feat[BE]: Enhance payment allocation logic to support FIFO consumption for sales transactions

internal/modules/repports/services/repport.service.go

@@ -464,9 +464,13 @@ func (s *repportService) GetCustomerPayment(ctx *fiber.Ctx, params *validation.C
 		if err != nil {
 			return nil, 0, err
 		}
-		result = append(result, item)
+
+		if len(item.Rows) > 0 {
+			result = append(result, item)
+		}
 	}
 
+	totalCustomers = int64(len(result))
 	return result, totalCustomers, nil
 }
 
@@ -503,14 +507,8 @@ func (s *repportService) processCustomerPayment(ctx context.Context, customerID
 			row.Status = status
 
 			if status == "LUNAS" {
-				if previousBalance >= tx.TotalPrice {
-					days := 0
-					row.AgingDay = &days
-				} else if paymentDate != nil {
+				if paymentDate != nil {
 					days := int(paymentDate.Sub(tx.TransDate).Hours() / 24)
-					if days < 0 {
-						days = 0
-					}
 					row.AgingDay = &days
 				} else {
 					days := 0
@@ -518,9 +516,6 @@ func (s *repportService) processCustomerPayment(ctx context.Context, customerID
 				}
 			} else {
 				days := int(time.Since(tx.TransDate).Hours() / 24)
-				if days < 0 {
-					days = 0
-				}
 				row.AgingDay = &days
 			}
 		} else if tx.TransactionType == "PAYMENT" {
@@ -586,6 +581,67 @@ func (s *repportService) determineSalesStatusAndPaymentDate(transactions []reppo
 	// 4. BELUM LUNAS: no payment at all
 
 	if previousBalance >= currentSales.TotalPrice {
+		// Cari payment yang digunakan untuk melunasi sales ini dengan FIFO
+		// Track payment allocations that are consumed by previous sales
+		type paymentAllocation struct {
+			date     time.Time
+			amount   float64
+			consumed float64
+		}
+		allocations := []paymentAllocation{}
+		runningBalance := 0.0
+
+		// Process all transactions before current sales to build allocation map
+		for i := 0; i < currentIndex; i++ {
+			if transactions[i].TransactionType == "PAYMENT" {
+				allocations = append(allocations, paymentAllocation{
+					date:     transactions[i].TransDate,
+					amount:   transactions[i].PaymentAmount,
+					consumed: 0,
+				})
+				runningBalance += transactions[i].PaymentAmount
+			} else if transactions[i].TransactionType == "SALES" {
+				salesAmount := transactions[i].TotalPrice
+				remainingToConsume := salesAmount
+
+				// Consume from oldest allocations first (FIFO)
+				for j := range allocations {
+					if remainingToConsume <= 0 {
+						break
+					}
+					available := allocations[j].amount - allocations[j].consumed
+					if available > 0 {
+						consume := available
+						if consume > remainingToConsume {
+							consume = remainingToConsume
+						}
+						allocations[j].consumed += consume
+						remainingToConsume -= consume
+					}
+				}
+				runningBalance -= salesAmount
+			}
+		}
+
+		// Now find which allocation covers the current sales
+		amountNeeded := currentSales.TotalPrice
+		for _, alloc := range allocations {
+			available := alloc.amount - alloc.consumed
+			if available > 0 {
+				if amountNeeded <= available {
+					// This allocation fully covers the sales
+					return "LUNAS", &alloc.date
+				} else {
+					// This allocation partially covers, continue to next
+					amountNeeded -= available
+				}
+			}
+		}
+
+		// If we get here, use the oldest allocation
+		if len(allocations) > 0 {
+			return "LUNAS", &allocations[0].date
+		}
 		return "LUNAS", nil
 	}