DiscountCodeUsage

// get active benefits for Contact, order by expiration date ascending
List<Benefit__c> beneList = [SELECT Id, BenefitLevel__c FROM Benefit__c WHERE Contact__c = :contactId ORDER BY ExpirationDate__c ASC];

// Get set of BenefitLevels referenced by the above
Map<Id, Benefit__c> beneMap = new Map<Id, Benefit__c>(beneList);

// get usage discount codes associated with these benefit levels
List<DiscountCodeBenefitLevelLink__c> memberDiscounts = [SELECT DiscountCode__r.Id, DiscountCode__r.MemberUsageLimit__c... 
    FROM DCBLL__c WHERE BenefitLevel__c IN :beneLevelSet];

// Map the Discount Codes by their Id and by their corresponding Benefit Level
Map<Id, DiscountCode__c> discountCodeMap
Map<Id, List<DiscountCode__c>> beneLevelDiscountCodeMap

// Get the DCU objects for these Benefit/DiscountCode combinations
List<DiscountCodeUsage__c> dcuList = [SELECT Id, Key, Benefit__c, DiscountCode__c, UsageCount__c FROM DiscountCodeUsage__c 
    WHERE Benefit__c IN :beneMap.keySet() AND DiscountCode__c IN : discountCodeMap.keySet()];
    
// Map the above by their Key field (contatenation of Discount.Id and Benefit.Id)
Map<String, DiscountCodeUsage__c> dcuMap

// For each TOI
discountAmount = 0;
for (TicketOrderItem__c item : itemList) {
	for (Benefit__c bene: beneList) {
	     // Get the DC associated with this Benefit and determine the discount amount.
		 List<DiscountCode__c> dcList = beneLevelDiscountCodeMap.get(bene.BenefitLevel__c);
		 for (DiscountCode__c dc : dcList) {
			 if (thisDiscountAmount > maxDiscountAmount) {
			 	// If it's a limited usage discount
				if (dc.MemberUsageLimit__c != null) {
					// Check to see if a DCU already exists
					DiscountCodeUsage__c dcu = dcuMap.get(appliedDC.Id + bene.Id);
					if (dcu != null) {
					    // Check to see if we've reached the usage limit... if so, continue
					    if (dcu.UsageCount__c + item.Quantity >  dcu.MemberUsageLimit__c) {
					        continue;
					    }
      				            dcu.UsageCount += item.Quantity;
					} else {
					    dcu = new DiscountCodeUsage__c(MemberUsageLimit__c = appliedDC.MemberUsageLimit__c, DiscountCode__c = applieDC.Id, Benefit__c = beneId);
					    dcu.UsageCount__c = toi.Quantity
					    item.DiscountCodeUsage__r = dcu;
					}
        				  // Apply the discount code to the item
					  item.DiscountCode__c = dc.Id;
					  ...
				}
			 }
		 }
	}
	// At this point, the maximal discount, based on the Contact's active Benefits, will be applied to the item
}