Serviceless rewrite, part 1

Signed-off-by: Samuel Holland <samuel@sholland.org>

app/src/main/java/com/wireguard/android/util/ExceptionLoggers.java

@@ -0,0 +1,38 @@
+package com.wireguard.android.util;
+
+import android.util.Log;
+
+import java9.util.concurrent.CompletionException;
+import java9.util.function.BiConsumer;
+
+/**
+ * Helpers for logging exceptions from asynchronous tasks. These can be passed to
+ * {@code CompletionStage.handle()} at the end of an asynchronous future chain.
+ */
+
+public enum ExceptionLoggers implements BiConsumer<Object, Throwable> {
+    D(Log.DEBUG),
+    E(Log.ERROR);
+
+    private static final String TAG = ExceptionLoggers.class.getSimpleName();
+
+    private final int priority;
+
+    ExceptionLoggers(final int priority) {
+        this.priority = priority;
+    }
+
+    public static Throwable unwrap(final Throwable throwable) {
+        if (throwable instanceof CompletionException)
+            return throwable.getCause();
+        return throwable;
+    }
+
+    @Override
+    public void accept(final Object result, final Throwable throwable) {
+        if (throwable != null)
+            Log.println(Log.ERROR, TAG, Log.getStackTraceString(throwable));
+        else if (priority <= Log.DEBUG)
+            Log.println(priority, TAG, "Future completed successfully");
+    }
+}