To do that you have to inherit account.move make sure from your context for Context Value? = {'default_move_type': 'in_invoice', 'display_account_trust': True}
ex : 

state = fields.Selection(
    string='State',
    selection=[('draft', 'Draft'), ('first_approve', 'First Approve'),('final_approve', 'Final Approve'), ('sent', 'Sent By Email'), ('customer', 'Waiting Customer Confirm'),('sale', 'Sale Order'),
               ('cancel', 'Cancelled') ],default='draft',
    required=False, )

so make your own function to control your bottom depending on context above