In odoo version 12 there is the facility to add the attachment by dragging and dropping in the main record

in the same way, there is the send message button and the log note button is there when we click on that the composer is open, so I want the facility to drag and drop the attachment into that particular composer that is getting opened on clicking the send message button and the log note button I have tried my best to add the attachment and even after dropping the attachment into the composer the file is added but still when I send it the attachment is getting added to the main record, not the composer. (NOt Expandable Wizard composer)

Please help us step by step code-wise for odoo 12

Thanks in advance