custom update table

I have the following table like this

code item   price   start date   end date 
--------------------------------------------------
art1         2.47    01/01/2015   31/03/2015
art1         1.23    01/04/2015   21/09/2015 
art1         3.55    22/09/2015   01/01/2018 
When I will add a new line which start date exists already between a start date and end date in the table .

I need to update the end date in the table with the start date -1 of the new line to be added
then insert the new line .
For example, I have a new line to added :

code item   price   start date   end date 
-----------------------------------------
art1         4      28/12/2015   31/05/2018
What I expect as a final result is the following table :

code item   price   start date   end date 
--------------------------------------------------
art1         2.47    01/01/2015   31/03/2015
art1         1.23    01/04/2015   21/09/2015 
art1         3.55    22/09/2015   27/12/2015 
art1           4      28/12/2015   31/05/2018