got a requirement like to calculate average in account based on particular record type of case. My requirement is:

I have a field called ARP in account currency. I want to calculate overall average of ARP field in particular record type called customer order whether Case details either new or add-on.

So I'm trying write a trigger a trigger.

Everything is working but after delete event is not working means.

Example when i create a case with ARPU will be 21.And if i delete the case it's still showing 21 in account level.Even i am trigger.old in trigger to handler class.


My trigger would be 

trigger ForARPU on case (after insert,after update,after delete) 
{  
    if(Trigger.isAfter && trigger.isInsert || Trigger.isAfter && trigger.isUpdate ) 
    {      
        //It will call a static method called ARPUInsert in ARPUCases class.
        ARPUCases.ARPUInsert(Trigger.New);
    
    }
    if(Trigger.isAfter && trigger.isDelete) 
    {     
        //It will call a static method called ARPUInsert in ARPUCases class.
        ARPUCases.ARPUDelete(Trigger.Old);
    
    }
}

Handler class would be 

/**
 * This class is used to calculate average of Arpu in customer order record type
 * with cases details either Add-on or New subscription and update in Related Account field called ARPU.
 * This class is fire whenever record type called customer order case has been inserted or updated or deleted.
 * @author  Pavan Kumar
 * @since   2016-09-28 
*/
public class ARPUCases 
{
    /** @var recordTypeID - is to filter cases with particular record type */
    /** @var Accountstoupdate - is to update the particular accounts */
    /** @var CaseIDs - is to retrive all related case id's */
     
    public static Set<Account> accSet = new Set<Account>();
    
    public static void ARPUInsert(List<Case>  CaseTriggers)
    {
        /** 
         * This method is to caluclate average of all ARPU amounts with case have customer order recordtype
         * as well as case details with either ADD-On (OR) New Subscription and update in related account
         * field called ARPU. 
         * This method will fire only when any case with record type called customer order is created as well updated. 
        */
        
        if (Trigger.isInsert || Trigger.isUpdate) 
        {
            Id recordTypeId = [Select Id From RecordType Where DeveloperName = 'Customer_Order'].Id;
     List<Account> Accountstoupdate =new List<Account>();
     List<Case> CaseIDs = new List<Case>();
            for (Case s : CaseTriggers)
            {
                if(s.RecordTypeId == recordTypeId && s.Case_Details__c =='New Subscription' || s.Case_Details__c =='Add On' ) 
                {
                    // Loop through and add caseId's to the list.
                    CaseIDs.add(s);
                }
            }
            /** @Var CaseAccountIds - to get accountId's of cases with list called CaseIDs */
            set<Id> CaseAccountIds = new set<Id>();
            
            for(Case c : [SELECT Id,ARPU__c,accountId FROM Case WHERE Id IN :CaseIDs])
            {
                // Loop through and add AccountId's to the list.
                CaseAccountIds.add(c.AccountId);
            }
            /** @Var Accountswithcases-to get account details to caluclate average */
            /** @Var results-to get average of particular account based on the cases */
            List<Account> Accountswithcases = [select Id,name,ARPU__c  from Account where id =:CaseAccountIds];
            Map<Id, AggregateResult> results = new Map<Id, AggregateResult>(
                [SELECT AccountId Id, AVG(ARPU__c) average FROM Case WHERE AccountId = :Accountswithcases GROUP BY AccountId]);
            For(account a1: Accountswithcases) 
            {
                if(results.get(a1.Id) != null) 
                {
                    // Loop through aggregate results array and typecast the average of ARPU and update in account level.
                    a1.ARPU__c = (Decimal)results.get(a1.Id).get('average');
                    Accountstoupdate.add(a1);
                }
                
            }
            if(Accountstoupdate.size()>0) 
            {
                // DML statement to update all the accounts related with cases
                update Accountstoupdate;
            }
        }
    }
    public static void ARPUDelete(List<Case>  CaseTriggers) 
    {
        /** 
         * This method is to caluclate average of all ARPU amounts with case have customer order recordtype
         * as well as case details with either ADD-On (OR) New Subscription and update in related account
         * field called ARPU. 
         * This method will fire only when any case with record type called customer order is deleted. 
        */
        
        if (Trigger.isDelete)
        {
            Id recordTypeId = [Select Id From RecordType Where DeveloperName = 'Customer_Order'].Id;
     List<Account> Accountstoupdate =new List<Account>();
     List<Case> CaseIDs = new List<Case>();
            for (Case s : CaseTriggers)
            {
                if(s.RecordTypeId == recordTypeId && s.Case_Details__c =='New Subscription' || s.Case_Details__c =='Add On') 
                {
                    // Loop through and add caseId's to the list.
                    CaseIDs.add(s);
                }
            }
            System.debug('Data in  CaseIDs:'+ CaseIDs.size());
            System.debug('Data in  details CaseIDs:'+ CaseIDs);
            /** @Var CaseAccountIds - to get accountId's of cases with list called CaseIDs */
            set<Id> CaseAccountIds = new set<Id>();
            for(Case c : CaseTriggers)
            {
                 // Loop through and add AccountId's to the list.
                CaseAccountIds.add(c.AccountId);
            }
            System.debug('After Data in  CaseAccountIds:'+ CaseAccountIds.size());
            System.debug('After Data Details in  CaseAccountIds:'+ CaseAccountIds);
            /** @Var Accountswithcases-to get account details to caluclate average */
            /** @Var results-to get average of particular account based on the cases */
            List<Account> Accountswithcases = [select Id,name,ARPU__c  from Account where id =:CaseAccountIds];
            Map<Id, AggregateResult> results = new Map<Id, AggregateResult>(
                [SELECT AccountId Id, AVG(ARPU__c) average FROM Case WHERE AccountId = :Accountswithcases GROUP BY AccountId]);
            System.debug('Results:'+ results.size());
            System.debug('Data in Accountswithcases:'+ Accountswithcases.size());
            For(account a1: Accountswithcases) 
            {
                if(results.get(a1.Id) != null ) 
                {
                    // Loop through aggregate results array and typecast the average of ARPU and update in account level.
                    a1.ARPU__c = (Decimal)results.get(a1.Id).get('average');
                    Accountstoupdate.add(a1);
                }
            }
            System.debug('After Results:'+  Accountstoupdate.size());
            System.debug('Size of the Results:'+  Accountstoupdate);
            if(Accountstoupdate.size()>0) 
            {
                // DML statement to update all the accounts related with cases.
                update Accountstoupdate;
            } 
        }
    }
}

I am attaching my debug logs