Fix bug in handling change of filename but not foldername

Fix a bug triggered in very special circumstances (primarily on windows)
that could cause duplicate files entries (hard links) to be created for
a books' files when changing the title and author. The bug was triggered
only if the title or author were between 32 and 35 characters in length
and the book entry had originally been created by a pre 1.x version of
calibre.

src/calibre/db/backend.py

@@ -1406,6 +1406,8 @@ class DB(object):
 
         source_ok = current_path and os.path.exists(spath)
         wam = WindowsAtomicFolderMove(spath) if iswindows and source_ok else None
+        format_map = {}
+        original_format_map = {}
         try:
             if not os.path.exists(tpath):
                 os.makedirs(tpath)
@@ -1416,16 +1418,28 @@ class DB(object):
                         windows_atomic_move=wam, use_hardlink=True)
                 for fmt in formats:
                     dest = os.path.join(tpath, fname+'.'+fmt.lower())
-                    self.copy_format_to(book_id, fmt, formats_field.format_fname(book_id, fmt), current_path,
+                    format_map[fmt] = dest
+                    ofmt_fname = formats_field.format_fname(book_id, fmt)
+                    original_format_map[fmt] = os.path.join(spath, ofmt_fname+'.'+fmt.lower())
+                    self.copy_format_to(book_id, fmt, ofmt_fname, current_path,
                                         dest, windows_atomic_move=wam, use_hardlink=True)
             # Update db to reflect new file locations
             for fmt in formats:
                 formats_field.table.set_fname(book_id, fmt, fname, self)
             path_field.table.set_path(book_id, path, self)
 
-            # Delete not needed directories
+            # Delete not needed files and directories
             if source_ok:
-                if os.path.exists(spath) and not samefile(spath, tpath):
+                if os.path.exists(spath):
+                    if samefile(spath, tpath):
+                        # The format filenames may have changed while the folder
+                        # name remains the same
+                        for fmt, opath in original_format_map.iteritems():
+                            npath = format_map.get(fmt, None)
+                            if npath and os.path.abspath(npath.lower()) != os.path.abspath(opath.lower()) and samefile(opath, npath):
+                                # opath and npath are different hard links to the same file
+                                os.unlink(opath)
+                    else:
                         if wam is not None:
                             wam.delete_originals()
                         self.rmtree(spath)

src/calibre/db/tests/filesystem.py

@@ -76,6 +76,8 @@ class FilesystemTest(BaseTest):
         f = open(fpath, 'rb')
         with self.assertRaises(IOError):
             cache.set_field('title', {1:'Moved'})
+        with self.assertRaises(IOError):
+            cache.remove_books({1})
         f.close()
         self.assertNotEqual(cache.field_for('title', 1), 'Moved', 'Title was changed despite file lock')
 
@@ -106,3 +108,15 @@ class FilesystemTest(BaseTest):
         self.assertLessEqual(len(cache.field_for('path', 1)), cache.backend.PATH_LIMIT * 2)
         fpath = cache.format_abspath(1, cache.formats(1)[0])
         self.assertLessEqual(len(fpath), len(cache.backend.library_path) + cache.backend.PATH_LIMIT * 4)
+
+    def test_fname_change(self):
+        ' Test the changing of the filename but not the folder name '
+        cache = self.init_cache()
+        title = 'a'*30 + 'bbb'
+        cache.backend.PATH_LIMIT = 100
+        cache.set_field('title', {3:title})
+        cache.add_format(3, 'TXT', BytesIO(b'xxx'))
+        cache.backend.PATH_LIMIT = 40
+        cache.set_field('title', {3:title})
+        fpath = cache.format_abspath(3, 'TXT')
+        self.assertEqual(sorted([os.path.basename(fpath)]), sorted(os.listdir(os.path.dirname(fpath))))