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;
    }
}

1. public class AccountRollupService { — a new, dedicated class.
2. public void adjustWonRevenue(Map<Id, Decimal> amountAdjustmentByAccountId) { — a clear, reusable name.
3. if (amountAdjustmentByAccountId.isEmpty()) { — the same early-exit as before.
4. return; — nothing to do.
5. } — closes the if.
6. (blank line)
7. List<Account> accounts = [ — the same query as applyAdjustments had.
8. SELECT Id, Total_Won_Revenue__c — the fields needed.
9. FROM Account — the object.
10. WHERE Id IN :amountAdjustmentByAccountId.keySet() — the affected accounts.
11. ]; — closes the query.
12. (blank line)
13. for (Account acc : accounts) { — loops over them.
14. Decimal current = acc.Total_Won_Revenue__c == null ? 0 : acc.Total_Won_Revenue__c; — defaults null to 0.
15. acc.Total_Won_Revenue__c = current + amountAdjustmentByAccountId.get(acc.Id); — applies the adjustment.
16. } — closes the loop.
17. (blank line)
18. update accounts; — one bulk update.
19. } — closes the method.
20. } — closes the class — 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);
    }
}

1. public class OpportunityTriggerHandler { — now has one job — detecting which Opportunities changed and by how much.
2. public void afterUpdate(List<Opportunity> newOpportunities, Map<Id, Opportunity> oldMap) { — the method.
3. Map<Id, Decimal> amountAdjustmentByAccountId = new Map<Id, Decimal>(); — the same collection as before.
4. (blank line)
5. for (Opportunity opp : newOpportunities) { — the same detection logic.
6. // ... build amountAdjustmentByAccountId exactly as before ... — unchanged from the earlier lesson.
7. } — closes the loop.
8. (blank line)
9. new AccountRollupService().adjustWonRevenue(amountAdjustmentByAccountId); — delegates the actual work to a different, focused class.
10. } — closes the method.
11. } — closes the class.

This is Module 14's Single Responsibility Principle, now spanning two classes instead of living inside one growing handler.