a generic, multi-source config interface

7 files changed, 278 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
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+# Revision history for conftrack
+
+## 0.0.1 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.
diff --git a/LICENSE b/LICENSE
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+Copyright (c) 2024, stuebinm
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of stuebinm nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/conftrack.cabal b/conftrack.cabal
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+cabal-version:      3.4
+name:               conftrack
+version:            0.0.1
+-- synopsis:
+-- description:
+license:            BSD-3-Clause
+license-file:       LICENSE
+author:             stuebinm
+maintainer:         stuebinm@disroot.org
+-- copyright:
+category:           Configuration
+build-type:         Simple
+extra-doc-files:    CHANGELOG.md
+-- extra-source-files:
+
+common warnings
+    ghc-options: -Wall
+
+library
+    import:           warnings
+    exposed-modules:  Conftrack
+                    , Conftrack.Value
+                    , Conftrack.Source
+    -- other-modules:
+    -- other-extensions:
+    build-depends:    base ^>=4.17.2.1
+                    , text
+                    , containers
+                    , mtl
+                    , transformers
+    hs-source-dirs:   src
+    default-language: GHC2021
+
+test-suite conftrack-test
+    import:           warnings
+    default-language: GHC2021
+    -- other-modules:
+    -- other-extensions:
+    type:             exitcode-stdio-1.0
+    hs-source-dirs:   test
+    main-is:          Main.hs
+    build-depends:
+        base ^>=4.17.2.1,
+        conftrack,
+        containers,
+        text
diff --git a/src/Conftrack.hs b/src/Conftrack.hs
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+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE OverloadedLists #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE LambdaCase #-}
+
+module Conftrack  where
+
+import Conftrack.Value (ConfigError(..), ConfigValue(..), Key, Origin(..))
+import Conftrack.Source (SomeSource (..), ConfigSource (..))
+
+import Prelude hiding (unzip)
+import Control.Monad.State (get, StateT (..), MonadState (..), gets)
+import Data.Functor ((<&>))
+import Control.Monad.Reader (MonadIO (liftIO))
+import Data.List.NonEmpty (NonEmpty, unzip)
+import qualified Data.List.NonEmpty as NonEmpty
+import Control.Monad (forM)
+import Data.Either (isRight)
+import Control.Monad.Trans.Except (ExceptT(..), runExceptT, throwE)
+import Control.Monad.Trans (lift)
+import Data.Text (Text)
+import qualified Data.Text as T
+import Data.Maybe (isJust)
+
+
+class Config a where
+  readConfig :: FetchMonad a
+
+type FetchMonad = StateT (NonEmpty SomeSource, [Origin], [Warning]) (ExceptT [ConfigError] IO)
+
+newtype Warning = Warning Text
+ deriving Show
+
+runFetchConfig :: Config a => NonEmpty SomeSource -> IO (Either [ConfigError] (a, [Origin], [Warning]))
+runFetchConfig sources = do
+  results <- runExceptT $ runStateT readConfig (sources, [], [])
+
+  case results of
+    Left a -> pure $ Left a
+    Right (result, (sources, origins, warnings)) -> do
+      unusedWarnings <- collectUnused sources
+      pure $ Right (result, origins, unusedWarnings <> warnings)
+
+readValue :: ConfigValue a => Key -> FetchMonad a
+readValue key = do
+  (sources, origins, warnings) <- get
+
+  -- TODO: this should short-curcuit here (so we have correct unused key sets)
+  stuff <- liftIO $ forM sources $ \(SomeSource (source, sourceState)) -> do
+    (eitherValue, newState) <- runStateT (fetchValue key source) sourceState
+    pure (eitherValue, SomeSource (source, newState))
+
+  let (maybeValues, states) = Data.List.NonEmpty.unzip stuff
+
+  let values = maybeValues <&> \case
+        Right (val, text) -> fromConfig val <&> (\val -> (val, Origin key text))
+        Left e -> Left e
+
+  val <- case fmap (\(Right a) -> a) $ NonEmpty.filter isRight values of
+    [] -> lift $ throwE [NotPresent]
+    val:_ -> pure val
+
+  put (states, snd val : origins, warnings)
+
+  pure (fst val)
+
+collectUnused :: NonEmpty SomeSource -> IO [Warning]
+collectUnused sources = do
+  forM sources (\(SomeSource (source, sourceState)) ->
+    runStateT (leftovers source) sourceState <&> fst)
+    <&> fmap (\(Just a) -> Warning $ "Unused Keys " <> T.pack (show a))
+        . NonEmpty.filter isJust
diff --git a/src/Conftrack/Source.hs b/src/Conftrack/Source.hs
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+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+module Conftrack.Source (ConfigSource(..), SomeSource(..), Trivial(..)) where
+
+import Conftrack.Value (Key, Value(..), ConfigError(..), Origin)
+
+import Control.Monad.State (get, modify, StateT (..), MonadState (..))
