How to use file_save to store pictures into a folder on server?

Question

what i want to perform (globally) is to import a csv file that contains data such as book_title, author, and the cover image of the books. The csv file is loaded, book_title and author are stored in their respective tables but for pictures, what i want is to put them manually (ftp for example) on a folder (doesn't matter if it's my default public folder or a new one) and store data in tables like : file_managed and field_data_field_cover_picture etc In my csv file, and for pictures column i just write filenames of every picture.

At the moment, i'm confused and this is my actual code :

$filename_cover = $get_filename.'.jpg'; <===from csv

        $add_cover_file = db_insert('file_managed')
        // ->key(array('fid' => rand()))
        ->fields(array(
            'uid' => $user->uid,
            'filename' => $filename_cover ,
            'uri' => 'public://couvertures/'.$filename_couv,<==my file 
            'filemime' => 'application/octet-stream',
            'status' => 1,
            'timestamp' => time()
        ))
        ->execute();

Now adding on the pictures covers table : (how to put the fid ?)

  $add_couverture = db_merge('field_data_field_photo_de_couverture')
        ->key(array('entity_id' => $newNode->nid, 'field_photo_de_couverture_fid'=>$add_couv_file->fid ))
        ->fields(array(
            'field_photo_de_couverture_fid'=>$get_fid ,
            'entity_id' => $newNode->nid,
            'delta' => 0,
            'bundle' => 'livre',
            'entity_type' => 'node'
        ))
        ->execute();

Answer 1

Try this:

$file = file_save((object)array(
    'filename' => $file_name,
    'uri' => $destination_uri,
    'status' => FILE_STATUS_PERMANENT,
    'filemime' => file_get_mimetype($destination_uri),
  ));
//at that point you can use the $file->fid
//do the magic on your custom table field_data_field_photo_de_couverture