Add Unit Tests to SnackbarCollection

chrome/android/java/src/org/chromium/chrome/browser/snackbar/SnackbarCollection.java

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.snackbar;
+
+import org.chromium.chrome.browser.snackbar.SnackbarManager.SnackbarController;
+
+import java.util.Deque;
+import java.util.Iterator;
+import java.util.LinkedList;
+import java.util.Queue;
+
+/**
+ * A collection of {@link Snackbar}s.

[newt (away), 2016/01/28 17:32:00]

Explain why this class exists :)

The current comment is basically useless; it just repeats the name of the class.
(Unfortunately, this is a relatively common pattern in our code.)

As a developer looking at this class for the first time, my major question would
be: "Why the heck do we need a custom collection for snackbars? Why not just use
an ArrayList?"

The comment doesn't need to be long, but it should be long enough to answer the
most fundamental question of why this class exists and what its primary function
is.

[Ian Wen, 2016/01/29 02:38:43]

Done.

+ */
+class SnackbarCollection {
+    private Deque<Snackbar> mStack = new LinkedList<>();
+    private Queue<Snackbar> mQueue = new LinkedList<>();
+
+    /**
+     * Adds a new snackbar to the collection. If the new snackbar is of
+     * {@link Snackbar#TYPE_ACTION} and current snackbar is of
+     * {@link Snackbar#TYPE_NOTIFICATION}, the current snackbar will be removed from the
+     * collection immediately.
+     */
+    public void add(Snackbar snackbar) {

[newt (away), 2016/01/28 17:32:00]

My personal preference is to remove "public" on all these methods, since they're
all package-private anyway due to the class scope anyway.

[Ian Wen, 2016/01/29 02:38:43]

Done.

+        if (snackbar.isTypeAction()) {
+            if (getCurrent() != null && !getCurrent().isTypeAction()) {
+                removeCurrent(false);
+            }
+            mStack.push(snackbar);
+        } else {
+            mQueue.offer(snackbar);
+        }
+    }
+
+    /**
+     * Removes the current snackbar from the collection.
+     * @param isAction Whether the removal is triggered by user clicking the action button.
+     */
+    public Snackbar removeCurrent(boolean isAction) {

[newt (away), 2016/01/28 17:32:00]

Since removeCurrent(false) shouldn't be called by outsiders, you might want to
make this method private and add a new public method
"removeCurrentDueToAction()" that calls removeCurrent(true).

[Ian Wen, 2016/01/29 02:38:42]

Ah good suggestion!! Done.

+        Snackbar current = !mStack.isEmpty() ? mStack.pop() : mQueue.poll();
+        if (current != null) {
+            SnackbarController controller = current.getController();
+            if (isAction) controller.onAction(current.getActionData());
+            else controller.onDismissNoAction(current.getActionData());
+        }
+        return current;
+    }
+
+    /**
+     * @return The snackbar that is currently displayed.
+     */
+    public Snackbar getCurrent() {
+        return !mStack.isEmpty() ? mStack.peek() : mQueue.peek();
+    }
+
+    public boolean isEmpty() {
+        return mStack.isEmpty() && mQueue.isEmpty();
+    }
+
+    public void clear() {
+        while (!isEmpty()) {
+            removeCurrent(false);
+        }
+    }
+
+    public void removeCurrentDueToTimeout() {
+        removeCurrent(false);
+        Snackbar current;
+        while ((current = getCurrent()) != null && current.isTypeAction()) {
+            removeCurrent(false);
+        }
+    }
+
+    public boolean removeMatchingSnackbars(SnackbarController controller) {
+        boolean snackbarRemoved = false;
+        Iterator<Snackbar> iter = mStack.iterator();
+        while (iter.hasNext()) {
+            Snackbar snackbar = iter.next();
+            if (snackbar.getController() == controller) {
+                iter.remove();
+                snackbarRemoved = true;
+            }
+        }
+        iter = mQueue.iterator();
+        while (iter.hasNext()) {
+            Snackbar snackbar = iter.next();
+            if (snackbar.getController() == controller) {
+                iter.remove();
+                snackbarRemoved = true;
+            }
+        }
+        return snackbarRemoved;
+    }
+
+    public boolean removeMatchingSnackbars(SnackbarController controller, Object data) {
+        boolean snackbarRemoved = false;
+        Iterator<Snackbar> iter = mStack.iterator();
+        while (iter.hasNext()) {
+            Snackbar snackbar = iter.next();
+            if (snackbar.getController() == controller
+                    && objectsAreEqual(snackbar.getActionData(), data)) {
+                iter.remove();
+                snackbarRemoved = true;
+            }
+        }
+        iter = mQueue.iterator();
+        while (iter.hasNext()) {
+            Snackbar snackbar = iter.next();
+            if (snackbar.getController() == controller
+                    && objectsAreEqual(snackbar.getActionData(), data)) {
+                iter.remove();
+                snackbarRemoved = true;
+            }
+        }
+        return snackbarRemoved;
+    }
+
+    private static boolean objectsAreEqual(Object a, Object b) {
+        if (a == null && b == null) return true;
+        if (a == null || b == null) return false;
+        return a.equals(b);
+    }
+}