Support for quick reply from notifications.

Fixes #483
Closes #3455
// FREEBIE

src/org/thoughtcrime/securesms/util/concurrent/ListenableFuture.java

@@ -0,0 +1,12 @@
+package org.thoughtcrime.securesms.util.concurrent;
+
+import java.util.concurrent.ExecutionException;
+
+public interface ListenableFuture<T> {
+  void addListener(Listener<T> listener);
+
+  public interface Listener<T> {
+    public void onSuccess(T result);
+    public void onFailure(ExecutionException e);
+  }
+}

src/org/thoughtcrime/securesms/util/concurrent/SettableFuture.java

@@ -0,0 +1,112 @@
+package org.thoughtcrime.securesms.util.concurrent;
+
+import java.util.LinkedList;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.Future;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+
+public class SettableFuture<T> implements Future<T>, ListenableFuture<T> {
+
+  private final List<Listener<T>> listeners = new LinkedList<>();
+
+  private          boolean   completed;
+  private          boolean   canceled;
+  private volatile T         result;
+  private volatile Throwable exception;
+
+  @Override
+  public synchronized boolean cancel(boolean mayInterruptIfRunning) {
+    if (!completed && !canceled) {
+      canceled = true;
+      return true;
+    }
+
+    return false;
+  }
+
+  @Override
+  public synchronized boolean isCancelled() {
+    return canceled;
+  }
+
+  @Override
+  public synchronized boolean isDone() {
+    return completed;
+  }
+
+  public boolean set(T result) {
+    synchronized (this) {
+      if (completed || canceled) return false;
+
+      this.result    = result;
+      this.completed = true;
+    }
+
+    notifyAllListeners();
+    return true;
+  }
+
+  public boolean setException(Throwable throwable) {
+    synchronized (this) {
+      if (completed || canceled) return false;
+
+      this.exception = throwable;
+      this.completed = true;
+    }
+
+    notifyAllListeners();
+    return true;
+  }
+
+  @Override
+  public synchronized T get() throws InterruptedException, ExecutionException {
+    while (!completed) wait();
+
+    if (exception != null) throw new ExecutionException(exception);
+    else                   return result;
+  }
+
+  @Override
+  public synchronized T get(long timeout, TimeUnit unit)
+      throws InterruptedException, ExecutionException, TimeoutException
+  {
+    long startTime = System.currentTimeMillis();
+
+    while (!completed && System.currentTimeMillis() - startTime > unit.toMillis(timeout)) {
+      wait(unit.toMillis(timeout));
+    }
+
+    if (!completed) throw new TimeoutException();
+    else            return get();
+  }
+
+  @Override
+  public void addListener(Listener<T> listener) {
+    synchronized (this) {
+      listeners.add(listener);
+
+      if (!completed) return;
+    }
+
+    notifyListener(listener);
+  }
+
+  private void notifyAllListeners() {
+    List<Listener<T>> localListeners;
+
+    synchronized (this) {
+      localListeners = new LinkedList<>(listeners);
+    }
+
+    for (Listener<T> listener : localListeners) {
+      notifyListener(listener);
+    }
+  }
+
+  private void notifyListener(Listener<T> listener) {
+    if (exception != null) listener.onFailure(new ExecutionException(exception));
+    else                   listener.onSuccess(result);
+  }
+}