Fix moving rows

Also fix associated tests.
Fixes #234

app/playlistmodel.py

@@ -856,15 +856,23 @@ class PlaylistModel(QAbstractTableModel):
         # Build a {current_row_number: new_row_number} dictionary
         row_map: dict[int, int] = {}
 
+        # The destination row number will need to be reduced by the
+        # number of rows being move from above the destination row
+        # otherwise rows below the destination row will end up above the
+        # moved rows.
+        adjusted_to_row = to_row_number - len([a for a in from_rows if a <= to_row_number])
+
         # Put the from_row row numbers into the row_map. Ultimately the
         # total number of elements in the playlist doesn't change, so
         # check that adding the moved rows starting at to_row won't
         # overshoot the end of the playlist.
-        if to_row_number + len(from_rows) > len(self.playlist_rows):
+        if adjusted_to_row + len(from_rows) > len(self.playlist_rows):
             next_to_row = len(self.playlist_rows) - len(from_rows)
         else:
-            next_to_row = to_row_number
+            next_to_row = adjusted_to_row
 
+        # zip iterates from_row and to_row simultaneously from the
+        # respective sequences inside zip()
         for from_row, to_row in zip(
             from_rows, range(next_to_row, next_to_row + len(from_rows))
         ):
@@ -873,7 +881,8 @@ class PlaylistModel(QAbstractTableModel):
         # Move the remaining rows to the row_map. We want to fill it
         # before (if there are gaps) and after (likewise) the rows that
         # are moving.
-        # This iterates old_row and new_row simultaneously.
+        # zip iterates old_row and new_row simultaneously from the
+        # respective sequences inside zip()
         for old_row, new_row in zip(
             [x for x in self.playlist_rows.keys() if x not in from_rows],
             [y for y in range(len(self.playlist_rows)) if y not in row_map.values()],

tests/test_playlistmodel.py

@@ -159,9 +159,9 @@ class TestMMMiscRowMove(unittest.TestCase):
             elif row == 3:
                 assert self.model.playlist_rows[row].note == str(4)
             elif row == 4:
-                assert self.model.playlist_rows[row].note == str(5)
-            elif row == 5:
                 assert self.model.playlist_rows[row].note == str(3)
+            elif row == 5:
+                assert self.model.playlist_rows[row].note == str(5)
 
     def test_move_rows_test3(self):
         # move row 4 to row 3
@@ -208,7 +208,7 @@ class TestMMMiscRowMove(unittest.TestCase):
             assert row in self.model.playlist_rows
             assert self.model.playlist_rows[row].plr_rownum == row
             new_order.append(int(self.model.playlist_rows[row].note))
-        assert new_order == [0, 2, 3, 6, 7, 8, 9, 1, 4, 5, 10]
+        assert new_order == [0, 2, 3, 6, 7, 1, 4, 5, 10, 8, 9]
 
     def test_move_rows_test6(self):
         # move rows [3, 6] → 5
@@ -221,7 +221,7 @@ class TestMMMiscRowMove(unittest.TestCase):
             assert row in self.model.playlist_rows
             assert self.model.playlist_rows[row].plr_rownum == row
             new_order.append(int(self.model.playlist_rows[row].note))
-        assert new_order == [0, 1, 2, 4, 5, 3, 6, 7, 8, 9, 10]
+        assert new_order == [0, 1, 2, 4, 3, 6, 5, 7, 8, 9, 10]
 
     def test_move_rows_test7(self):
         # move rows [3, 5, 6] → 8
@@ -234,7 +234,7 @@ class TestMMMiscRowMove(unittest.TestCase):
             assert row in self.model.playlist_rows
             assert self.model.playlist_rows[row].plr_rownum == row
             new_order.append(int(self.model.playlist_rows[row].note))
-        assert new_order == [0, 1, 2, 4, 7, 8, 9, 10, 3, 5, 6]
+        assert new_order == [0, 1, 2, 4, 7, 3, 5, 6, 8, 9, 10]
 
     def test_move_rows_test8(self):
         # move rows [7, 8, 10] → 5