public class MaintenanceRequestHelper {
    public static void updateWorkOrders(List<Case> newRequest, Map<Id , Case> oldRequest){
        System.debug('oldRequest' +oldRequest);
        System.debug('newRequest' +newRequest);
        List<Case> newRequestList = new List<Case>();
        Map<Id , Decimal> minCycle = new Map<Id, Decimal>();
        Set<Id>  setId = new Set<Id>();

        for (case c : newRequest){
            setId.add(c.Id);
        }
        List<AggregateResult> minCycles =
            [SELECT Maintenance_Request__c, Min (Equipment__r.Maintenance_Cycle__c)
             FROM Work_Part__c WHERE Maintenance_Request__c =: setId
             GROUP BY Maintenance_Request__c];
        for(AggregateResult temp : minCycles){
            Id idMap = (Id) temp.get('Maintenance_Request__c');
            Decimal decimalMap = (Decimal) temp.get('expr0');
            minCycle.put(idMap,decimalMap);
        }

        for (case j : newRequest){
            case oldCase = oldRequest.get(j.Id);
            system.debug('oldCase'+ oldCase);
            if((j.Type == ('Routine Maintenance') || j.Type == ('Repair')) &&
               j.IsClosed && !oldCase.IsClosed ){
                   Case nInsert = new Case();
                   nInsert.Vehicle__c = j.Vehicle__c;
                   nInsert.Type = 'Routine Maintenance';
                   nInsert.Subject = '';
                   nInsert.Date_Reported__c = Date.today();
                   nInsert.Equipment__c = j.Equipment__c;
                   integer cycle;
                   system.debug('nInsert' + nInsert);
                   if (minCycle.get(j.Id)!= null){
                       cycle = (integer)minCycle.get(j.Id);
                       nInsert.Date_Due__c = Date.today().addDays(cycle);
                   }
                   else{
                       cycle = 0;
                       nInsert.Date_Due__c = Date.today().addDays(cycle);
                   }
                   newRequestList.add(nInsert);
               }
        }
        insert newRequestList;
        system.debug('newRequestList' + newRequestList);
    }
}