How can hook some code before deleting a comment? How can I add few lines of code before comments get deleted. there must be some hook or something by which we can do this. I am getting nothing relevant by Googling.

Any help appreciated.
Strange enough, but there is no predelete hook present with Drupal 7 core, or even not provided by the entity module.

However the good news is Drupal 8 has this feature!