[NTP Snippets] Show a status card when there are no available snippets

chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
new file mode 100644
index 0000000000000000000000000000000000000000..143d95928144b6d3a64230b90a4e9aca00907b9f
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ntp/snippets/SnippetHeaderViewHolder.java
@@ -0,0 +1,109 @@
+// Copyright 2015 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.ntp.snippets;
+
+import android.animation.Animator;
+import android.animation.Animator.AnimatorListener;
+import android.animation.ObjectAnimator;
+import android.support.v7.widget.RecyclerView;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+
+import org.chromium.chrome.R;
+import org.chromium.chrome.browser.ntp.cards.NewTabPageListItem;
+import org.chromium.chrome.browser.ntp.cards.NewTabPageViewHolder;
+
+/**
+ * A class that represents the view for a single card snippet.
+ */
+public class SnippetHeaderViewHolder extends NewTabPageViewHolder {
+    private static final int ANIMATION_DURATION_MS = 300;
+
+    private final int mMaxSnippetHeaderHeight;
+    private SnippetHeaderListItem mHeader;
+    private Animator mAnimator;
+
+    public static View createView(ViewGroup parent) {
+        return LayoutInflater.from(parent.getContext())
+                .inflate(R.layout.new_tab_page_snippets_card, parent, false);
+    }
+
+    public SnippetHeaderViewHolder(final View cardView) {
+        super(cardView);
+        mMaxSnippetHeaderHeight = cardView.getResources().getDimensionPixelSize(
+                R.dimen.snippets_article_header_height);
+    }
+
+    @Override
+    public void onBindViewHolder(NewTabPageListItem header) {
+        mHeader = (SnippetHeaderListItem) header;
+        animateFade();
+    }
+
+    /**
+     * Update the view for the scroll-triggered fade in/out animation.
+     * @param omniBoxHeight The height of the omnibox displayed over the NTP, we use this to offset
+     *          the start point of the transition.
+     */
+    public void onScrolled(int omniBoxHeight) {
+        RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) itemView.getLayoutParams();
+        int headerHeight = 0;
+
+        // Measurement used to multiply the max snippet height to get a range on when to start
+        // modifying the display of article header.
+        final int numberHeaderHeight = 2;
+        // Used to indicate when to start modifying the snippet header.
+        int heightToStartChangingHeader = mMaxSnippetHeaderHeight * numberHeaderHeight;
+        int snippetHeaderTop = itemView.getTop();
+
+        // Check if snippet header top is within range to start showing the snippet header.
+        if (snippetHeaderTop < omniBoxHeight + heightToStartChangingHeader) {
+            // The amount of space the article header has scrolled into the
+            // |heightToStartChangingHeader|.
+            int amountScrolledIntoHeaderSpace =
+                    heightToStartChangingHeader - (snippetHeaderTop - omniBoxHeight);
+
+            // Remove the |numberHeaderHeight| to get the actual header height we want to
+            // display. Never let the height be more than the |maxSnippetHeaderHeight|.
+            headerHeight = Math.min(
+                    amountScrolledIntoHeaderSpace / numberHeaderHeight, mMaxSnippetHeaderHeight);
+
+        }
+
+        if (mHeader.isVisible()) itemView.setAlpha((float) headerHeight / mMaxSnippetHeaderHeight);
+        params.height = headerHeight;
+        itemView.setLayoutParams(params);
+    }
+
+    /**
+     * Make the header fade in or out depending on the model's state.
+     * @see SnippetHeaderListItem#isVisible()
+     */
+    private void animateFade() {
+        if (mAnimator != null) mAnimator.cancel();
+
+        float currentAlpha = itemView.getAlpha();
+        float targetAlpha = mHeader.isVisible() ? 1f : 0f;
+
+        if (currentAlpha == targetAlpha) return;
+
+        mAnimator = ObjectAnimator.ofFloat(itemView, View.ALPHA, currentAlpha, targetAlpha);
+        mAnimator.setDuration(ANIMATION_DURATION_MS);
+        mAnimator.addListener(new AnimatorListener() {
+            @Override
+            public void onAnimationStart(Animator animator) {}
+            @Override
+            public void onAnimationRepeat(Animator animator) {}
+            @Override
+            public void onAnimationEnd(Animator animator) {
+                mAnimator = null;
+            }
+            @Override
+            public void onAnimationCancel(Animator animator) {}
+        });
+        mAnimator.start();
+    }
+}