+import Data.Map.Strict (Map)
+import qualified Data.Map.Strict as M
+import Data.Function ((&))
+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])
+
+data SomeSource = forall source. ConfigSource source
+   => SomeSource (source, ConfigState 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/Value.hs b/src/Conftrack/Value.hs
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+++ b/src/Conftrack/Value.hs
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+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE QuantifiedConstraints #-}
+{-# LANGUAGE ImpredicativeTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+
+module Conftrack.Value (Value(..), ConfigError(..), Key(..), ConfigValue(..), Origin(..)) where
+
+import Data.Text(Text)
+import Data.List.NonEmpty (NonEmpty)
+
+data Value =
+  ConfigText Text
+  | ConfigInteger Integer
+  | ConfigOther Text Text
+  deriving Show
+
+newtype Key = Key (NonEmpty Text)
+  deriving newtype (Eq, Ord, Show)
+
+data ConfigError =
+  ParseError
+  | NotPresent
+  deriving Show
+
+class ConfigValue a where
+  fromConfig :: Value -> Either ConfigError a
+
+data Origin = Origin Key Text
+  deriving Show
+
+instance ConfigValue Text where
+  fromConfig (ConfigText a) = Right a
+  fromConfig _ = Left ParseError
+
+instance ConfigValue Integer where
+  fromConfig (ConfigInteger a) = Right a
+  fromConfig _ = Left ParseError
diff --git a/test/Main.hs b/test/Main.hs
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+{-# LANGUAGE OverloadedLists #-}
+{-# LANGUAGE OverloadedStrings #-}
+module Main (main) where
+
+import Conftrack
+import Conftrack.Value
+import Conftrack.Source
+
+import qualified Data.Map.Strict as M
+import Data.Text (Text)
+import Control.Exception (assert)
+
+data TestType = TestType { testFoo :: Text, testBar :: Integer }
+  deriving (Show, Eq)
+
+instance Config TestType where
+  readConfig = TestType
+    <$> readValue (Key ["foo"])
+    <*> readValue (Key ["bar"])
+
+main :: IO ()
+main = do
+  let trivial = Trivial (M.fromList [(Key ["foo"], ConfigText "foo"), (Key ["bar"], ConfigInteger 10)])
+  Right (config :: TestType, _, _) <- runFetchConfig [SomeSource (trivial, [])]
+  () <- assert (config == TestType "foo" 10) (pure ())
+
+  let trivial = Trivial (M.fromList [(Key ["fo"], ConfigText "foo"), (Key ["bar"], ConfigInteger 10)])
+  Left [NotPresent] <- runFetchConfig @TestType [SomeSource (trivial, [])]
+
+  let stack1 = Trivial (M.fromList [(Key ["foo"], ConfigText "foo")])
+  let stack2 = Trivial (M.fromList [(Key ["bar"], ConfigInteger 10), (Key ["foo"], ConfigText "blub")])
+  Right (config :: TestType, origins, warnings) <- runFetchConfig [SomeSource (stack1, []), SomeSource (stack2, [])]
+  () <- assert (config == TestType "foo" 11) (pure ())
+  print origins
+  print warnings
+
+  print config