Show a changelog.

* Changelog is HTML, shown via HTMLViewer, which is also used by
  Settings -> About -> Legal
* Changelog file: <device>-<channel>-changelog.html
* Show changelog if it exists upon tapping the notification, or
  the settings entry.

Potential TODOs:
* The view can be zoomed in and out (which may be useful),
  and also scrolled around easily (not so useful).

AndroidManifest.xml

@@ -63,5 +63,15 @@
                 <action android:name="android.settings.SYSTEM_UPDATE_SETTINGS" />
             </intent-filter>
         </activity>
+
+        <provider
+            android:name="android.support.v4.content.FileProvider"
+            android:authorities="app.seamlessupdate.client.fileprovider"
+            android:exported="false"
+            android:grantUriPermissions="true">
+            <meta-data
+                android:name="android.support.FILE_PROVIDER_PATHS"
+                android:resource="@xml/file_paths" />
+        </provider>
     </application>
 </manifest>

res/values/strings.xml

@@ -25,4 +25,7 @@
     <string name="idle_reboot_summary">Automatically reboot once the device is idle after successfully installing an update</string>
     <string name="check_for_updates_title">Updates</string>
     <string name="check_for_updates_summary">Tap to check for updates</string>
+    <string name="changelog_title">Changelog</string>
+    <string name="changelog_summary">Tap to view changelog</string>
+    <string name="changelog_unavailable">Changelog unavailable</string>
 </resources>

res/xml/file_paths.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<paths xmlns:android="http://schemas.android.com/apk/res/android">
+    <cache-path name="current.html" path="changelog/" />
+</paths>

res/xml/settings.xml

@@ -8,6 +8,10 @@
             android:title="@string/check_for_updates_title"
             android:summary="@string/check_for_updates_summary" />
 
+    <Preference android:key="changelog"
+            android:title="@string/changelog_title"
+            android:summary="@string/changelog_summary" />
+
     <ListPreference android:key="channel"
             android:title="@string/channel_title"
             android:summary="%s"

src/app/seamlessupdate/client/NotificationHandler.java

@@ -4,8 +4,13 @@
 import android.app.NotificationChannel;
 import android.app.NotificationManager;
 import android.app.PendingIntent;
+import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
+import android.net.Uri;
+import android.support.v4.content.FileProvider;
+
+import java.io.File;
 
 import static android.app.NotificationManager.IMPORTANCE_LOW;
 import static app.seamlessupdate.client.Service.isAbUpdate;
@@ -19,6 +24,7 @@ public class NotificationHandler {
     private static final String NOTIFICATION_CHANNEL_ID_PROGRESS = "progress";
     private static final int PENDING_REBOOT_ID = 1;
     private static final int PENDING_SETTINGS_ID = 2;
+    private static final int PENDING_CHANGELOG_ID = 3;
 
     private final Context context;
     private final NotificationManager notificationManager;
@@ -32,7 +38,7 @@ public class NotificationHandler {
     void showDownloadNotification(int progress, int max) {
         String title = context.getString(R.string.notification_download_title);
         Notification.Builder builder = new Notification.Builder(context, NOTIFICATION_CHANNEL_ID_PROGRESS)
-                .setContentIntent(getPendingSettingsIntent())
+                .setContentIntent(getPendingChangelogIntent())
                 .setContentTitle(title)
                 .setOngoing(true)
                 .setSmallIcon(R.drawable.ic_system_update_white_24dp);
@@ -58,7 +64,7 @@ void showRebootNotification() {
         notificationManager.createNotificationChannel(channel);
         notificationManager.notify(NOTIFICATION_ID_REBOOT, new Notification.Builder(context, NOTIFICATION_CHANNEL_ID)
                 .addAction(R.drawable.ic_restart, rebootText, reboot)
-                .setContentIntent(getPendingSettingsIntent())
+                .setContentIntent(getPendingChangelogIntent())
                 .setContentTitle(title)
                 .setContentText(text)
                 .setOngoing(true)
@@ -69,7 +75,7 @@ void showRebootNotification() {
     void showInstallNotification(int progress, int max) {
         String title = context.getString(R.string.notification_install_title);
         Notification.Builder builder = new Notification.Builder(context, NOTIFICATION_CHANNEL_ID_PROGRESS)
-                .setContentIntent(getPendingSettingsIntent())
+                .setContentIntent(getPendingChangelogIntent())
                 .setContentTitle(title)
                 .setOngoing(true)
                 .setProgress(max, progress, false)
@@ -87,8 +93,13 @@ private void createProgressNotificationChannel() {
         notificationManager.createNotificationChannel(channel);
     }
 
-    private PendingIntent getPendingSettingsIntent() {
-        return PendingIntent.getActivity(context, PENDING_SETTINGS_ID, new Intent(context, Settings.class), 0);
+    private PendingIntent getPendingChangelogIntent() {
+        Intent intent = Settings.getChangelogIntent(context, "current.html");
+        if (intent != null) {
+            return PendingIntent.getActivity(context, PENDING_CHANGELOG_ID, intent, 0);
+        } else {
+            return null;
+        }
     }
 
