Apex Trigger :-


trigger TruckSupplyActual on Truck_Supply_Actual__c (after insert, after update) {
    if(Trigger.isAfter && Trigger.isInsert) 
    {
        TriggerHandler.insertRecord(Trigger.new);
    }
    if(Trigger.isBefore || Trigger.isAfter && Trigger.isUpdate )
    {
        TriggerHandler.updateRecord(Trigger.newMap, Trigger.oldMap);
    }
}

--------------------------------------------------------------------------------------------------------------


Apex Handler Class :-


public class TriggerHandler {
    public static void insertRecord(list<Truck_Supply_Actual__c> recordList ){
        list<Truck_Supply_Booking__c> truckSupplyBookinggList = new list<Truck_Supply_Booking__c>();
        for(Truck_Supply_Actual__c a : recordList){
            if(a.Amount__c != null){
                Decimal i = a.Amount__c;
                for(Integer j=1;j<=i;j++){
                    Truck_Supply_Booking__c truckSupplyBookingList = new Truck_Supply_Booking__c();
                    truckSupplyBookingList.Truck_Supply_Actual__c = a.ID;
                    truckSupplyBookingList.Date__c = system.today();
                    truckSupplyBookingList.Status__c = 'Available';
                    truckSupplyBookingList.truck__c = a.Truck__c;
                    truckSupplyBookinggList.add(truckSupplyBookingList);
                    
                }
            }
              insert truckSupplyBookinggList;
        }    
    }
    
    public static void updateRecord(Map<id,Truck_Supply_Actual__c> newValues , Map <id,Truck_Supply_Actual__c> oldValues){
        list<Truck_Supply_Booking__c> truckSupplyBookinggList = new list<Truck_Supply_Booking__c>(); 
        for(Truck_Supply_Actual__c a : newValues.values())
        { 
            if(oldValues.get(a.Id).Additional_Amount__c != newValues.get(a.Id).Additional_Amount__c)
            {    
                Truck_Supply_Actual__c record = [Select Id, Additional_Amount__c From Truck_Supply_Actual__c WHERE id =: a.Id]; 
                record.Additional_1_Created__c = true;
                update record;
                Decimal i = newValues.get(a.Id).Additional_Amount__c;
                for(Integer j=1;j<=i;j++){
                    Truck_Supply_Booking__c truckSupplyBookingList = new Truck_Supply_Booking__c();
                    truckSupplyBookingList.Truck_Supply_Actual__c = a.Id;
                    truckSupplyBookingList.Date__c = a.Date__c;
                    truckSupplyBookingList.Status__c = 'Available';
                    truckSupplyBookingList.truck__c = a.Truck__c;
                    truckSupplyBookinggList.add(truckSupplyBookingList);
                }
            }
            
            // -------------------------------- 2 -----------------------------------
            
             if(oldValues.get(a.Id).Additional_Amount_2__c != newValues.get(a.Id).Additional_Amount_2__c)
            {    
                Truck_Supply_Actual__c recordd = [Select Id, Additional_Amount_2__c From Truck_Supply_Actual__c WHERE id =: a.Id]; 
                recordd.Additional_2_Created__c = true;
                update recordd;
                Decimal i = newValues.get(a.Id).Additional_Amount_2__c;
                for(Integer j=1;j<=i;j++){
                    Truck_Supply_Booking__c truckSupplyBookingList = new Truck_Supply_Booking__c();
                    truckSupplyBookingList.Truck_Supply_Actual__c = a.Id;
                    truckSupplyBookingList.Date__c = a.Date__c;
                    truckSupplyBookingList.Status__c = 'Available';
                    truckSupplyBookingList.truck__c = a.Truck__c;
                    truckSupplyBookinggList.add(truckSupplyBookingList);
                }
            }
            
            //------------------------------------- 3 ----------------------------
            
                         if(oldValues.get(a.Id).Additional_Amount_3__c != newValues.get(a.Id).Additional_Amount_3__c)
            {    
                Truck_Supply_Actual__c recordd = [Select Id, Additional_Amount_3__c From Truck_Supply_Actual__c WHERE id =: a.Id]; 
                recordd.Additional_3_Created__c = true;
                update recordd;
                Decimal i = newValues.get(a.Id).Additional_Amount_3__c;
                for(Integer j=1;j<=i;j++){
                    Truck_Supply_Booking__c truckSupplyBookingList = new Truck_Supply_Booking__c();
                    truckSupplyBookingList.Truck_Supply_Actual__c = a.Id;
                    truckSupplyBookingList.Date__c = a.Date__c;
                    truckSupplyBookingList.Status__c = 'Available';
                    truckSupplyBookingList.truck__c = a.Truck__c;
                    truckSupplyBookinggList.add(truckSupplyBookingList);
                }
            }
            
        }
        insert truckSupplyBookinggList;
    }
}