Reduce duplication

and move platform-independent code out of Android module where it is expensive
to build/test.

obelisk/frontend/android-src/FrontendPaths.hs

 -- | Implement platform-specific path-related operations for the Android
 -- platform.
-module FrontendPaths (getFilesDir, platformEventCallback, runWithRef) where
+module FrontendPaths (getFilesDir, runWithRef) where
 
 import Control.Concurrent (threadDelay)
 import Control.Monad (forever)
-import Control.Monad.IO.Class (liftIO)
 import Data.Default.Class (def)
 import Data.IORef (IORef, newIORef, readIORef)
 import Data.String (fromString)
-import JSDOM (currentWindow)
-import JSDOM.History (back)
-import JSDOM.Types (MonadDOM)
-import JSDOM.Window (getHistory)
 import Language.Javascript.JSaddle (JSM)
 import MainWidget (startMainWidget)
 import System.IO (hSetBuffering, stdout, stderr, BufferMode(LineBuffering))
 import qualified Android.HaskellActivity as Android
-import PlatformEvents
+import PlatformEvents (PlatformEventCallbacks(..))
 
 -- | Get the path to a directory that is private to the application where
 -- internal application data may be written (and read back).
@@ -28,22 +23,6 @@ import PlatformEvents
 getFilesDir :: IO (Maybe FilePath)
 getFilesDir = Android.getHaskellActivity >>= Android.getFilesDir
 
--- | Handle Android events related to our Activity.
-platformEventCallback :: MonadDOM m => PlatformEvent -> m ()
-platformEventCallback BackPressed = navigateBack
-
--- | Perform a standard "back" navigation through route history.
-navigateBack :: MonadDOM m => m ()
-navigateBack = do
-  windowM <- currentWindow
-  case windowM of
-    -- No window, no history navigation...
-    Nothing -> liftIO $ do
-      print "Back button but no window ..."
-    Just window -> do
-      history <- getHistory window
-      back history
-
 -- | Instantiate the frontend hooked up to Android-specific platform event
 -- sources.  The frontend is responsible for populating an IORef with a
 -- structure holding its handlers for those events.
@@ -69,7 +48,6 @@ runWithRef makeJSM = do
         let startPage = fromString "file:///android_asset/index.html"
         startMainWidget a startPage (makeJSM (Just activityCallbackRef))
     , Android._activityCallbacks_onBackPressed = do
-          print $ "Back pressed!"
           f <- readIORef activityCallbackRef
           onBackPressed f
     }

obelisk/frontend/frontend.cabal

@@ -60,6 +60,7 @@ library
     Controller
     Frontend
     FrontendPaths
+    Navigation
     PlatformEvents
     Static
     Pages.FileBrowser

obelisk/frontend/linux-src/FrontendPaths.hs

 -- | Implement platform-specific path-related operations for the Linux
 -- platform.
-module FrontendPaths (getFilesDir, platformEventCallback, runWithRef) where
+module FrontendPaths (getFilesDir, runWithRef) where
 
 import Data.IORef (IORef, newIORef)
 import System.Environment.XDG.BaseDir (getUserDataDir)
 import System.Directory (createDirectoryIfMissing)
-import JSDOM.Types (MonadDOM)
-import Control.Monad.IO.Class (liftIO)
 import Reflex.Dom (run)
 import PlatformEvents
 import Language.Javascript.JSaddle (JSM)
@@ -23,13 +21,6 @@ getFilesDir = do
   createDirectoryIfMissing True dataPath
   pure $ Just dataPath
 
--- | Handle platform events on Linux (*not* for `ob run`).
---
--- Since we don't run in this configuration and we don't expect any such
--- events on Linux anyway, there is no real behavior here.
-platformEventCallback :: (Show a, MonadDOM m) => a -> m ()
-platformEventCallback = liftIO . print
-
 -- | Run a frontend on Linux (not `ob run`).
 runWithRef :: (Maybe (IORef PlatformEventCallbacks) -> JSM ()) -> IO ()
 runWithRef makeJSM =

obelisk/frontend/src/Frontend.hs

@@ -17,7 +17,7 @@ import Controller (pageFromRoute)
 import Static (mainCss, materialComponentsCss, materialComponentsJs, materialIconsCss, robotoCss)
 import PlatformEvents (PlatformEventCallbacks(..), PlatformEvent(..))
 import JSDOM.Types (liftJSM)
-import FrontendPaths (platformEventCallback)
+import Navigation (platformEventCallback)
 import Data.Default.Class (def)
 
 -- A frontend with no platform event integration.  This is necessary for

obelisk/frontend/src/Navigation.hs

+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+
+module Navigation where
+
+import JSDOM (currentWindow)
+import JSDOM.History (back)
+import JSDOM.Window (getHistory)
+import JSDOM.Types (MonadDOM)
+import Control.Monad.IO.Class (liftIO)
+
+import PlatformEvents (PlatformEvent(..))
+
+-- | Handle platform events.
+platformEventCallback :: MonadDOM m => PlatformEvent -> m ()
+platformEventCallback BackPressed = navigateBack
+
+-- | Perform a standard "back" navigation through route history.
+navigateBack :: MonadDOM m => m ()
+navigateBack = do
+    windowM <- currentWindow
+    case windowM of
+      -- No window, no history navigation...
+      Nothing -> liftIO $ do
+        print "Back button but no window ..."
+      Just window -> do
+        history <- getHistory window
+        back history