Add withDbConnString

In prod, we don't want to use gargoyle and do want to use a setting from
a committed config as opposed to an uncommitted file on the db path.

Author: Ericson2314

gargoyle-postgresql-connect/src/Gargoyle/PostgreSQL/Connect.hs

@@ -1,6 +1,11 @@
-module Gargoyle.PostgreSQL.Connect (withDb, openDb) where
+{-# LANGUAGE LambdaCase #-}
+module Gargoyle.PostgreSQL.Connect
+  ( openDb
+  , withDb
+  , withDbConnString
+  ) where
 
-import Control.Monad ((>=>))
+import Control.Monad ((<=<))
 import Data.ByteString (ByteString)
 import qualified Data.ByteString.Char8 as C8
 import Data.Pool (Pool, createPool)
@@ -18,15 +23,26 @@ import System.Directory (doesFileExist)
 -- order to open and start the database. Otherwise, it will create the
 -- database for you if it doesn't exist.
 withDb :: String -> (Pool Connection -> IO a) -> IO a
-withDb dbPath a = do
+withDb dbPath k = do
   dbExists <- doesFileExist dbPath
-  if dbExists
+  flip withDbConnString k =<< if dbExists
     -- use the file contents as the uri for an existing server
-    then C8.readFile dbPath >>= openDb . head . C8.lines >>= a
+    then Left . head . C8.lines <$> C8.readFile dbPath
     -- otherwise assume it's a folder for a local database
-    else do
-      g <- postgresNix
-      withGargoyle g dbPath $ openDb >=> a
+    else pure $ Right dbPath
+
+-- | Either connects to a database at the given connection string in the Left
+-- case, or uses gargoyle at the filepath specified in the Right case.  Allows
+-- to keep the connection string at a different place from the gargoyle
+-- cluster.
+withDbConnString :: Either ByteString FilePath -> (Pool Postgresql -> IO a) -> IO a
+withDbConnString = \case
+  -- use the file contents as the uri for an existing server
+  Left connStr -> (>>=) (openDb connStr)
+  -- otherwise assume it's a folder for a local database
+  Right gargoylePath -> \k -> do
+    g <- postgresNix
+    withGargoyle g gargoylePath $ k <=< openDb
 
 openDb :: ByteString -> IO (Pool Connection)
 openDb dbUri = createPool (connectPostgreSQL dbUri) close 1 5 20