Split the code into library and application

lib/SlackBuilder/Config.hs

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+module SlackBuilder.Config
+    ( Settings(..)
+    , MaintainerSettings(..)
+    , settingsCodec
+    ) where
+
+import Data.Text (Text)
+import Toml ((.=))
+import qualified Toml
+
+data Settings = Settings
+    { ghToken :: !Text
+    , repository :: !FilePath
+    , branch :: Text
+    , downloadURL :: Text
+    , remotePath :: Text
+    , maintainer :: MaintainerSettings
+    } deriving (Eq, Show)
+
+data MaintainerSettings = MaintainerSettings
+    { name :: !Text
+    , email :: !Text
+    } deriving (Eq, Show)
+
+settingsCodec :: Toml.TomlCodec Settings
+settingsCodec = Settings
+    <$> Toml.text "gh_token" .= ghToken
+    <*> Toml.string "repository" .= repository
+    <*> Toml.text "branch" .= branch
+    <*> Toml.text "download_url" .= downloadURL
+    <*> Toml.text "remote_path" .= remotePath
+    <*> Toml.table maintainerSettingsCodec "maintainer" .= maintainer
+
+maintainerSettingsCodec :: Toml.TomlCodec MaintainerSettings
+maintainerSettingsCodec = MaintainerSettings
+    <$> Toml.text "name" .= name
+    <*> Toml.text "email" .= email

lib/SlackBuilder/Package.hs

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+module SlackBuilder.Package
+    ( DownloadPlaceholder(..)
+    , Download(..)
+    , DownloadTemplate(..)
+    , PackageInfo(..)
+    , Maintainer(..)
+    , Updater(..)
+    , infoTemplate
+    , renderDownloadWithVersion
+    ) where
+
+import Data.List.NonEmpty (NonEmpty(..))
+import Data.Text (Text)
+import qualified Data.Text as Text
+import Text.URI (URI(..))
+import qualified Text.URI as URI
+import Crypto.Hash (Digest, MD5)
+import GHC.Records (HasField(..))
+import System.FilePath (takeBaseName)
+import Data.List (partition)
+import SlackBuilder.Trans
+import Control.Monad.Catch (MonadThrow)
+
+-- | Download URI with the MD5 checksum of the target.
+data Download = Download
+    { download :: URI
+    , md5sum :: Digest MD5
+    , is64 :: Bool
+    } deriving (Eq, Show)
+
+-- | Data used to generate an .info file.
+data PackageInfo = PackageInfo
+    { path :: FilePath
+    , version :: Text
+    , homepage :: Text
+    , requires :: [Text]
+    , maintainer :: Maintainer
+    } deriving (Eq, Show)
+
+-- | Package maintainer information.
+data Maintainer = Maintainer
+    { name :: Text
+    , email :: Text
+    } deriving (Eq, Show)
+
+-- | Appears in the download URI template and specifies which part of the URI
+-- should be replaced with the package version.
+data DownloadPlaceholder
+    = StaticPlaceholder Text
+    | VersionPlaceholder
+    deriving Eq
+
+instance Show DownloadPlaceholder
+  where
+    show (StaticPlaceholder staticPlaceholder) = Text.unpack staticPlaceholder
+    show VersionPlaceholder = "{version}"
+
+-- | List of URI components, including version placeholders.
+newtype DownloadTemplate = DownloadTemplate (NonEmpty DownloadPlaceholder)
+    deriving Eq
+
+instance Show DownloadTemplate
+  where
+    show (DownloadTemplate components) = concatMap show components
+
+-- | Replaces placeholders in the URL template with the given version.
+renderDownloadWithVersion :: MonadThrow m => DownloadTemplate -> Text -> m URI
+renderDownloadWithVersion (DownloadTemplate components) version =
+    URI.mkURI $ foldr f "" components
+  where
+    f (StaticPlaceholder staticPlaceholder) accumulator = accumulator <> staticPlaceholder
+    f VersionPlaceholder accumulator = accumulator <> version
+
+-- | Function used to get the latest version of a source.
+data Updater = Updater (SlackBuilderT (Maybe Text)) DownloadTemplate
+
+packageName :: PackageInfo -> Text
+packageName PackageInfo{ path } = Text.pack $ takeBaseName path
+
+infoTemplate :: PackageInfo -> [Download] -> Text
+infoTemplate package downloads =
+    let (downloads64, downloads32) = partition (getField @"is64") downloads
+        (download32, md5sum32, download64, md5sum64) = downloadEntries downloads64 downloads32
+ 
+     in Text.unlines
+        [ "PRGNAM=\"" <> packageName package <> "\""
+        , "VERSION=\"" <> getField @"version" package <> "\""
+        , "HOMEPAGE=\"" <> getField @"homepage" package <> "\""
+        , "DOWNLOAD=\"" <> download32 <> "\""
+        , "MD5SUM=\"" <> md5sum32 <> "\""
+        , "DOWNLOAD_x86_64=\"" <> download64 <> "\""
+        , "MD5SUM_x86_64=\"" <> md5sum64 <> "\""
+        , "REQUIRES=\"" <> Text.unwords (getField @"requires" package) <> "\""
+        , "MAINTAINER=\"" <> getField @"name" (getField @"maintainer" package) <> "\""
+        , "EMAIL=\"" <> getField @"email" (getField @"maintainer" package) <> "\""
+        ]
+
+downloadEntries :: [Download] -> [Download] -> (Text, Text, Text, Text)
+downloadEntries downloads64 downloads32 =
+    let download32 =
+            if null downloads32 && not (null downloads64)
+            then
+                "UNSUPPORTED"
+            else
+                Text.intercalate " \\\n          "
+                    $ URI.render . getField @"download" <$> downloads32
+
+        md5sum32 = Text.intercalate " \\\n        "
+            $ Text.pack . show . getField @"md5sum" <$> downloads32
+        download64 = Text.intercalate " \\\n          "
+            $ URI.render . getField @"download" <$> downloads64
+        md5sum64 = Text.intercalate " \\\n        "
+            $ Text.pack . show . getField @"md5sum" <$> downloads64
+ 
+     in (download32, md5sum32, download64, md5sum64)

lib/SlackBuilder/Trans.hs

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+module SlackBuilder.Trans
+    ( SlackBuilderT(..)
+    ) where
+
+import Control.Monad.Trans.Reader (ReaderT(..))
+import SlackBuilder.Config
+import Control.Monad.IO.Class (MonadIO(..))
+
+newtype SlackBuilderT a = SlackBuilderT
+    { runSlackBuilderT :: ReaderT Settings IO a
+    }
+
+instance Functor SlackBuilderT
+  where
+    fmap f (SlackBuilderT slackBuilderT) = SlackBuilderT $ f <$> slackBuilderT
+
+instance Applicative SlackBuilderT
+  where
+    pure = SlackBuilderT . pure
+    (SlackBuilderT f) <*> (SlackBuilderT x) = SlackBuilderT $ f <*> x
+
+instance Monad SlackBuilderT
+  where
+    return = pure
+    (SlackBuilderT x) >>= f = SlackBuilderT $ x >>= runSlackBuilderT . f
+
+instance MonadIO SlackBuilderT
+  where
+    liftIO = SlackBuilderT . liftIO