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/io/ChunkFileInputStream.java

@@ -5,21 +5,23 @@ import org.schabi.newpipe.streams.io.SharpStream;
 import java.io.IOException;
 
 public class ChunkFileInputStream extends SharpStream {
+    private static final int REPORT_INTERVAL = 256 * 1024;
 
     private SharpStream source;
     private final long offset;
     private final long length;
     private long position;
 
-    public ChunkFileInputStream(SharpStream target, long start) throws IOException {
-        this(target, start, target.length());
-    }
+    private long progressReport;
+    private final ProgressReport onProgress;
 
-    public ChunkFileInputStream(SharpStream target, long start, long end) throws IOException {
+    public ChunkFileInputStream(SharpStream target, long start, long end, ProgressReport callback) throws IOException {
         source = target;
         offset = start;
         length = end - start;
         position = 0;
+        onProgress = callback;
+        progressReport = REPORT_INTERVAL;
 
         if (length < 1) {
             source.close();
@@ -60,12 +62,12 @@ public class ChunkFileInputStream extends SharpStream {
     }
 
     @Override
-    public int read(byte b[]) throws IOException {
+    public int read(byte[] b) throws IOException {
         return read(b, 0, b.length);
     }
 
     @Override
-    public int read(byte b[], int off, int len) throws IOException {
+    public int read(byte[] b, int off, int len) throws IOException {
         if ((position + len) > length) {
             len = (int) (length - position);
         }
@@ -76,6 +78,11 @@ public class ChunkFileInputStream extends SharpStream {
         int res = source.read(b, off, len);
         position += res;
 
+        if (onProgress != null && position > progressReport) {
+            onProgress.report(position);
+            progressReport = position + REPORT_INTERVAL;
+        }
+
         return res;
     }
 

app/src/main/java/us/shandian/giga/io/CircularFileWriter.java

@@ -174,12 +174,12 @@ public class CircularFileWriter extends SharpStream {
     }
 
     @Override
-    public void write(byte b[]) throws IOException {
+    public void write(byte[] b) throws IOException {
         write(b, 0, b.length);
     }
 
     @Override
-    public void write(byte b[], int off, int len) throws IOException {
+    public void write(byte[] b, int off, int len) throws IOException {
         if (len == 0) {
             return;
         }
@@ -261,7 +261,7 @@ public class CircularFileWriter extends SharpStream {
     @Override
     public void rewind() throws IOException {
         if (onProgress != null) {
-            onProgress.report(-out.length - aux.length);// rollback the whole progress
+            onProgress.report(0);// rollback the whole progress
         }
 
         seek(0);
@@ -357,16 +357,6 @@ public class CircularFileWriter extends SharpStream {
         long check();
     }
 
-    public interface ProgressReport {
-
-        /**
-         * Report the size of the new file
-         *
-         * @param progress the new size
-         */
-        void report(long progress);
-    }
-
     public interface WriteErrorHandle {
 
         /**
@@ -381,10 +371,10 @@ public class CircularFileWriter extends SharpStream {
 
     class BufferedFile {
 
-        protected final SharpStream target;
+        final SharpStream target;
 
         private long offset;
-        protected long length;
+        long length;
 
         private byte[] queue = new byte[QUEUE_BUFFER_SIZE];
         private int queueSize;
@@ -397,16 +387,16 @@ public class CircularFileWriter extends SharpStream {
             this.target = target;
         }
 
-        protected long getOffset() {
+        long getOffset() {
             return offset + queueSize;// absolute offset in the file
         }
 
-        protected void close() {
+        void close() {
             queue = null;
             target.close();
         }
 
-        protected void write(byte b[], int off, int len) throws IOException {
+        void write(byte[] b, int off, int len) throws IOException {
             while (len > 0) {
                 // if the queue is full, the method available() will flush the queue
                 int read = Math.min(available(), len);
@@ -436,7 +426,7 @@ public class CircularFileWriter extends SharpStream {
             target.seek(0);
         }
 
-        protected int available() throws IOException {
+        int available() throws IOException {
             if (queueSize >= queue.length) {
                 flush();
                 return queue.length;
@@ -451,7 +441,7 @@ public class CircularFileWriter extends SharpStream {
             target.seek(0);
         }
 
-        protected void seek(long absoluteOffset) throws IOException {
+        void seek(long absoluteOffset) throws IOException {
             if (absoluteOffset == offset) {
                 return;// nothing to do
             }

app/src/main/java/us/shandian/giga/io/ProgressReport.java

@@ -0,0 +1,11 @@
+package us.shandian.giga.io;
+
+public interface ProgressReport {
+
+    /**
+     * Report the size of the new file
+     *
+     * @param progress the new size
+     */
+    void report(long progress);
+}