I Have two custom objects:
-Visit
Representative (lookup User)
Customer (lookup Contact)
StartDate (Date)
EndDate (Date)
Status (picklist)

-Target
Representative (lookup User)
Customer (lookup Contact)
StartDate (Date)
EndDate (Date)
Actual Calls Count (Number)

When Visit`s status change to 'Close' need increment Target`s Actual Calls Count by 1 with next condition:

1) Date from Visit`s StartDate field must be in between Target`s StartDate and EndDate.
2) Contact in Visit`s Customer field must be the same that Contact Target`s Customer field
3) User in Target`s Representative field must be the same that User Target`s Representative field
4) Need that counter have worked only one time for one visit.

How can I do it? (Without triggers)