Calculating Business Hours via Trigger and Class

Question

I currently have business hours / Holidays removed from business hour calculations using formula fields. The issue with that is, is an employe works on a holiday or weekend, the formula shows a negative number and I can not figure out a way to resolve that issue, so I am attempting to move to Apex to calculate the number of business hours and holidays. When attempting to do so via an after insert / after update trigger which calls a class to use the business hour object and the diff method I receive the following error: Method does not exist or incorrect signature: void diff(Id, DateTime, DateTime) from the type BusinessHours

Any idea what my issue is here, and how to resolve?

Trigger Code:

trigger ticketTrigger on Ticket__c (after insert, after update) {
    
    List<Ticket__c> ticketsToUpdate = new List<Ticket__c>();
    
    for(Ticket__c tickets : Trigger.New){
        ticketTriggerHandler.sla(Trigger.new); 
    }
    
}

Class Code:

public class ticketTriggerHandler {

    public static void sla(List<Ticket__c> newTickets){
        
        BusinessHours bh = [SELECT ID FROM BusinessHours WHERE IsDefault=true];
        
        list<Ticket__c> ticketsToUpdate = new List<Ticket__c>();
        
        List<Ticket__c> ticketsFromTrigger = newTickets;
        
        for(Ticket__c t : ticketsFromTrigger){
            DateTime create = t.Created_Date__c;
            DateTime Respond = t.Responded_Date__c;
            DateTime Resolve = t.Resolved_Date__c;
            Integer RespondDiff = bh.diff(bh.id, create, Respond);
            Integer ResolveDiff = bh.diff(bh.Id, create, Resolve);
            t.RespondedHours__c = RespondDiff;
            t.ResolvedHours = ResolveDiff;
            ticketsToUpdate.add(t);
        }
        if(ticketsToUpdate.size()>0){
            update ticketsToUpdate;
        }
    }
}

UPDATED CODE::::::::

public class ticketTriggerHandler {

@invocableMethod
public static void sla(List<Ticket__c> newTickets){
    List<ID> ticketIds = new List<ID>();
    for(Ticket__c t : newTickets){
        ticketIds.add(t.Id);
    }
    updateTicket(ticketIds);
}

public static void updateTicket(List<ID> newTickets){
    ID TicketId = newTickets[0];
    
    Ticket__c ticketsFromTrigger = [SELECT ID, Created_Date__c, Responded_Date__c, Resolved_Date__c, Total_Responded_Hours__c, Total_Resolved_Hours__c FROM Ticket__c
                      WHERE ID=: newTickets];
    
    BusinessHours bh = [SELECT ID FROM BusinessHours WHERE IsDefault=true];
    
    list<Ticket__c> ticketsToUpdate = new List<Ticket__c>();
    
        DateTime create = ticketsFromTrigger.Created_Date__c;
        DateTime Respond = ticketsFromTrigger.Responded_Date__c;
        DateTime Resolve = ticketsFromTrigger.Resolved_Date__c;
        if(ticketsFromTrigger.Responded_Date__c != null){
            Long RespondDiff = BusinessHours.diff(bh.id, create, Respond);
            Double hours = RespondDiff / 3600000;
            
            Long RespondDiff2 = BusinessHours.diff(bh.Id, create, Respond);
            Decimal de = BusinessHours.diff(bh.Id, create, Resolve);
            de = ((de/(1*60*60*1000))-(RespondDiff/(1*60*60*1000)));
            
            Decimal DeRespond = ((de/100)*60);
            ticketsFromTrigger.Total_Responded_Hours__c = ((RespondDiff/(1*60*60*1000))+DeRespond);
        }
        If(ticketsFromTrigger.Resolved_Date__c != null){
            Long ResolveDiff = BusinessHours.diff(bh.Id, create, Resolve);
            Double hours2 = ResolveDiff/3600000;
            
            Long ResolvedDiff2 = BusinessHours.diff(bh.Id, create, Resolve);
            Decimal de1 = BusinessHours.diff(bh.Id, create, Resolve);
            de1 = ((de1/(1*60*60*1000))-(ResolvedDiff2/(1*60*60*1000)));
            
            Decimal de2 = ((de1/100)*60);
            ticketsFromTrigger.Total_Resolved_Hours__c = ((ResolvedDiff2/(1*60*60*1000))+de2);
        }
        ticketsToUpdate.add(ticketsFromTrigger);

    if(ticketsToUpdate.size()>0){
        update ticketsToUpdate;
    }
}

}

Images from record where math is not correct. Anyone that can help give a second set of eyes and advise what changes need to be made to make the math work?

Answer 1

As per the BusinessHours documentation:

All methods are static.

So you should use: BusinessHours.diff(bh.id, create, Respond) instead of trying to use a method from the instance you queried, which does not exist.