Support drag reordering for downloads

Resolve #54

app/src/main/java/com/hippo/ehviewer/EhDB.java

@@ -111,6 +111,30 @@ public class EhDB {
         return list;
     }
 
+    public static synchronized void moveDownloadInfo(int fromPosition, int toPosition) {
+        if (fromPosition == toPosition) {
+            return;
+        }
+
+        boolean reverse = fromPosition > toPosition;
+        int offset = reverse ? toPosition : fromPosition;
+        int limit = reverse ? fromPosition - toPosition + 1 : toPosition - fromPosition + 1;
+
+        DownloadsDao dao = db.downloadsDao();
+        List<DownloadInfo> list = dao.list(offset, limit);
+
+        int step = reverse ? 1 : -1;
+        int start = reverse ? limit - 1 : 0;
+        int end = reverse ? 0 : limit - 1;
+        long toTime = list.get(end).time;
+        for (int i = end; reverse ? i < start : i > start; i += step) {
+            list.get(i).time = list.get(i + step).time;
+        }
+        list.get(start).time = toTime;
+
+        dao.update(list);
+    }
+
     // Insert or update
     public static synchronized void putDownloadInfo(DownloadInfo downloadInfo) {
         DownloadsDao dao = db.downloadsDao();

app/src/main/java/com/hippo/ehviewer/dao/DownloadsDao.kt

@@ -11,9 +11,15 @@ interface DownloadsDao : BasicDao<DownloadInfo> {
     @Query("SELECT * FROM DOWNLOADS ORDER BY TIME DESC")
     override fun list(): List<DownloadInfo>
 
+    @Query("SELECT * FROM DOWNLOADS ORDER BY TIME DESC LIMIT :limit OFFSET :offset")
+    fun list(offset: Int, limit: Int): List<DownloadInfo>
+
     @Query("SELECT * FROM DOWNLOADS WHERE GID = :gid")
     fun load(gid: Long): DownloadInfo?
 
+    @Update
+    fun update(downloadInfos: List<DownloadInfo>)
+
     @Update
     fun update(downloadInfo: DownloadInfo)
 

app/src/main/java/com/hippo/ehviewer/ui/scene/DownloadsScene.kt

@@ -286,6 +286,8 @@ class DownloadsScene : BaseToolbarScene(), DownloadInfoListener, OnClickFabListe
             mRecyclerView!!.scrollToPosition(mInitPosition)
             mInitPosition = -1
         }
+        val itemTouchHelper = ItemTouchHelper(DownloadItemTouchHelperCallback())
+        itemTouchHelper.attachToRecyclerView(mRecyclerView)
         mFastScroller!!.attachToRecyclerView(mRecyclerView)
         val handlerDrawable = HandlerDrawable()
         handlerDrawable.setColor(theme.resolveColor(com.google.android.material.R.attr.colorPrimary))
@@ -1149,7 +1151,6 @@ class DownloadsScene : BaseToolbarScene(), DownloadInfoListener, OnClickFabListe
             )
         }
 
-        @SuppressLint("NotifyDataSetChanged")
         override fun onMove(
             recyclerView: RecyclerView,
             viewHolder: RecyclerView.ViewHolder,
@@ -1164,7 +1165,7 @@ class DownloadsScene : BaseToolbarScene(), DownloadInfoListener, OnClickFabListe
             downloadManager.moveLabel(fromPosition - 1, toPosition - 1)
             val item = mLabels.removeAt(fromPosition)
             mLabels.add(toPosition, item)
-            mLabelAdapter!!.notifyDataSetChanged()
+            mLabelAdapter!!.notifyItemMoved(fromPosition, toPosition)
             return true
         }
 
@@ -1192,6 +1193,42 @@ class DownloadsScene : BaseToolbarScene(), DownloadInfoListener, OnClickFabListe
         }
     }
 
+    private inner class DownloadItemTouchHelperCallback : ItemTouchHelper.Callback() {
+        override fun getMovementFlags(
+            recyclerView: RecyclerView,
+            viewHolder: RecyclerView.ViewHolder
+        ): Int {
+            return makeMovementFlags(
+                ItemTouchHelper.UP or ItemTouchHelper.DOWN,
+                0
+            )
+        }
+
+        override fun onMove(
+            recyclerView: RecyclerView,
+            viewHolder: RecyclerView.ViewHolder,
+            target: RecyclerView.ViewHolder
+        ): Boolean {
+            val fromPosition = viewHolder.bindingAdapterPosition
+            val toPosition = target.bindingAdapterPosition
+            if (fromPosition == toPosition) {
+                return false
+            }
+            lifecycleScope.launchIO {
+                EhDB.moveDownloadInfo(fromPosition, toPosition)
+                val item = mList!!.removeAt(fromPosition)
+                mList!!.add(toPosition, item)
+                withUIContext {
+                    mAdapter!!.notifyItemMoved(fromPosition, toPosition)
+                }
+            }
+            return true
+        }
+
+        override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
+        }
+    }
+
     companion object {
         const val KEY_GID = "gid"
         const val KEY_ACTION = "action"