 }

src/app/seamlessupdate/client/Service.java

@@ -7,6 +7,7 @@
 import static android.os.UpdateEngine.UpdateStatusConstants.FINALIZING;
 
 import android.app.IntentService;
+import android.content.Context;
 import android.content.Intent;
 import android.content.SharedPreferences;
 import android.os.Build;
@@ -255,6 +256,8 @@ protected void onHandleIntent(final Intent intent) {
                 return;
             }
 
+            downloadChangelog(this, channel);
+
             String downloadFile = preferences.getString(PREFERENCE_DOWNLOAD_FILE, null);
             long downloaded = UPDATE_PATH.length();
             int contentLength;
@@ -327,4 +330,25 @@ protected void onHandleIntent(final Intent intent) {
             TriggerUpdateReceiver.completeWakefulIntent(intent);
         }
     }
+
+    private void downloadChangelog(Context context, String channel) {
+        Log.d(TAG, "fetching changelog for " + DEVICE + "-" + channel);
+        final String changelogName = DEVICE + "-" + channel + "-changelog.html";
+        try {
+            final File changelogPath = new File(context.getCacheDir(), "changelog");
+            final File changelogFile = new File(changelogPath, "current.html");
+            changelogPath.mkdirs();
+            InputStream input = fetchData(changelogName).getInputStream();
+            final OutputStream output = new FileOutputStream(changelogFile);
+            int bytesRead;
+            final byte[] buffer = new byte[8192];
+            while ((bytesRead = input.read(buffer)) != -1) {
+                output.write(buffer, 0, bytesRead);
+            }
+            output.close();
+            input.close();
+        } catch (IOException e) {
+            Log.d(TAG, "failed to fetch changelog");
+        }
+    }
 }

src/app/seamlessupdate/client/Settings.java

@@ -1,20 +1,27 @@
 package app.seamlessupdate.client;
 
+import android.content.ContentResolver;
 import android.content.Context;
+import android.content.Intent;
 import android.content.SharedPreferences;
 import android.os.Bundle;
 import android.os.UserManager;
 import android.preference.ListPreference;
 import android.preference.Preference;
 import android.preference.PreferenceActivity;
 import android.preference.PreferenceManager;
+import android.net.Uri;
+import android.support.v4.content.FileProvider;
+
+import java.io.File;
 
 public class Settings extends PreferenceActivity {
     private static final String KEY_CHANNEL = "channel";
     private static final String KEY_NETWORK_TYPE = "network_type";
     private static final String KEY_BATTERY_NOT_LOW = "battery_not_low";
     private static final String KEY_IDLE_REBOOT = "idle_reboot";
     private static final String KEY_CHECK_FOR_UDPATES = "check_for_updates";
+    private static final String KEY_CHANGELOG = "changelog";
     static final String KEY_WAITING_FOR_REBOOT = "waiting_for_reboot";
 
     static SharedPreferences getPreferences(final Context context) {
@@ -61,6 +68,17 @@ public void onCreate(final Bundle savedInstanceState) {
             return true;
         });
 
+        final Preference changelog = findPreference(KEY_CHANGELOG);
+        changelog.setOnPreferenceClickListener((final Preference preference) -> {
+            Intent intent = getChangelogIntent(this, "current.html");
+            if (intent != null) {
+                startActivity(intent);
+            } else {
+                changelog.setSummary(getString(R.string.changelog_unavailable));
+            }
+            return true;
+        });
+
         final Preference channel = findPreference(KEY_CHANNEL);
         channel.setOnPreferenceChangeListener((final Preference preference, final Object newValue) -> {
             getPreferences(this).edit().putString(KEY_CHANNEL,(String) newValue).apply();
@@ -104,5 +122,29 @@ public void onResume() {
         super.onResume();
         final ListPreference networkType = (ListPreference) findPreference(KEY_NETWORK_TYPE);
         networkType.setValue(Integer.toString(getNetworkType(this)));
+        final Preference changelog = findPreference(KEY_CHANGELOG);
+        changelog.setSummary(getString(R.string.changelog_summary));
+    }
+
+    static Intent getChangelogIntent(Context context, String filename) {
+        // From com.android.settings.SettingsLicenseActivity.showHtmlFromUri()
+        // Kick off external viewer due to WebView security restrictions; we
+        // carefully point it at HTMLViewer, since it offers to decompress
+        // before viewing.
+        final File changelogPath = new File(context.getCacheDir(), "changelog");
+        final File changelogFile = new File(changelogPath, filename);
+        if (!changelogFile.exists()) {
+            return null;
+        }
+        final Uri uri = FileProvider.getUriForFile(context, "app.seamlessupdate.client.fileprovider", changelogFile);
+        final Intent intent = new Intent(Intent.ACTION_VIEW);
+        intent.setDataAndType(uri, "text/html");
+        intent.putExtra(Intent.EXTRA_TITLE, context.getString(R.string.changelog_title));
+        if (ContentResolver.SCHEME_CONTENT.equals(uri.getScheme())) {
+            intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
+        }
+        intent.addCategory(Intent.CATEGORY_DEFAULT);
+        intent.setPackage("com.android.htmlviewer");
+        return intent;
     }
 }