handler.go

func init() {
	rnd = renderer.New()
	sess, err := mgo.Dial(hostName)
	checkErr(err)
	sess.SetMode(mgo.Monotonic, true)
	db = sess.DB(dbName)
}

func homeHandler(w http.ResponseWriter, r *http.Request) {
	err := rnd.Template(w, http.StatusOK, []string{"static/home.tpl"}, nil)
	checkErr(err)
}

func createTodo(w http.ResponseWriter, r *http.Request) {
	var t todo

	if err := json.NewDecoder(r.Body).Decode(&t); err != nil {
		rnd.JSON(w, http.StatusProcessing, err)
		return
	}

	// simple validation
	if t.Title == "" {
		rnd.JSON(w, http.StatusBadRequest, renderer.M{
			"message": "The title field is requried",
		})
		return
	}

	// if input is okay, create a todo
	tm := todoModel{
		ID:        bson.NewObjectId(),
		Title:     t.Title,
		Completed: false,
		CreatedAt: time.Now(),
	}
	if err := db.C(collectionName).Insert(&tm); err != nil {
		rnd.JSON(w, http.StatusProcessing, renderer.M{
			"message": "Failed to save todo",
			"error":   err,
		})
		return
	}

	rnd.JSON(w, http.StatusCreated, renderer.M{
		"message": "Todo created successfully",
		"todo_id": tm.ID.Hex(),
	})
}

func updateTodo(w http.ResponseWriter, r *http.Request) {
	id := strings.TrimSpace(chi.URLParam(r, "id"))

	if !bson.IsObjectIdHex(id) {
		rnd.JSON(w, http.StatusBadRequest, renderer.M{
			"message": "The id is invalid",
		})
		return
	}

	var t todo

	if err := json.NewDecoder(r.Body).Decode(&t); err != nil {
		rnd.JSON(w, http.StatusProcessing, err)
		return
	}

	// simple validation
	if t.Title == "" {
		rnd.JSON(w, http.StatusBadRequest, renderer.M{
			"message": "The title field is requried",
		})
		return
	}

	// if input is okay, update a todo
	if err := db.C(collectionName).
		Update(
			bson.M{"_id": bson.ObjectIdHex(id)},
			bson.M{"title": t.Title, "completed": t.Completed},
		); err != nil {
		rnd.JSON(w, http.StatusProcessing, renderer.M{
			"message": "Failed to update todo",
			"error":   err,
		})
		return
	}

	rnd.JSON(w, http.StatusOK, renderer.M{
		"message": "Todo updated successfully",
	})
}

func fetchTodos(w http.ResponseWriter, r *http.Request) {
	todos := []todoModel{}

	if err := db.C(collectionName).
		Find(bson.M{}).
		All(&todos); err != nil {
		rnd.JSON(w, http.StatusProcessing, renderer.M{
			"message": "Failed to fetch todo",
			"error":   err,
		})
		return
	}

	todoList := []todo{}
	for _, t := range todos {
		todoList = append(todoList, todo{
			ID:        t.ID.Hex(),
			Title:     t.Title,
			Completed: t.Completed,
			CreatedAt: t.CreatedAt,
		})
	}

	rnd.JSON(w, http.StatusOK, renderer.M{
		"data": todoList,
	})
}

func deleteTodo(w http.ResponseWriter, r *http.Request) {
	id := strings.TrimSpace(chi.URLParam(r, "id"))

	if !bson.IsObjectIdHex(id) {
		rnd.JSON(w, http.StatusBadRequest, renderer.M{
			"message": "The id is invalid",
		})
		return
	}

	if err := db.C(collectionName).RemoveId(bson.ObjectIdHex(id)); err != nil {
		rnd.JSON(w, http.StatusProcessing, renderer.M{
			"message": "Failed to delete todo",
			"error":   err,
		})
		return
	}

	rnd.JSON(w, http.StatusOK, renderer.M{
		"message": "Todo deleted successfully",
	})
}



func todoHandlers() http.Handler {
	rg := chi.NewRouter()
	rg.Group(func(r chi.Router) {
		r.Get("/", fetchTodos)
		r.Post("/", createTodo)
		r.Put("/{id}", updateTodo)
		r.Delete("/{id}", deleteTodo)
	})
	return rg
}

func checkErr(err error) {
	if err != nil {
		log.Fatal(err) //respond with error page or message
	}
}