Rollup summary for lookup relationship

trigger Rollup on Concur_Reports__c (after insert, after delete, after undelete,after update) {

boolean delflag=false;

Set<Id> crids=new Set<Id>();

Map<Id,List<Concur_Reports__c>> rollup=new Map<Id,List<Concur_Reports__c>>();

List<id> opplist= new List<id>();

if(Trigger.isInsert || Trigger.isUndelete || Trigger.isUpdate ){

For(Concur_Reports__c  con1 : Trigger.new){

crids.add(con1.id);

opplist.add(con1.Opportunity__c);

 if(rollup.containsKey(con1.Opportunity__c)){

rollup.get(con1.Opportunity__c).add(con1);

 }

else{

rollup.put(con1.Opportunity__c,new list<Concur_Reports__c>{con1});

}

}

}

 else if(Trigger.isDelete){

 delflag=True;

 For(Concur_Reports__c con1 : Trigger.old){

crids.add(con1.id);

opplist.add(con1.Opportunity__c);

if(rollup.containsKey(con1.Opportunity__c)){

rollup.get(con1.Opportunity__c).add(con1);

 }

else{

rollup.put(con1.Opportunity__c,new list<Concur_Reports__c>{con1});

}

}

}

    

    system.debug('%%%%%%%%%%%%%%%%%%%%%%%%%%'+rollup);

    List<Opportunity> OppUpdateList = New List<Opportunity>() ;

     Map<Id,Opportunity> oppidsfilter=new  Map<Id,Opportunity>([SELECT AccountId,Total_Expense__c,Amount,CampaignId,CloseDate,CreatedById,CreatedDate,CurrentGenerators__c,DeliveryInstallationStatus__c,Description,develoepername__c,ExpectedRevenue,Expense__c,Id,IsClosed,IsDeleted,IsPrivate,IsWon,LastActivityDate,LastModifiedById,LastModifiedDate,LastReferencedDate,LastViewedDate,LeadSource,MainCompetitors__c,Name,NextStep,OrderNumber__c,OwnerId,Pricebook2Id,Probability,RecordTypeId,StageName,SystemModstamp,TotalOpportunityQuantity,TrackingNumber__c,Type FROM Opportunity where id in:opplist]);

   Integer total;

   if(rollup.keyset()!=Null)

   {

  for(Id ids:rollup.keyset())

  {

  total=0;

   List<Concur_Reports__c> cr3=rollup.get(ids);

   Opportunity oppr=oppidsfilter.get(ids);

  

   for(Concur_Reports__c cr4:cr3)

   {

   total=total+Integer.valueof(cr4.ReportTotal__c);

    system.debug('%%%%%%%%%%total%%%%%%%%%%%%'+total);

   }

   if(oppr!=Null){

 if(delflag!=True){

oppr.Expense__c=oppr.Expense__c+total;

  }

  else{

   oppr.Expense__c=oppr.Expense__c-total;

  }

  OppUpdateList.add(oppr);

   system.debug('%%%%%%%%%%OppUpdateList%%%%%%%%%%%%'+OppUpdateList);

    }

  }

try{

    if(OppUpdateList.size()>0){

    Update OppUpdateList;

} else  {

}

}

catch(exception ex){

}

}

 }