Only launch FlashActivity if app is foreground

app/src/main/java/com/topjohnwu/magisk/di/ApplicationModule.kt

@@ -1,12 +1,14 @@
 package com.topjohnwu.magisk.di
 
+import android.app.Activity
+import android.app.Application
 import android.content.Context
+import android.os.Bundle
 import androidx.preference.PreferenceManager
 import com.skoumal.teanity.rxbus.RxBus
 import com.topjohnwu.magisk.App
 import org.koin.dsl.module
 
-
 val applicationModule = module {
     single { RxBus() }
     factory { get<Context>().resources }
@@ -15,4 +17,31 @@ val applicationModule = module {
     factory(Protected) { get<App>().protectedContext }
     single(SUTimeout) { get<Context>(Protected).getSharedPreferences("su_timeout", 0) }
     single { PreferenceManager.getDefaultSharedPreferences(get<Context>(Protected)) }
-}
+    single { ActivityTracker() as Application.ActivityLifecycleCallbacks }
+    factory { (get<Application.ActivityLifecycleCallbacks>() as ActivityTracker).foreground }
+}
+
+private class ActivityTracker : Application.ActivityLifecycleCallbacks {
+
+    var foreground: Activity? = null
+
+    override fun onActivityCreated(activity: Activity, bundle: Bundle?) {}
+
+    override fun onActivityStarted(activity: Activity) {}
+
+    @Synchronized
+    override fun onActivityResumed(activity: Activity) {
+        foreground = activity
+    }
+
+    @Synchronized
+    override fun onActivityPaused(activity: Activity) {
+        foreground = null
+    }
+
+    override fun onActivityStopped(activity: Activity) {}
+
+    override fun onActivitySaveInstanceState(activity: Activity, bundle: Bundle) {}
+
+    override fun onActivityDestroyed(activity: Activity) {}
+}