feat: add top items on admin page

backend/handlers/analytics_handler.go

@@ -0,0 +1,34 @@
+package handlers
+
+import (
+	"net/http"
+
+	"github.com/gin-gonic/gin"
+
+	"fishfish/database"
+)
+
+func GetTopItems(c *gin.Context) {
+	type TopItem struct {
+		Name         string  `json:"name"`
+		Revenue      float64 `json:"revenue"`
+		Price        float64 `json:"price"`
+		SaleQuantity float64 `json:"sale_quantity"`
+		Unit         string  `json:"unit"`
+	}
+
+	results := []TopItem{}
+
+	err := database.DB.Table("order_items").
+		Select("items.name, SUM(order_items.price * order_items.quantity) AS revenue, order_items.price, SUM(order_items.quantity) as sale_quantity, items.unit").
+		Joins("JOIN items ON items.id = order_items.item_id").
+		Group("items.name, order_items.price, items.unit").
+		Order("revenue DESC").
+		Limit(5).
+		Scan(&results).Error
+	if err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": err.Error()})
+	}
+
+	c.JSON(http.StatusOK, results)
+}