just
-     & pure
diff --git a/src/Conftrack/Source/Aeson.hs b/src/Conftrack/Source/Aeson.hs
new file mode 100644
index 0000000..97353d0
--- /dev/null
+++ b/src/Conftrack/Source/Aeson.hs
@@ -0,0 +1,101 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE LambdaCase #-}
+
+module Conftrack.Source.Aeson (JsonSource(..), mkJsonSource, mkJsonSourceWith, mkJsonFileSource) where
+
+import Conftrack.Value (Key (..), ConfigError(..), Value (..), KeyPart)
+import Conftrack.Source (SomeSource(..), ConfigSource (..))
+
+import Prelude hiding (readFile)
+import qualified Data.Aeson as A
+import Control.Monad.State (get, modify, MonadState (..))
+import Data.Function ((&))
+import Data.Text (Text)
+import qualified Data.Aeson.Text as A
+import qualified Data.Text as T
+import qualified Data.Text.Lazy as LT
+import qualified Data.Aeson.Types as A
+import qualified Data.Aeson.Key as A
+import Data.Aeson.Types (unexpected)
+import qualified Data.List.NonEmpty as NonEmpty
+import Control.Monad ((>=>))
+import Data.Functor ((<&>))
+import System.OsPath (OsPath)
+import qualified System.OsPath as OS
+import System.File.OsPath (readFile)
+import qualified Data.Aeson.KeyMap as A
+import qualified Data.Text.Encoding as BS
+
+data JsonSource = JsonSource
+  { jsonSourceValue :: A.Value
+  , jsonSourceDescription :: Text
+  } deriving (Show)
+
+mkJsonSource :: A.Value -> SomeSource
+mkJsonSource value = mkJsonSourceWith ("JSON string " <> LT.toStrict (A.encodeToLazyText value)) value
+
+mkJsonSourceWith :: Text -> A.Value -> SomeSource
+mkJsonSourceWith description value = SomeSource (source, [])
+  where source = JsonSource value description
+
+mkJsonFileSource :: OsPath -> IO (Maybe SomeSource)
+mkJsonFileSource path = do
+  bytes <- readFile path
+  pathAsText <- OS.decodeUtf path <&> LT.toStrict . LT.pack
+  pure $ A.decode bytes
+    <&> mkJsonSourceWith ("JSON file " <> pathAsText)
+
+instance ConfigSource JsonSource where
+  type SourceState JsonSource = [Key]
+
+  fetchValue key@(Key parts) JsonSource{..} = do
+    case A.parseEither (lookupJsonPath (NonEmpty.toList parts) >=> parseJsonValue) jsonSourceValue of
+      Left a -> pure $ Left (ParseError (T.pack a))
+      Right val -> do
+        modify (key :)
+        pure $ Right (val, jsonSourceDescription)
+
+  leftovers JsonSource{..} = do
+    used <- get
+
+    allJsonPaths jsonSourceValue
+     & filter (`notElem` used)
+     & Just
+     & pure
+
+-- | this is essentially a FromJSON instance for Value, but not written as one
+-- so as to not introduce an orphan
+parseJsonValue :: A.Value -> A.Parser Value
+parseJsonValue = \case
+  (A.String bytes) -> pure $ ConfigString (BS.encodeUtf8 bytes)
+  (A.Number num) ->
+    A.parseJSON (A.Number num) <&> ConfigInteger
+  (A.Bool b) -> pure $ ConfigBool b
+  A.Null -> pure ConfigNull
+  (A.Object _) -> unexpected "unexpected json object"
+  (A.Array _) -> unexpected "unexpected json array"
+
+lookupJsonPath ::  [KeyPart] -> A.Value -> A.Parser A.Value
+lookupJsonPath [] value = pure value
+lookupJsonPath (part:parts) value = do
+  A.withObject "blub" (\obj -> obj A..: A.fromText part) value
+  >>= lookupJsonPath parts
+
+allJsonPaths :: A.Value -> [Key]
+allJsonPaths = fmap keyToKey . subKeys []
+  where
+    keyToKey keys = Key (fmap aesonKeyToText keys)
+    aesonKeyToText (key :: A.Key) = case A.parseMaybe A.parseJSON (A.toJSON key) of
+      Nothing -> error "key not representable as text; this is a bug in conftrack-aeson."
+      Just a -> a
+    subKeys prefix (A.Object keymap) =
+      A.foldMapWithKey (\key v -> subKeys (prefix <> [key]) v) keymap
+    subKeys prefix _ = case NonEmpty.nonEmpty prefix of
+      Just key -> [key]
+      _ -> undefined
diff --git a/src/Conftrack/Source/Trivial.hs b/src/Conftrack/Source/Trivial.hs
new file mode 100644
index 0000000..bb06e77
--- /dev/null
+++ b/src/Conftrack/Source/Trivial.hs
@@ -0,0 +1,41 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Conftrack.Source.Trivial where
+
+import Conftrack.Value (Key, Value(..), ConfigError(..), Origin)
+import Conftrack.Source (SomeSource(..), ConfigSource (..))
+
+import Control.Monad.State (get, modify, StateT (..), MonadState (..))
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as M
+import Data.Function ((&))
+import qualified Data.Text as T
+
+
+newtype Trivial = Trivial (Map Key Value)
+
+mkTrivialSource :: [(Key, Value)] -> SomeSource
+mkTrivialSource pairs = SomeSource (source, [])
+  where source = Trivial (M.fromList pairs)
+
+instance ConfigSource Trivial where
+  type SourceState Trivial = [Key]
+  fetchValue key (Trivial tree) = do
+    case M.lookup key tree of
+      Nothing -> pure $ Left NotPresent
+      Just val -> do
+        modify (key :)
+        pure $ Right (val, "Trivial source with keys "<> T.pack (show (M.keys tree)))
+
+  leftovers (Trivial tree) = do
+    used <- get
+
+    M.keys tree
+     & filter (`notElem` used)
+     & Just
+     & pure