public class StageProcessingHandler {
    public static void processStaging(List<StageRecord__c> incomingRecords) {
        // Ensure processing if there are records to avoid unnecessary queries/calculations
        if (incomingRecords == null || incomingRecords.isEmpty()) {
            return;
        }

        Map<Id, StageRecord__c> currentDataMap = new Map<Id, StageRecord__c>();
        Map<String, StageRecord__c> freshDataMap = new Map<String, StageRecord__c>();

        // Divide incoming records into respective maps based on LinkID__c or MortgageID__c
        for (StageRecord__c record : incomingRecords) {
            if (record.LinkID__c != null) {
                currentDataMap.put(record.LinkID__c, record);
            } else if (record.MortgageID__c != null) {
                freshDataMap.put(record.MortgageID__c, record);
            }
        }

        // Skip if there is no fresh data to process
        if (freshDataMap.isEmpty()) {
            return;
        }

        // Retrieve matching deals from the database
        Map<Id, Deal> dealMap = new Map<Id, Deal>([
            SELECT Id, MortgageID__c FROM Deal WHERE MortgageID__c IN :freshDataMap.keySet()
        ]);

        // Handle existing deals and check for absent deals using a separate method 
        Map<Id,Deal> absentData = Deal_Processing.getDealInstances(dealMap.keySet());

        List<Deal> newEntries = new List<Deal>();
        
        // Map the absent deals to be inserted
        for (Deal loanDeal : absentData.values()) {
            Deal adjustedDeal = Deal_Processing.applyMapping(loanDeal);
            if (adjustedDeal != null) { // Null check for safe processing.
                newEntries.add(adjustedDeal);
            }
        }

        // Insert all new entries in bulk if there are any
        if (!newEntries.isEmpty()) {
            try {
                insert newEntries;
            } catch (DmlException ex) {
                // Log the error and handle failed inserts appropriately
                System.debug('Failed to insert deals: ' + ex.getMessage());
            }
        }
    }
}