code cleanup

* migrate few annotations to androidx
* mission recovery: better error handling (except StreamExtractor.getErrorMessage() method always returns an error)
* post-processing: more detailed progress

[file specific changes]

DownloadMission.java
* remove redundant/boilerplate code (again)
* make few variables volatile
* better file "length" approximation
* use "done" variable to count the amount of bytes downloaded (simplify percent calc in UI code)

Postprocessing.java
* if case of error use "ERROR_POSTPROCESSING" instead of "ERROR_UNKNOWN_EXCEPTION"
* simplify source stream init

DownloadManager.java
* move all "service message sending" code to DownloadMission
* remove not implemented method "notifyUserPendingDownloads()" also his unused strings

DownloadManagerService.java
* use START_STICKY instead of START_NOT_STICKY
* simplify addMissionEventListener()/removeMissionEventListener() methods (always are called from the main thread)

Deleter.java
* better method definition

MissionAdapter.java
* better method definition
* code cleanup
* the UI is now refreshed every 750ms
* simplify download progress calculation
* indicates if the download is actually recovering
* smooth download speed measure
* show estimated remain time

MainFragment.java:
* check if viewPager is null (issued by "Apply changes" feature of Android Studio)

app/src/main/java/us/shandian/giga/util/Utility.java

@@ -4,13 +4,14 @@ import android.content.ClipData;
 import android.content.ClipboardManager;
 import android.content.Context;
 import android.os.Build;
+import android.util.Log;
+import android.widget.Toast;
+
 import androidx.annotation.ColorInt;
 import androidx.annotation.DrawableRes;
 import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import androidx.core.content.ContextCompat;
-import android.util.Log;
-import android.widget.Toast;
 
 import org.schabi.newpipe.R;
 import org.schabi.newpipe.streams.io.SharpStream;
@@ -26,6 +27,7 @@ import java.io.Serializable;
 import java.net.HttpURLConnection;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.util.Locale;
 
 import us.shandian.giga.io.StoredFileHelper;
 
@@ -39,26 +41,28 @@ public class Utility {
     }
 
     public static String formatBytes(long bytes) {
+        Locale locale = Locale.getDefault();
         if (bytes < 1024) {
-            return String.format("%d B", bytes);
+            return String.format(locale, "%d B", bytes);
         } else if (bytes < 1024 * 1024) {
-            return String.format("%.2f kB", bytes / 1024d);
+            return String.format(locale, "%.2f kB", bytes / 1024d);
         } else if (bytes < 1024 * 1024 * 1024) {
-            return String.format("%.2f MB", bytes / 1024d / 1024d);
+            return String.format(locale, "%.2f MB", bytes / 1024d / 1024d);
         } else {
-            return String.format("%.2f GB", bytes / 1024d / 1024d / 1024d);
+            return String.format(locale, "%.2f GB", bytes / 1024d / 1024d / 1024d);
         }
     }
 
-    public static String formatSpeed(float speed) {
+    public static String formatSpeed(double speed) {
+        Locale locale = Locale.getDefault();
         if (speed < 1024) {
-            return String.format("%.2f B/s", speed);
+            return String.format(locale, "%.2f B/s", speed);
         } else if (speed < 1024 * 1024) {
-            return String.format("%.2f kB/s", speed / 1024);
+            return String.format(locale, "%.2f kB/s", speed / 1024);
         } else if (speed < 1024 * 1024 * 1024) {
-            return String.format("%.2f MB/s", speed / 1024 / 1024);
+            return String.format(locale, "%.2f MB/s", speed / 1024 / 1024);
         } else {
-            return String.format("%.2f GB/s", speed / 1024 / 1024 / 1024);
+            return String.format(locale, "%.2f GB/s", speed / 1024 / 1024 / 1024);
         }
     }
 
@@ -188,12 +192,11 @@ public class Utility {
         switch (type) {
             case MUSIC:
                 return R.drawable.music;
+            default:
             case VIDEO:
                 return R.drawable.video;
             case SUBTITLE:
                 return R.drawable.subtitle;
-            default:
-                return R.drawable.video;
         }
     }
 
@@ -274,4 +277,25 @@ public class Utility {
 
         return -1;
     }
+
+    private static String pad(int number) {
+        return number < 10 ? ("0" + number) : String.valueOf(number);
+    }
+
+    public static String stringifySeconds(double seconds) {
+        int h = (int) Math.floor(seconds / 3600);
+        int m = (int) Math.floor((seconds - (h * 3600)) / 60);
+        int s = (int) (seconds - (h * 3600) - (m * 60));
+
+        String str = "";
+
+        if (h < 1 && m < 1) {
+            str = "00:";
+        } else {
+            if (h > 0) str = pad(h) + ":";
+            if (m > 0) str += pad(m) + ":";
+        }
+
+        return str + pad(s);
+    }
 }