trigger OLITrigger on OpportunityLineItem (before insert, before update, before delete) {
    
 //Code block to enable bypassing of triggers using field off users record  
    String currentUserId = UserInfo.getUserId();
    User currentUser = [SELECT Bypass_Triggers__c FROM User WHERE Id = :currentUserId LIMIT 1];
    if (currentUser.Bypass_Triggers__c) return;
        
    If(System.Trigger.isInsert){
    
      For(OpportunityLineItem oli: Trigger.New){
    
        oli.Original_Total_Cost__c = oli.TotalPrice;
        
      }
  }
    
  If(System.Trigger.isUpdate){

       For(OpportunityLineItem oli : [SELECT TotalPrice,Original_Total_Cost__c,Opportunity.StageName FROM OpportunityLineItem Where Id IN: Trigger.New]){
           
      if(oli.Opportunity.StageName == 'Closed Won')
     {
         //Do Nothing
     }
           
      else  if(Trigger.oldmap.get(oli.id).TotalPrice == Trigger.newmap.get(oli.id).TotalPrice)
           {
               // Do nothing  
            }
                  
     else if(Trigger.oldmap.get(oli.id).TotalPrice != Trigger.newmap.get(oli.id).TotalPrice)
     {
          oli.Original_Total_Cost__c = Trigger.oldmap.get(oli.id).TotalPrice;
     }
       }
  }
       
  If(System.Trigger.isBefore &&System.Trigger.isDelete){
    
  For(OpportunityLineItem oli : Trigger.old)
    {
        if(oli.number_of_invoice_lines__c == 0 || oli.number_of_invoice_lines__c == null){

        list<Line_Item_Details__c> LineItemDetailsId=[Select Id FROM Line_Item_Details__c Where id =:oli.Line_Item_Details__c];     
        delete LineItemDetailsId;
        }
        
        else if(oli.number_of_invoice_lines__c >= 1) 
        {
            oli.addError('You can not delete this Product as it has Invoiced Schedules');
        }
       
    }
    }

}