Gracefully handle reverting to corrupt files

Offer the user an option to abort the revert procedure, restoring the
original file again. Randomly stumbled across this due to the FIXME (at
least I'm assuming this is what the FIXME referred to?) for snapshots,
but this also implements it for backups.

Note that I'm keeping the temp backup around - gets cleaned up at exit
anyways, and it may give computer-savvy users an out if they
accidentally click 'No' on the new popup.

Also no longer swallows the traceback for the FileError, deprinting it
to the BugDump instead so that one can actually figure out why the
reverting failed.

Author: Infernio

Mopy/bash/basher/files_links.py

@@ -219,10 +219,11 @@ def Execute(self):
             #--Copy file
             self.window.data_store.copy_info(fileName, destDir, destName)
 
-class File_RevertToSnapshot(OneItemLink): # MODS LINK !
+class File_RevertToSnapshot(OneItemLink):
     """Revert to Snapshot."""
     _text = _(u'Revert to Snapshot...')
-    _help = _(u"Revert to a previously created snapshot from the Bash/Snapshots dir.")
+    _help = _(u'Revert to a previously created snapshot from the '
+              u'Bash/Snapshots dir.')
 
     @balt.conversation
     def Execute(self):
@@ -239,20 +240,32 @@ def Execute(self):
         if not snapPath: return
         snapName = snapPath.tail
         #--Warning box
-        message = (_(u"Revert %s to snapshot %s dated %s?") % (
+        message = (_(u'Revert %s to snapshot %s dated %s?') % (
             fileName.s, snapName.s, format_date(snapPath.mtime)))
         if not self._askYes(message, _(u'Revert to Snapshot')): return
         with balt.BusyCursor():
-            destPath = self._selected_info.getPath()
+            destPath = self._selected_info.abs_path
             current_mtime = destPath.mtime
+            # Make a temp backup first in case reverting to snapshot fails
+            destPath.copyTo(destPath.temp)
             snapPath.copyTo(destPath)
             # keep load order but recalculate the crc
             self._selected_info.setmtime(current_mtime, crc_changed=True)
             try:
                 self.window.data_store.new_info(fileName, notify_bain=True)
-            except exception.FileError: # FIXME(ut) - we just lost the correct file
-                balt.showError(self,_(u'Snapshot file is corrupt!'))
+            except exception.FileError:
+                # Reverting to snapshot failed - may be corrupt
+                bolt.deprint(u'Failed to revert to snapshot', traceback=True)
                 self.window.panel.ClearDetails()
+                if self._askYes(
+                    _(u'Failed to revert %s to snapshot %s. The snapshot file '
+                      u'may be corrupt. Do you want to restore the original '
+                      u"file again? 'No' keeps the reverted, possibly broken "
+                      u'snapshot instead.') % (fileName.s, snapName.s),
+                        title=_(u'Revert to Snapshot - Error')):
+                    # Restore the known good file again - no error check needed
+                    destPath.untemp()
+                    self.window.data_store.new_info(fileName, notify_bain=True)
         # don't refresh saves as neither selection state nor load order change
         self.window.RefreshUI(redraw=[fileName], refreshSaves=False)
 
@@ -277,8 +290,8 @@ def _initData(self, window, selection):
         super(_RevertBackup, self)._initData(window, selection)
         self.backup_path = self._selected_info.backup_dir.join(
             self._selected_item) + (u'f' if self.first else u'')
-        self._help = _(u"Revert %(file)s to its first backup") if self.first \
-            else _(u"Revert %(file)s to its last backup")
+        self._help = _(u'Revert %(file)s to its first backup') if self.first \
+            else _(u'Revert %(file)s to its last backup')
         self._help %= {'file': self._selected_item}
 
     def _enable(self):
@@ -288,17 +301,33 @@ def _enable(self):
     @balt.conversation
     def Execute(self):
         #--Warning box
-        message = _(u"Revert %s to backup dated %s?") % (
-            self._selected_item.s, format_date(self.backup_path.mtime))
+        sel_file = self._selected_item
+        backup_date = format_date(self.backup_path.mtime)
+        message = _(u'Revert %s to backup dated %s?') % (sel_file.s,
+                                                         backup_date)
         if not self._askYes(message): return
         with balt.BusyCursor():
+            # Make a temp backup first in case reverting to backup fails
+            info_path = self._selected_info.abs_path
+            info_path.copyTo(info_path.temp)
             try:
                 self._selected_info.revert_backup(self.first)
-                self.window.RefreshUI(redraw=[self._selected_item],
-                                      refreshSaves=False)
             except exception.FileError:
-                self._showError(_(u'Old file is corrupt!'))
-                self.window.RefreshUI(refreshSaves=True)
+                # Reverting to backup failed - may be corrupt
+                bolt.deprint(u'Failed to revert to backup', traceback=True)
+                self.window.panel.ClearDetails()
+                if self._askYes(
+                    _(u'Failed to revert %s to backup dated %s. The backup '
+                      u'file may be corrupt. Do you want to restore the '
+                      u"original file again? 'No' keeps the reverted, "
+                      u'possibly broken backup instead.') % (sel_file.s,
+                                                             backup_date),
+                        title=_(u'Revert to Backup - Error')):
+                    # Restore the known good file again - no error check needed
+                    info_path.untemp()
+                    self.window.data_store.new_info(sel_file, notify_bain=True)
+        # don't refresh saves as neither selection state nor load order change
+        self.window.RefreshUI(redraw=[sel_file], refreshSaves=False)
 
 class File_RevertToBackup(ChoiceLink):
     """Revert to last or first backup."""