core: System.Nix.Hash add HashAlgo

prereq for replacing SomeNamedDigest
with (DSum HashAlgo Digest)

Author: Ericson2314

cabal.project

@@ -4,4 +4,3 @@ packages:
 
 package hnix-store-remote
   flags: +build-readme +io-testsuite
-

hnix-store-core/hnix-store-core.cabal

@@ -37,6 +37,7 @@ common commons
     , ExistentialQuantification
     , FlexibleContexts
     , FlexibleInstances
+    , GADTs
     , StandaloneDeriving
     , ScopedTypeVariables
     , StandaloneDeriving
@@ -48,6 +49,7 @@ common commons
     , InstanceSigs
     , KindSignatures
     , MultiParamTypeClasses
+    , MultiWayIf
     , TupleSections
     , LambdaCase
     , BangPatterns
@@ -83,6 +85,7 @@ library
     , case-insensitive
     , cereal
     , containers
+    , constraints-extras
     , data-default-class
     , generic-arbitrary < 1.1
     -- Required for cryptonite low-level type convertion
@@ -97,7 +100,8 @@ library
     , nix-derivation >= 1.1.1 && <2
     , QuickCheck
     , quickcheck-instances
-    , saltine
+    , saltine >= 0.2 && < 0.3
+    , some > 1.0.5 && < 2
     , time
     , text
     , unix

hnix-store-core/src/System/Nix/Hash.hs

@@ -1,14 +1,18 @@
 {-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TemplateHaskell #-}
 {-# OPTIONS_GHC -Wno-orphans #-}
 {-|
 Description : Cryptographic hashing interface for hnix-store, on top
               of the cryptohash family of libraries.
 -}
 
 module System.Nix.Hash
-  ( NamedAlgo(..)
+  ( HashAlgo(..)
+  , NamedAlgo(..)
+  , algoToText
+  , textToAlgo
   , SomeNamedDigest(..)
   , mkNamedDigest
 
@@ -23,6 +27,10 @@ module System.Nix.Hash
 
 import Crypto.Hash (Digest, HashAlgorithm, MD5(..), SHA1(..), SHA256(..), SHA512(..))
 import Data.ByteString (ByteString)
+import Data.Constraint.Extras (Has(has))
+import Data.Constraint.Extras.TH (deriveArgDict)
+import Data.Kind (Type)
+import Data.Some (Some(Some))
 import Data.Text (Text)
 import Data.Text.Lazy.Builder (Builder)
 import System.Nix.Base (BaseEncoding(..))
@@ -67,6 +75,32 @@ instance Arbitrary (Digest SHA256) where
 instance Arbitrary (Digest SHA512) where
   arbitrary = Crypto.Hash.hash @ByteString <$> arbitrary
 
+data HashAlgo :: Type -> Type where
+  HashAlgo_MD5 :: HashAlgo MD5
+  HashAlgo_SHA1 :: HashAlgo SHA1
+  HashAlgo_SHA256 :: HashAlgo SHA256
+  HashAlgo_SHA512 :: HashAlgo SHA512
+
+deriveArgDict ''HashAlgo
+
+algoToText :: forall t. HashAlgo t -> Text
+algoToText x = has @NamedAlgo x (algoName @t)
+
+_hashAlgoValue :: HashAlgo a -> a
+_hashAlgoValue = \case
+  HashAlgo_MD5 -> MD5
+  HashAlgo_SHA1 -> SHA1
+  HashAlgo_SHA256 -> SHA256
+  HashAlgo_SHA512 -> SHA512
+
+textToAlgo :: Text -> Either String (Some HashAlgo)
+textToAlgo = \case
+    "md5"    -> Right $ Some HashAlgo_MD5
+    "sha1"   -> Right $ Some HashAlgo_SHA1
+    "sha256" -> Right $ Some HashAlgo_SHA256
+    "sha512" -> Right $ Some HashAlgo_SHA512
+    name     -> Left $ "Unknown hash name: " <> Data.Text.unpack name
+
 -- | A digest whose 'NamedAlgo' is not known at compile time.
 data SomeNamedDigest = forall a . NamedAlgo a => SomeDigest (Digest a)