A mock "orders" microservice in Go (Toy Example)

main.go

package main

import (
	"encoding/json"
	"fmt"
	"log"
	"net/http"
)

// Order represents an order entity
type Order struct {
	ID     int     `json:"id"`
	UserID int     `json:"user_id"`
	Amount float64 `json:"amount"`
	Status string  `json:"status"`
}

// OrderService encapsulates business logic for orders
type OrderService struct {
	orders []Order
}

// NewOrderService creates a new OrderService with mock data
func NewOrderService() *OrderService {
	return &OrderService{
		orders: []Order{
			{ID: 1, UserID: 1, Amount: 99.99, Status: "pending"},
			{ID: 2, UserID: 2, Amount: 49.50, Status: "shipped"},
			{ID: 3, UserID: 1, Amount: 15.00, Status: "delivered"},
		},
	}
}

// GetOrdersByUser returns all orders for a given user
func (s *OrderService) GetOrdersByUser(userID int) []Order {
	var result []Order
	for _, o := range s.orders {
		if o.UserID == userID {
			result = append(result, o)
		}
	}
	return result
}

// GetAllOrders returns all orders
func (s *OrderService) GetAllOrders() []Order {
	return s.orders
}

// OrderHandler encapsulates the HTTP layer
type OrderHandler struct {
	service *OrderService
}

// NewOrderHandler creates a new OrderHandler
func NewOrderHandler(service *OrderService) *OrderHandler {
	return &OrderHandler{service: service}
}

// ServeHTTP implements http.Handler for OrderHandler
func (h *OrderHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	w.Header().Set("Content-Type", "application/json")
	if r.Method == http.MethodGet {
		// Optionally filter by user_id query param
		userIDs, ok := r.URL.Query()["user_id"]
		if ok && len(userIDs) > 0 {
			// For simplicity, ignore error handling for Atoi
			userID := 0
			fmt.Sscanf(userIDs[0], "%d", &userID)
			orders := h.service.GetOrdersByUser(userID)
			json.NewEncoder(w).Encode(orders)
			return
		}
		orders := h.service.GetAllOrders()
		json.NewEncoder(w).Encode(orders)
		return
	}
	w.WriteHeader(http.StatusMethodNotAllowed)
}

func main() {
	orderService := NewOrderService()
	orderHandler := NewOrderHandler(orderService)

	http.Handle("/orders", orderHandler)
	log.Println("Orders service running on :8081...")
	log.Fatal(http.ListenAndServe(":8081", nil))
}