Provide DB-specific locations through conditional compilation

Use a single data structure, `databaseLocation`, to describe either a work directory or in-memory when compiled for SQLite
or a remote URL when compiled for PostgreSQL. This provides strong type safety but comes at the cost of having to include a
argument parser in the DB modules, which is not really where it belongs. Alternatively, conditional compilation could be
added to the argument parsing module, but that also seems out of place. Ultimately, including all 3 alternatives in
`databaseLocation` and validating at runtime may be a cleaner solution, despite the loss of type safety.

src/Kupo.hs

@@ -64,6 +64,7 @@ import Kupo.App.Database
     ( ConnectionType (..)
     , DBPool (..)
     , copyDatabase
+    , mkDBPool
     )
 import Kupo.App.Health
     ( connectionStatusToggle
@@ -132,9 +133,6 @@ import System.Exit
     ( ExitCode (..)
     )
 
-import Kupo.App.Database.SQLite
-    ( mkDBPool
-    )
 import qualified Kupo.Data.Health as Health
 
 --
@@ -190,7 +188,7 @@ kupoWith tr withProducer withFetchBlock =
         , configuration = config@Configuration
             { serverHost
             , serverPort
-            , workDir
+            , databaseLocation
             , inputManagement
             , longestRollback
             , deferIndexes
@@ -205,7 +203,7 @@ kupoWith tr withProducer withFetchBlock =
     --         , maxConcurrentWriters = if isReadOnlyReplica config then 0 else maxConcurrentWriters
     --         }
 
-    dbPool <- liftIO $ mkDBPool (isReadOnlyReplica config) (tracerDatabase tr) workDir longestRollback
+    dbPool <- liftIO $ mkDBPool (isReadOnlyReplica config) (tracerDatabase tr) databaseLocation longestRollback
 
     let run action
             | isReadOnlyReplica config =

src/Kupo/App/Database.hs

@@ -34,9 +34,13 @@ module Kupo.App.Database
     , rollbackQryDeleteCheckpoints
 
       -- * Setup
-    , copyDatabase
     , ConnectionType (..)
     , DBPool (..)
+    , mkDBPool
+    , copyDatabase
+
+      -- ** Option Parser
+    , databaseLocationOptionParser
 
       -- * Internal
     , installIndexes
@@ -50,10 +54,11 @@ module Kupo.App.Database
 import Kupo.App.Database.Postgres
 #else
 import Kupo.App.Database.SQLite
+#endif
+
 import Kupo.App.Database.Types
     ( ConnectionType (..)
     , DBPool (..)
     , DBTransaction
     , Database (..)
     )
-#endif