start of the vue + mvc example and a simple session binding

Former-commit-id: 994f00952352c93d270ad197cb843f3222fb37c0

_examples/tutorial/vuejs-todo-mvc/src/todo/item.go

@@ -0,0 +1,24 @@
+package todo
+
+type State uint32
+
+const (
+	StateActive State = iota
+	StateCompleted
+)
+
+func ParseState(s string) State {
+	switch s {
+	case "completed":
+		return StateCompleted
+	default:
+		return StateActive
+	}
+}
+
+type Item struct {
+	OwnerID      string
+	ID           int64
+	Body         string
+	CurrentState State
+}

_examples/tutorial/vuejs-todo-mvc/src/todo/service.go

@@ -0,0 +1,53 @@
+package todo
+
+type Service interface {
+	GetByID(id int64) (Item, bool)
+	GetByOwner(owner string) []Item
+	Complete(item Item) bool
+	Save(newItem Item) error
+}
+
+type MemoryService struct {
+	items map[int64]Item
+}
+
+func (s *MemoryService) getLatestID() (id int64) {
+	for k := range s.items {
+		if k > id {
+			id = k
+		}
+	}
+
+	return
+}
+
+func (s *MemoryService) GetByID(id int64) (Item, bool) {
+	item, found := s.items[id]
+	return item, found
+}
+
+func (s *MemoryService) GetByOwner(owner string) (items []Item) {
+	for _, item := range s.items {
+		if item.OwnerID != owner {
+			continue
+		}
+		items = append(items, item)
+	}
+	return
+}
+
+func (s *MemoryService) Complete(item Item) bool {
+	item.CurrentState = StateCompleted
+	return s.Save(item) == nil
+}
+
+func (s *MemoryService) Save(newItem Item) error {
+	if newItem.ID == 0 {
+		// create
+		newItem.ID = s.getLatestID() + 1
+	}
+
+	//  full replace here for the shake of simplicy)
+	s.items[newItem.ID] = newItem
+	return nil
+}