How To Force Search API To Reindex a Node / an Entity

By default Search API (Drupal 7) reindexes a node when the node gets updated. But what if you want to reindex a node / an entity on demand or via some other hook i.e. outside of update cycle?

Turned out it is a quite simple exercise. You just need to execute this function call whenever you want to reindex a node / an entity:

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