Add Service Classes

Module 24's handler-class pattern already separates the trigger from its logic — but the rollup logic itself (applyAdjustments) is currently only reachable through OpportunityTriggerHandler. If a future data-migration script needed to recalculate every Account's Total_Won_Revenue__c from scratch, it couldn't reuse this logic without going through a fake trigger context.

public class AccountRollupService {
    public void adjustWonRevenue(Map<Id, Decimal> amountAdjustmentByAccountId) {
        if (amountAdjustmentByAccountId.isEmpty()) {
            return;
        }

        List<Account> accounts = [
            SELECT Id, Total_Won_Revenue__c
            FROM Account
            WHERE Id IN :amountAdjustmentByAccountId.keySet()
        ];

        for (Account acc : accounts) {
            Decimal current = acc.Total_Won_Revenue__c == null ? 0 : acc.Total_Won_Revenue__c;
            acc.Total_Won_Revenue__c = current + amountAdjustmentByAccountId.get(acc.Id);
        }

        update accounts;
    }
}

Same logic as the previous applyAdjustments method, now living in its own class with a clear, reusable name — AccountRollupService.adjustWonRevenue() can be called from the trigger handler, a batch job, or a one-off Execute Anonymous script equally easily.

public class OpportunityTriggerHandler {
    public void afterUpdate(List<Opportunity> newOpportunities, Map<Id, Opportunity> oldMap) {
        Map<Id, Decimal> amountAdjustmentByAccountId = new Map<Id, Decimal>();

        for (Opportunity opp : newOpportunities) {
            // ... build amountAdjustmentByAccountId exactly as before ...
        }

        new AccountRollupService().adjustWonRevenue(amountAdjustmentByAccountId);
    }
}

OpportunityTriggerHandler now has one job — detecting which Opportunities changed and by how much — while AccountRollupService has a different, focused job: actually applying an adjustment to Accounts. This is Module 14's Single Responsibility Principle, now spanning two classes instead of living inside one growing handler.