[Android O] Refactor channel initialization

chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelsInitializer.java

Index: chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelsInitializer.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelsInitializer.java b/chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelsInitializer.java
new file mode 100644
index 0000000000000000000000000000000000000000..040d7881d4ac5fd996636a08e0de21689e38fc1a
--- /dev/null
+++ b/chrome/android/java/src/org/chromium/chrome/browser/notifications/ChannelsInitializer.java
@@ -0,0 +1,124 @@
+// Copyright 2017 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.notifications;
+
+import android.annotation.TargetApi;
+import android.app.NotificationManager;
+import android.os.Build;
+import android.support.annotation.StringDef;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Initializes our notification channels.
+ */
+public class ChannelsInitializer {
+    // To define a new channel, add the channel ID to this StringDef and add a new entry to
+    // PredefinedChannels.MAP below with the appropriate channel parameters.
+    @StringDef({CHANNEL_ID_BROWSER, CHANNEL_ID_SITES})
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface ChannelId {}
+    public static final String CHANNEL_ID_BROWSER = "browser";
+    public static final String CHANNEL_ID_SITES = "sites";
+
+    @StringDef({CHANNEL_GROUP_ID_GENERAL})
+    @Retention(RetentionPolicy.SOURCE)
+    private @interface ChannelGroupId {}
+    static final String CHANNEL_GROUP_ID_GENERAL = "general";
+
+    // Map defined in static inner class so it's only initialized lazily.
+    @TargetApi(Build.VERSION_CODES.N) // for NotificationManager.IMPORTANCE_* constants
+    private static class PredefinedChannels {
+        private static final Map<String, Channel> MAP;
+        static {
+            Map<String, Channel> map = new HashMap<>();
+            map.put(CHANNEL_ID_BROWSER,
+                    new Channel(CHANNEL_ID_BROWSER,
+                            org.chromium.chrome.R.string.notification_category_browser,
+                            NotificationManager.IMPORTANCE_LOW, CHANNEL_GROUP_ID_GENERAL));
+            map.put(CHANNEL_ID_SITES,
+                    new Channel(CHANNEL_ID_SITES,
+                            org.chromium.chrome.R.string.notification_category_sites,
+                            NotificationManager.IMPORTANCE_DEFAULT, CHANNEL_GROUP_ID_GENERAL));
+            MAP = Collections.unmodifiableMap(map);
+        }
+    }
+
+    // Map defined in static inner class so it's only initialized lazily.
+    private static class PredefinedChannelGroups {
+        private static final Map<String, ChannelGroup> MAP;
+        static {
+            Map<String, ChannelGroup> map = new HashMap<>();
+            map.put(CHANNEL_GROUP_ID_GENERAL,
+                    new ChannelGroup(CHANNEL_GROUP_ID_GENERAL,
+                            org.chromium.chrome.R.string.notification_category_group_general));
+            MAP = Collections.unmodifiableMap(map);
+        }
+    }
+
+    private final NotificationManagerProxy mNotificationManager;
+
+    public ChannelsInitializer(NotificationManagerProxy notificationManagerProxy) {
+        mNotificationManager = notificationManagerProxy;
+    }
+
+    /**
+     * Ensures the given channel has been created on the notification manager so a notification
+     * can be safely posted to it. This should only be used for channels that are predefined in
+     * ChannelsInitializer.
+     *
+     * Calling this is a (potentially lengthy) no-op if the channel has already been created.
+     *
+     * @param channelId The ID of the channel to be initialized.
+     */
+    public void ensureInitialized(@ChannelId String channelId) {
+        if (!PredefinedChannels.MAP.containsKey(channelId)) {
+            throw new IllegalStateException("Could not initialize channel: " + channelId);
+        }
+        Channel channel = PredefinedChannels.MAP.get(channelId);
+        // Channel group must be created before the channel.
+        mNotificationManager.createNotificationChannelGroup(
+                PredefinedChannelGroups.MAP.get(channel.mGroupId));
+        mNotificationManager.createNotificationChannel(channel);
+    }
+
+    /**
+     * Helper class containing notification channel properties.
+     */
+    public static class Channel {
+        @ChannelId
+        final String mId;
+        final int mNameResId;
+        final int mImportance;
+        @ChannelGroupId
+        final String mGroupId;
+
+        Channel(@ChannelId String id, int nameResId, int importance,
+                @ChannelGroupId String groupId) {
+            this.mId = id;
+            this.mNameResId = nameResId;
+            this.mImportance = importance;
+            this.mGroupId = groupId;
+        }
+    }
+
+    /**
+     * Helper class containing notification channel group properties.
+     */
+    public static class ChannelGroup {
+        @ChannelGroupId
+        final String mId;
+        final int mNameResId;
+
+        ChannelGroup(@ChannelGroupId String id, int nameResId) {
+            this.mId = id;
+            this.mNameResId = nameResId;
+        }
+    }
+}